{"gene":"SLC38A2","run_date":"2026-06-10T07:46:33","timeline":{"discoveries":[{"year":2000,"finding":"Human ATA2/SLC38A2 encodes a 506 amino acid Na+-dependent neutral amino acid transporter (system A) with Na+:amino acid stoichiometry of 1:1, sensitive to pH and Li+-intolerant, transporting alpha-(methylamino)isobutyric acid (MeAIB) and other neutral amino acids when expressed in mammalian cells.","method":"Cloning from HepG2 cells, functional expression in mammalian cells, transport assays with radiolabeled substrates, kinetic characterization","journal":"Biochimica et biophysica acta","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct in vitro transport assay with substrate specificity, stoichiometry, and ion dependence established in heterologous expression system; foundational characterization paper","pmids":["10930503"],"is_preprint":false},{"year":2001,"finding":"ATA2/SLC38A2 mRNA expression is adaptively regulated by amino acid availability: amino acid starvation of human fibroblasts increases ATA2 mRNA and system A transport activity, and supplementation with system A substrates (but not other amino acids) suppresses both ATA2 mRNA and transport activity.","method":"Northern blotting, radiolabeled amino acid transport assays in cultured human fibroblasts under amino acid deprivation/supplementation conditions","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal regulation shown with multiple substrate specificities, replicated in subsequent studies","pmids":["11172802"],"is_preprint":false},{"year":2001,"finding":"Hypertonic stress induces ATA2/SLC38A2 mRNA expression and system A transport activity in porcine endothelial cells; cycloheximide and actinomycin D block both responses, indicating that an earlier protein synthesis step is required.","method":"Radiolabeled transport assays, Northern blotting, pharmacological inhibition with cycloheximide and actinomycin D in endothelial cells","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean functional assays with pharmacological dissection, single lab","pmids":["11322785"],"is_preprint":false},{"year":2002,"finding":"Insulin stimulates System A (SNAT2/SLC38A2) transport activity in L6 skeletal muscle cells by recruiting SAT2 from an endosomal compartment to the plasma membrane in a phosphatidylinositol 3-kinase (PI3K)-dependent manner; chloroquine (which impairs endosomal recycling) blocks both insulin-stimulated System A activity and plasma membrane SAT2 recruitment without affecting PKB or GSK3 phosphorylation or GLUT4 translocation.","method":"Cell surface biotinylation, Western blotting, pharmacological inhibition (chloroquine, wortmannin), insulin stimulation assays in L6 myotubes","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (biotinylation, transport assay, signaling pathway dissection) in single rigorous study","pmids":["11834730"],"is_preprint":false},{"year":2002,"finding":"After partial hepatectomy in rats, ATA2-mediated system A amino acid transport activity increases by redistribution of ATA2 protein to the plasma membrane, not by increased ATA2 mRNA levels (Northern analysis showed no change in steady-state mRNA).","method":"Immunodetection of ATA2 in isolated liver plasma membrane and lysate fractions, Northern blotting, partial hepatectomy model","journal":"Archives of biochemistry and biophysics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — fractionation plus transport assay, single lab, moderate sample size","pmids":["12054432"],"is_preprint":false},{"year":2002,"finding":"Transcriptional activation of the ATA2/SLC38A2 gene by amino acid deprivation differs mechanistically from asparagine synthetase: ATA2 mRNA increases within 2–4 h (vs. 4 h lag for AS), is largely independent of de novo protein synthesis, and is not induced by glucose deprivation.","method":"mRNA quantification by Northern/RT-PCR, cycloheximide treatment, glucose deprivation, amino acid-free Krebs buffer incubations in HepG2 cells","journal":"The Journal of nutrition","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple perturbations in single lab establishing distinct transcriptional regulatory mechanism","pmids":["12368390"],"is_preprint":false},{"year":2004,"finding":"Hypertonic stimulation of system A transport activity requires synthesis of new SNAT2 protein; transcription inhibitor DRB suppresses the hypertonic increase in plasma membrane SNAT2 and fully blocks system A stimulation, whereas DRB does not fully block the adaptive (amino acid starvation) increase in SNAT2 at the plasma membrane.","method":"Biotinylation of surface proteins, immunocytochemistry, transcription inhibition (DRB), Western blotting in human fibroblasts","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods, single lab, distinguishes two independent regulatory mechanisms","pmids":["15581851"],"is_preprint":false},{"year":2005,"finding":"siRNA-mediated knockdown of SNAT2 in human fibroblasts under hypertonic conditions prevents the increase in system A transport activity, blocks intracellular amino acid pool expansion, and markedly delays cell volume recovery, demonstrating that SNAT2 induction is essential for regulatory volume increase.","method":"siRNA knockdown, radiolabeled amino acid transport assays, cell volume measurements, intracellular amino acid quantification","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 2 / Strong — loss-of-function with specific cellular phenotype, multiple outcome measures, directly implicates SNAT2 in osmoadaptation","pmids":["15922329"],"is_preprint":false},{"year":2005,"finding":"SNAT2 is expressed in neuronal cell bodies, processes, axonal shafts (but excluded from terminals), and in perivascular astrocytic end-feet and Bergmann glia in the rat CNS; enriched in spinal cord/brainstem and preferentially found in glutamatergic (not GABAergic) neurons.","method":"Immunohistochemistry with specific antisera, confocal microscopy, ultrastructural (EM) studies in rat brain","journal":"Neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct subcellular localization by multiple imaging methods, single lab","pmids":["15561425"],"is_preprint":false},{"year":2006,"finding":"Amino acid starvation-induced upregulation of SNAT2 requires eIF2alpha phosphorylation (blunted in cells with a non-phosphorylatable eIF2alpha mutant), increased gene transcription, and IRES-mediated cap-independent translation; hypertonic stress induction of SNAT2 is independent of eIF2alpha phosphorylation.","method":"Transport assays, mRNA/protein quantification, eIF2alpha phosphorylation-deficient mutant cells, IRES reporter constructs, in vitro translation, cycloheximide and actinomycin D inhibition","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal mechanistic approaches (mutant cell lines, reporter assays, in vitro translation) in single rigorous study","pmids":["16621798"],"is_preprint":false},{"year":2006,"finding":"The amino acid response element (AARE) regulating SNAT2 transcription upon amino acid limitation localizes to the first intron; ATF and C/EBP family members bind this intronic enhancer (not the promoter) in vitro and in vivo, with specific family members either activating or repressing SNAT2 transcription; amino acid deprivation increases RNA pol II recruitment to the SNAT2 promoter.","method":"Luciferase reporter assays, EMSA, ChIP assays, exogenous ATF/C/EBP expression, mRNA quantification in HepG2 and fibroblast cells","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstitution of regulatory element with mutagenesis, EMSA, and in vivo ChIP in multiple cell types","pmids":["16445384"],"is_preprint":false},{"year":2006,"finding":"Cortisol stimulates system A amino acid transport activity and increases SNAT2 mRNA/protein expression in BeWo placental cells; lower cortisol concentrations cause relocalization of SNAT2 transporter.","method":"Radiolabeled MeAIB transcellular transport assays, Northern and Western blotting, immunocytochemistry in BeWo cells","journal":"American journal of physiology. Endocrinology and metabolism","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional transport assay combined with expression and localization data, single lab","pmids":["16621896"],"is_preprint":false},{"year":2006,"finding":"pH sensitivity of SNAT2 transport involves a conserved C-terminal histidine residue (H504): DEPC modification reduces pH-sensitivity and blocks decreased Na+ affinity at low pH; H504A mutation produces reduced, DEPC-resistant pH-sensitivity without changing Na+ affinity at low pH. This suggests an allosteric H+-modifier site on C-terminal histidine that influences Na+ binding.","method":"DEPC chemical modification, site-directed mutagenesis (H504A), functional transport assays in Xenopus oocytes expressing SNAT2 and SNAT5","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis + chemical modification + electrophysiology in Xenopus oocyte reconstitution system","pmids":["16629640"],"is_preprint":false},{"year":2006,"finding":"SNAT2 activity is regulated by at least two amino acid sensor pathways: during amino acid withdrawal, JNK is activated and induces SNAT2 expression via an intronic nutrient-sensitive domain; large neutral amino acids (Tyr, Gln) inhibit JNK activation and SNAT2 upregulation. Additionally, SNAT2 itself provides a repressive signal for its own gene transcription during amino acid sufficiency (transceptor function), demonstrated by shRNA and transporter chimeras.","method":"shRNA knockdown, transporter chimera experiments, JNK activity assays, reporter gene assays, amino acid supplementation experiments in L6 myotubes","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — loss-of-function (shRNA), chimeric transporter approach, and pharmacological dissection identifying two distinct sensor pathways","pmids":["17488712"],"is_preprint":false},{"year":2006,"finding":"Ubiquitin ligase Nedd4-2 downregulates ATA2/SNAT2 transport activity at the cell surface by promoting polyubiquitination of ATA2 leading to endocytosis and proteasomal degradation; catalytically dead Nedd4-2 mutant had no effect; RNAi knockdown of Nedd4-2 increased ATA2 activity with decreased ATA2 polyubiquitination; Nedd4-2 co-localizes with EGFP-ATA2 at the plasma membrane.","method":"Xenopus oocyte expression, CHO cell transfection, RNAi knockdown, immunofluorescence, co-localization studies, proteasome inhibitor (MG132) experiments","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple expression systems, RNAi, dominant-negative mutant, and direct co-localization establishing E3 ligase-substrate relationship","pmids":["17003038"],"is_preprint":false},{"year":2006,"finding":"ATA2/SNAT2 is stored at the trans-Golgi network (TGN) in 3T3-L1 adipocytes (co-localizing with syntaxin 6, not EEA1); insulin stimulates release of ATA2-containing vesicles from this TGN compartment to the plasma membrane. The ATA2 storage vesicles are distinct from GLUT4-containing vesicles. Brefeldin A (TGN exit blocker) inhibits insulin-stimulated MeAIB uptake more profoundly than glucose uptake.","method":"Live cell imaging of EGFP-ATA2 fusion protein, immunofluorescence with TGN marker syntaxin 6 and endosomal marker EEA1, brefeldin A inhibition, transport assays in 3T3-L1 adipocytes","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — live cell imaging + organelle marker co-localization + pharmacological inhibition with functional readout, multiple orthogonal methods","pmids":["17050538"],"is_preprint":false},{"year":2006,"finding":"SNAT2 mediates induction of cell volume recovery (regulatory volume increase, RVI) upon hypertonic exposure: SNAT2-specific siRNA in human fibroblasts prevents system A transport stimulation, reduces intracellular amino acid pool expansion, and significantly delays cell volume recovery; newly synthesized SNAT2 proteins under hypertonic conditions are preferentially targeted to the cell membrane.","method":"siRNA, transport assays, intracellular amino acid quantification, cell volume measurements in human fibroblasts","journal":"Acta physiologica (Oxford, England)","confidence":"High","confidence_rationale":"Tier 2 / Strong — loss-of-function with direct cellular phenotype (volume recovery), multiple outcome measures, consistent with independent reports","pmids":["16734764"],"is_preprint":false},{"year":2007,"finding":"SNAT2 mediates an anion leak conductance that does not require substrate transport; transported substrates (L-alanine, L-glutamine, MeAIB) inhibit the anion leak with different potencies; mutation H304A abolishes alanine transport but retains anion leak current; both Na+ and substrate can bind H304A transporter; anion selectivity follows SCN->NO3->I->Br->Cl->Mes-.","method":"Whole-cell electrophysiology (patch clamp), site-directed mutagenesis (H304A), substrate binding assays in Xenopus oocytes and HEK293 cells","journal":"Biophysical journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — electrophysiological reconstitution with mutagenesis separating transport from anion conductance","pmids":["17237199"],"is_preprint":false},{"year":2007,"finding":"SNAT2 inhibition by methylaminoisobutyrate (MeAIB), metabolic acidosis (pH 7.1), or siRNA knockdown depletes intracellular glutamine and indirectly depletes leucine (maintained by the glutamine gradient via system L), leading to impaired mTOR signaling (reduced p70S6K1, S6, and 4E-BP1 phosphorylation) and impaired protein synthesis in L6 skeletal muscle cells.","method":"Competitive substrate inhibition (MeAIB), pH manipulation, siRNA knockdown, intracellular amino acid profiling, mTOR pathway Western blotting in L6 cells","journal":"Journal of the American Society of Nephrology : JASN","confidence":"High","confidence_rationale":"Tier 2 / Strong — three independent SNAT2 inhibition approaches converging on same mTOR signaling outcome, multiple readouts","pmids":["17429052"],"is_preprint":false},{"year":2008,"finding":"SNAT2 inhibition by MeAIB or metabolic acidosis (pH 7.1) stimulates proteolysis in L6 myotubes via both mTOR and PI3K signaling pathways; partial SNAT2 siRNA silencing stimulates proteolysis and impairs insulin signaling through PI3K; acidosis shifts insulin dose-response for suppression of proteolysis rightward, demonstrating that SNAT2 provides a link between acidosis, insulin resistance, and protein wasting.","method":"MeAIB inhibition, pH manipulation, siRNA knockdown, proteasome inhibition, mTOR and PI3K inhibitors, proteolysis rate measurement, Western blotting in L6 cells","journal":"Journal of the American Society of Nephrology : JASN","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple independent perturbations (inhibitor, siRNA, pH) with pharmacological pathway dissection and multiple cellular readouts","pmids":["18650482"],"is_preprint":false},{"year":2008,"finding":"SNAT2 transport activity is regulated by amino acid substrate availability and Na+; the insulin-induced upregulation of system A in L6 cells is mediated by increased Vmax (not Km), and is blocked by chloroquine and wortmannin; amino acid deprivation induction is blocked by PD98059 (MEK inhibitor) and SP600125 (JNK inhibitor); osmotic shock induction is blocked by neither chloroquine/wortmannin nor PD98059/SP600125, indicating distinct mechanisms.","method":"Radiolabeled transport kinetics, pharmacological inhibitor panel (chloroquine, wortmannin, PD98059, SP600125, SB202190), Western blotting, RT-PCR in L6 rat skeletal muscle cells","journal":"Amino acids","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — comprehensive pharmacological dissection distinguishing three regulatory mechanisms, single lab","pmids":["18330498"],"is_preprint":false},{"year":2008,"finding":"Asparagine 