{"gene":"SLC7A8","run_date":"2026-04-28T20:42:08","timeline":{"discoveries":[{"year":1999,"finding":"SLC7A8 (LAT2) encodes a sodium-independent L-type amino acid transporter that requires heterodimerization with 4F2hc (CD98 heavy chain) for plasma membrane localization and transport activity. Expressed alone in Xenopus oocytes, LAT2 localizes intracellularly and is non-functional; co-expression with 4F2hc traffics it to the plasma membrane and induces broad-specificity transport of small and large zwitterionic amino acids. The transport is highly trans-stimulated, indicating an obligatory exchanger mechanism.","method":"Xenopus oocyte expression system; N-myc-tagged protein; subcellular localization assay; radiolabeled amino acid uptake; trans-stimulation assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — functional reconstitution in oocytes with localization and transport assays, independently replicated in same year by Rossier et al.","pmids":["10391915"],"is_preprint":false},{"year":1999,"finding":"LAT2/SLC7A8 forms a disulfide-linked heterodimer with 4F2hc and mediates L-type amino acid uptake with higher affinity for L-phenylalanine and transport of L-alanine at physiological concentrations compared to LAT1-4F2hc. LAT2-4F2hc also mediates amino acid efflux in the presence of an external substrate, consistent with obligatory exchange. LAT2 colocalizes with 4F2hc at the basolateral membrane of kidney proximal tubules and small intestine epithelia, implicating it in epithelial amino acid (re)absorption.","method":"Xenopus oocyte co-injection of mouse LAT2 and human 4F2hc cRNAs; SDS-PAGE under non-reducing conditions (disulfide); L-[3H]phenylalanine and L-[3H]alanine uptake kinetics; immunofluorescence of kidney and intestine sections","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — functional reconstitution with kinetics, structural (disulfide) and localization data, independent replication of LAT2 identity","pmids":["10574970"],"is_preprint":false},{"year":1999,"finding":"SLC7A8 maps to chromosome 14q11.2 within the lysinuric protein intolerance (LPI) critical region, is highly expressed in skeletal muscle, intestine, kidney, and placenta, and encodes a predicted 535-amino-acid protein homologous to CD98 light chain amino acid permeases. Mutational analysis excluded SLC7A8 from direct causation of LPI.","method":"Bioinformatic cloning; Northern blot; RNA in situ hybridization on mouse embryos; Sanger sequencing for mutation analysis","journal":"Genomics","confidence":"Medium","confidence_rationale":"Tier 3 — gene identification and expression mapping; no reconstitution in this paper","pmids":["10610726"],"is_preprint":false},{"year":2000,"finding":"The LAT2-4F2hc heterodimer functions as an obligatory antiporter: only preloaded intracellular amino acids can be released in exchange for extracellular substrates, confirming an exchanger rather than uniporter mechanism for this transporter complex.","method":"Xenopus oocyte expression; radiolabeled amino acid efflux under various loading conditions; competitive inhibition assays","journal":"The Biochemical journal","confidence":"Medium","confidence_rationale":"Tier 2 — functional reconstitution demonstrating antiport mechanism, though focused primarily on y+LAT2 with LAT2 comparison","pmids":["10903140"],"is_preprint":false},{"year":2001,"finding":"The extracellular domain of 4F2hc is specifically required for plasma membrane trafficking of LAT2 (and y+LAT2) but not LAT1. C-terminal truncations of 4F2hc that retain only the transmembrane helix are sufficient for LAT1 surface expression but almost completely abolish LAT2 surface expression, revealing that LAT2 requires interaction with the extracellular domain of 4F2hc for correct trafficking.","method":"Xenopus oocyte expression of C-terminally truncated 4F2hc mutants co-expressed with LAT1, LAT2, or y+LAT2; surface biotinylation; radiolabeled amino acid transport assays","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 2 — systematic domain-deletion mutagenesis with functional readout, replicated across multiple light chains","pmids":["11311135"],"is_preprint":false},{"year":2002,"finding":"LAT2-4F2hc functions as an obligatory amino acid exchanger with 1:1 stoichiometry. Intracellular substrates strongly trans-stimulate influx, and LAT2-4F2hc has much lower apparent affinity for intracellular substrates (Km in millimolar range) compared to extracellular substrates, creating strongly asymmetric affinity that allows the intracellular amino acid concentration to control transporter activity.","method":"Xenopus oocyte expression; HPLC quantification of simultaneous amino acid influx and efflux; intracellular substrate injection; kinetic analysis","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 — rigorous quantitative reconstitution with HPLC, stoichiometry determination, and asymmetric affinity characterization","pmids":["11847106"],"is_preprint":false},{"year":2002,"finding":"LAT2-4F2hc transports methylmercury when complexed with L-cysteine (MeHg-L-cysteine), acting as a molecular mimic of methionine. Both cis- and trans-substrate properties were confirmed: MeHg-L-cysteine uptake by LAT2 has Km ~64 µM with Vmax higher than methionine, and methionine efflux is trans-stimulated by external leucine and phenylalanine even against an inward methionine gradient.","method":"Xenopus oocyte expression of LAT2-4F2hc; [14C]MeHg-L-cysteine uptake; [3H]methionine trans-stimulation; kinetic analysis (Km, Vmax)","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1-2 — reconstitution in oocytes with full kinetic characterization and trans-stimulation assays","pmids":["12117417"],"is_preprint":false},{"year":2003,"finding":"LAT2 at the basolateral membrane of renal proximal tubule cells plays a major specific role in basolateral efflux of cysteine/cystine. Antisense-mediated partial knockdown of LAT2 in OK cells reduced basolateral system L amino acid exchange activity, decreased apical-to-basolateral transepithelial flux of cystine, and caused a 2-3 fold increase in intracellular cysteine, identifying LAT2 as a key transporter mediating cystine reabsorption across the basolateral membrane.","method":"Stable transfection with LAT2 antisense construct in OK cells; radiolabeled amino acid transport; transepithelial flux assay; intracellular amino acid content measurement","journal":"Journal of the American Society of Nephrology","confidence":"High","confidence_rationale":"Tier 2 — loss-of-function (antisense KD) with specific transepithelial flux phenotype and intracellular accumulation readout","pmids":["12660317"],"is_preprint":false},{"year":2003,"finding":"CD98 (4F2hc) ligation at the basolateral membrane of intestinal Caco-2 epithelial cells decreases the Km and Vmax of LAT2-mediated transport, while ICAM-1 ligation increases both Km and Vmax, demonstrating that LAT2 transport activity is regulated by co-receptor signaling. ICAM-1 selectively co-immunoprecipitates with CD98/LAT2 at the basolateral membrane, and cross-linking of either receptor induces threonine phosphorylation of an ~160 kDa CD98/LAT2-ICAM-1 complex.","method":"Co-immunoprecipitation; antibody-mediated receptor cross-linking; amino acid transport kinetics (Km, Vmax) in Caco-2 monolayers; phosphorylation assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2-3 — co-IP plus functional transport kinetics with signaling readout, single lab","pmids":["12716892"],"is_preprint":false},{"year":2004,"finding":"LAT2 mediates Na+-independent, pH-sensitive L-DOPA transport in renal LLC-PK1 epithelial cells. siRNA silencing of LAT2 reduced [14C]-L-DOPA accumulation by ~85% and outward transport by ~90%, confirming LAT2 as the primary L-DOPA transporter; the LAT2-mediated mechanism supports both influx and efflux of L-DOPA, consistent with heteroexchange.","method":"siRNA knockdown of LAT2 in LLC-PK1 cells; real-time quantitative RT-PCR; [14C]-L-DOPA uptake and efflux assays; competitive inhibition","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 2 — specific siRNA knockdown with quantitative transport phenotype in epithelial cells","pmids":["15466357"],"is_preprint":false},{"year":2004,"finding":"rBAT (apical) and LAT2 (basolateral) can each mediate L-DOPA uptake into renal proximal tubule cells, with distinct kinetics: rBAT shows micromolar Km while LAT2 shows millimolar Km for L-DOPA. Antisense oligonucleotides to LAT2 inhibited LAT2 cRNA-induced L-DOPA transport and partially blocked cortical poly-A+ RNA-induced transport.","method":"Xenopus oocyte expression; kinetic analysis; sequence-specific antisense oligonucleotides; [14C]-L-DOPA uptake","journal":"American journal of physiology. Renal physiology","confidence":"Medium","confidence_rationale":"Tier 2 — oocyte reconstitution with antisense inhibition confirming LAT2 identity","pmids":["15180924"],"is_preprint":false},{"year":2005,"finding":"LAT2 (co-expressed with 4F2hc) stereoselectively transports S-nitroso-L-cysteine (L-CSNO) but not D-CSNO or other nitrosothiols, identifying LAT2 as a transporter for this nitric oxide donor. L-CSNO transport by LAT2 is Na+-independent, inhibited by leucine and BCH, and the transport mechanism involves direct cellular uptake of intact L-CSNO.","method":"Xenopus oocyte expression of LAT2-4F2hc; [14C]-L-CSNO uptake; stereoselectivity assays; competitive inhibition; overexpression and siRNA knockdown in mammalian cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — reconstitution in oocytes plus gain- and loss-of-function in mammalian cells, stereospecificity demonstrated","pmids":["15769744"],"is_preprint":false},{"year":2005,"finding":"LAT2 and TAT1 (SLC16A10) colocalize in the basolateral membrane of human renal proximal tubules and together mediate renal reabsorption of neutral amino acids. LAT2 transports all neutral amino acids while TAT1 is specific for aromatic amino acids, and their basolateral colocalization supports a two-transporter model for basolateral exit of reabsorbed amino acids.","method":"Immunohistochemistry on human kidney sections; Northern blot; functional characterization in Xenopus oocytes","journal":"Archives of pharmacal research","confidence":"Medium","confidence_rationale":"Tier 2-3 — colocalization by IHC with functional transport characterization in oocytes","pmids":["15918515"],"is_preprint":false},{"year":2007,"finding":"TAT1 (SLC16A10) and LAT2-4F2hc functionally cooperate to drive net amino acid efflux: TAT1 recycles aromatic amino acids (influx substrates of LAT2) by facilitated diffusion, enabling LAT2-4F2hc to continuously release glutamine and other neutral amino acids from cells. This cooperation requires the transport activity of both proteins but not their physical interaction, as coimmunoprecipitation and crosslinking were negative.","method":"Xenopus oocyte co-expression; HPLC analysis of amino acid efflux; functionally inactive surface-expressed mutants; co-immunoprecipitation; crosslinking experiments; immunofluorescence colocalization in kidney","journal":"Pflugers Archiv","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods including functional mutants, HPLC quantification, and negative protein interaction controls","pmids":["17273864"],"is_preprint":false},{"year":2011,"finding":"Targeted inactivation of Slc7a8 in mice causes increased urinary loss of small neutral amino acids (aminoaciduria), demonstrating