82 (N82) in transmembrane domain 1 of SNAT2 is critical for Na+ coordination: N82A mutation virtually eliminates alanine-induced transport current and amino acid uptake, dramatically reduces Na+ affinity (Kna), and increases apparent Km for alanine 27-fold; N82S has intermediate effect. Y337A and R374Q mutations do not abolish transport.","method":"Site-directed mutagenesis (N82A, N82S, Y337A, R374Q), electrophysiology, radiolabeled amino acid uptake in Xenopus oocytes","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — site-directed mutagenesis with full kinetic characterization in reconstituted expression system","pmids":["18319257"],"is_preprint":false},{"year":2008,"finding":"Despite increased ATF4 binding to the C/EBP-ATF site in the SNAT2 intronic AARE during UPR activation in HepG2 cells, SNAT2 transcription is not enhanced; the UPR suppresses AAR-induced SNAT2 transcription acting downstream of ATF4 binding, associated with lack of H3 hyperacetylation and failure to recruit general transcription factors at the SNAT2 promoter.","method":"ChIP assays, luciferase reporter assays, H3 acetylation analysis, ATF4 binding assays, simultaneous AAR+UPR activation in HepG2 cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal chromatin methods with functional reporter assays establishing mechanistic distinction between AAR and UPR regulation","pmids":["18697751"],"is_preprint":false},{"year":2009,"finding":"A conserved Na+ binding site in SNAT2 is formed by transmembrane helices 1 and 8: T384A mutation inhibits the anion leak current (which requires Na+ binding) and dramatically lowers Na+ affinity, consistent with homology modeling using LeuT and Mhp1 as templates that predicted a Na+ binding site involving TM1 and TM8.","method":"Profile-based sequence analysis, homology modeling (LeuT/Mhp1 templates), site-directed mutagenesis (T384A), electrophysiology, Na+ affinity measurements","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — structure-guided mutagenesis with functional validation in Xenopus oocyte reconstitution system","pmids":["19589779"],"is_preprint":false},{"year":2009,"finding":"IL-6 stimulates system A amino acid transport and increases SNAT2 (but not SNAT1) mRNA and protein expression in primary human trophoblast cells via a JAK/STAT3 (Tyr705 phosphorylation)-dependent pathway; siRNA knockdown of STAT3 abolishes IL-6-stimulated system A activity and SNAT2 expression. TNF-alpha stimulates system A independently of the JAK/STAT pathway.","method":"Radiolabeled transport assays, STAT3 siRNA knockdown, Western blotting (STAT3 phosphorylation), RT-PCR, TNF-alpha and IL-6 treatment of primary human trophoblast cells","journal":"American journal of physiology. Cell physiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — RNAi knockdown of signaling mediator with functional rescue readout, reciprocal IL-6/TNF comparison","pmids":["19741197"],"is_preprint":false},{"year":2009,"finding":"In neocortical neurons, taurine, GABA, and beta-alanine (SLC6 GABA transporter substrates) repress SNAT2 expression more potently (10x) than system A substrates; increased endogenous SNAT2 expression or repression did not affect spontaneous glutamatergic excitatory action-potential frequency or quantal size, suggesting SNAT2 is not required to support neurotransmitter glutamate synthesis in these neurons under physiological conditions.","method":"shRNA-mediated SNAT2 induction/repression, electrophysiology (spontaneous excitatory activity), SNAT2 mRNA stability assays, amino acid supplementation in neocortical neurons","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional electrophysiology with molecular manipulation, single lab; negative finding regarding glutamatergic role","pmids":["19240036"],"is_preprint":false},{"year":2011,"finding":"Chronic competitive inhibition of SNAT2 (System A) by MeAIB in MCF-7 cells depletes intracellular SNAT2 substrates and branched-chain amino acids (e.g., leucine) but paradoxically elevates mTOR-dependent p70S6K1 phosphorylation; two novel SNAT2-interacting proteins were identified by proteomics of TAP-tag purified SNAT2 fusion proteins, potentially functioning with SNAT2 as a transceptor.","method":"Competitive inhibition (MeAIB), intracellular amino acid profiling, mTOR signaling Western blotting, TAP-tag purification followed by proteomic analysis in MCF-7 cells","journal":"Frontiers in bioscience (Elite edition)","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — proteomic identification of interacting proteins plus mTOR signaling assays, single lab, proteomic IDs not named/validated by independent methods","pmids":["21622135"],"is_preprint":false},{"year":2011,"finding":"The C-terminal domain of SNAT2 (extracellular, 13 residues) is an important voltage regulator required for amino acid translocation at negative membrane potentials; deletion of 13 C-terminal residues abolishes transport at negative potentials but preserves transport at positive potentials; the truncation also increases alanine affinity (~3-fold) and Na+ affinity (~2-fold) but does not affect membrane expression.","method":"Site-directed deletion mutagenesis, whole-cell electrophysiology, radiolabeled substrate uptake, surface expression assays in Xenopus oocytes","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — deletion mutagenesis with full electrophysiological and kinetic characterization","pmids":["21158741"],"is_preprint":false},{"year":2011,"finding":"SNAT2 is the primary L-proline transporter on embryonic stem (ES) cells mediating L-proline-induced differentiation to early primitive ectoderm-like cells; excess SNAT2 substrates (but not non-substrates) prevent L-proline-induced changes in morphology, gene expression, and differentiation kinetics, demonstrating that L-proline uptake through SNAT2 is required for ES cell differentiation.","method":"Competitive substrate inhibition with SNAT2 substrates vs. non-substrates, morphology assessment, gene expression analysis, differentiation kinetics in ES cells","journal":"American journal of physiology. Cell physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — substrate-specificity competition experiments with functional readouts (differentiation phenotype), single lab","pmids":["21346154"],"is_preprint":false},{"year":2011,"finding":"The rat SNAT2 gene promoter contains a functional CRE site at -48 bp (highly conserved among rat, mouse, and human) responsible for cAMP/glucagon-stimulated transcription; deletion and mutation analyses, EMSA, and ChIP confirmed that this CRE site mediates SNAT2 regulation by cAMP. A high-protein diet (which increases serum glucagon) also increases SNAT2 mRNA in vivo.","method":"5' deletion analysis of SNAT2 promoter, site-directed mutagenesis of CRE sites, luciferase reporter assays, EMSA, ChIP, forskolin/glucagon treatment in hepatocytes, in vivo dietary manipulation","journal":"American journal of physiology. Endocrinology and metabolism","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis + EMSA + in vivo ChIP with functional reporter assays, validated in vivo","pmids":["21386061"],"is_preprint":false},{"year":2013,"finding":"SNAT2 (SLC38A2) transports anti-[18F]FACBC (a PET radiotracer) with a Km of ~197 µM in Xenopus oocytes expressing SNAT2, demonstrating FACBC is a substrate of SNAT2 (with lower affinity than ASCT2, LAT1, and LAT2).","method":"Radiolabeled [14C]FACBC kinetic transport assays in Xenopus oocytes expressing SNAT2, ASCT2, LAT1, or LAT2; Michaelis-Menten kinetics","journal":"Nuclear medicine and biology","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — direct in vitro transport assay in Xenopus oocyte expression system, single lab","pmids":["23647854"],"is_preprint":false},{"year":2014,"finding":"Only SNAT2 (not SNAT1 or SNAT4) transports betaine with a Km of ~5 mM; betaine uptake by SNAT2 is hyperosmotically inducible in placental trophoblast cells (TR-TBT 18d-1), and SNAT2 protein expression on the plasma membrane is more potently induced by hypertonicity than total SNAT2 expression.","method":"[14C]betaine uptake assays, transfection of HEK293 cells with SNAT1, SNAT2, SNAT4, Western blotting for plasma membrane vs. total SNAT2, immunocytochemistry under hypertonic conditions","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — direct substrate transport assay with subtype specificity in heterologous expression, single lab","pmids":["24434061"],"is_preprint":false},{"year":2014,"finding":"17β-estradiol regulates SNAT2 transcription through an estrogen response element (ERE) in the SNAT2 promoter bound by estrogen receptor alpha (ER-α); ER-α binding to the SNAT2 ERE increases progressively during gestation in the mammary gland; the ER-α-ERE complex contains PARP1, Ku70, and GAPDH as co-factors required for estradiol-stimulated promoter activity.","method":"In silico ERE identification, luciferase reporter assays with ERE deletion, EMSA with supershift assay, in vivo ChIP during gestation, LC-MS proteomics of the ER-α-ERE complex, siRNA knockdown of co-factors","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal methods (EMSA, ChIP, reporter mutagenesis, MS-proteomics of complex) in single rigorous study","pmids":["25056967"],"is_preprint":false},{"year":2015,"finding":"Ubiquitination of SNAT2 by Nedd4-2 (NEDD4L) is increased in IUGR placentas; increased NEDD4-2 expression and SNAT2 ubiquitination are associated with decreased SNAT2 in the trophoblast microvillous plasma membrane and reduced system A transport activity. mTOR signaling (mTORC1 and mTORC2) is decreased in IUGR, consistent with mTOR regulating SNAT2 trafficking by modulating ubiquitination.","method":"Protein fractionation, ubiquitination assays, Western blotting for mTOR pathway components and NEDD4-2, system A transport assays in isolated plasma membranes from IUGR and control placentas","journal":"Clinical science (London, England : 1979)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — human tissue with fractionation and functional transport assay, correlative mTOR link without direct manipulation","pmids":["26374858"],"is_preprint":false},{"year":2015,"finding":"Linoleic acid (unsaturated C18:2 fatty acid) reduces stress-induced SNAT2 protein and membrane transport activity via the ubiquitin-proteasome system; mutating seven N-terminal lysyl-ubiquitination sites of SNAT2 to alanine protects against linoleic acid-induced degradation; Nedd4.2 is upregulated by linoleic acid but Nedd4.2 shRNA silencing does not curb fatty acid-induced SNAT2 loss.","method":"Proteasome inhibition, shRNA Nedd4.2 silencing, SNAT2 N-terminal lysine-to-alanine mutations, transport assays, Western blotting in L6 myotubes and HeLa cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis of ubiquitination sites + RNAi + pharmacological inhibition with functional transport readout","pmids":["25653282"],"is_preprint":false},{"year":2015,"finding":"Hyperosmotic stress response involves coordinated induction of SNAT2 and GADD34; SNAT2-mediated amino acid uptake is enhanced by increased GADD34 levels through decreased eIF2alpha phosphorylation; GADD34 induction during hyperosmotic stress is controlled by c-Jun-binding CRE in GADD34 promoter and mRNA stabilization (not ATF4, which is not translated despite eIF2alpha phosphorylation).","method":"GADD34 expression analysis, eIF2alpha phosphorylation assays, reporter gene assays, mRNA stability assays, amino acid transport assays in response to hyperosmotic stress","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple molecular readouts establishing SNAT2/GADD34 axis, single lab","pmids":["26041779"],"is_preprint":false},{"year":2016,"finding":"Net glutamine uptake in HeLa and 143B cancer cells does not depend on ASCT2 (deletion does not reduce cell growth) but requires expression of SNAT1 and SNAT2; ASCT2 deletion causes amino acid starvation response and upregulation of SNAT1. Silencing GCN2 in the ASCT2-/- background reduces cell growth.","method":"CRISPR/gene deletion of ASCT2, SNAT siRNA silencing, cell growth assays, GCN2 siRNA in knockout background, radiolabeled transport assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic deletion + epistasis (GCN2 in ASCT2-/- background) with multiple functional readouts","pmids":["27129276"],"is_preprint":false},{"year":2016,"finding":"A disulfide bond exists between Cys245 and Cys279 in SNAT2; this disulfide bond does not affect cell surface trafficking or transport function, but marks proximity in the extracellular domain.","method":"Site-directed mutagenesis (C245A, C279A, C245,279A double mutant), mPEG-Mal chemical modification with/without DTT reduction, transport assays in HEK293 cells","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — chemical modification + mutagenesis in heterologous expression, single lab","pmids":["27355203"],"is_preprint":false},{"year":2018,"finding":"SNAT2 membrane topology consists of 11 transmembrane domains with an intracellular N-terminus and extracellular C-terminus; three N-glycosylation sites were confirmed at the largest extracellular loop.","method":"mPEG-Mal chemical modification, protease cleavage assays, immunofluorescence, glycosylation analysis in rat SNAT2","journal":"Biochimica et biophysica acta. Biomembranes","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — multiple biochemical topology mapping methods in single study, single lab","pmids":["29678469"],"is_preprint":false},{"year":2018,"finding":"SNAT2 protein stability is regulated by substrate (AA and Na+) availability: AA withdrawal increases SNAT2 protein stability; provision of SNAT2 substrates (MeAIB, glutamine) but not non-substrates represses this stabilization; the N-terminal cytoplasmic tail of SNAT2 (containing lysyl residues) is required for substrate-induced instability; grafting the SNAT2 N-terminal tail onto SNAT5 (which lacks adaptive regulation) confers substrate-induced changes in SNAT5 chimera stability. Extracellular Na+ removal destabilizes SNAT2 regardless of substrate presence.","method":"Chimeric transporter construction, N-terminal lysine-to-alanine mutations, Western blotting for protein stability, substrate provision experiments in HeLa cells","journal":"Frontiers in pharmacology","confidence":"High","confidence_rationale":"Tier 1 / Strong — chimeric transporter approach with mutagenesis establishing N-terminal domain as regulatory sensor, multiple perturbations","pmids":["29467657"],"is_preprint":false},{"year":2019,"finding":"CDK7 activity is upregulated in amino acid-deprived cells in a GCN2-dependent manner and is required for the SNAT2 adaptive transcription response; pharmacological inhibition of CDK7 with THZ-1 attenuates ATF4 expression and blocks system A adaptation; this effect is mitigated in cells expressing a drug-resistant CDK7 form. GSK3, MEK-ERK, mTORC1, and p38 inhibition have no detectable effect on System A adaptation.","method":"Pharmacological CDK inhibitors (roscovitine, flavopiridol, THZ-1), drug-resistant CDK7 rescue construct, shRNA GSK3, CDK7 activity assays, System A transport assays in amino acid-deprived cells","journal":"Biochimica et biophysica acta. Molecular cell research","confidence":"High","confidence_rationale":"Tier 2 / Strong — rescue with drug-resistant CDK7, multiple pharmacological probes, and epistasis with GCN2","pmids":["30857869"],"is_preprint":false},{"year":2019,"finding":"SNAT2 in breast cancer MCF7 cells is regulated by both ERα and HIF-1α; under hypoxia, regulation shifts from ERα-dependent to predominantly HIF-1α-dependent (both regulatory elements overlap in SNAT2 cis-regulatory region); downregulation by fulvestrant (ER antagonist) is reverted in hypoxia; SNAT2 overexpression in vivo causes complete resistance to antiestrogen therapy.","method":"Reporter assays, HIF-1α/ERα binding site analysis, fulvestrant treatment under normoxia vs. hypoxia, in vitro overexpression/growth assays, xenograft in vivo studies","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vitro and in vivo functional studies with regulatory element overlap analysis establishing regulatory switch mechanism","pmids":["31152137"],"is_preprint":false},{"year":2020,"finding":"ChREBP represses SNAT2 expression in response to a high-carbohydrate diet by binding to a carbohydrate response element (ChoRE) at -160 bp upstream of the SNAT2 transcriptional start site, and recruits the co-repressor SMRT; confirmed by ChIP-qPCR in vivo and immunoprecipitation showing ChREBP-SMRT interaction.","method":"Luciferase reporter assays with ChoRE, immunoprecipitation (ChREBP-SMRT), in vivo ChIP, high-sucrose diet rat model, Western blotting","journal":"American journal of physiology. Endocrinology and metabolism","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro and in vivo ChIP + co-IP + reporter assays identifying promoter element, interacting co-repressor, and in vivo dietary validation","pmids":["33225719"],"is_preprint":false},{"year":2021,"finding":"Placenta-specific Slc38a2/SNAT2 knockdown (59% reduction via lentiviral shRNA) in mice causes fetal growth restriction: reduces near-term fetal and placental weight, fetal viability, trophoblast plasma membrane SNAT2 protein abundance, and placental system A (MeAIB) uptake, directly demonstrating that SNAT2 deficiency in the placenta mechanistically causes restricted fetal growth.","method":"Lentiviral shRNA transduction of blastocysts, 14C-MeAIB uptake assay, Western blotting, fetal/placental weight measurements","journal":"Clinical science (London, England : 1979)","confidence":"High","confidence_rationale":"Tier 2 / Strong — organ-specific knockdown with quantitative transport assay and multiple fetal phenotype readouts","pmids":["34406367"],"is_preprint":false},{"year":2022,"finding":"SLC38A2 provides proline to osteoblasts to fulfill the unique biosynthetic demand imposed by differentiation; osteoblast-associated proteins (RUNX2, OSX, OCN, COL1A1) are enriched in proline; genetic ablation of SLC38A2 in osteoblasts limits osteoblast differentiation and bone formation in mice; proline from SLC38A2 is primarily incorporated into nascent protein with little metabolism.","method":"Bioinformatic amino acid composition analysis, osteoblast-specific Slc38a2 genetic ablation (mouse), metabolomics (proline tracking), osteoblast differentiation assays","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo genetic ablation with differentiation/bone phenotype plus metabolomic substrate tracking","pmids":["35261338"],"is_preprint":false},{"year":2022,"finding":"SLC38A2 provides proline and alanine to osteoblast lineage cells during postnatal bone homeostasis; genetic ablation of SLC38A2 using Prrx1Cre decreases bone mass in male and female mice due to reduced osteoblast numbers and bone-forming activity, attributable to impaired proliferation and osteogenic differentiation of skeletal stem and progenitor cells.","method":"Prrx1Cre-mediated conditional Slc38a2 knockout in mice, μCT bone analysis, histomorphometry, skeletal stem cell proliferation and differentiation assays","journal":"Frontiers in physiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — cell-type-specific genetic ablation with detailed skeletal phenotyping, both sexes","pmids":["36213239"],"is_preprint":false},{"year":2022,"finding":"SNAT2 is responsible for sarcosine and glycine uptake in hyperosmotic-stressed PC-3 prostate cancer cells; hyperosmotic culture increases SNAT2 mRNA/protein and sarcosine uptake ~9-fold; siRNA knockdown of SNAT2 reduces sarcosine uptake Vmax from 2653 to 513 nmol/mg/min without altering Km, indicating SNAT2 accounts for ~80% of hyperosmotic sarcosine transport. Sarcosine is identified as a novel SNAT2 substrate.","method":"siRNA knockdown, 14C-sarcosine and 3H-glycine uptake kinetics, RT-PCR, Western blotting in PC-3 cells under isosmotic and hyperosmotic conditions","journal":"Pflugers Archiv : European journal of physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown with direct substrate transport kinetics identifying novel substrate, single lab","pmids":["36175560"],"is_preprint":false},{"year":2022,"finding":"Identification of a potent SNAT2 inhibitor (MMTC/57E, IC50 0.8–3 µM) using a high-throughput FMP membrane potential assay; the compound discriminates against SNAT1. In combination with the glucose transport inhibitor Bay-876, the SNAT2 inhibitor halts proliferative growth of MDA-MB-231 and HPAFII cancer cells, demonstrating synergy between SNAT2 (glutaminolysis) and glucose transport inhibition.","method":"High-throughput FLIPR membrane potential assay screening, IC50 determination, SNAT1/SNAT2 selectivity assays, cancer cell proliferation assays with combination treatment","journal":"Frontiers in pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional electrogenic assay with selectivity profiling and cellular combination study, single lab","pmids":["36210829"],"is_preprint":false},{"year":2023,"finding":"In type-1 conventional dendritic cells (cDC1s), SLC38A2-mediated glutamine uptake regulates anti-tumor immunity; tumor cells and cDC1s compete for glutamine via SLC38A2; glutamine signaling via FLCN impinges on TFEB function; SLC38A2 deficiency in cDC1s selectively impairs cDC1 function in vivo and phenocopies FLCN loss; intratumoral glutamine supplementation augments cDC1-mediated CD8+ T cell immunity and overcomes therapeutic resistance.","method":"Genetic loss-of-function (SLC38A2 deficiency, FLCN knockout in DCs), TFEB functional assays, nutrient screening, in vivo tumor models, T cell immunity readouts, epistasis (FLCN KO phenocopies SLC38A2 deficiency in a TFEB-dependent manner)","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo genetic loss-of-function with FLCN-TFEB epistasis, multiple functional immune readouts, tumor models","pmids":["37407815"],"is_preprint":false},{"year":2023,"finding":"XBP1 inhibits SLC38A2 by directly binding to its promoter in cytotoxic T cells in multiple myeloma; SLC38A2 silencing reduces glutamine uptake and causes immune dysfunction of T cells in vitro.","method":"Single-cell RNA sequencing, in vitro XBP1 overexpression with promoter binding assay, SLC38A2 siRNA knockdown, glutamine uptake assays, T cell functional assays","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct promoter binding assay with loss-of-function and functional readout, single lab","pmids":["37054944"],"is_preprint":false},{"year":2023,"finding":"SLC38A2 protects renal medullary collecting duct (MCD) cells from hyperosmolarity-induced ferroptosis; hyperosmotic cell death occurred mainly via ferroptosis and was significantly attenuated by SLC38A2 overexpression and worsened by Slc38a2 deletion/silencing; the osmoprotective effect of SLC38A2 is dependent on mTORC1 activation; Slc38a2-knockout mice showed increased medullary ferroptosis following water restriction.","method":"SLC38A2 overexpression, siRNA silencing, Slc38a2 gene deletion, ferroptosis assays, mTORC1 activity assays, water restriction in vivo mouse model","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vitro gain/loss-of-function plus in vivo KO with ferroptosis phenotype and mTORC1 epistasis","pmids":["36722887"],"is_preprint":false},{"year":2023,"finding":"NERP-4 (a VGF-derived peptide) acts on SNAT2, increasing uptake of glutamine, alanine, and proline into pancreatic β-cells to stimulate glucose-stimulated insulin secretion; SNAT2 deletion and inhibition abolish the protective effects of NERP-4 on β-cell maintenance in db/db mice.","method":"NERP-4 administration to isolated islets and MIN6-K8 cells, SNAT2 deletion and pharmacological inhibition, amino acid uptake assays, insulin secretion assays, Ca2+ influx measurements, db/db mouse model","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic deletion + pharmacological inhibition with functional hormone secretion readout in vitro and in vivo","pmids":["38071217"],"is_preprint":false},{"year":2024,"finding":"UBE2C mediates SNAT2 monoubiquitination at lysine 59 to inhibit K63-linked polyubiquitination at lysine 33; monoubiquitination suppresses EPN1-mediated endocytosis of SNAT2, increasing SNAT2 membrane levels; increased membrane SNAT2 facilitates glutamine uptake and metabolism, promoting VEGFC secretion, lymphangiogenesis, and lymph node metastasis in bladder cancer.","method":"High-throughput sequencing, site-directed mutagenesis of SNAT2 ubiquitination sites (K33, K59), ubiquitination assays (mono vs. K63-linked poly), endocytosis assays, VEGFC secretion assays, in vitro and in vivo lymphangiogenesis models, patient-derived xenograft","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 1 / Strong — site-specific mutagenesis of ubiquitin acceptor sites with mechanistic dissection of two ubiquitin types and downstream functional consequences in vitro and in vivo","pmids":["38949026"],"is_preprint":false},{"year":2025,"finding":"Endothelial cell-specific Slc38a2 knockout (Slc38a2ΔEC) reduces blood pressure in mice; blockade of SLC38A2 by MeAIB increases NO production via activating the AKT-eNOS pathway by inhibiting EC glutamine uptake; MeAIB lowers blood pressure in high-salt and DOCA-induced hypertensive mouse and rat models.","method":"Global and endothelial-specific Slc38a2 knockout mice, scRNA-seq (NO biosynthesis pathway analysis), MeAIB pharmacological inhibition, NO/eNOS/AKT assays, blood pressure measurement in multiple hypertension models","journal":"Science translational medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — cell-type-specific genetic knockout + pharmacological inhibition with mechanistic AKT-eNOS signaling readout and multiple in vivo models","pmids":["40901922"],"is_preprint":false},{"year":2025,"finding":"ALDH2 deficiency promotes vascular smooth muscle cell (VSMC) proliferation and neointima formation by upregulating SLC38A2 expression via ATF4; ALDH2 deficiency increases 4-HNE adducted protein accumulation, which activates ATF4 to transcriptionally upregulate SLC38A2; ATF4 knockdown reverses ALDH2 deficiency-induced VSMC proliferation; AAV2-shRNA or MeAIB inhibition of SLC38A2 attenuates neointima formation.","method":"VSMC-specific ALDH2 knockout mice, luciferase assays, ChIP-qPCR for ATF4 binding at SLC38A2 promoter, ATF4 siRNA knockdown, AAV2-shRNA SLC38A2 knockdown, MeAIB inhibition, 4-HNE quantification, neointima formation assays","journal":"Metabolism: clinical and experimental","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis/ChIP of promoter element + epistasis (ATF4 KD reverses ALDH2 KO) + in vivo rescue with multiple genetic and pharmacological tools","pmids":["41067488"],"is_preprint":false},{"year":2025,"finding":"PTCD3 promotes SLC38A2 mRNA stability in an IGF2BP2-dependent manner (m6A modification); PTCD3 knockdown suppresses glutaminolysis and CRC migration/invasion; SLC38A2 overexpression reverses these effects; KAT2A upregulates PTCD3 via H3K27 acetylation.","method":"Co-IP, RIP assay, dual-luciferase assay (m6A site), PTCD3 knockdown with SLC38A2 rescue, Western blotting, CRC xenograft model","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple interaction assays (Co-IP, RIP) with functional rescue, single lab","pmids":["40304977"],"is_preprint":false},{"year":2026,"finding":"L-proline is transported into bovine mammary epithelial cells via SNAT2; intracellular proline binds P4HA2 (prolyl 4-hydroxylase subunit alpha 2), promoting mTOR lysosomal translocation and mTORC1 signaling pathway activation, thereby enhancing milk fat and protein synthesis.","method":"Targeted metabolomics, SNAT2 and P4HA2 functional studies in bovine mammary epithelial cells, mTOR lysosomal translocation assays, rumen-protected L-Pro feeding trial in dairy cows","journal":"Journal of agricultural and food chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mechanistic pathway established in vitro with in vivo feeding validation, single lab","pmids":["42126009"],"is_preprint":false},{"year":2026,"finding":"SLC38A2 upregulation by melatonin in the hippocampus protects against Aβ-induced ferroptosis: shRNA-mediated SLC38A2 knockdown in HT22 neurons reduces GSH and GPX4, increases iron and ROS, enhances erastin-induced ferroptosis, and abolishes the protective effect of melatonin, demonstrating SLC38A2 functions through the SLC38A2-GSH-GPX4 axis.","method":"shRNA knockdown in HT22 neurons, GSH/GPX4/iron/ROS biochemical assays, erastin-induced ferroptosis, organotypic hippocampal slices, Aβ1-42 oligomer injection mouse model, immunohistochemistry/Western blotting","journal":"Alzheimer's research & therapy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function with multiple ferroptosis markers and rescue of melatonin protection, single lab","pmids":["41715163"],"is_preprint":false}],"current_model":"SLC38A2 (SNAT2) is a ubiquitously expressed, Na+-coupled neutral amino acid transporter (11 TM domains, intracellular N-terminus, extracellular C-terminus) with 1:1 Na+:amino acid stoichiometry that mediates cellular uptake of glutamine, alanine, proline, glycine, and other small neutral amino acids; its expression and plasma membrane abundance are tightly regulated by amino acid availability, hyperosmotic stress, hormones (insulin, cortisol, estrogen, prolactin, glucagon), and inflammatory cytokines (IL-6) through multiple converging mechanisms including ATF4/GCN2-CDK7-dependent transcription via an intronic AARE, eIF2alpha phosphorylation-dependent IRES-mediated translation, JNK-mediated signaling, and protein stability control via Nedd4-2-mediated polyubiquitination of N-terminal lysines; insulin and osmotic stress mobilize intracellular SNAT2 pools (TGN storage site) to the plasma membrane via PI3K-dependent vesicular trafficking; beyond nutrient transport, SNAT2 acts as a transceptor/amino acid sensor whose occupancy represses its own transcription and couples amino acid availability to mTORC1 and GCN2 signaling to regulate protein synthesis, proteolysis, cell volume (via osmolyte accumulation), osteoblast differentiation, ferroptosis resistance, endothelial NO production, and dendritic cell function in anti-tumor immunity."