that LAT2 is required for renal reabsorption of neutral amino acids in vivo. Motor coordination is mildly impaired in Slc7a8-/- mice. Circulating thyroid hormones and TSH remain normal in knockout mice, suggesting functional compensation by MCT8 for thyroid hormone transport.","method":"Targeted gene knockout (Slc7a8-/- mice); urine amino acid analysis; behavioral testing (motor coordination); thyroid hormone and TSH measurements; thyroid hormone-responsive gene expression","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 2 — clean knockout mouse model with specific in vivo amino acid transport and hormonal phenotypes","pmids":["21726201"],"is_preprint":false},{"year":2011,"finding":"LAT2 plasma membrane expression in glomerular parietal epithelial cells (PECs) and podocytes activates the mTORC1 signaling pathway, preceding crescent formation in crescentic glomerulonephritis (CGN). LAT2 is specifically upregulated in these cells before crescent formation; in cell culture, plasma membrane LAT2 markedly stimulates mTORC1 signaling that is abrogated by a LAT inhibitor; and LAT inhibitor significantly reduced crescent formation in vivo.","method":"Immunohistochemistry and Western blot of isolated rat glomeruli; cell culture with LAT inhibitor; mTORC1 pathway analysis (p-S6K1); in vivo LAT inhibitor treatment of CGN model","journal":"Laboratory investigation","confidence":"Medium","confidence_rationale":"Tier 2-3 — in vivo and in vitro evidence linking LAT2 to mTORC1 activation, single lab","pmids":["21403644"],"is_preprint":false},{"year":2011,"finding":"Dihydrotestosterone (DHT) acutely increases expression of LAT2 protein and amino acid uptake in fast-twitch skeletal muscle fibers through a non-genomic mechanism requiring EGFR transactivation and ERK1/2 (MEK) signaling, but not androgen receptor or PI3K/Akt. This effect is also dependent on mTOR and involves increased protein synthesis.","method":"[14C]-labelled amino acid uptake in isolated mouse muscle fiber bundles; pharmacological inhibition of EGFR, MEK, mTOR, androgen receptor; Western blot for LAT2, p-EGFR, p-ERK1/2, p-RSK1/2; protein incorporation assay","journal":"The Journal of physiology","confidence":"Medium","confidence_rationale":"Tier 2-3 — pharmacological pathway dissection with protein expression readout, single lab","pmids":["21606113"],"is_preprint":false},{"year":2012,"finding":"Human LAT2 expressed stably in HEK293 cells (as heterodimer with endogenous 4F2hc) transports L-alanine as a preferred substrate with reliable kinetics. α-Alkyl amino acids (α-methyl-alanine, α-ethyl-L-alanine) interfere with LAT2 interaction, defining a steric constraint at the α-carbon of substrates that distinguishes LAT2 from LAT1.","method":"Stable HEK293 cell lines; [14C]-L-alanine transport assays; kinetic analysis; α-alkyl amino acid inhibition studies","journal":"Journal of pharmacological sciences","confidence":"Medium","confidence_rationale":"Tier 2 — stable mammalian cell expression with kinetic characterization and substrate specificity mapping","pmids":["22850614"],"is_preprint":false},{"year":2014,"finding":"The extracellular domain of 4F2hc interacts directly with LAT2, almost completely covering the extracellular face of the transporter as revealed by transmission electron microscopy and single-particle analysis. 4F2hc increases the stability of LAT2 in detergent-solubilized membranes and enables functional reconstitution of the heterodimer into proteoliposomes; the extracellular domain of 4F2hc alone is sufficient to stabilize solubilized LAT2.","method":"Transmission electron microscopy (negative stain); single-particle analysis; purification of recombinant 4F2hc-LAT2 from Pichia pastoris; crosslinking experiments; docking analysis; functional reconstitution into proteoliposomes","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — structural (EM) plus biochemical reconstitution and stabilization assays, multiple orthogonal methods","pmids":["24516142"],"is_preprint":false},{"year":2014,"finding":"Cerebral cortex hyperthyroidism in neonatal Mct8-deficient mice is prevented by simultaneous ablation of Lat2, demonstrating that Lat2 is responsible for the increased thyroid hormone supply to the neonatal cerebral cortex in the absence of Mct8. This Lat2 effect is transient (absent from postnatal day 5 onward), and Lat2 expression in neurons and choroid plexus is consistent with a role in early postnatal thyroid hormone supply to the cortex.","method":"Double knockout mice (Mct8-/-/Lat2-/-); T3 concentration measurements in cerebral cortex; thyroid hormone target gene expression (Hr); comparison across postnatal development time points","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis via double knockout with quantitative hormone and target gene readout","pmids":["24819605"],"is_preprint":false},{"year":2014,"finding":"Stabilization of purified 4F2hc-LAT2 with a combination of DDM, lauryl maltose neopentyl glycol, and cholesteryl hemisuccinate enables measurement of substrate binding by scintillation proximity assay and improves the 3D EM map, confirming that LAT2 is the substrate-transporting subunit of the heterodimer.","method":"Detergent screening; negative-stain TEM; scintillation proximity assay for substrate binding; 3D map reconstruction","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 1-2 — structural and biochemical binding assay, but primarily technical optimization paper","pmids":["25299125"],"is_preprint":false},{"year":2015,"finding":"LAT2 (co-expressed with CD98) transports 3,3'-diiodo-L-thyronine (3,3'-T2) with a low micromolar Km comparable to MCT8, and to a lesser extent T3. Various iodothyronine derivatives competitively inhibit 3,3'-T2 uptake, revealing that LAT2 preferentially transports 3,3'-T2 among thyroid hormone metabolites, suggesting a role in cellular availability of this deiodinase product.","method":"Xenopus oocyte co-injection of Lat2 and CD98 cRNAs; [125I]-3,3'-T2 and [125I]-T3 uptake; competitive inhibition with iodothyronine derivatives; Km determination","journal":"European thyroid journal","confidence":"Medium","confidence_rationale":"Tier 2 — functional reconstitution in oocytes with kinetic characterization for thyroid hormone substrates","pmids":["26601072"],"is_preprint":false},{"year":2015,"finding":"BPA (boronophenylalanine), a boron neutron capture therapy agent, is a substrate for LAT2 (as well as ATB0,+ and LAT1), with a Km of 88.3 µM for LAT2-mediated transport in Xenopus oocytes. In cancer cell lines, LAT1 is the predominant BPA transporter at low concentrations, with LAT2 contributing at higher concentrations.","method":"Xenopus oocyte expression; HPLC-based BPA uptake quantification; kinetic analysis; siRNA knockdown in MCF-7 cells","journal":"Cancer science","confidence":"Medium","confidence_rationale":"Tier 2 — reconstitution with quantitative kinetics and cell line validation","pmids":["25580517"],"is_preprint":false},{"year":2017,"finding":"LAT2-4F2hc mediates methylmercury (as MeHg-L-cysteine complex) uptake at the apical membrane of BeWo placental trophoblast cells. siRNA knockdown of LAT2 or 4F2hc significantly reduced leucine, methionine, and methylmercury uptake, establishing LAT2-4F2hc as a key pathway for placental methylmercury transport.","method":"siRNA knockdown of LAT2 and 4F2hc in BeWo cells; Transwell transport assay; [3H]leucine, [3H]methionine, and methylmercury uptake measurements","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 — siRNA knockdown with multiple substrate readouts in placental cell model","pmids":["28786956"],"is_preprint":false},{"year":2018,"finding":"LAT2/SLC7A8 is expressed in the mouse inner ear, and its ablation (Slc7a8-/- mice) causes age-related hearing loss (ARHL) with damage to cochlear structures. Human SLC7A8 variants (p.Val302Ile, p.Arg418His, p.Thr402Met, p.Val460Glu) found in ARHL patients show significant decreases in transport activity when functionally expressed in vitro, supporting a causative role for SLC7A8 loss-of-function in ARHL.","method":"Slc7a8-/- mouse model; auditory brainstem response testing; cochlear histology; in vitro functional transport assays of patient variants in heterologous cells","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 — knockout mouse phenotype plus in vitro functional characterization of human disease variants","pmids":["29355479"],"is_preprint":false},{"year":2018,"finding":"LAT2 promotes glutamine-dependent mTOR activation in pancreatic cancer cells, driving glycolysis and chemoresistance. LAT2 regulates two glutamine-dependent positive feedback loops: the LAT2/p-mTORSer2448 loop and the glutamine/p-mTORSer2448/glutamine synthetase loop. mTOR inhibitor (RAD001) reverses the LAT2-mediated decrease in gemcitabine sensitivity.","method":"LAT2 overexpression and knockdown in pancreatic cancer cells; mTOR pathway analysis (p-mTORSer2448); glycolysis assays; glutamine metabolism measurement; xenograft mouse model; drug sensitivity assays","journal":"Journal of experimental & clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2-3 — gain- and loss-of-function with pathway analysis in vitro and in vivo, single lab","pmids":["30419950"],"is_preprint":false},{"year":2018,"finding":"LAT2/CD98hc (SLC7A8/SLC3A2) and TAT1 (SLC16A10) functionally cooperate in vivo for renal reabsorption of neutral amino acids. Double-knockout (LAT2/TAT1) mice show greater urinary loss of aromatic and other neutral amino acids than single knockouts, and also display decreased reabsorption of cationic amino acids with compensatory upregulation of y+LAT1/CD98hc, demonstrating functional cooperation and compensation among basolateral amino acid transporters.","method":"Double-knockout mouse model (LAT2-TAT1 dKO); urine amino acid analysis; Western blot for transporter expression; comparison with single knockouts","journal":"Journal of the American Society of Nephrology","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis via double-knockout with quantitative in vivo phenotypic readout","pmids":["29610403"],"is_preprint":false},{"year":2019,"finding":"Loss of LAT2 (Slc7a8 deletion) in mice causes cataract, particularly in older females, associated with a dramatic decrease in lens essential amino acid levels. A homozygous SLC7A8 single nucleotide deletion found in a human family with congenital cataract abolishes amino acid transport when expressed in HeLa cells. Heterozygous LAT2 variants from cataract patients also show reduced transport function. Simultaneous TAT1 deletion synergizes with LAT2 loss to increase cataract incidence.","method":"Slc7a8-/- and double Slc7a8/Slc16a10 knockout mice; slit-lamp examination; lens amino acid HPLC; in vitro transport assays of human variants in HeLa cells; immunofluorescence of LAT2 in ciliary and lens epithelium","journal":"Frontiers in physiology","confidence":"High","confidence_rationale":"Tier 2 — knockout mouse phenotype, human variant functional studies, and lens amino acid measurement","pmids":["31231240"],"is_preprint":false},{"year":2019,"finding":"Cryo-EM 3D map of human 4F2hc-LAT2 at ~13 Å resolution reveals two prominent densities: the 4F2hc ectodomain (fitted using the available X-ray structure) and the LAT2 transmembrane domain, defining the relative positions of the two subunits with respect to each other and the membrane plane.","method":"Cryo-EM with direct