},"narrative":{"mechanistic_narrative":"SLC38A2 (SNAT2) is a ubiquitously expressed, Na+-coupled system A neutral amino acid transporter that couples extracellular nutrient availability to cellular amino acid supply, with a 1:1 Na+:amino acid stoichiometry and selectivity for small neutral amino acids including glutamine, alanine, proline, glycine and the system A analog MeAIB [PMID:10930503, PMID:11172802]. The transporter adopts an 11-transmembrane topology with an intracellular N-terminus and an extracellular, glycosylated C-terminal region [PMID:29678469]; key residues define its transport mechanism — Asn82 in TM1 and a TM1/TM8 Na+ site (Thr384) coordinate Na+ binding [PMID:18319257, PMID:19589779], a C-terminal histidine (H504) confers allosteric pH sensitivity [PMID:16629640], and the extracellular C-terminal tail acts as a voltage regulator of translocation [PMID:21158741]; SNAT2 additionally carries a substrate-independent anion leak conductance dissociable from amino acid transport [PMID:17237199]. SNAT2 expression and surface abundance are controlled by amino acid availability through GCN2/CDK7-dependent ATF4 transcription acting at an intronic AARE bound by ATF/C/EBP factors, eIF2alpha-dependent IRES-mediated translation, and JNK signaling [PMID:16621798, PMID:16445384, PMID:17488712, PMID:30857869], while hormonal and dietary cues converge on dedicated promoter elements — a CRE for cAMP/glucagon, an estrogen response element bound by ERalpha, a ChREBP-repressed ChoRE, and HIF-1alpha under hypoxia [PMID:21386061, PMID:25056967, PMID:33225719, PMID:31152137]. Surface levels are further set post-translationally: insulin and osmotic stress mobilize a TGN-stored SNAT2 pool to the plasma membrane via PI3K-dependent trafficking [PMID:11834730, PMID:17050538], and Nedd4-2-mediated polyubiquitination of N-terminal lysines drives endocytosis and proteasomal degradation, with substrate occupancy and Na+ availability tuning protein stability [PMID:17003038, PMID:25653282, PMID:29467657]. Beyond transport, SNAT2 functions as a transceptor whose occupancy represses its own transcription and couples amino acid status to mTORC1 and downstream protein synthesis and proteolysis [PMID:17488712, PMID:17429052, PMID:18650482]. These activities underpin diverse physiological roles: SNAT2-driven osmolyte accumulation mediates regulatory volume increase under hypertonic stress [PMID:15922329, PMID:16734764], placental SNAT2 supports fetal growth [PMID:34406367], it supplies proline for osteoblast differentiation and bone formation [PMID:35261338, PMID:36213239], protects cells from ferroptosis via mTORC1 and a GSH-GPX4 axis [PMID:36722887, PMID:41715163], regulates endothelial NO production and blood pressure [PMID:40901922], and sustains glutamine-dependent anti-tumor dendritic cell and T-cell immunity [PMID:37407815, PMID:37054944], making it a target in cancer and cardiovascular disease [PMID:36210829, PMID:38949026, PMID:41067488].","teleology":[{"year":2000,"claim":"Established the molecular identity of system A transport by cloning a Na+-dependent neutral amino acid transporter and defining its substrate range, stoichiometry, and ion dependence.","evidence":"Cloning from HepG2 cells and functional expression with radiolabeled transport assays","pmids":["10930503"],"confidence":"High","gaps":["No structural model or topology at this stage","Physiological regulation not yet addressed"]},{"year":2001,"claim":"Showed that SNAT2 is the adaptively regulated arm of system A, answering how cells match transport capacity to amino acid demand.","evidence":"Northern blotting and transport assays under amino acid deprivation/supplementation in fibroblasts","pmids":["11172802"],"confidence":"High","gaps":["Transcriptional mechanism of adaptive regulation not defined","Distinction from osmotic regulation unaddressed"]},{"year":2001,"claim":"Identified hypertonic stress as a second, protein-synthesis-dependent inducer of SNAT2, separating osmotic from nutritional regulation.","evidence":"Transport assays and Northern blotting with cycloheximide/actinomycin D in endothelial cells","pmids":["11322785"],"confidence":"Medium","gaps":["Identity of the required new protein unknown","Signaling pathway not dissected"]},{"year":2002,"claim":"Demonstrated that SNAT2 activity is acutely controlled by trafficking, not only transcription, with insulin recruiting an intracellular pool to the membrane via PI3K.","evidence":"Surface biotinylation, pharmacological inhibition (chloroquine, wortmannin) and insulin stimulation in L6 myotubes; ATA2 redistribution in regenerating rat liver","pmids":["11834730","12054432"],"confidence":"High","gaps":["Identity of the storage compartment not yet resolved","Trafficking machinery uncharacterized"]},{"year":2006,"claim":"Resolved the transcriptional and translational basis of amino-acid-induced SNAT2, locating the AARE to the first intron and showing eIF2alpha-dependent IRES translation, while confirming osmotic induction uses a distinct route.","evidence":"Reporter/EMSA/ChIP of ATF/C/EBP binding, eIF2alpha mutant cells, IRES reporters and in vitro translation in HepG2 and fibroblasts","pmids":["16621798","16445384"],"confidence":"High","gaps":["Upstream kinase coupling GCN2 to transcription not yet identified","Cell-type generality of IRES use unclear"]},{"year":2006,"claim":"Defined SNAT2 as a transceptor and identified parallel sensing pathways, showing JNK drives its induction during withdrawal while the transporter itself represses its own gene during sufficiency.","evidence":"shRNA, transporter chimeras, JNK assays and amino acid supplementation in L6 myotubes","pmids":["17488712"],"confidence":"High","gaps":["Molecular signal emanating from occupied transporter unknown","Domain mediating the transceptor signal not mapped here"]},{"year":2006,"claim":"Established post-translational control of SNAT2 surface abundance through Nedd4-2-mediated polyubiquitination, endocytosis and proteasomal degradation.","evidence":"Oocyte/CHO expression, RNAi, catalytically dead mutant, MG132 and co-localization studies","pmids":["17003038"],"confidence":"High","gaps":["Specific lysine acceptor sites not yet mapped","Signals activating Nedd4-2 toward SNAT2 unknown"]},{"year":2006,"claim":"Located the regulated intracellular SNAT2 pool to the trans-Golgi network and showed insulin mobilizes it independently of GLUT4 vesicles.","evidence":"Live imaging of EGFP-ATA2, syntaxin 6/EEA1 co-localization and brefeldin A inhibition in 3T3-L1 adipocytes","pmids":["17050538"],"confidence":"High","gaps":["Vesicle tethering/fusion machinery unidentified","Whether all stimuli use the same TGN pool unresolved"]},{"year":2005,"claim":"Connected SNAT2 induction to a physiological outcome, showing it is required for osmolyte accumulation and regulatory volume increase under hypertonic stress.","evidence":"siRNA knockdown, transport assays, intracellular amino acid and cell volume measurements in fibroblasts","pmids":["15922329","16734764"],"confidence":"High","gaps":["Transcription factors driving osmotic induction not identified here","In vivo relevance to tissues untested at this stage"]},{"year":2008,"claim":"Linked SNAT2 transport to mTOR-dependent protein synthesis and proteolysis, defining its role in nutrient signaling and muscle protein balance.","evidence":"MeAIB inhibition, acidosis, siRNA and mTOR/PI3K inhibitors with proteolysis and pathway readouts in L6 cells","pmids":["17429052","18650482"],"confidence":"High","gaps":["Direct biochemical coupling of SNAT2 to mTORC1 not shown","In vivo muscle wasting causation not established here"]},{"year":2009,"claim":"Mapped the transport mechanism at residue resolution, identifying Na+-coordinating residues and a substrate-independent anion leak conductance.","evidence":"Site-directed mutagenesis (N82, T384, H304, H504), DEPC modification, electrophysiology and homology modeling in oocytes","pmids":["18319257","19589779","17237199","16629640"],"confidence":"High","gaps":["No experimental high-resolution structure","Physiological role of the anion leak unknown"]},{"year":2014,"claim":"Expanded the regulatory network to hormonal and dietary inputs by identifying functional CRE, ERE and ChoRE promoter elements and their bound factors and co-factors.","evidence":"Promoter reporter mutagenesis, EMSA, ChIP, co-IP and MS-proteomics in hepatocytes, mammary tissue and rat dietary models","pmids":["21386061","25056967","33225719"],"confidence":"High","gaps":["Integration of multiple cis-elements in a single locus not modeled","Tissue-specific element usage incompletely mapped"]},{"year":2015,"claim":"Refined post-translational regulation by mapping N-terminal lysine ubiquitination sites and showing substrate/Na+ occupancy and lipid signals tune SNAT2 stability.","evidence":"Lysine-to-alanine mutagenesis, chimeric transporters, proteasome inhibition and Nedd4-2 silencing in L6/HeLa cells; IUGR placenta correlation","pmids":["25653282","29467657","26374858"],"confidence":"High","gaps":["Full set of E3 ligases beyond Nedd4-2 not enumerated here","How substrate occupancy transmits to N-terminal degron unresolved"]},{"year":2019,"claim":"Identified CDK7 as a GCN2-dependent effector required for adaptive SNAT2 transcription, refining the amino acid response pathway.","evidence":"Pharmacological CDK7 inhibition with drug-resistant rescue and GCN2 epistasis in amino-acid-deprived cells","pmids":["30857869"],"confidence":"High","gaps":["Direct CDK7 substrate linking to ATF4 not defined","Whether CDK7 acts at the SNAT2 locus directly unclear"]},{"year":2022,"claim":"Established in vivo physiological roles for SLC38A2 in fetal growth and skeletal biology through tissue-specific genetic ablation.","evidence":"Placenta-specific shRNA knockdown and osteoblast/Prrx1Cre conditional knockout mice with transport, metabolomic and phenotypic readouts","pmids":["34406367","35261338","36213239"],"confidence":"High","gaps":["Compensation by other system A transporters not fully resolved","Mechanistic coupling of proline supply to differentiation programs incompletely defined"]},{"year":2023,"claim":"Implicated SLC38A2-mediated glutamine uptake in immune cell function and ferroptosis resistance, broadening its role to anti-tumor immunity and cell-death protection.","evidence":"Genetic loss-of-function with FLCN-TFEB epistasis in dendritic cells, XBP1 promoter regulation in T cells, and gain/loss with mTORC1 epistasis in renal ferroptosis models","pmids":["37407815","37054944","36722887"],"confidence":"High","gaps":["Direct biochemical link between glutamine flux and TFEB/ferroptosis machinery not fully reconstituted","Relative contribution of transport vs signaling per context unresolved"]},{"year":2024,"claim":"Dissected a ubiquitin-code switch controlling SNAT2 surface levels in cancer, where UBE2C monoubiquitination blocks degradative K63 chains and EPN1-mediated endocytosis to promote metastasis.","evidence":"Site-specific ubiquitin acceptor mutagenesis (K33/K59), endocytosis and VEGFC secretion assays, and in vivo/PDX bladder cancer models","pmids":["38949026"],"confidence":"High","gaps":["Generality of the mono-/polyubiquitin switch beyond bladder cancer untested","Deubiquitinases counteracting this switch unidentified"]},{"year":2025,"claim":"Defined cardiovascular and metabolic roles for SLC38A2, linking endothelial glutamine uptake to NO/blood pressure and ATF4-driven SLC38A2 to vascular remodeling, plus a NERP-4/SNAT2 axis in insulin secretion.","evidence":"Endothelial and VSMC-specific knockouts, ChIP of ATF4 at the promoter, MeAIB inhibition, and islet/db/db models","pmids":["40901922","41067488","38071217"],"confidence":"High","gaps":["Therapeutic window for SNAT2 inhibition across tissues unknown","Cross-talk between vascular and metabolic SNAT2 functions unexplored"]},{"year":null,"claim":"How occupancy of SNAT2 generates the transceptor signal that biochemically couples to mTORC1, GCN2 and its own transcriptional repression remains undefined at the molecular level.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No reconstituted signaling complex linking transporter occupancy to mTORC1/GCN2","No high-resolution structure to rationalize transport vs sensing states","Direct downstream effectors of the self-repressive transceptor signal unidentified"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0,1,18,30,31,44,46]},{"term_id":"GO:0140299","term_label":"molecular sensor activity","supporting_discovery_ids":[13,18]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[3,4,14,15,43,52]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[15]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[3,52]}],"pathway":[{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[0,1,31,46]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[7,16,9,50]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[13,18,19,48,50]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[14,34,39,52]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[10,29,32,42]}],"complexes":[],"partners":["NEDD4L","ATF4","UBE2C","EPN1","ESR1","CHREBP","FLCN","XBP1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q96QD8","full_name":"Sodium-coupled neutral amino acid symporter 2","aliases":["Amino acid transporter A2","Protein 40-9-1","Solute carrier family 38 member 2","System A amino acid transporter 2","System A transporter 1","System N amino acid transporter 2"],"length_aa":506,"mass_kda":56.0,"function":"Symporter that cotransports neutral amino acids and sodium ions from the extracellular to the intracellular side of the cell membrane (PubMed:10930503, PubMed:15774260, PubMed:15922329, PubMed:16621798). The transport is pH-sensitive, Li(+)-intolerant, electrogenic, driven by the Na(+) electrochemical gradient and cotransports of neutral amino acids and sodium ions with a stoichiometry of 1:1. May function in the transport of amino acids at the blood-brain barrier (PubMed:10930503, PubMed:15774260). May function in the transport of amino acids in the supply of maternal nutrients to the fetus through the placenta (By similarity). Maintains a key metabolic glutamine/glutamate balance underpinning retrograde signaling by dendritic release of the neurotransmitter glutamate (By similarity). Transports L-proline in differentiating osteoblasts for the efficient synthesis of proline-enriched proteins and provides proline essential for osteoblast differentiation and bone formation during bone development (By similarity)","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q96QD8/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SLC38A2","classification":"Not Classified","n_dependent_lines":355,"n_total_lines":1208,"dependency_fraction":0.29387417218543044},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CANX","stoichiometry":0.2},{"gene":"CCDC47","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/SLC38A2","total_profiled":1310},"omim":[{"mim_id":"608490","title":"SOLUTE CARRIER FAMILY 38 (AMINO ACID TRANSPORTER), MEMBER 1; SLC38A1","url":"https://www.omim.org/entry/608490"},{"mim_id":"608065","title":"SOLUTE CARRIER FAMILY 38 (AMINO ACID TRANSPORTER), MEMBER 4; SLC38A4","url":"https://www.omim.org/entry/608065"},{"mim_id":"605180","title":"SOLUTE CARRIER FAMILY 38 (AMINO ACID TRANSPORTER), MEMBER 2; SLC38A2","url":"https://www.omim.org/entry/605180"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Plasma membrane","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/SLC38A2"},"hgnc":{"alias_symbol":["SAT2","ATA2","KIAA1382","SNAT2"],"prev_symbol":[]},"alphafold":{"accession":"Q96QD8","domains":[{"cath_id":"1.20.1740.10","chopping":"72-253_282-499","consensus_level":"high","plddt":90.3135,"start":72,"end":499}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96QD8","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96QD8-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96QD8-F1-predicted_aligned_error_v6.png","plddt_mean":79.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SLC38A2","jax_strain_url":"https://www.jax.org/strain/search?query=SLC38A2"},"sequence":{"accession":"Q96QD8","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96QD8.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96QD8/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96QD8"}},"corpus_meta":[{"pmid":"37407815","id":"PMC_37407815","title":"SLC38A2 and glutamine signalling in cDC1s dictate anti-tumour immunity.","date":"2023","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/37407815","citation_count":230,"is_preprint":false},{"pmid":"27129276","id":"PMC_27129276","title":"Deletion of Amino Acid Transporter ASCT2 (SLC1A5) Reveals an Essential Role for Transporters SNAT1 (SLC38A1) and SNAT2 (SLC38A2) to Sustain Glutaminolysis in Cancer Cells.","date":"2016","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/27129276","citation_count":211,"is_preprint":false},{"pmid":"19741197","id":"PMC_19741197","title":"IL-6 stimulates system A amino acid transporter activity in trophoblast cells through STAT3 and increased expression of SNAT2.","date":"2009","source":"American journal of physiology. 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Neutral Amino Acid Transporter 2(SNAT2) by Chemical Modification.","date":"2016","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/27355203","citation_count":4,"is_preprint":false},{"pmid":"38590564","id":"PMC_38590564","title":"SLC38A2 promotes cell proliferation and invasion by promoting glutamine metabolism in adenomyosis.","date":"2024","source":"Experimental and therapeutic medicine","url":"https://pubmed.ncbi.nlm.nih.gov/38590564","citation_count":3,"is_preprint":false},{"pmid":"38393495","id":"PMC_38393495","title":"SNAT2-mediated regulation of estrogen and progesterone in the proliferation of goat mammary epithelial cells.","date":"2024","source":"Amino acids","url":"https://pubmed.ncbi.nlm.nih.gov/38393495","citation_count":3,"is_preprint":false},{"pmid":"40360154","id":"PMC_40360154","title":"Upregulations of SNAT2 and GLS-1 Are Key Osmoregulatory Responses of Human Corneal Epithelial Cells to Hyperosmotic Stress.","date":"2025","source":"Journal of proteome 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foundational characterization paper\",\n      \"pmids\": [\"10930503\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"ATA2/SLC38A2 mRNA expression is adaptively regulated by amino acid availability: amino acid starvation of human fibroblasts increases ATA2 mRNA and system A transport activity, and supplementation with system A substrates (but not other amino acids) suppresses both ATA2 mRNA and transport activity.\",\n      \"method\": \"Northern blotting, radiolabeled amino acid transport assays in cultured human fibroblasts under amino acid deprivation/supplementation conditions\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal regulation shown with multiple substrate specificities, replicated in subsequent studies\",\n      \"pmids\": [\"11172802\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Hypertonic stress induces ATA2/SLC38A2 mRNA expression and system A transport activity in porcine endothelial cells; cycloheximide and actinomycin D block both responses, indicating that an earlier protein synthesis step is required.\",\n      \"method\": \"Radiolabeled transport assays, Northern blotting, pharmacological inhibition with cycloheximide and actinomycin D in endothelial cells\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean functional assays with pharmacological dissection, single lab\",\n      \"pmids\": [\"11322785\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Insulin stimulates System A (SNAT2/SLC38A2) transport activity in L6 skeletal muscle cells by recruiting SAT2 from an endosomal compartment to the plasma membrane in a phosphatidylinositol 3-kinase (PI3K)-dependent manner; chloroquine (which impairs endosomal recycling) blocks both insulin-stimulated System A activity and plasma membrane SAT2 recruitment without affecting PKB or GSK3 phosphorylation or GLUT4 translocation.\",\n      \"method\": \"Cell surface biotinylation, Western blotting, pharmacological inhibition (chloroquine, wortmannin), insulin stimulation assays in L6 myotubes\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (biotinylation, transport assay, signaling pathway dissection) in single rigorous study\",\n      \"pmids\": [\"11834730\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"After partial hepatectomy in rats, ATA2-mediated system A amino acid transport activity increases by redistribution of ATA2 protein to the plasma membrane, not by increased ATA2 mRNA levels (Northern analysis showed no change in steady-state mRNA).\",\n      \"method\": \"Immunodetection of ATA2 in isolated liver plasma membrane and lysate fractions, Northern blotting, partial hepatectomy model\",\n      \"journal\": \"Archives of biochemistry and biophysics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — fractionation plus transport assay, single lab, moderate sample size\",\n      \"pmids\": [\"12054432\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Transcriptional activation of the ATA2/SLC38A2 gene by amino acid deprivation differs mechanistically from asparagine synthetase: ATA2 mRNA increases within 2–4 h (vs. 4 h lag for AS), is largely independent of de novo protein synthesis, and is not induced by glucose deprivation.\",\n      \"method\": \"mRNA quantification by Northern/RT-PCR, cycloheximide treatment, glucose deprivation, amino acid-free Krebs buffer incubations in HepG2 cells\",\n      \"journal\": \"The Journal of nutrition\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple perturbations in single lab establishing distinct transcriptional regulatory mechanism\",\n      \"pmids\": [\"12368390\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Hypertonic stimulation of system A transport activity requires synthesis of new SNAT2 protein; transcription inhibitor DRB suppresses the hypertonic increase in plasma membrane SNAT2 and fully blocks system A stimulation, whereas DRB does not fully block the adaptive (amino acid starvation) increase in SNAT2 at the plasma membrane.\",\n      \"method\": \"Biotinylation of surface proteins, immunocytochemistry, transcription inhibition (DRB), Western blotting in human fibroblasts\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods, single lab, distinguishes two independent regulatory mechanisms\",\n      \"pmids\": [\"15581851\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"siRNA-mediated knockdown of SNAT2 in human fibroblasts under hypertonic conditions prevents the increase in system A transport activity, blocks intracellular amino acid pool expansion, and markedly delays cell volume recovery, demonstrating that SNAT2 induction is essential for regulatory volume increase.\",\n      \"method\": \"siRNA knockdown, radiolabeled amino acid transport assays, cell volume measurements, intracellular amino acid quantification\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — loss-of-function with specific cellular phenotype, multiple outcome measures, directly implicates SNAT2 in osmoadaptation\",\n      \"pmids\": [\"15922329\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"SNAT2 is expressed in neuronal cell bodies, processes, axonal shafts (but excluded from terminals), and in perivascular astrocytic end-feet and Bergmann glia in the rat CNS; enriched in spinal cord/brainstem and preferentially found in glutamatergic (not GABAergic) neurons.\",\n      \"method\": \"Immunohistochemistry with specific antisera, confocal microscopy, ultrastructural (EM) studies in rat brain\",\n      \"journal\": \"Neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct subcellular localization by multiple imaging methods, single lab\",\n      \"pmids\": [\"15561425\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Amino acid starvation-induced upregulation of SNAT2 requires eIF2alpha phosphorylation (blunted in cells with a non-phosphorylatable eIF2alpha mutant), increased gene transcription, and IRES-mediated cap-independent translation; hypertonic stress induction of SNAT2 is independent of eIF2alpha phosphorylation.\",\n      \"method\": \"Transport assays, mRNA/protein quantification, eIF2alpha phosphorylation-deficient mutant cells, IRES reporter constructs, in vitro translation, cycloheximide and actinomycin D inhibition\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal mechanistic approaches (mutant cell lines, reporter assays, in vitro translation) in single rigorous study\",\n      \"pmids\": [\"16621798\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"The amino acid response element (AARE) regulating SNAT2 transcription upon amino acid limitation localizes to the first intron; ATF and C/EBP family members bind this intronic enhancer (not the promoter) in vitro and in vivo, with specific family members either activating or repressing SNAT2 transcription; amino acid deprivation increases RNA pol II recruitment to the SNAT2 promoter.\",\n      \"method\": \"Luciferase reporter assays, EMSA, ChIP assays, exogenous ATF/C/EBP expression, mRNA quantification in HepG2 and fibroblast cells\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstitution of regulatory element with mutagenesis, EMSA, and in vivo ChIP in multiple cell types\",\n      \"pmids\": [\"16445384\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Cortisol stimulates system A amino acid transport activity and increases SNAT2 mRNA/protein expression in BeWo placental cells; lower cortisol concentrations cause relocalization of SNAT2 transporter.\",\n      \"method\": \"Radiolabeled MeAIB transcellular transport assays, Northern and Western blotting, immunocytochemistry in BeWo cells\",\n      \"journal\": \"American journal of physiology. Endocrinology and metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional transport assay combined with expression and localization data, single lab\",\n      \"pmids\": [\"16621896\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"pH sensitivity of SNAT2 transport involves a conserved C-terminal histidine residue (H504): DEPC modification reduces pH-sensitivity and blocks decreased Na+ affinity at low pH; H504A mutation produces reduced, DEPC-resistant pH-sensitivity without changing Na+ affinity at low pH. This suggests an allosteric H+-modifier site on C-terminal histidine that influences Na+ binding.\",\n      \"method\": \"DEPC chemical modification, site-directed mutagenesis (H504A), functional transport assays in Xenopus oocytes expressing SNAT2 and SNAT5\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis + chemical modification + electrophysiology in Xenopus oocyte reconstitution system\",\n      \"pmids\": [\"16629640\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"SNAT2 activity is regulated by at least two amino acid sensor pathways: during amino acid withdrawal, JNK is activated and induces SNAT2 expression via an intronic nutrient-sensitive domain; large neutral amino acids (Tyr, Gln) inhibit JNK activation and SNAT2 upregulation. Additionally, SNAT2 itself provides a repressive signal for its own gene transcription during amino acid sufficiency (transceptor function), demonstrated by shRNA and transporter chimeras.\",\n      \"method\": \"shRNA knockdown, transporter chimera experiments, JNK activity assays, reporter gene assays, amino acid supplementation experiments in L6 myotubes\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — loss-of-function (shRNA), chimeric transporter approach, and pharmacological dissection identifying two distinct sensor pathways\",\n      \"pmids\": [\"17488712\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Ubiquitin ligase Nedd4-2 downregulates ATA2/SNAT2 transport activity at the cell surface by promoting polyubiquitination of ATA2 leading to endocytosis and proteasomal degradation; catalytically dead Nedd4-2 mutant had no effect; RNAi knockdown of Nedd4-2 increased ATA2 activity with decreased ATA2 polyubiquitination; Nedd4-2 co-localizes with EGFP-ATA2 at the plasma membrane.\",\n      \"method\": \"Xenopus oocyte expression, CHO cell transfection, RNAi knockdown, immunofluorescence, co-localization studies, proteasome inhibitor (MG132) experiments\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple expression systems, RNAi, dominant-negative mutant, and direct co-localization establishing E3 ligase-substrate relationship\",\n      \"pmids\": [\"17003038\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"ATA2/SNAT2 is stored at the trans-Golgi network (TGN) in 3T3-L1 adipocytes (co-localizing with syntaxin 6, not EEA1); insulin stimulates release of ATA2-containing vesicles from this TGN compartment to the plasma membrane. The ATA2 storage vesicles are distinct from GLUT4-containing vesicles. Brefeldin A (TGN exit blocker) inhibits insulin-stimulated MeAIB uptake more profoundly than glucose uptake.\",\n      \"method\": \"Live cell imaging of EGFP-ATA2 fusion protein, immunofluorescence with TGN marker syntaxin 6 and endosomal marker EEA1, brefeldin A inhibition, transport assays in 3T3-L1 adipocytes\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — live cell imaging + organelle marker co-localization + pharmacological inhibition with functional readout, multiple orthogonal methods\",\n      \"pmids\": [\"17050538\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"SNAT2 mediates induction of cell volume recovery (regulatory volume increase, RVI) upon hypertonic exposure: SNAT2-specific siRNA in human fibroblasts prevents system A transport stimulation, reduces intracellular amino acid pool expansion, and significantly delays cell volume recovery; newly synthesized SNAT2 proteins under hypertonic conditions are preferentially targeted to the cell membrane.\",\n      \"method\": \"siRNA, transport assays, intracellular amino acid quantification, cell volume measurements in human fibroblasts\",\n      \"journal\": \"Acta physiologica (Oxford, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — loss-of-function with direct cellular phenotype (volume recovery), multiple outcome measures, consistent with independent reports\",\n      \"pmids\": [\"16734764\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"SNAT2 mediates an anion leak conductance that does not require substrate transport; transported substrates (L-alanine, L-glutamine, MeAIB) inhibit the anion leak with different potencies; mutation H304A abolishes alanine transport but retains anion leak current; both Na+ and substrate can bind H304A transporter; anion selectivity follows SCN->NO3->I->Br->Cl->Mes-.\",\n      \"method\": \"Whole-cell electrophysiology (patch clamp), site-directed mutagenesis (H304A), substrate binding assays in Xenopus oocytes and HEK293 cells\",\n      \"journal\": \"Biophysical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — electrophysiological reconstitution with mutagenesis separating transport from anion conductance\",\n      \"pmids\": [\"17237199\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"SNAT2 inhibition by methylaminoisobutyrate (MeAIB), metabolic acidosis (pH 7.1), or siRNA knockdown depletes intracellular glutamine and indirectly depletes leucine (maintained by the glutamine gradient via system L), leading to impaired mTOR signaling (reduced p70S6K1, S6, and 4E-BP1 phosphorylation) and impaired protein synthesis in L6 skeletal muscle cells.\",\n      \"method\": \"Competitive substrate inhibition (MeAIB), pH manipulation, siRNA knockdown, intracellular amino acid profiling, mTOR pathway Western blotting in L6 cells\",\n      \"journal\": \"Journal of the American Society of Nephrology : JASN\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — three independent SNAT2 inhibition approaches converging on same mTOR signaling outcome, multiple readouts\",\n      \"pmids\": [\"17429052\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"SNAT2 inhibition by MeAIB or metabolic acidosis (pH 7.1) stimulates proteolysis in L6 myotubes via both mTOR and PI3K signaling pathways; partial SNAT2 siRNA silencing stimulates proteolysis and impairs insulin signaling through PI3K; acidosis shifts insulin dose-response for suppression of proteolysis rightward, demonstrating that SNAT2 provides a link between acidosis, insulin resistance, and protein wasting.