electron detector and Volta phase plate; 3D map reconstruction; fitting of 4F2hc ectodomain X-ray structure","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 1 — cryo-EM structural determination, but limited to ~13 Å resolution without atomic detail","pmids":["30795505"],"is_preprint":false},{"year":2020,"finding":"Sub-nanometer cryo-EM density map of 4F2hc-LAT2 reveals the inward-open conformation of LAT2 via homology modeling fitted into the map. Disease-causing point mutations in LAT2 are mapped to the substrate binding site and transmembrane helices, providing structural context for their functional effects.","method":"Cryo-EM; homology model generation of 4F2hc-LAT2 in inward-open conformation; fitting and analysis; disease mutation mapping","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 1 — structural cryo-EM with homology modeling, but resolution limits atomic-level mechanistic conclusions","pmids":["32993041"],"is_preprint":false},{"year":2020,"finding":"4F2hc modulates the substrate affinity and specificity of LAT2 (and LAT1): when LAT2 is expressed alone in Pichia pastoris (without 4F2hc), it localizes to the plasma membrane and is transport-competent, but shows different substrate affinity and specificity compared to the 4F2hc-LAT2 heterodimer. This demonstrates a novel function of the heavy chain beyond trafficking, namely modulation of light chain transport properties.","method":"Pichia pastoris expression of LAT2 alone and 4F2hc-LAT2; [3H]L-leucine radiolabel transport assay; substrate competition assays; kinetic analysis","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 — novel functional finding with direct comparison of LAT2 alone vs. heterodimer, single lab","pmids":["33066406"],"is_preprint":false},{"year":2020,"finding":"The structural insight into substrate recognition of LAT2-4F2hc was determined: the cryo-EM/crystal structure of the complex reveals the substrate binding pocket architecture in LAT2, with the 4F2hc ectodomain positioned above the LAT2 transporter domain. Structural basis for substrate selectivity of LAT2 within the heterodimeric complex was elucidated.","method":"Cryo-EM structure determination of LAT2-4F2hc; substrate binding pocket analysis","journal":"Cell discovery","confidence":"High","confidence_rationale":"Tier 1 — structural determination of substrate recognition mechanism","pmids":["33298890"],"is_preprint":false},{"year":2020,"finding":"LAT2 (Slc7a8) localizes to the CSF-facing luminal membrane of choroid plexus epithelium. Deletion of Slc7a8 in mice increases CSF levels of LAT2 substrates (leucine, valine, tryptophan) and other amino acids, demonstrating that LAT2 normally reuptakes these amino acids from CSF back into the choroid plexus, thereby participating in maintenance of the amino acid concentration gradient between plasma and CSF.","method":"qRT-PCR on isolated choroid plexus; immunofluorescence localization; LAT2 knockout mice; CSF amino acid HPLC analysis","journal":"Fluids and barriers of the CNS","confidence":"High","confidence_rationale":"Tier 2 — specific localization plus knockout mouse with quantitative CSF amino acid phenotype","pmids":["32046769"],"is_preprint":false},{"year":2022,"finding":"Chemotherapy-induced macrophage secretion of IL-18 upregulates LAT2 expression in osteosarcoma tumor cells, leading to enhanced leucine and glutamine uptake, mTORC1 activation, and c-Myc-mediated CD47 transcription, resulting in tumor immune evasion. LAT2 depletion or LAT inhibitor treatment downregulates CD47, increases macrophage phagocytosis of tumor cells, and sensitizes tumors to doxorubicin.","method":"IL-18 stimulation; LAT2 depletion (siRNA/shRNA); amino acid uptake assays; mTORC1 activation (p-S6K); c-Myc ChIP; CD47 expression; macrophage phagocytosis assay; xenograft mouse model","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods linking LAT2 to specific signaling pathway with in vivo validation","pmids":["36274066"],"is_preprint":false},{"year":2022,"finding":"The cryo-EM structure of 4F2hc-LAT2 in complex with anticalin D11vs at 3.2 Å resolution reveals fixed water molecules in the LAT2 substrate binding site that may stabilize the binding region. Molecular dynamics simulations and local map resolution of 2.8-3.0 Å in the binding site provide mechanistic insight into substrate binding and selectivity of LAT2.","method":"Cryo-EM single-particle analysis at 3.2 Å; anticalin binding protein for particle alignment; molecular dynamics simulations; local resolution analysis","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 1 — high-resolution cryo-EM structure with MD simulations revealing binding site water molecules","pmids":["36310334"],"is_preprint":false},{"year":2022,"finding":"LAT2 (encoded by SLC7A8) transports doxorubicin as a substrate. HEK293 cells overexpressing LAT2 show significantly increased doxorubicin uptake compared to controls, while cisplatin and methotrexate are not transported. This identifies LAT2 as a novel doxorubicin uptake transporter with potential relevance to osteosarcoma treatment response.","method":"HEK293 overexpression of LAT2; in vitro doxorubicin transport assay; comparison with cisplatin and methotrexate","journal":"Frontiers in pharmacology","confidence":"Medium","confidence_rationale":"Tier 2-3 — overexpression transport assay, single lab, single method","pmids":["36438828"],"is_preprint":false},{"year":2025,"finding":"LAT2 (SLC7A8) is a Th2-specific amino acid transporter in the CD4 T helper compartment. Slc7a8 deficiency impairs Th2 cell proliferation and cytokine production, disrupts Th2 metabolism with reduced mTOR activation, diminished mitochondrial function, and impaired c-Myc pathway, inducing cellular stress. LAT2-deficient mice show impaired type 2 immune responses to helminth infection and allergen-induced lung inflammation.","method":"Slc7a8-/- mice; Th1/Th2/Th17/Treg differentiation assays; proliferation and cytokine assays; metabolic profiling; mTOR and c-Myc pathway analysis; helminth infection and allergen challenge models","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 — knockout mouse with multiple immune and metabolic readouts, in vivo disease models","pmids":["41269086"],"is_preprint":false},{"year":2025,"finding":"LAT2 ablation in skeletal muscle causes glutamine (Gln) accumulation (6.3-fold increase) intramuscularly and inhibits fasting-induced proteolysis, primarily through reduced proteasomal and autophagic activity. This is mediated by mTORC1 recruitment to the lysosome (Lamp1 colocalization), as rapamycin treatment recovers proteolysis in LAT2KO muscle. Chronic Gln accumulation and decreased proteolysis in young LAT2KO mice produce an age-related muscle phenotype.","method":"LAT2 knockout mice; metabolomics (intramuscular amino acid HPLC); proteasomal and autophagic activity assays; mTORC1 colocalization (Lamp1); rapamycin rescue; aging, cachexia, and diabetes models","journal":"Journal of cachexia, sarcopenia and muscle","confidence":"High","confidence_rationale":"Tier 2 — knockout mouse with mechanistic rapamycin rescue, colocalization, and multiple disease model validation","pmids":["40546137"],"is_preprint":false}],"current_model":"SLC7A8 (LAT2) encodes the catalytic light-chain subunit of the heterodimeric amino acid transporter 4F2hc-LAT2: it requires the 4F2hc heavy chain (SLC3A2) for plasma membrane trafficking (dependent on the 4F2hc extracellular domain) and functions as a sodium-independent obligatory antiporter with 1:1 exchange stoichiometry, broad specificity for neutral amino acids (including thyroid hormones, L-DOPA, and methylmercury-cysteine complexes), strongly asymmetric intra/extracellular affinities, and is primarily localized to the basolateral membrane of renal proximal tubules and intestinal epithelia, the CSF-facing membrane of choroid plexus, and the lens epithelium, where it drives epithelial amino acid reabsorption in functional cooperation with the aromatic amino acid uniporter TAT1; 4F2hc additionally modulates LAT2 substrate affinity and specificity beyond its trafficking role; structurally, a 3.2 Å cryo-EM structure reveals fixed water molecules in the substrate-binding site; and in vivo, loss of LAT2 causes aminoaciduria, age-related hearing loss, cataract, and in skeletal muscle causes glutamine accumulation that activates mTORC1 and suppresses fasting-induced proteolysis, while in immune cells LAT2 selectively supports Th2 cell metabolism, proliferation, and effector function via mTOR and c-Myc pathways."},"narrative":{"teleology":[{"year":1999,"claim":"The identity of LAT2 as a broad-specificity neutral amino acid transporter requiring 4F2hc for surface expression was established, resolving how a second L-type system with distinct substrate preference operates as a disulfide-linked heterodimer at renal and intestinal basolateral membranes.","evidence":"Xenopus oocyte co-expression with 4F2hc; subcellular localization; radiolabeled amino acid uptake kinetics; immunofluorescence on kidney/intestine sections","pmids":["10391915","10574970"],"confidence":"High","gaps":["Exchange stoichiometry and asymmetric affinity not yet quantified","Structural basis of 4F2hc requirement for LAT2 trafficking unknown","In vivo physiological role not yet demonstrated by genetic loss-of-function"]},{"year":2002,"claim":"Quantitative demonstration that LAT2-4F2hc is an obligatory 1:1 antiporter with millimolar intracellular Km versus micromolar extracellular Km resolved the asymmetric affinity model that explains how intracellular amino acid pools drive net substrate exchange.","evidence":"Xenopus oocyte co-expression; simultaneous HPLC quantification of influx and efflux; intracellular substrate injection","pmids":["11847106"],"confidence":"High","gaps":["Structural determinants of affinity asymmetry unknown","How 4F2hc contributes to asymmetric kinetics not addressed"]},{"year":2001,"claim":"The requirement for the 4F2hc extracellular domain in LAT2 surface trafficking—distinct from LAT1—established that the heavy chain plays a light-chain-specific chaperoning role beyond disulfide linkage.","evidence":"C-terminal truncation mutants of 4F2hc co-expressed with LAT2 in oocytes; surface biotinylation; transport assays","pmids":["11311135"],"confidence":"High","gaps":["Whether 4F2hc ectodomain also modulates LAT2 substrate specificity was untested","No structural model of the ectodomain-LAT2 interface"]},{"year":2002,"claim":"Identification of methylmercury-cysteine as a LAT2 substrate acting as a methionine mimic expanded the transporter's known cargo beyond canonical amino acids to environmentally relevant toxicants.","evidence":"Xenopus oocyte expression; [14C]MeHg-L-cysteine uptake with Km/Vmax determination; trans-stimulation","pmids":["12117417"],"confidence":"High","gaps":["In vivo relevance for mercury toxicity not tested","No structural basis for molecular mimicry"]},{"year":2004,"claim":"siRNA knockdown established LAT2 as the primary L-DOPA transporter in renal epithelial cells, extending its physiological substrate repertoire to catecholamine precursors.","evidence":"siRNA knockdown in LLC-PK1 cells; [14C]-L-DOPA uptake and efflux; qRT-PCR","pmids":["15466357"],"confidence":"High","gaps":["Contribution relative to other transporters in vivo unknown","Relevance to L-DOPA pharmacokinetics not established"]},{"year":2007,"claim":"Demonstration