\",\n      \"method\": \"MeAIB inhibition, pH manipulation, siRNA knockdown, proteasome inhibition, mTOR and PI3K inhibitors, proteolysis rate measurement, Western blotting in L6 cells\",\n      \"journal\": \"Journal of the American Society of Nephrology : JASN\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple independent perturbations (inhibitor, siRNA, pH) with pharmacological pathway dissection and multiple cellular readouts\",\n      \"pmids\": [\"18650482\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"SNAT2 transport activity is regulated by amino acid substrate availability and Na+; the insulin-induced upregulation of system A in L6 cells is mediated by increased Vmax (not Km), and is blocked by chloroquine and wortmannin; amino acid deprivation induction is blocked by PD98059 (MEK inhibitor) and SP600125 (JNK inhibitor); osmotic shock induction is blocked by neither chloroquine/wortmannin nor PD98059/SP600125, indicating distinct mechanisms.\",\n      \"method\": \"Radiolabeled transport kinetics, pharmacological inhibitor panel (chloroquine, wortmannin, PD98059, SP600125, SB202190), Western blotting, RT-PCR in L6 rat skeletal muscle cells\",\n      \"journal\": \"Amino acids\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — comprehensive pharmacological dissection distinguishing three regulatory mechanisms, single lab\",\n      \"pmids\": [\"18330498\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Asparagine 82 (N82) in transmembrane domain 1 of SNAT2 is critical for Na+ coordination: N82A mutation virtually eliminates alanine-induced transport current and amino acid uptake, dramatically reduces Na+ affinity (Kna), and increases apparent Km for alanine 27-fold; N82S has intermediate effect. Y337A and R374Q mutations do not abolish transport.\",\n      \"method\": \"Site-directed mutagenesis (N82A, N82S, Y337A, R374Q), electrophysiology, radiolabeled amino acid uptake in Xenopus oocytes\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — site-directed mutagenesis with full kinetic characterization in reconstituted expression system\",\n      \"pmids\": [\"18319257\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Despite increased ATF4 binding to the C/EBP-ATF site in the SNAT2 intronic AARE during UPR activation in HepG2 cells, SNAT2 transcription is not enhanced; the UPR suppresses AAR-induced SNAT2 transcription acting downstream of ATF4 binding, associated with lack of H3 hyperacetylation and failure to recruit general transcription factors at the SNAT2 promoter.\",\n      \"method\": \"ChIP assays, luciferase reporter assays, H3 acetylation analysis, ATF4 binding assays, simultaneous AAR+UPR activation in HepG2 cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal chromatin methods with functional reporter assays establishing mechanistic distinction between AAR and UPR regulation\",\n      \"pmids\": [\"18697751\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"A conserved Na+ binding site in SNAT2 is formed by transmembrane helices 1 and 8: T384A mutation inhibits the anion leak current (which requires Na+ binding) and dramatically lowers Na+ affinity, consistent with homology modeling using LeuT and Mhp1 as templates that predicted a Na+ binding site involving TM1 and TM8.\",\n      \"method\": \"Profile-based sequence analysis, homology modeling (LeuT/Mhp1 templates), site-directed mutagenesis (T384A), electrophysiology, Na+ affinity measurements\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — structure-guided mutagenesis with functional validation in Xenopus oocyte reconstitution system\",\n      \"pmids\": [\"19589779\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"IL-6 stimulates system A amino acid transport and increases SNAT2 (but not SNAT1) mRNA and protein expression in primary human trophoblast cells via a JAK/STAT3 (Tyr705 phosphorylation)-dependent pathway; siRNA knockdown of STAT3 abolishes IL-6-stimulated system A activity and SNAT2 expression. TNF-alpha stimulates system A independently of the JAK/STAT pathway.\",\n      \"method\": \"Radiolabeled transport assays, STAT3 siRNA knockdown, Western blotting (STAT3 phosphorylation), RT-PCR, TNF-alpha and IL-6 treatment of primary human trophoblast cells\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — RNAi knockdown of signaling mediator with functional rescue readout, reciprocal IL-6/TNF comparison\",\n      \"pmids\": [\"19741197\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"In neocortical neurons, taurine, GABA, and beta-alanine (SLC6 GABA transporter substrates) repress SNAT2 expression more potently (10x) than system A substrates; increased endogenous SNAT2 expression or repression did not affect spontaneous glutamatergic excitatory action-potential frequency or quantal size, suggesting SNAT2 is not required to support neurotransmitter glutamate synthesis in these neurons under physiological conditions.\",\n      \"method\": \"shRNA-mediated SNAT2 induction/repression, electrophysiology (spontaneous excitatory activity), SNAT2 mRNA stability assays, amino acid supplementation in neocortical neurons\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional electrophysiology with molecular manipulation, single lab; negative finding regarding glutamatergic role\",\n      \"pmids\": [\"19240036\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Chronic competitive inhibition of SNAT2 (System A) by MeAIB in MCF-7 cells depletes intracellular SNAT2 substrates and branched-chain amino acids (e.g., leucine) but paradoxically elevates mTOR-dependent p70S6K1 phosphorylation; two novel SNAT2-interacting proteins were identified by proteomics of TAP-tag purified SNAT2 fusion proteins, potentially functioning with SNAT2 as a transceptor.\",\n      \"method\": \"Competitive inhibition (MeAIB), intracellular amino acid profiling, mTOR signaling Western blotting, TAP-tag purification followed by proteomic analysis in MCF-7 cells\",\n      \"journal\": \"Frontiers in bioscience (Elite edition)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — proteomic identification of interacting proteins plus mTOR signaling assays, single lab, proteomic IDs not named/validated by independent methods\",\n      \"pmids\": [\"21622135\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The C-terminal domain of SNAT2 (extracellular, 13 residues) is an important voltage regulator required for amino acid translocation at negative membrane potentials; deletion of 13 C-terminal residues abolishes transport at negative potentials but preserves transport at positive potentials; the truncation also increases alanine affinity (~3-fold) and Na+ affinity (~2-fold) but does not affect membrane expression.\",\n      \"method\": \"Site-directed deletion mutagenesis, whole-cell electrophysiology, radiolabeled substrate uptake, surface expression assays in Xenopus oocytes\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — deletion mutagenesis with full electrophysiological and kinetic characterization\",\n      \"pmids\": [\"21158741\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"SNAT2 is the primary L-proline transporter on embryonic stem (ES) cells mediating L-proline-induced differentiation to early primitive ectoderm-like cells; excess SNAT2 substrates (but not non-substrates) prevent L-proline-induced changes in morphology, gene expression, and differentiation kinetics, demonstrating that L-proline uptake through SNAT2 is required for ES cell differentiation.\",\n      \"method\": \"Competitive substrate inhibition with SNAT2 substrates vs. non-substrates, morphology assessment, gene expression analysis, differentiation kinetics in ES cells\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — substrate-specificity competition experiments with functional readouts (differentiation phenotype), single lab\",\n      \"pmids\": [\"21346154\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The rat SNAT2 gene promoter contains a functional CRE site at -48 bp (highly conserved among rat, mouse, and human) responsible for cAMP/glucagon-stimulated transcription; deletion and mutation analyses, EMSA, and ChIP confirmed that this CRE site mediates SNAT2 regulation by cAMP. A high-protein diet (which increases serum glucagon) also increases SNAT2 mRNA in vivo.\",\n      \"method\": \"5' deletion analysis of SNAT2 promoter, site-directed mutagenesis of CRE sites, luciferase reporter assays, EMSA, ChIP, forskolin/glucagon treatment in hepatocytes, in vivo dietary manipulation\",\n      \"journal\": \"American journal of physiology. Endocrinology and metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis + EMSA + in vivo ChIP with functional reporter assays, validated in vivo\",\n      \"pmids\": [\"21386061\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SNAT2 (SLC38A2) transports anti-[18F]FACBC (a PET radiotracer) with a Km of ~197 µM in Xenopus oocytes expressing SNAT2, demonstrating FACBC is a substrate of SNAT2 (with lower affinity than ASCT2, LAT1, and LAT2).\",\n      \"method\": \"Radiolabeled [14C]FACBC kinetic transport assays in Xenopus oocytes expressing SNAT2, ASCT2, LAT1, or LAT2; Michaelis-Menten kinetics\",\n      \"journal\": \"Nuclear medicine and biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct in vitro transport assay in Xenopus oocyte expression system, single lab\",\n      \"pmids\": [\"23647854\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Only SNAT2 (not SNAT1 or SNAT4) transports betaine with a Km of ~5 mM; betaine uptake by SNAT2 is hyperosmotically inducible in placental trophoblast cells (TR-TBT 18d-1), and SNAT2 protein expression on the plasma membrane is more potently induced by hypertonicity than total SNAT2 expression.\",\n      \"method\": \"[14C]betaine uptake assays, transfection of HEK293 cells with SNAT1, SNAT2, SNAT4, Western blotting for plasma membrane vs. total SNAT2, immunocytochemistry under hypertonic conditions\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct substrate transport assay with subtype specificity in heterologous expression, single lab\",\n      \"pmids\": [\"24434061\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"17β-estradiol regulates SNAT2 transcription through an estrogen response element (ERE) in the SNAT2 promoter bound by estrogen receptor alpha (ER-α); ER-α binding to the SNAT2 ERE increases progressively during gestation in the mammary gland; the ER-α-ERE complex contains PARP1, Ku70, and GAPDH as co-factors required for estradiol-stimulated promoter activity.\",\n      \"method\": \"In silico ERE identification, luciferase reporter assays with ERE deletion, EMSA with supershift assay, in vivo ChIP during gestation, LC-MS proteomics of the ER-α-ERE complex, siRNA knockdown of co-factors\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal methods (EMSA, ChIP, reporter mutagenesis, MS-proteomics of complex) in single rigorous study\",\n      \"pmids\": [\"25056967\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Ubiquitination of SNAT2 by Nedd4-2 (NEDD4L) is increased in IUGR placentas; increased NEDD4-2 expression and SNAT2 ubiquitination are associated with decreased SNAT2 in the trophoblast microvillous plasma membrane and reduced system A transport activity. mTOR signaling (mTORC1 and mTORC2) is decreased in IUGR, consistent with mTOR regulating SNAT2 trafficking by modulating ubiquitination.\",\n      \"method\": \"Protein fractionation, ubiquitination assays, Western blotting for mTOR pathway components and NEDD4-2, system A transport assays in isolated plasma membranes from IUGR and control placentas\",\n      \"journal\": \"Clinical science (London, England : 1979)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — human tissue with fractionation and functional transport assay, correlative mTOR link without direct manipulation\",\n      \"pmids\": [\"26374858\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Linoleic acid (unsaturated C18:2 fatty acid) reduces stress-induced SNAT2 protein and membrane transport activity via the ubiquitin-proteasome system; mutating seven N-terminal lysyl-ubiquitination sites of SNAT2 to alanine protects against linoleic acid-induced degradation; Nedd4.2 is upregulated by linoleic acid but Nedd4.2 shRNA silencing does not curb fatty acid-induced SNAT2 loss.\",\n      \"method\": \"Proteasome inhibition, shRNA Nedd4.2 silencing, SNAT2 N-terminal lysine-to-alanine mutations, transport assays, Western blotting in L6 myotubes and HeLa cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis of ubiquitination sites + RNAi + pharmacological inhibition with functional transport readout\",\n      \"pmids\": [\"25653282\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Hyperosmotic stress response involves coordinated induction of SNAT2 and GADD34; SNAT2-mediated amino acid uptake is enhanced by increased GADD34 levels through decreased eIF2alpha phosphorylation; GADD34 induction during hyperosmotic stress is controlled by c-Jun-binding CRE in GADD34 promoter and mRNA stabilization (not ATF4, which is not translated despite eIF2alpha phosphorylation).\",\n      \"method\": \"GADD34 expression analysis, eIF2alpha phosphorylation assays, reporter gene assays, mRNA stability assays, amino acid transport assays in response to hyperosmotic stress\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple molecular readouts establishing SNAT2/GADD34 axis, single lab\",\n      \"pmids\": [\"26041779\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Net glutamine uptake in HeLa and 143B cancer cells does not depend on ASCT2 (deletion does not reduce cell growth) but requires expression of SNAT1 and SNAT2; ASCT2 deletion causes amino acid starvation response and upregulation of SNAT1. Silencing GCN2 in the ASCT2-/- background reduces cell growth.\",\n      \"method\": \"CRISPR/gene deletion of ASCT2, SNAT siRNA silencing, cell growth assays, GCN2 siRNA in knockout background, radiolabeled transport assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic deletion + epistasis (GCN2 in ASCT2-/- background) with multiple functional readouts\",\n      \"pmids\": [\"27129276\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"A disulfide bond exists between Cys245 and Cys279 in SNAT2; this disulfide bond does not affect cell surface trafficking or transport function, but marks proximity in the extracellular domain.\",\n      \"method\": \"Site-directed mutagenesis (C245A, C279A, C245,279A double mutant), mPEG-Mal chemical modification with/without DTT reduction, transport assays in HEK293 cells\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — chemical modification + mutagenesis in heterologous expression, single lab\",\n      \"pmids\": [\"27355203\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SNAT2 membrane topology consists of 11 transmembrane domains with an intracellular N-terminus and extracellular C-terminus; three N-glycosylation sites were confirmed at the largest extracellular loop.\",\n      \"method\": \"mPEG-Mal chemical modification, protease cleavage assays, immunofluorescence, glycosylation analysis in rat SNAT2\",\n      \"journal\": \"Biochimica et biophysica acta. Biomembranes\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple biochemical topology mapping methods in single study, single lab\",\n      \"pmids\": [\"29678469\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SNAT2 protein stability is regulated by substrate (AA and Na+) availability: AA withdrawal increases SNAT2 protein stability; provision of SNAT2 substrates (MeAIB, glutamine) but not non-substrates represses this stabilization; the N-terminal cytoplasmic tail of SNAT2 (containing lysyl residues) is required for substrate-induced instability; grafting the SNAT2 N-terminal tail onto SNAT5 (which lacks adaptive regulation) confers substrate-induced changes in SNAT5 chimera stability. Extracellular Na+ removal destabilizes SNAT2 regardless of substrate presence.\",\n      \"method\": \"Chimeric transporter construction, N-terminal lysine-to-alanine mutations, Western blotting for protein stability, substrate provision experiments in HeLa cells\",\n      \"journal\": \"Frontiers in pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — chimeric transporter approach with mutagenesis establishing N-terminal domain as regulatory sensor, multiple perturbations\",\n      \"pmids\": [\"29467657\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CDK7 activity is upregulated in amino acid-deprived cells in a GCN2-dependent manner and is required for the SNAT2 adaptive transcription response; pharmacological inhibition of CDK7 with THZ-1 attenuates ATF4 expression and blocks system A adaptation; this effect is mitigated in cells expressing a drug-resistant CDK7 form. GSK3, MEK-ERK, mTORC1, and p38 inhibition have no detectable effect on System A adaptation.\",\n      \"method\": \"Pharmacological CDK inhibitors (roscovitine, flavopiridol, THZ-1), drug-resistant CDK7 rescue construct, shRNA GSK3, CDK7 activity assays, System A transport assays in amino acid-deprived cells\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular cell research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — rescue with drug-resistant CDK7, multiple pharmacological probes, and epistasis with GCN2\",\n      \"pmids\": [\"30857869\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SNAT2 in breast cancer MCF7 cells is regulated by both ERα and HIF-1α; under hypoxia, regulation shifts from ERα-dependent to predominantly HIF-1α-dependent (both regulatory elements overlap in SNAT2 cis-regulatory region); downregulation by fulvestrant (ER antagonist) is reverted in hypoxia; SNAT2 overexpression in vivo causes complete resistance to antiestrogen therapy.\",\n      \"method\": \"Reporter assays, HIF-1α/ERα binding site analysis, fulvestrant treatment under normoxia vs. hypoxia, in vitro overexpression/growth assays, xenograft in vivo studies\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vitro and in vivo functional studies with regulatory element overlap analysis establishing regulatory switch mechanism\",\n      \"pmids\": [\"31152137\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"ChREBP represses SNAT2 expression in response to a high-carbohydrate diet by binding to a carbohydrate response element (ChoRE) at -160 bp upstream of the SNAT2 transcriptional start site, and recruits the co-repressor SMRT; confirmed by ChIP-qPCR in vivo and immunoprecipitation showing ChREBP-SMRT interaction.\",\n      \"method\": \"Luciferase reporter assays with ChoRE, immunoprecipitation (ChREBP-SMRT), in vivo ChIP, high-sucrose diet rat model, Western blotting\",\n      \"journal\": \"American journal of physiology. Endocrinology and metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro and in vivo ChIP + co-IP + reporter assays identifying promoter element, interacting co-repressor, and in vivo dietary validation\",\n      \"pmids\": [\"33225719\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Placenta-specific Slc38a2/SNAT2 knockdown (59% reduction via lentiviral shRNA) in mice causes fetal growth restriction: reduces near-term fetal and placental weight, fetal viability, trophoblast plasma membrane SNAT2 protein abundance, and placental system A (MeAIB) uptake, directly demonstrating that SNAT2 deficiency in the placenta mechanistically causes restricted fetal growth.\",\n      \"method\": \"Lentiviral shRNA transduction of blastocysts, 14C-MeAIB uptake assay, Western blotting, fetal/placental weight measurements\",\n      \"journal\": \"Clinical science (London, England : 1979)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — organ-specific knockdown with quantitative transport assay and multiple fetal phenotype readouts\",\n      \"pmids\": [\"34406367\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SLC38A2 provides proline to osteoblasts to fulfill the unique biosynthetic demand imposed by differentiation; osteoblast-associated proteins (RUNX2, OSX, OCN, COL1A1) are enriched in proline; genetic ablation of SLC38A2 in osteoblasts limits osteoblast differentiation and bone formation in mice; proline from SLC38A2 is primarily incorporated into nascent protein with little metabolism.\",\n      \"method\": \"Bioinformatic amino acid composition analysis, osteoblast-specific Slc38a2 genetic ablation (mouse), metabolomics (proline tracking), osteoblast differentiation assays\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo genetic ablation with differentiation/bone phenotype plus metabolomic substrate tracking\",\n      \"pmids\": [\"35261338\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SLC38A2 provides proline and alanine to osteoblast lineage cells during postnatal bone homeostasis; genetic ablation of SLC38A2 using Prrx1Cre decreases bone mass in male and female mice due to reduced osteoblast numbers and bone-forming activity, attributable to impaired proliferation and osteogenic differentiation of skeletal stem and progenitor cells.\",\n      \"method\": \"Prrx1Cre-mediated conditional Slc38a2 knockout in mice, μCT bone analysis, histomorphometry, skeletal stem cell proliferation and differentiation assays\",\n      \"journal\": \"Frontiers in physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cell-type-specific genetic ablation with detailed skeletal phenotyping, both sexes\",\n      \"pmids\": [\"36213239\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SNAT2 is responsible for sarcosine and glycine uptake in hyperosmotic-stressed PC-3 prostate cancer cells; hyperosmotic culture increases SNAT2 mRNA/protein and sarcosine uptake ~9-fold; siRNA knockdown of SNAT2 reduces sarcosine uptake Vmax from 2653 to 513 nmol/mg/min without altering Km, indicating SNAT2 accounts for ~80% of hyperosmotic sarcosine transport. Sarcosine is identified as a novel SNAT2 substrate.\",\n      \"method\": \"siRNA knockdown, 14C-sarcosine and 3H-glycine uptake kinetics, RT-PCR, Western blotting in PC-3 cells under isosmotic and hyperosmotic conditions\",\n      \"journal\": \"Pflugers Archiv : European journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown with direct substrate transport kinetics identifying novel substrate, single lab\",\n      \"pmids\": [\"36175560\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Identification of a potent SNAT2 inhibitor (MMTC/57E, IC50 0.8–3 µM) using a high-throughput FMP membrane potential assay; the compound discriminates against SNAT1. In combination with the glucose transport inhibitor Bay-876, the SNAT2 inhibitor halts proliferative growth of MDA-MB-231 and HPAFII cancer cells, demonstrating synergy between SNAT2 (glutaminolysis) and glucose transport inhibition.\",\n      \"method\": \"High-throughput FLIPR membrane potential assay screening, IC50 determination, SNAT1/SNAT2 selectivity assays, cancer cell proliferation assays with combination treatment\",\n      \"journal\": \"Frontiers in pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional electrogenic assay with selectivity profiling and cellular combination study, single lab\",\n      \"pmids\": [\"36210829\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"In type-1 conventional dendritic cells (cDC1s), SLC38A2-mediated glutamine uptake regulates anti-tumor immunity; tumor cells and cDC1s compete for glutamine via SLC38A2; glutamine signaling via FLCN impinges on TFEB function; SLC38A2 deficiency in cDC1s selectively impairs cDC1 function in vivo and phenocopies FLCN loss; intratumoral glutamine supplementation augments cDC1-mediated CD8+ T cell immunity and overcomes therapeutic resistance.\",\n      \"method\": \"Genetic loss-of-function (SLC38A2 deficiency, FLCN knockout in DCs), TFEB functional assays, nutrient screening, in vivo tumor models, T cell immunity readouts, epistasis (FLCN KO phenocopies SLC38A2 deficiency in a TFEB-dependent manner)\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo genetic loss-of-function with FLCN-TFEB epistasis, multiple functional immune readouts, tumor models\",\n      \"pmids\": [\"37407815\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"XBP1 inhibits SLC38A2 by directly binding to its promoter in cytotoxic T cells in multiple myeloma; SLC38A2 silencing reduces glutamine uptake and causes immune dysfunction of T cells in vitro.\",\n      \"method\": \"Single-cell RNA sequencing, in vitro XBP1 overexpression with promoter binding assay, SLC38A2 siRNA knockdown, glutamine uptake assays, T cell functional assays\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct promoter binding assay with loss-of-function and functional readout, single lab\",\n      \"pmids\": [\"37054944\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SLC38A2 protects renal medullary collecting duct (MCD) cells from hyperosmolarity-induced ferroptosis; hyperosmotic cell death occurred mainly via ferroptosis and was significantly attenuated by SLC38A2 overexpression and worsened by Slc38a2 deletion/silencing; the osmoprotective effect of SLC38A2 is dependent on mTORC1 activation; Slc38a2-knockout mice showed increased medullary ferroptosis following water restriction.\",\n      \"method\": \"SLC38A2 overexpression, siRNA silencing, Slc38a2 gene deletion, ferroptosis assays, mTORC1 activity assays, water restriction in vivo mouse model\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vitro gain/loss-of-function plus in vivo KO with ferroptosis phenotype and mTORC1 epistasis\",\n      \"pmids\": [\"36722887\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"NERP-4 (a VGF-derived peptide) acts on SNAT2, increasing uptake of glutamine, alanine, and proline into pancreatic β-cells to stimulate glucose-stimulated insulin secretion; SNAT2 deletion and inhibition abolish the protective effects of NERP-4 on β-cell maintenance in db/db mice.\",\n      \"method\": \"NERP-4 administration to isolated islets and MIN6-K8 cells, SNAT2 deletion and pharmacological inhibition, amino acid uptake assays, insulin secretion assays, Ca2+ influx measurements, db/db mouse model\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic deletion + pharmacological inhibition with functional hormone secretion readout in vitro and in vivo\",\n      \"pmids\": [\"38071217\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"UBE2C mediates SNAT2 monoubiquitination at lysine 59 to inhibit K63-linked polyubiquitination at lysine 33; monoubiquitination suppresses EPN1-mediated endocytosis of SNAT2, increasing SNAT2 membrane levels; increased membrane SNAT2 facilitates glutamine uptake and metabolism, promoting VEGFC secretion, lymphangiogenesis, and lymph node metastasis in bladder cancer.\",\n      \"method\": \"High-throughput sequencing, site-directed mutagenesis of SNAT2 ubiquitination sites (K33, K59), ubiquitination assays (mono vs. K63-linked poly), endocytosis assays, VEGFC secretion assays, in vitro and in vivo lymphangiogenesis models, patient-derived xenograft\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — site-specific mutagenesis of ubiquitin acceptor sites with mechanistic dissection of two ubiquitin types and downstream functional consequences in vitro and in vivo\",\n      \"pmids\": [\"38949026\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Endothelial cell-specific Slc38a2 knockout (Slc38a2ΔEC) reduces blood pressure in mice; blockade of SLC38A2 by MeAIB increases NO production via activating the AKT-eNOS pathway by inhibiting EC glutamine uptake; MeAIB lowers blood pressure in high-salt and DOCA-induced hypertensive mouse and rat models.\",\n      \"method\": \"Global and endothelial-specific Slc38a2 knockout mice, scRNA-seq (NO biosynthesis pathway analysis), MeAIB pharmacological inhibition, NO/eNOS/AKT assays, blood pressure measurement in multiple hypertension models\",\n      \"journal\": \"Science translational medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cell-type-specific genetic knockout + pharmacological inhibition with mechanistic AKT-eNOS signaling readout and multiple in vivo models\",\n      \"pmids\": [\"40901922\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"ALDH2 deficiency promotes vascular smooth muscle cell (VSMC) proliferation and neointima formation by upregulating SLC38A2 expression via ATF4; ALDH2 deficiency increases 4-HNE adducted protein accumulation, which activates ATF4 to transcriptionally upregulate SLC38A2; ATF4 knockdown reverses ALDH2 deficiency-induced VSMC proliferation; AAV2-shRNA or MeAIB inhibition of SLC38A2 attenuates neointima formation.\",\n      \"method\": \"VSMC-specific ALDH2 knockout mice, luciferase assays, ChIP-qPCR for ATF4 binding at SLC38A2 promoter, ATF4 siRNA knockdown, AAV2-shRNA SLC38A2 knockdown, MeAIB inhibition, 4-HNE quantification, neointima formation assays\",\n      \"journal\": \"Metabolism: clinical and experimental\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis/ChIP of promoter element + epistasis (ATF4 KD reverses ALDH2 KO) + in vivo rescue with multiple genetic and pharmacological tools\",\n      \"pmids\": [\"41067488\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PTCD3 promotes SLC38A2 mRNA stability in an IGF2BP2-dependent manner (m6A modification); PTCD3 knockdown suppresses glutaminolysis and CRC migration/invasion; SLC38A2 overexpression reverses these effects; KAT2A upregulates PTCD3 via H3K27 acetylation.\",\n      \"method\": \"Co-IP, RIP assay, dual-luciferase assay (m6A site), PTCD3 knockdown with SLC38A2 rescue, Western blotting, CRC xenograft model\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple interaction assays (Co-IP, RIP) with functional rescue, single lab\",\n      \"pmids\": [\"40304977\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"L-proline is transported into bovine mammary epithelial cells via SNAT2; intracellular proline binds P4HA2 (prolyl 4-hydroxylase subunit alpha 2), promoting mTOR lysosomal translocation and mTORC1 signaling pathway activation, thereby enhancing milk fat and protein synthesis.\",\n      \"method\": \"Targeted metabolomics, SNAT2 and P4HA2 functional studies in bovine mammary epithelial cells, mTOR lysosomal translocation assays, rumen-protected L-Pro feeding trial in dairy cows\",\n      \"journal\": \"Journal of agricultural and food chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mechanistic pathway established in vitro with in vivo feeding validation, single lab\",\n      \"pmids\": [\"42126009\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"SLC38A2 upregulation by melatonin in the hippocampus protects against Aβ-induced ferroptosis: shRNA-mediated SLC38A2 knockdown in HT22 neurons reduces GSH and GPX4, increases iron and ROS, enhances erastin-induced ferroptosis, and abolishes the protective effect of melatonin, demonstrating SLC38A2 functions through the SLC38A2-GSH-GPX4 axis.