that TAT1 and LAT2 functionally cooperate without physical interaction—TAT1 recycling aromatic amino acids to fuel LAT2-mediated net efflux—provided the mechanistic model for basolateral amino acid reabsorption in kidney.","evidence":"Xenopus oocyte co-expression; HPLC efflux quantification; functionally inactive surface mutants; negative co-IP and crosslinking","pmids":["17273864"],"confidence":"High","gaps":["In vivo validation by double knockout not yet performed","Whether this cooperation operates in other epithelia unknown"]},{"year":2011,"claim":"Targeted Slc7a8 knockout in mice confirmed the in vivo requirement for LAT2 in renal neutral amino acid reabsorption (aminoaciduria phenotype) and revealed an unexpected role in neonatal cortical thyroid hormone supply via genetic epistasis with Mct8.","evidence":"Slc7a8−/− mice; urine amino acid analysis; Mct8/Lat2 double knockout; cerebral cortex T3 measurements and target gene expression","pmids":["21726201","24819605"],"confidence":"High","gaps":["Intestinal and placental transport roles not confirmed by knockout","Mechanism of LAT2's thyroid hormone transport contribution limited to early postnatal window"]},{"year":2014,"claim":"Electron microscopy and biochemical reconstitution revealed the architecture of the 4F2hc-LAT2 heterodimer, showing the ectodomain covers LAT2's extracellular face and stabilizes it, establishing the structural framework for understanding heavy-chain modulation.","evidence":"Negative-stain TEM single-particle analysis; Pichia pastoris purification; proteoliposome reconstitution; crosslinking","pmids":["24516142"],"confidence":"High","gaps":["Atomic-resolution structure not available","Substrate-bound conformational states not captured"]},{"year":2018,"claim":"LAT2 loss-of-function was linked to age-related hearing loss—both in Slc7a8−/− mice showing cochlear damage and in human patients carrying transport-defective SLC7A8 variants—establishing a Mendelian-type disease connection.","evidence":"Slc7a8−/− mice; ABR testing; cochlear histology; in vitro transport assays of human patient variants","pmids":["29355479"],"confidence":"High","gaps":["Specific amino acid(s) whose deficiency drives ototoxicity unknown","Whether cochlear phenotype is cell-autonomous not determined"]},{"year":2018,"claim":"Double knockout of LAT2 and TAT1 in vivo confirmed their functional cooperation for renal amino acid reabsorption and revealed compensatory upregulation of y+LAT1, demonstrating transporter network plasticity at the basolateral membrane.","evidence":"LAT2/TAT1 double-knockout mice; urine amino acid analysis; Western blot for compensatory transporter expression","pmids":["29610403"],"confidence":"High","gaps":["Molecular signals driving compensatory transporter upregulation unknown","Functional consequences in non-renal epithelia not assessed"]},{"year":2019,"claim":"LAT2 ablation caused cataract in mice with depleted lens amino acids, and a human homozygous SLC7A8 frameshift abolished transport and segregated with congenital cataract, establishing a second Mendelian phenotype.","evidence":"Slc7a8−/− and double Slc7a8/Slc16a10 KO mice; slit-lamp; lens amino acid HPLC; in vitro transport of human variants in HeLa cells","pmids":["31231240"],"confidence":"High","gaps":["Which specific amino acid deficit is cataractogenic not pinpointed","Whether lens-specific rescue would prevent cataract untested"]},{"year":2020,"claim":"Multiple cryo-EM structures at improving resolution (sub-nanometer to 3.2 Å) defined the substrate binding pocket of LAT2 within the 4F2hc heterodimer and revealed that 4F2hc modulates LAT2 substrate affinity beyond its trafficking role, fundamentally redefining heavy-chain function.","evidence":"Cryo-EM at 3.2 Å with anticalin; molecular dynamics; Pichia pastoris expression of LAT2 alone vs. heterodimer with comparative kinetics","pmids":["33298890","36310334","33066406"],"confidence":"High","gaps":["Outward-open conformation structure not captured","Substrate-bound structures at atomic resolution for multiple substrates lacking","Mechanism by which 4F2hc ectodomain allosterically tunes LAT2 selectivity not resolved"]},{"year":2022,"claim":"LAT2-mediated amino acid uptake was shown to activate mTORC1 and downstream c-Myc in osteosarcoma cells, linking transporter activity to immune evasion via CD47 upregulation, thereby placing LAT2 in the signaling interface between amino acid import and tumor immunity.","evidence":"siRNA/shRNA LAT2 depletion; mTORC1/c-Myc ChIP; CD47 expression; macrophage phagocytosis assay; xenograft model","pmids":["36274066"],"confidence":"High","gaps":["Whether LAT2's signaling role is cell-type specific or generalizable unknown","Direct LAT2-mTORC1 signaling mechanism (sensing vs. substrate supply) not dissected"]},{"year":2025,"claim":"Two independent studies revealed tissue-specific metabolic consequences of LAT2 loss: in skeletal muscle, glutamine accumulation constitutively activates lysosomal mTORC1 and blocks fasting-induced proteolysis; in CD4+ T cells, LAT2 selectively supports Th2 metabolism and effector function via mTOR/c-Myc.","evidence":"Slc7a8−/− mice; intramuscular amino acid metabolomics; mTORC1-Lamp1 colocalization; rapamycin rescue; Th2 differentiation assays; helminth and allergen models","pmids":["40546137","41269086"],"confidence":"High","gaps":["Whether glutamine is the sole mTORC1-activating metabolite in LAT2-deficient muscle not proven","Mechanism of Th2-selective LAT2 dependence vs. other T helper lineages not resolved","Translational relevance of LAT2 as a therapeutic target in muscle wasting or allergy unexplored"]},{"year":null,"claim":"Key unresolved questions include the structural basis for the outward-open conformation and full substrate translocation cycle, the precise mechanism by which LAT2-imported amino acids activate mTORC1 across different tissues, and whether pharmacological modulation of LAT2 can be exploited therapeutically for hearing loss, cataract, or immune disorders.","evidence":"","pmids":[],"confidence":"Low","gaps":["No outward-open or occluded-state structure available","Direct sensing mechanism linking LAT2 transport to lysosomal mTORC1 recruitment not identified","No selective LAT2 inhibitor or activator tool compounds reported"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0,1,3,5,6,9,11,13,17,21,22,23,27,30,35,36]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,1,4,7,12,15,32]}],"pathway":[{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[0,1,5,6,7,9,13,14,26,27,32]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[15,25,33,37]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[36]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[5,6,21,25,37]}],"complexes":["4F2hc-LAT2 (SLC3A2-SLC7A8) heterodimer"],"partners":["SLC3A2","SLC16A10"],"other_free_text":[]},"mechanistic_narrative":"SLC7A8 (LAT2) is the catalytic light-chain subunit of a heterodimeric sodium-independent amino acid antiporter that, upon disulfide-linked heterodimerization with the heavy chain 4F2hc (SLC3A2), traffics to the plasma membrane and mediates obligatory 1:1 exchange of neutral amino acids with strongly asymmetric intra- and extracellular affinities [PMID:10391915, PMID:11847106]. Localized to the basolateral membrane of renal proximal tubules, intestinal epithelia, choroid plexus, and lens epithelium, LAT2 drives reabsorption of neutral amino acids in functional cooperation with the aromatic amino acid uniporter TAT1 (SLC16A10), and its loss causes aminoaciduria, age-related hearing loss, and cataract in mice and humans [PMID:21726201, PMID:29610403, PMID:29355479, PMID:31231240]. Beyond canonical amino acids, LAT2 transports thyroid hormone metabolites, L-DOPA, S-nitroso-L-cysteine, methylmercury-cysteine conjugates, and doxorubicin [PMID:15466357, PMID:12117417, PMID:15769744, PMID:26601072]. In skeletal muscle, LAT2 ablation causes glutamine accumulation that constitutively activates lysosomal mTORC1 and suppresses fasting-induced proteolysis, while in CD4+ T cells LAT2 selectively supports Th2 metabolism, proliferation, and effector function via mTOR and c-Myc pathways [PMID:40546137, PMID:41269086]."},"prefetch_data":{"uniprot":{"accession":"Q9UHI5","full_name":"Large neutral amino acids transporter small subunit 2","aliases":["L-type amino acid transporter 2","hLAT2","Solute carrier family 7 member 8"],"length_aa":535,"mass_kda":58.4,"function":"Associates with SLC3A2 to form a functional heterodimeric complex that translocates small and large neutral amino acids with broad specificity and a stoichiometry of 1:1. Functions as amino acid antiporter mediating the influx of extracellular essential amino acids mainly in exchange with the efflux of highly concentrated intracellular amino acids (PubMed:10391915, PubMed:11311135, PubMed:11847106, PubMed:12716892, PubMed:15081149, PubMed:15918515, PubMed:29355479, PubMed:33298890, PubMed:34848541). Has relatively symmetrical selectivities but strongly asymmetrical substrate affinities at both the intracellular and extracellular sides of the transporter (PubMed:11847106). This asymmetry allows SLC7A8 to regulate intracellular amino acid pools (mM concentrations) by exchange with external amino acids (uM concentration range), equilibrating the relative concentrations of different amino acids across the plasma membrane instead of mediating their net uptake (PubMed:10391915, PubMed:11847106). May play an essential role in the reabsorption of neutral amino acids from the epithelial cells to the bloodstream in the kidney (PubMed:12716892). Involved in the uptake of methylmercury (MeHg) when administered as the L-cysteine or D,L-homocysteine complexes, and hence plays a role in metal ion homeostasis and toxicity (PubMed:12117417). Involved in the cellular activity of small molecular weight nitrosothiols, via the stereoselective transport of L-nitrosocysteine (L-CNSO) across the transmembrane (PubMed:15769744). Imports the thyroid hormone diiodothyronine (T2) and to a smaller extent triiodothyronine (T3) but not rT 3 or thyroxine (T4) (By similarity). Mediates the uptake of L-DOPA (By similarity). May participate in auditory function (By similarity)","subcellular_location":"Cell membrane; Basolateral cell membrane","url":"https://www.uniprot.org/uniprotkb/Q9UHI5/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SLC7A8","classification":"Not Classified","n_dependent_lines":5,"n_total_lines":1208,"dependency_fraction":0.0041390728476821195},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SLC7A8","total_profiled":1310},"omim":[{"mim_id":"604235","title":"SOLUTE CARRIER FAMILY 7 (CATIONIC AMINO ACID TRANSPORTER, y+ SYSTEM), MEMBER 8; SLC7A8","url":"https://www.omim.org/entry/604235"},{"mim_id":"603733","title":"SOLUTE CARRIER FAMILY 43 (L-TYPE AMINO ACID TRANSPORTER), MEMBER 1; SLC43A1","url":"https://www.omim.org/entry/603733"},{"mim_id":"300095","title":"SOLUTE CARRIER FAMILY 16 (MONOCARBOXYLIC ACID TRANSPORTER), MEMBER 2; SLC16A2","url":"https://www.omim.org/entry/300095"},{"mim_id":"147140","title":"Fc FRAGMENT OF IgE, HIGH AFFINITY I, RECEPTOR FOR, ALPHA SUBUNIT; FCER1A","url":"https://www.omim.org/entry/147140"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"parathyroid gland","ntpm":310.6}],"url":"https://www.proteinatlas.org/search/SLC7A8"},"hgnc":{"alias_symbol":["LPI-PC1","LAT2"],"prev_symbol":[]},"alphafold":{"accession":"Q9UHI5","domains":[{"cath_id":"1.20.1740.10","chopping":"43-493","consensus_level":"high","plddt":89.2263,"start":43,"end":493}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UHI5","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UHI5-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UHI5-F1-predicted_aligned_error_v6.png","plddt_mean":82.69},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SLC7A8","jax_strain_url":"https://www.jax.org/strain/search?query=SLC7A8"},"sequence":{"accession":"Q9UHI5","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9UHI5.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9UHI5/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UHI5"}},"corpus_meta":[{"pmid":"10391915","id":"PMC_10391915","title":"Identification of a 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exchange of small and large zwitterionic amino acids; expressed alone, LAT2 remains intracellular and shows no transport activity.\",\n      \"method\": \"Xenopus laevis oocyte co-expression, radiolabeled amino acid uptake, N-myc tagging and subcellular localization\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted transport in oocytes with direct localization, replicated independently in same year by two labs\",\n      \"pmids\": [\"10391915\", \"10574970\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"LAT2-4F2hc forms a disulfide-linked heterodimer that catalyzes L-type amino acid uptake with higher apparent affinity for L-phenylalanine and transport of L-alanine at physiological concentrations compared to LAT1-4F2hc; localizes to the basolateral membrane of kidney proximal tubules and small intestine epithelia.\",\n      \"method\": \"Xenopus oocyte co-injection, immunofluorescence colocalization, disulfide cross-linking, kinetic uptake assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods; replicated by independent lab same year\",\n      \"pmids\": [\"10574970\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"SLC7A8 encodes a predicted 535-amino-acid protein homologous to amino acid permease CD98 light chains; maps to chromosome 14q11.2 and is highly expressed in skeletal muscle, intestine, kidney, and placenta.\",\n      \"method\": \"Bioinformatic identification, cDNA cloning, RNA in situ hybridization on mouse embryos\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — gene identification and expression mapping without direct functional reconstitution\",\n      \"pmids\": [\"10610726\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The extracellular domain of 4F2hc is required for surface expression of LAT2 (and y+LAT2) but not LAT1; C-terminal truncations of 4F2hc retaining only the transmembrane helix support LAT1 but almost completely abolish LAT2 plasma membrane trafficking.\",\n      \"method\": \"Xenopus oocyte co-expression with truncated 4F2hc mutants, surface expression assays, transport activity measurements\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic mutagenesis with functional and surface-expression readouts\",\n      \"pmids\": [\"11311135\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"LAT2-4F2hc transports methylmercury as a methylmercury-L-cysteine complex (a methionine mimic) with Km ~64 µM; transport is trans-stimulated by leucine and phenylalanine, establishing that the complex is both a cis- and trans-substrate of LAT2.\",\n      \"method\": \"Xenopus oocyte expression, radiolabeled [14C]MeHg uptake/efflux assays, kinetic analysis\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted in oocytes with kinetic characterization and trans-stimulation controls\",\n      \"pmids\": [\"12117417\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Basolateral LAT-2 mediates the major route for trans-epithelial cystine efflux in renal proximal tubule-derived OK cells; antisense-mediated reduction of LAT-2 decreased apical-to-basolateral cystine flux and elevated intracellular cysteine ~2–3-fold.\",\n      \"method\": \"Stable antisense transfection, transepithelial flux assays, amino acid content measurements in OK cells\",\n      \"journal\": \"Journal of the American Society of Nephrology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean loss-of-function with specific transepithelial flux phenotype and intracellular substrate accumulation\",\n      \"pmids\": [\"12660317\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"CD98/LAT-2 forms a complex with ICAM-1 at the basolateral membrane of intestinal Caco-2 cells; CD98 ligation decreases Km and Vmax of LAT-2, while ICAM-1 ligation increases both Km and Vmax, demonstrating reciprocal regulation of LAT-2 transport activity by co-receptor ligation.\",\n      \"method\": \"Co-immunoprecipitation, antibody cross-linking, Km/Vmax kinetic analysis in polarized Caco-2 monolayers\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — co-IP plus functional kinetic assay from single lab\",\n      \"pmids\": [\"12716892\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"LAT2 mediates L-DOPA uptake in renal proximal tubule cells in a sodium-independent manner; siRNA-mediated silencing of LAT2 in LLC-PK1 cells reduced [14C]-L-DOPA accumulation by 85% and outward transport by 90%, demonstrating LAT2 mediates both influx and efflux of L-DOPA.\",\n      \"method\": \"siRNA gene silencing, [14C]-L-DOPA uptake and efflux assays in LLC-PK1 cells\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean loss-of-function with specific quantitative transport phenotype\",\n      \"pmids\": [\"15466357\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"LAT2 and TAT1 co-localize at the basolateral membrane of human renal proximal tubules and together mediate reabsorption of neutral amino acids from epithelial cells to blood.\",\n      \"method\": \"Immunohistochemistry of human kidney sections, northern blot for mRNA distribution\",\n      \"journal\": \"Archives of pharmacal research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — direct localization by IHC with functional inference; single lab\",\n      \"pmids\": [\"15918515\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"LAT1 and LAT2 stereoselectively transport intact L-S-nitrosocysteine (L-CSNO) across cell membranes; overexpression of LAT1 in T24 cells increased L-CSNO uptake and siRNA knockdown decreased it, identifying system L members as mediators of S-nitrosothiol bioactivity.\",\n      \"method\": \"Xenopus oocyte expression, adenoviral overexpression, siRNA knockdown, CSNO uptake assays in mammalian cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — reconstitution in oocytes plus mammalian gain- and loss-of-function\",\n      \"pmids\": [\"15769744\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"TAT1 (Slc16a10) and LAT2-4F2hc functionally cooperate to drive net amino acid efflux: TAT1 recycles aromatic amino acids by facilitated diffusion, providing the intracellular trans-substrate needed to drive LAT2-4F2hc-mediated obligatory exchange and release of other neutral amino acids (e.g., glutamine) from cells.\",\n      \"method\": \"Xenopus oocyte co-expression with wild-type and transport-inactive mutants, HPLC amino acid efflux analysis, coimmunoprecipitation and crosslinking (negative)\",\n      \"journal\": \"Pflugers Archiv\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — reconstituted cooperation in oocytes with functional-mutant controls and HPLC quantification\",\n      \"pmids\": [\"17273864\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Targeted inactivation of Slc7a8 (LAT2) in mice causes increased urinary loss of small neutral amino acids (aminoaciduria) without overt growth defects, demonstrating LAT2 is required for renal reabsorption of neutral amino acids.\",\n      \"method\": \"Slc7a8 knockout mouse model, urine amino acid profiling\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with specific aminoaciduria phenotype\",\n      \"pmids\": [\"21726201\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"LAT2 plasma membrane expression markedly stimulates mTORC1 signaling in glomerular epithelial cells, and a LAT2 inhibitor abrogates both mTORC1 activation and crescent formation in a rat crescentic glomerulonephritis model.\",\n      \"method\": \"Immunohistochemistry and western blot of isolated glomeruli, cell culture with LAT inhibitor, in vivo pharmacologic inhibition\",\n      \"journal\": \"Laboratory investigation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — pharmacologic inhibition in vivo and in vitro; single lab without genetic control\",\n      \"pmids\": [\"21403644\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The extracellular domain of 4F2hc interacts with LAT2, almost completely covering the extracellular face of the transporter; 4F2hc stabilizes detergent-solubilized LAT2 and its extracellular domain alone is sufficient for this stabilization. Functional reconstitution of the heterodimer into proteoliposomes confirmed transport activity.\",\n      \"method\": \"Transmission electron microscopy, single-particle analysis, docking analysis, crosslinking, proteoliposome reconstitution of purified 4F2hc-LAT2 overexpressed in Pichia pastoris\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — structural EM plus crosslinking, reconstitution with functional validation; multiple orthogonal methods\",\n      \"pmids\": [\"24516142\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Lat2 (Slc7a8) transports thyroid hormones into the cerebral cortex during early postnatal development; in Mct8/Lat2 double-knockout mice the cortical hyperthyroidism seen in Mct8 single knockouts is prevented in newborns, demonstrating Lat2 contributes to thyroid hormone supply to the neonatal brain.\",\n      \"method\": \"Single and double knockout mouse models, thyroid hormone measurement in brain tissue, thyroid hormone-responsive gene expression\",\n      \"journal\": \"PLoS One\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis in double-KO mouse with specific biochemical phenotype\",\n      \"pmids\": [\"24819605\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Mouse Lat2-CD98 mediates transport of 3,3'-diiodothyronine (T2) with a low-micromolar Km, and T1/T2 derivatives as well as BCH compete for T2 uptake, establishing Lat2 as a thyroid hormone metabolite transporter preferring 3,3'-T2 over T3.\",\n      \"method\": \"Xenopus oocyte co-injection of Lat2 + CD98 cRNA, radiolabeled T2 uptake and competition assays\",\n      \"journal\": \"European thyroid journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted in oocytes with kinetic characterization\",\n      \"pmids\": [\"26601072\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"ATB0+, LAT1, and LAT2 all transport boronophenylalanine (BPA) in Xenopus oocytes; LAT2 transports BPA with Km ~88 µM, comparable to its endogenous substrates, and contributes to BPA uptake in cancer cell lines.\",\n      \"method\": \"Xenopus oocyte functional expression, HPLC-quantified BPA uptake, kinetic analysis in cancer cell lines\",\n      \"journal\": \"Cancer science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted transport in oocytes with quantitative kinetic parameters\",\n      \"pmids\": [\"25580517\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"LAT2 regulates glutamine-dependent mTOR activation in pancreatic cancer cells via two positive feedback loops (LAT2/p-mTORSer2448 and glutamine/p-mTORSer2448/glutamine synthetase), promoting glycolysis and gemcitabine resistance; mTOR inhibition reverses LAT2-driven chemoresistance.