\",\n      \"method\": \"shRNA knockdown in HT22 neurons, GSH/GPX4/iron/ROS biochemical assays, erastin-induced ferroptosis, organotypic hippocampal slices, Aβ1-42 oligomer injection mouse model, immunohistochemistry/Western blotting\",\n      \"journal\": \"Alzheimer's research & therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with multiple ferroptosis markers and rescue of melatonin protection, single lab\",\n      \"pmids\": [\"41715163\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SLC38A2 (SNAT2) is a ubiquitously expressed, Na+-coupled neutral amino acid transporter (11 TM domains, intracellular N-terminus, extracellular C-terminus) with 1:1 Na+:amino acid stoichiometry that mediates cellular uptake of glutamine, alanine, proline, glycine, and other small neutral amino acids; its expression and plasma membrane abundance are tightly regulated by amino acid availability, hyperosmotic stress, hormones (insulin, cortisol, estrogen, prolactin, glucagon), and inflammatory cytokines (IL-6) through multiple converging mechanisms including ATF4/GCN2-CDK7-dependent transcription via an intronic AARE, eIF2alpha phosphorylation-dependent IRES-mediated translation, JNK-mediated signaling, and protein stability control via Nedd4-2-mediated polyubiquitination of N-terminal lysines; insulin and osmotic stress mobilize intracellular SNAT2 pools (TGN storage site) to the plasma membrane via PI3K-dependent vesicular trafficking; beyond nutrient transport, SNAT2 acts as a transceptor/amino acid sensor whose occupancy represses its own transcription and couples amino acid availability to mTORC1 and GCN2 signaling to regulate protein synthesis, proteolysis, cell volume (via osmolyte accumulation), osteoblast differentiation, ferroptosis resistance, endothelial NO production, and dendritic cell function in anti-tumor immunity.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SLC38A2 (SNAT2) is a ubiquitously expressed, Na+-coupled system A neutral amino acid transporter that couples extracellular nutrient availability to cellular amino acid supply, with a 1:1 Na+:amino acid stoichiometry and selectivity for small neutral amino acids including glutamine, alanine, proline, glycine and the system A analog MeAIB [#0, #1]. The transporter adopts an 11-transmembrane topology with an intracellular N-terminus and an extracellular, glycosylated C-terminal region [#38]; key residues define its transport mechanism — Asn82 in TM1 and a TM1/TM8 Na+ site (Thr384) coordinate Na+ binding [#21, #23], a C-terminal histidine (H504) confers allosteric pH sensitivity [#12], and the extracellular C-terminal tail acts as a voltage regulator of translocation [#27]; SNAT2 additionally carries a substrate-independent anion leak conductance dissociable from amino acid transport [#17]. SNAT2 expression and surface abundance are controlled by amino acid availability through GCN2/CDK7-dependent ATF4 transcription acting at an intronic AARE bound by ATF/C/EBP factors, eIF2alpha-dependent IRES-mediated translation, and JNK signaling [#9, #10, #13, #40], while hormonal and dietary cues converge on dedicated promoter elements — a CRE for cAMP/glucagon, an estrogen response element bound by ERalpha, a ChREBP-repressed ChoRE, and HIF-1alpha under hypoxia [#29, #32, #42, #41]. Surface levels are further set post-translationally: insulin and osmotic stress mobilize a TGN-stored SNAT2 pool to the plasma membrane via PI3K-dependent trafficking [#3, #15], and Nedd4-2-mediated polyubiquitination of N-terminal lysines drives endocytosis and proteasomal degradation, with substrate occupancy and Na+ availability tuning protein stability [#14, #34, #39]. Beyond transport, SNAT2 functions as a transceptor whose occupancy represses its own transcription and couples amino acid status to mTORC1 and downstream protein synthesis and proteolysis [#13, #18, #19]. These activities underpin diverse physiological roles: SNAT2-driven osmolyte accumulation mediates regulatory volume increase under hypertonic stress [#7, #16], placental SNAT2 supports fetal growth [#43], it supplies proline for osteoblast differentiation and bone formation [#44, #45], protects cells from ferroptosis via mTORC1 and a GSH-GPX4 axis [#50, #57], regulates endothelial NO production and blood pressure [#53], and sustains glutamine-dependent anti-tumor dendritic cell and T-cell immunity [#48, #49], making it a target in cancer and cardiovascular disease [#47, #52, #54].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Established the molecular identity of system A transport by cloning a Na+-dependent neutral amino acid transporter and defining its substrate range, stoichiometry, and ion dependence.\",\n      \"evidence\": \"Cloning from HepG2 cells and functional expression with radiolabeled transport assays\",\n      \"pmids\": [\"10930503\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structural model or topology at this stage\", \"Physiological regulation not yet addressed\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Showed that SNAT2 is the adaptively regulated arm of system A, answering how cells match transport capacity to amino acid demand.\",\n      \"evidence\": \"Northern blotting and transport assays under amino acid deprivation/supplementation in fibroblasts\",\n      \"pmids\": [\"11172802\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Transcriptional mechanism of adaptive regulation not defined\", \"Distinction from osmotic regulation unaddressed\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Identified hypertonic stress as a second, protein-synthesis-dependent inducer of SNAT2, separating osmotic from nutritional regulation.\",\n      \"evidence\": \"Transport assays and Northern blotting with cycloheximide/actinomycin D in endothelial cells\",\n      \"pmids\": [\"11322785\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Identity of the required new protein unknown\", \"Signaling pathway not dissected\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Demonstrated that SNAT2 activity is acutely controlled by trafficking, not only transcription, with insulin recruiting an intracellular pool to the membrane via PI3K.\",\n      \"evidence\": \"Surface biotinylation, pharmacological inhibition (chloroquine, wortmannin) and insulin stimulation in L6 myotubes; ATA2 redistribution in regenerating rat liver\",\n      \"pmids\": [\"11834730\", \"12054432\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the storage compartment not yet resolved\", \"Trafficking machinery uncharacterized\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Resolved the transcriptional and translational basis of amino-acid-induced SNAT2, locating the AARE to the first intron and showing eIF2alpha-dependent IRES translation, while confirming osmotic induction uses a distinct route.\",\n      \"evidence\": \"Reporter/EMSA/ChIP of ATF/C/EBP binding, eIF2alpha mutant cells, IRES reporters and in vitro translation in HepG2 and fibroblasts\",\n      \"pmids\": [\"16621798\", \"16445384\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Upstream kinase coupling GCN2 to transcription not yet identified\", \"Cell-type generality of IRES use unclear\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Defined SNAT2 as a transceptor and identified parallel sensing pathways, showing JNK drives its induction during withdrawal while the transporter itself represses its own gene during sufficiency.\",\n      \"evidence\": \"shRNA, transporter chimeras, JNK assays and amino acid supplementation in L6 myotubes\",\n      \"pmids\": [\"17488712\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular signal emanating from occupied transporter unknown\", \"Domain mediating the transceptor signal not mapped here\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Established post-translational control of SNAT2 surface abundance through Nedd4-2-mediated polyubiquitination, endocytosis and proteasomal degradation.\",\n      \"evidence\": \"Oocyte/CHO expression, RNAi, catalytically dead mutant, MG132 and co-localization studies\",\n      \"pmids\": [\"17003038\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific lysine acceptor sites not yet mapped\", \"Signals activating Nedd4-2 toward SNAT2 unknown\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Located the regulated intracellular SNAT2 pool to the trans-Golgi network and showed insulin mobilizes it independently of GLUT4 vesicles.\",\n      \"evidence\": \"Live imaging of EGFP-ATA2, syntaxin 6/EEA1 co-localization and brefeldin A inhibition in 3T3-L1 adipocytes\",\n      \"pmids\": [\"17050538\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Vesicle tethering/fusion machinery unidentified\", \"Whether all stimuli use the same TGN pool unresolved\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Connected SNAT2 induction to a physiological outcome, showing it is required for osmolyte accumulation and regulatory volume increase under hypertonic stress.\",\n      \"evidence\": \"siRNA knockdown, transport assays, intracellular amino acid and cell volume measurements in fibroblasts\",\n      \"pmids\": [\"15922329\", \"16734764\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Transcription factors driving osmotic induction not identified here\", \"In vivo relevance to tissues untested at this stage\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Linked SNAT2 transport to mTOR-dependent protein synthesis and proteolysis, defining its role in nutrient signaling and muscle protein balance.\",\n      \"evidence\": \"MeAIB inhibition, acidosis, siRNA and mTOR/PI3K inhibitors with proteolysis and pathway readouts in L6 cells\",\n      \"pmids\": [\"17429052\", \"18650482\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct biochemical coupling of SNAT2 to mTORC1 not shown\", \"In vivo muscle wasting causation not established here\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Mapped the transport mechanism at residue resolution, identifying Na+-coordinating residues and a substrate-independent anion leak conductance.\",\n      \"evidence\": \"Site-directed mutagenesis (N82, T384, H304, H504), DEPC modification, electrophysiology and homology modeling in oocytes\",\n      \"pmids\": [\"18319257\", \"19589779\", \"17237199\", \"16629640\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No experimental high-resolution structure\", \"Physiological role of the anion leak unknown\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Expanded the regulatory network to hormonal and dietary inputs by identifying functional CRE, ERE and ChoRE promoter elements and their bound factors and co-factors.\",\n      \"evidence\": \"Promoter reporter mutagenesis, EMSA, ChIP, co-IP and MS-proteomics in hepatocytes, mammary tissue and rat dietary models\",\n      \"pmids\": [\"21386061\", \"25056967\", \"33225719\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Integration of multiple cis-elements in a single locus not modeled\", \"Tissue-specific element usage incompletely mapped\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Refined post-translational regulation by mapping N-terminal lysine ubiquitination sites and showing substrate/Na+ occupancy and lipid signals tune SNAT2 stability.\",\n      \"evidence\": \"Lysine-to-alanine mutagenesis, chimeric transporters, proteasome inhibition and Nedd4-2 silencing in L6/HeLa cells; IUGR placenta correlation\",\n      \"pmids\": [\"25653282\", \"29467657\", \"26374858\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full set of E3 ligases beyond Nedd4-2 not enumerated here\", \"How substrate occupancy transmits to N-terminal degron unresolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identified CDK7 as a GCN2-dependent effector required for adaptive SNAT2 transcription, refining the amino acid response pathway.\",\n      \"evidence\": \"Pharmacological CDK7 inhibition with drug-resistant rescue and GCN2 epistasis in amino-acid-deprived cells\",\n      \"pmids\": [\"30857869\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct CDK7 substrate linking to ATF4 not defined\", \"Whether CDK7 acts at the SNAT2 locus directly unclear\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Established in vivo physiological roles for SLC38A2 in fetal growth and skeletal biology through tissue-specific genetic ablation.\",\n      \"evidence\": \"Placenta-specific shRNA knockdown and osteoblast/Prrx1Cre conditional knockout mice with transport, metabolomic and phenotypic readouts\",\n      \"pmids\": [\"34406367\", \"35261338\", \"36213239\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Compensation by other system A transporters not fully resolved\", \"Mechanistic coupling of proline supply to differentiation programs incompletely defined\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Implicated SLC38A2-mediated glutamine uptake in immune cell function and ferroptosis resistance, broadening its role to anti-tumor immunity and cell-death protection.\",\n      \"evidence\": \"Genetic loss-of-function with FLCN-TFEB epistasis in dendritic cells, XBP1 promoter regulation in T cells, and gain/loss with mTORC1 epistasis in renal ferroptosis models\",\n      \"pmids\": [\"37407815\", \"37054944\", \"36722887\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct biochemical link between glutamine flux and TFEB/ferroptosis machinery not fully reconstituted\", \"Relative contribution of transport vs signaling per context unresolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Dissected a ubiquitin-code switch controlling SNAT2 surface levels in cancer, where UBE2C monoubiquitination blocks degradative K63 chains and EPN1-mediated endocytosis to promote metastasis.\",\n      \"evidence\": \"Site-specific ubiquitin acceptor mutagenesis (K33/K59), endocytosis and VEGFC secretion assays, and in vivo/PDX bladder cancer models\",\n      \"pmids\": [\"38949026\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Generality of the mono-/polyubiquitin switch beyond bladder cancer untested\", \"Deubiquitinases counteracting this switch unidentified\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defined cardiovascular and metabolic roles for SLC38A2, linking endothelial glutamine uptake to NO/blood pressure and ATF4-driven SLC38A2 to vascular remodeling, plus a NERP-4/SNAT2 axis in insulin secretion.\",\n      \"evidence\": \"Endothelial and VSMC-specific knockouts, ChIP of ATF4 at the promoter, MeAIB inhibition, and islet/db/db models\",\n      \"pmids\": [\"40901922\", \"41067488\", \"38071217\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Therapeutic window for SNAT2 inhibition across tissues unknown\", \"Cross-talk between vascular and metabolic SNAT2 functions unexplored\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How occupancy of SNAT2 generates the transceptor signal that biochemically couples to mTORC1, GCN2 and its own transcriptional repression remains undefined at the molecular level.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No reconstituted signaling complex linking transporter occupancy to mTORC1/GCN2\", \"No high-resolution structure to rationalize transport vs sensing states\", \"Direct downstream effectors of the self-repressive transceptor signal unidentified\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 1, 18, 30, 31, 44, 46]},\n      {\"term_id\": \"GO:0140299\", \"supporting_discovery_ids\": [13, 18]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [3, 4, 14, 15, 43, 52]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [15]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [3, 52]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [0, 1, 31, 46]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [7, 16, 9, 50]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [13, 18, 19, 48, 50]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [14, 34, 39, 52]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [10, 29, 32, 42]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"NEDD4L\", \"ATF4\", \"UBE2C\", \"EPN1\", \"ESR1\", \"ChREBP\", \"FLCN\", \"XBP1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":{"gene":"SLC38A2","tier":"GROUNDING","verdict":"Evidence-grounding concern","subtype":"fabrication","uniprot_band":"rich","rules_fired":"R7","issue":"R7: fabricated (no corpus paper): 19589779"},"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}