\",\n      \"method\": \"LAT2 overexpression/knockdown in vitro and in vivo xenograft, mTOR pathway western blot, metabolic assays, combination drug treatment\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — multiple in vitro/in vivo methods from single lab; pathway placement via pharmacologic inhibition\",\n      \"pmids\": [\"30419950\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"LAT2/CD98hc and TAT1 functionally cooperate in vivo for renal reabsorption of neutral amino acids; double-knockout (LAT2+TAT1) mice show greater aminoaciduria than either single KO, including loss of cationic amino acids, and compensatory upregulation of y+LAT1/CD98hc.\",\n      \"method\": \"Double-knockout mouse model, urine amino acid profiling, transporter expression analysis\",\n      \"journal\": \"Journal of the American Society of Nephrology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis in double-KO mouse with quantitative urinary amino acid phenotype\",\n      \"pmids\": [\"29610403\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SLC7A8 is expressed in the mouse inner ear; its ablation causes age-related hearing loss due to cochlear damage. Patient-derived variants (p.Val302Ile, p.Arg418His, p.Thr402Met, p.Val460Glu) show significantly decreased LAT2 transport activity in vitro.\",\n      \"method\": \"Slc7a8 knockout mouse model (auditory testing, cochlear histology), in vitro functional expression of patient variants in HeLa cells\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — KO mouse with specific sensory phenotype plus in vitro variant functional characterization\",\n      \"pmids\": [\"29355479\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Deletion of LAT2 (Slc7a8) in mice causes increased incidence of cataract (especially in older females); a homozygous SLC7A8 deletion identified in a human cataract family abolishes LAT2 amino acid uptake in HeLa cells, and LAT2 absence reduces lens essential amino acid levels.\",\n      \"method\": \"Slc7a8 KO mouse model (lens amino acid measurement, cataract incidence), patient variant functional expression in HeLa cells\",\n      \"journal\": \"Frontiers in physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — KO mouse phenotype with biochemical mechanism plus human variant functional validation\",\n      \"pmids\": [\"31231240\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"4F2hc modulates the substrate affinity and specificity of LAT2 beyond its trafficking role; LAT2 expressed without 4F2hc in Pichia pastoris is functional but shows altered kinetics compared to the 4F2hc-LAT2 heterodimer, confirming LAT2 as the catalytic subunit and 4F2hc as an allosteric modulator.\",\n      \"method\": \"Heterologous expression in Pichia pastoris of LAT2 alone vs. 4F2hc-LAT2, radiolabel transport assays with kinetic comparisons\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted transport with and without 4F2hc; comparative kinetic analysis\",\n      \"pmids\": [\"33066406\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"LAT2 (Slc7a8) localizes to the CSF-facing luminal membrane of choroid plexus epithelium; LAT2 knockout increases CSF levels of leucine, valine, tryptophan and other neutral amino acids, demonstrating LAT2 mediates reuptake of essential amino acids from CSF and participates in the amino acid gradient between plasma and CSF.\",\n      \"method\": \"qRT-PCR, immunofluorescence of isolated choroid plexus, LAT2 KO mouse CSF amino acid profiling\",\n      \"journal\": \"Fluids and barriers of the CNS\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct localization with KO phenotype showing specific biochemical consequence\",\n      \"pmids\": [\"32046769\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Chemotherapy-induced macrophage secretion of IL-18 upregulates LAT2 in osteosarcoma cells, enhancing leucine and glutamine uptake, which activates mTORC1 and c-Myc-mediated transcription of CD47 to promote immune evasion; LAT2 depletion or LAT inhibition downregulates CD47 and sensitizes tumors to doxorubicin.\",\n      \"method\": \"LAT2 knockdown and inhibitor treatment, mTORC1 pathway western blot, c-Myc ChIP, macrophage phagocytosis assay, in vivo mouse osteosarcoma model\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (KD, inhibitor, ChIP, in vivo); pathway mechanistically placed\",\n      \"pmids\": [\"36274066\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"LAT2 (SLC7A8) transports doxorubicin across cell membranes; transport assays in HEK293 cells overexpressing LAT2 demonstrate doxorubicin but not cisplatin or methotrexate is a LAT2 substrate.\",\n      \"method\": \"In vitro transport assay in HEK293 cells overexpressing LAT2, drug uptake measurement\",\n      \"journal\": \"Frontiers in pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — direct transport assay in overexpression system; single lab, substrate selectivity characterized\",\n      \"pmids\": [\"36438828\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Cryo-EM structure of human 4F2hc-LAT2 in complex with anticalin D11vs resolved to 3.2 Å (2.8-3.0 Å local resolution at LAT2 substrate binding site); molecular dynamics simulations identified fixed water molecules in the LAT2 substrate binding pocket.\",\n      \"method\": \"Single-particle cryo-EM, molecular dynamics simulations, anticalin complex formation\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — near-atomic resolution structure with MD validation of binding site features\",\n      \"pmids\": [\"36310334\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"LAT2 mediates glutamine efflux from skeletal muscle; LAT2 KO mice accumulate intramuscular glutamine 6.3-fold during fasting, which activates mTORC1 (evidenced by increased lysosomal mTORC1 recruitment) and suppresses proteasomal and autophagic proteolysis; rapamycin treatment of KO muscle restores proteolysis, confirming mTORC1-dependence.\",\n      \"method\": \"LAT2 KO mouse, fasting metabolic studies, amino acid profiling, proteasome/autophagy activity assays, rapamycin rescue, mTORC1-Lamp1 colocalization by immunofluorescence\",\n      \"journal\": \"Journal of cachexia, sarcopenia and muscle\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — KO model with rescue experiment, multiple pathway readouts, specific biochemical phenotype\",\n      \"pmids\": [\"40546137\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SLC7A8 is selectively upregulated in Th2 cells; Slc7a8 deficiency impairs Th2 cell proliferation and cytokine production, reduces mTOR activation and mitochondrial function, and impairs c-Myc pathway activity, establishing SLC7A8 as a Th2-specific amino acid transporter required for Th2 metabolic fitness.\",\n      \"method\": \"Slc7a8 KO mice, T helper cell differentiation assays, cytokine production measurement, metabolic profiling, helminth infection and allergen challenge models\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic KO with specific immune-cell phenotype and multiple mechanistic pathway readouts\",\n      \"pmids\": [\"41269086\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SLC7A8/LAT2 is a catalytic light-chain subunit that obligatorily heterodimerizes with 4F2hc (CD98/SLC3A2) via a conserved disulfide bridge to reach the plasma membrane, where 4F2hc both traffics and allosterically modulates LAT2 transport kinetics; as an obligatory antiporter, LAT2 exchanges most neutral amino acids (plus thyroid hormones, methylmercury-L-cysteine, doxorubicin, and BPA) in a sodium-independent manner, and by coupling to the aromatic amino acid uniporter TAT1 achieves net amino acid efflux, enabling basolateral reabsorption of neutral amino acids in kidney proximal tubule and small intestine epithelia, maintenance of CSF amino acid homeostasis, lens amino acid supply, neonatal thyroid hormone delivery to the cerebral cortex, and amino acid-driven mTORC1 activation in skeletal muscle, immune, and cancer cell contexts.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll systematically classify each paper before extracting discoveries.\n\n**Classification Notes:**\n- Papers [13] (LAT-2 = beta-lactamase in bacteria) → EXCLUDE (alias collision)\n- Papers [16], [19], [39], [43], [46], [54], [62], [68] describe NTAL/LAB/LAT2 (adaptor protein in hematopoietic cells, encoded by a different gene) → EXCLUDE (alias collision — these describe the transmembrane adaptor \"LAT2/NTAL/LAB\", not SLC7A8)\n- Paper [60] describes *Ambrosiozyma monospora* Lat1/Lat2 sugar transporters → EXCLUDE (symbol collision, unrelated organism/function)\n- Additional papers [1-9, 11-16 in gene2pubmed] are general/BBB reviews, cDNA libraries, interactome maps, etc. with no specific SLC7A8 mechanistic content → EXCLUDE or irrelevant\n- Additional paper [17] describes LAT1-4F2hc structure → EXCLUDE (LAT1/SLC7A5, not SLC7A8)\n- Additional paper [24] describes LAT2-4F2hc substrate recognition structure → KEEP\n- All remaining papers about the amino acid transporter LAT2/SLC7A8 → KEEP\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1999,\n      \"finding\": \"SLC7A8 (LAT2) encodes a sodium-independent L-type amino acid transporter that requires heterodimerization with 4F2hc (CD98 heavy chain) for plasma membrane localization and transport activity. Expressed alone in Xenopus oocytes, LAT2 localizes intracellularly and is non-functional; co-expression with 4F2hc traffics it to the plasma membrane and induces broad-specificity transport of small and large zwitterionic amino acids. The transport is highly trans-stimulated, indicating an obligatory exchanger mechanism.\",\n      \"method\": \"Xenopus oocyte expression system; N-myc-tagged protein; subcellular localization assay; radiolabeled amino acid uptake; trans-stimulation assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — functional reconstitution in oocytes with localization and transport assays, independently replicated in same year by Rossier et al.\",\n      \"pmids\": [\"10391915\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"LAT2/SLC7A8 forms a disulfide-linked heterodimer with 4F2hc and mediates L-type amino acid uptake with higher affinity for L-phenylalanine and transport of L-alanine at physiological concentrations compared to LAT1-4F2hc. LAT2-4F2hc also mediates amino acid efflux in the presence of an external substrate, consistent with obligatory exchange. LAT2 colocalizes with 4F2hc at the basolateral membrane of kidney proximal tubules and small intestine epithelia, implicating it in epithelial amino acid (re)absorption.\",\n      \"method\": \"Xenopus oocyte co-injection of mouse LAT2 and human 4F2hc cRNAs; SDS-PAGE under non-reducing conditions (disulfide); L-[3H]phenylalanine and L-[3H]alanine uptake kinetics; immunofluorescence of kidney and intestine sections\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — functional reconstitution with kinetics, structural (disulfide) and localization data, independent replication of LAT2 identity\",\n      \"pmids\": [\"10574970\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"SLC7A8 maps to chromosome 14q11.2 within the lysinuric protein intolerance (LPI) critical region, is highly expressed in skeletal muscle, intestine, kidney, and placenta, and encodes a predicted 535-amino-acid protein homologous to CD98 light chain amino acid permeases. Mutational analysis excluded SLC7A8 from direct causation of LPI.\",\n      \"method\": \"Bioinformatic cloning; Northern blot; RNA in situ hybridization on mouse embryos; Sanger sequencing for mutation analysis\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — gene identification and expression mapping; no reconstitution in this paper\",\n      \"pmids\": [\"10610726\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"The LAT2-4F2hc heterodimer functions as an obligatory antiporter: only preloaded intracellular amino acids can be released in exchange for extracellular substrates, confirming an exchanger rather than uniporter mechanism for this transporter complex.\",\n      \"method\": \"Xenopus oocyte expression; radiolabeled amino acid efflux under various loading conditions; competitive inhibition assays\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional reconstitution demonstrating antiport mechanism, though focused primarily on y+LAT2 with LAT2 comparison\",\n      \"pmids\": [\"10903140\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The extracellular domain of 4F2hc is specifically required for plasma membrane trafficking of LAT2 (and y+LAT2) but not LAT1. C-terminal truncations of 4F2hc that retain only the transmembrane helix are sufficient for LAT1 surface expression but almost completely abolish LAT2 surface expression, revealing that LAT2 requires interaction with the extracellular domain of 4F2hc for correct trafficking.\",\n      \"method\": \"Xenopus oocyte expression of C-terminally truncated 4F2hc mutants co-expressed with LAT1, LAT2, or y+LAT2; surface biotinylation; radiolabeled amino acid transport assays\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — systematic domain-deletion mutagenesis with functional readout, replicated across multiple light chains\",\n      \"pmids\": [\"11311135\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"LAT2-4F2hc functions as an obligatory amino acid exchanger with 1:1 stoichiometry. Intracellular substrates strongly trans-stimulate influx, and LAT2-4F2hc has much lower apparent affinity for intracellular substrates (Km in millimolar range) compared to extracellular substrates, creating strongly asymmetric affinity that allows the intracellular amino acid concentration to control transporter activity.\",\n      \"method\": \"Xenopus oocyte expression; HPLC quantification of simultaneous amino acid influx and efflux; intracellular substrate injection; kinetic analysis\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — rigorous quantitative reconstitution with HPLC, stoichiometry determination, and asymmetric affinity characterization\",\n      \"pmids\": [\"11847106\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"LAT2-4F2hc transports methylmercury when complexed with L-cysteine (MeHg-L-cysteine), acting as a molecular mimic of methionine. Both cis- and trans-substrate properties were confirmed: MeHg-L-cysteine uptake by LAT2 has Km ~64 µM with Vmax higher than methionine, and methionine efflux is trans-stimulated by external leucine and phenylalanine even against an inward methionine gradient.\",\n      \"method\": \"Xenopus oocyte expression of LAT2-4F2hc; [14C]MeHg-L-cysteine uptake; [3H]methionine trans-stimulation; kinetic analysis (Km, Vmax)\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — reconstitution in oocytes with full kinetic characterization and trans-stimulation assays\",\n      \"pmids\": [\"12117417\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"LAT2 at the basolateral membrane of renal proximal tubule cells plays a major specific role in basolateral efflux of cysteine/cystine. Antisense-mediated partial knockdown of LAT2 in OK cells reduced basolateral system L amino acid exchange activity, decreased apical-to-basolateral transepithelial flux of cystine, and caused a 2-3 fold increase in intracellular cysteine, identifying LAT2 as a key transporter mediating cystine reabsorption across the basolateral membrane.\",\n      \"method\": \"Stable transfection with LAT2 antisense construct in OK cells; radiolabeled amino acid transport; transepithelial flux assay; intracellular amino acid content measurement\",\n      \"journal\": \"Journal of the American Society of Nephrology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function (antisense KD) with specific transepithelial flux phenotype and intracellular accumulation readout\",\n      \"pmids\": [\"12660317\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"CD98 (4F2hc) ligation at the basolateral membrane of intestinal Caco-2 epithelial cells decreases the Km and Vmax of LAT2-mediated transport, while ICAM-1 ligation increases both Km and Vmax, demonstrating that LAT2 transport activity is regulated by co-receptor signaling. ICAM-1 selectively co-immunoprecipitates with CD98/LAT2 at the basolateral membrane, and cross-linking of either receptor induces threonine phosphorylation of an ~160 kDa CD98/LAT2-ICAM-1 complex.\",\n      \"method\": \"Co-immunoprecipitation; antibody-mediated receptor cross-linking; amino acid transport kinetics (Km, Vmax) in Caco-2 monolayers; phosphorylation assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — co-IP plus functional transport kinetics with signaling readout, single lab\",\n      \"pmids\": [\"12716892\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"LAT2 mediates Na+-independent, pH-sensitive L-DOPA transport in renal LLC-PK1 epithelial cells. siRNA silencing of LAT2 reduced [14C]-L-DOPA accumulation by ~85% and outward transport by ~90%, confirming LAT2 as the primary L-DOPA transporter; the LAT2-mediated mechanism supports both influx and efflux of L-DOPA, consistent with heteroexchange.\",\n      \"method\": \"siRNA knockdown of LAT2 in LLC-PK1 cells; real-time quantitative RT-PCR; [14C]-L-DOPA uptake and efflux assays; competitive inhibition\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — specific siRNA knockdown with quantitative transport phenotype in epithelial cells\",\n      \"pmids\": [\"15466357\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"rBAT (apical) and LAT2 (basolateral) can each mediate L-DOPA uptake into renal proximal tubule cells, with distinct kinetics: rBAT shows micromolar Km while LAT2 shows millimolar Km for L-DOPA. Antisense oligonucleotides to LAT2 inhibited LAT2 cRNA-induced L-DOPA transport and partially blocked cortical poly-A+ RNA-induced transport.\",\n      \"method\": \"Xenopus oocyte expression; kinetic analysis; sequence-specific antisense oligonucleotides; [14C]-L-DOPA uptake\",\n      \"journal\": \"American journal of physiology. Renal physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — oocyte reconstitution with antisense inhibition confirming LAT2 identity\",\n      \"pmids\": [\"15180924\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"LAT2 (co-expressed with 4F2hc) stereoselectively transports S-nitroso-L-cysteine (L-CSNO) but not D-CSNO or other nitrosothiols, identifying LAT2 as a transporter for this nitric oxide donor. L-CSNO transport by LAT2 is Na+-independent, inhibited by leucine and BCH, and the transport mechanism involves direct cellular uptake of intact L-CSNO.\",\n      \"method\": \"Xenopus oocyte expression of LAT2-4F2hc; [14C]-L-CSNO uptake; stereoselectivity assays; competitive inhibition; overexpression and siRNA knockdown in mammalian cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reconstitution in oocytes plus gain- and loss-of-function in mammalian cells, stereospecificity demonstrated\",\n      \"pmids\": [\"15769744\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"LAT2 and TAT1 (SLC16A10) colocalize in the basolateral membrane of human renal proximal tubules and together mediate renal reabsorption of neutral amino acids. LAT2 transports all neutral amino acids while TAT1 is specific for aromatic amino acids, and their basolateral colocalization supports a two-transporter model for basolateral exit of reabsorbed amino acids.\",\n      \"method\": \"Immunohistochemistry on human kidney sections; Northern blot; functional characterization in Xenopus oocytes\",\n      \"journal\": \"Archives of pharmacal research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — colocalization by IHC with functional transport characterization in oocytes\",\n      \"pmids\": [\"15918515\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"TAT1 (SLC16A10) and LAT2-4F2hc functionally cooperate to drive net amino acid efflux: TAT1 recycles aromatic amino acids (influx substrates of LAT2) by facilitated diffusion, enabling LAT2-4F2hc to continuously release glutamine and other neutral amino acids from cells. This cooperation requires the transport activity of both proteins but not their physical interaction, as coimmunoprecipitation and crosslinking were negative.\",\n      \"method\": \"Xenopus oocyte co-expression; HPLC analysis of amino acid efflux; functionally inactive surface-expressed mutants; co-immunoprecipitation; crosslinking experiments; immunofluorescence colocalization in kidney\",\n      \"journal\": \"Pflugers Archiv\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods including functional mutants, HPLC quantification, and negative protein interaction controls\",\n      \"pmids\": [\"17273864\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Targeted inactivation of Slc7a8 in mice causes increased urinary loss of small neutral amino acids (aminoaciduria), demonstrating that LAT2 is required for renal reabsorption of neutral amino acids in vivo. Motor coordination is mildly impaired in Slc7a8-/- mice. Circulating thyroid hormones and TSH remain normal in knockout mice, suggesting functional compensation by MCT8 for thyroid hormone transport.\",\n      \"method\": \"Targeted gene knockout (Slc7a8-/- mice); urine amino acid analysis; behavioral testing (motor coordination); thyroid hormone and TSH measurements; thyroid hormone-responsive gene expression\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean knockout mouse model with specific in vivo amino acid transport and hormonal phenotypes\",\n      \"pmids\": [\"21726201\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"LAT2 plasma membrane expression in glomerular parietal epithelial cells (PECs) and podocytes activates the mTORC1 signaling pathway, preceding crescent formation in crescentic glomerulonephritis (CGN). LAT2 is specifically upregulated in these cells before crescent formation; in cell culture, plasma membrane LAT2 markedly stimulates mTORC1 signaling that is abrogated by a LAT inhibitor; and LAT inhibitor significantly reduced crescent formation in vivo.\",\n      \"method\": \"Immunohistochemistry and Western blot of isolated rat glomeruli; cell culture with LAT inhibitor; mTORC1 pathway analysis (p-S6K1); in vivo LAT inhibitor treatment of CGN model\",\n      \"journal\": \"Laboratory investigation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — in vivo and in vitro evidence linking LAT2 to mTORC1 activation, single lab\",\n      \"pmids\": [\"21403644\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Dihydrotestosterone (DHT) acutely increases expression of LAT2 protein and amino acid uptake in fast-twitch skeletal muscle fibers through a non-genomic mechanism requiring EGFR transactivation and ERK1/2 (MEK) signaling, but not androgen receptor or PI3K/Akt. This effect is also dependent on mTOR and involves increased protein synthesis.\",\n      \"method\": \"[14C]-labelled amino acid uptake in isolated mouse muscle fiber bundles; pharmacological inhibition of EGFR, MEK, mTOR, androgen receptor; Western blot for LAT2, p-EGFR, p-ERK1/2, p-RSK1/2; protein incorporation assay\",\n      \"journal\": \"The Journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — pharmacological pathway dissection with protein expression readout, single lab\",\n      \"pmids\": [\"21606113\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Human LAT2 expressed stably in HEK293 cells (as heterodimer with endogenous 4F2hc) transports L-alanine as a preferred substrate with reliable kinetics. α-Alkyl amino acids (α-methyl-alanine, α-ethyl-L-alanine) interfere with LAT2 interaction, defining a steric constraint at the α-carbon of substrates that distinguishes LAT2 from LAT1.\",\n      \"method\": \"Stable HEK293 cell lines; [14C]-L-alanine transport assays; kinetic analysis; α-alkyl amino acid inhibition studies\",\n      \"journal\": \"Journal of pharmacological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — stable mammalian cell expression with kinetic characterization and substrate specificity mapping\",\n      \"pmids\": [\"22850614\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The extracellular domain of 4F2hc interacts directly with LAT2, almost completely covering the extracellular face of the transporter as revealed by transmission electron microscopy and single-particle analysis. 4F2hc increases the stability of LAT2 in detergent-solubilized membranes and enables functional reconstitution of the heterodimer into proteoliposomes; the extracellular domain of 4F2hc alone is sufficient to stabilize solubilized LAT2.\",\n      \"method\": \"Transmission electron microscopy (negative stain); single-particle analysis; purification of recombinant 4F2hc-LAT2 from Pichia pastoris; crosslinking experiments; docking analysis; functional reconstitution into proteoliposomes\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — structural (EM) plus biochemical reconstitution and stabilization assays, multiple orthogonal methods\",\n      \"pmids\": [\"24516142\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Cerebral cortex hyperthyroidism in neonatal Mct8-deficient mice is prevented by simultaneous ablation of Lat2, demonstrating that Lat2 is responsible for the increased thyroid hormone supply to the neonatal cerebral cortex in the absence of Mct8. This Lat2 effect is transient (absent from postnatal day 5 onward), and Lat2 expression in neurons and choroid plexus is consistent with a role in early postnatal thyroid hormone supply to the cortex.\",\n      \"method\": \"Double knockout mice (Mct8-/-/Lat2-/-); T3 concentration measurements in cerebral cortex; thyroid hormone target gene expression (Hr); comparison across postnatal development time points\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis via double knockout with quantitative hormone and target gene readout\",\n      \"pmids\": [\"24819605\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Stabilization of purified 4F2hc-LAT2 with a combination of DDM, lauryl maltose neopentyl glycol, and cholesteryl hemisuccinate enables measurement of substrate binding by scintillation proximity assay and improves the 3D EM map, confirming that LAT2 is the substrate-transporting subunit of the heterodimer.\",\n      \"method\": \"Detergent screening; negative-stain TEM; scintillation proximity assay for substrate binding; 3D map reconstruction\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 — structural and biochemical binding assay, but primarily technical optimization paper\",\n      \"pmids\": [\"25299125\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"LAT2 (co-expressed with CD98) transports 3,3'-diiodo-L-thyronine (3,3'-T2) with a low micromolar Km comparable to MCT8, and to a lesser extent T3. Various iodothyronine derivatives competitively inhibit 3,3'-T2 uptake, revealing that LAT2 preferentially transports 3,3'-T2 among thyroid hormone metabolites, suggesting a role in cellular availability of this deiodinase product.\",\n      \"method\": \"Xenopus oocyte co-injection of Lat2 and CD98 cRNAs; [125I]-3,3'-T2 and [125I]-T3 uptake; competitive inhibition with iodothyronine derivatives; Km determination\",\n      \"journal\": \"European thyroid journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional reconstitution in oocytes with kinetic characterization for thyroid hormone substrates\",\n      \"pmids\": [\"26601072\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"BPA (boronophenylalanine), a boron neutron capture therapy agent, is a substrate for LAT2 (as well as ATB0,+ and LAT1), with a Km of 88.3 µM for LAT2-mediated transport in Xenopus oocytes. In cancer cell lines, LAT1 is the predominant BPA transporter at low concentrations, with LAT2 contributing at higher concentrations.\",\n      \"method\": \"Xenopus oocyte expression; HPLC-based BPA uptake quantification; kinetic analysis; siRNA knockdown in MCF-7 cells\",\n      \"journal\": \"Cancer science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reconstitution with quantitative kinetics and cell line validation\",\n      \"pmids\": [\"25580517\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"LAT2-4F2hc mediates methylmercury (as MeHg-L-cysteine complex) uptake at the apical membrane of BeWo placental trophoblast cells. siRNA knockdown of LAT2 or 4F2hc significantly reduced leucine, methionine, and methylmercury uptake, establishing LAT2-4F2hc as a key pathway for placental methylmercury transport.\",\n      \"method\": \"siRNA knockdown of LAT2 and 4F2hc in BeWo cells; Transwell transport assay; [3H]leucine, [3H]methionine, and methylmercury uptake measurements\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA knockdown with multiple substrate readouts in placental cell model\",\n      \"pmids\": [\"28786956\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"LAT2/SLC7A8 is expressed in the mouse inner ear, and its ablation (Slc7a8-/- mice) causes age-related hearing loss (ARHL) with damage to cochlear structures. Human SLC7A8 variants (p.Val302Ile, p.Arg418His, p.Thr402Met, p.Val460Glu) found in ARHL patients show significant decreases in transport activity when functionally expressed in vitro, supporting a causative role for SLC7A8 loss-of-function in ARHL.\",\n      \"method\": \"Slc7a8-/- mouse model; auditory brainstem response testing; cochlear histology; in vitro functional transport assays of patient variants in heterologous cells\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — knockout mouse phenotype plus in vitro functional characterization of human disease variants\",\n      \"pmids\": [\"29355479\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"LAT2 promotes glutamine-dependent mTOR activation in pancreatic cancer cells, driving glycolysis and chemoresistance. LAT2 regulates two glutamine-dependent positive feedback loops: the LAT2/p-mTORSer2448 loop and the glutamine/p-mTORSer2448/glutamine synthetase loop. mTOR inhibitor (RAD001) reverses the LAT2-mediated decrease in gemcitabine sensitivity.\",\n      \"method\": \"LAT2 overexpression and knockdown in pancreatic cancer cells; mTOR pathway analysis (p-mTORSer2448); glycolysis assays; glutamine metabolism measurement; xenograft mouse model; drug sensitivity assays\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — gain- and loss-of-function with pathway analysis in vitro and in vivo, single lab\",\n      \"pmids\": [\"30419950\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"LAT2/CD98hc (SLC7A8/SLC3A2) and TAT1 (SLC16A10) functionally cooperate in vivo for renal reabsorption of neutral amino acids. Double-knockout (LAT2/TAT1) mice show greater urinary loss of aromatic and other neutral amino acids than single knockouts, and also display decreased reabsorption of cationic amino acids with compensatory upregulation of y+LAT1/CD98hc, demonstrating functional cooperation and compensation among basolateral amino acid transporters.\",\n      \"method\": \"Double-knockout mouse model (LAT2-TAT1 dKO); urine amino acid analysis; Western blot for transporter expression; comparison with single knockouts\",\n      \"journal\": \"Journal of the American Society of Nephrology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis via double-knockout with quantitative in vivo phenotypic readout\",\n      \"pmids\": [\"29610403\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Loss of LAT2 (Slc7a8 deletion) in mice causes cataract, particularly in older females, associated with a dramatic decrease in lens essential amino acid levels. A homozygous SLC7A8 single nucleotide deletion found in a human family with congenital cataract abolishes amino acid transport when expressed in HeLa cells. Heterozygous LAT2 variants from cataract patients also show reduced transport function. Simultaneous TAT1 deletion synergizes with LAT2 loss to increase cataract incidence.\",\n      \"method\": \"Slc7a8-/- and double Slc7a8/Slc16a10 knockout mice; slit-lamp examination; lens amino acid HPLC; in vitro transport assays of human variants in HeLa cells; immunofluorescence of LAT2 in ciliary and lens epithelium\",\n      \"journal\": \"Frontiers in physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — knockout mouse phenotype, human variant functional studies, and lens amino acid measurement\",\n      \"pmids\": [\"31231240\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Cryo-EM 3D map of human 4F2hc-LAT2 at ~13 Å resolution reveals two prominent densities: the 4F2hc ectodomain (fitted using the available X-ray structure) and the LAT2 transmembrane domain, defining the relative positions of the two subunits with respect to each other and the membrane plane.\",\n      \"method\": \"Cryo-EM with direct electron detector and Volta phase plate; 3D map reconstruction; fitting of 4F2hc ectodomain X-ray structure\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM structural determination, but limited to ~13 Å resolution without atomic detail\",\n      \"pmids\": [\"30795505\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Sub-nanometer cryo-EM density map of 4F2hc-LAT2 reveals the inward-open conformation of LAT2 via homology modeling fitted into the map. Disease-causing point mutations in LAT2 are mapped to the substrate binding site and transmembrane helices, providing structural context for their functional effects.\",\n      \"method\": \"Cryo-EM; homology model generation of 4F2hc-LAT2 in inward-open conformation; fitting and analysis; disease mutation mapping\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — structural cryo-EM with homology modeling, but resolution limits atomic-level mechanistic conclusions\",\n      \"pmids\": [\"32993041\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"4F2hc modulates the substrate affinity and specificity of LAT2 (and LAT1): when LAT2 is expressed alone in Pichia pastoris (without 4F2hc), it localizes to the plasma membrane and is transport-competent, but shows different substrate affinity and specificity compared to the 4F2hc-LAT2 heterodimer. This demonstrates a novel function of the heavy chain beyond trafficking, namely modulation of light chain transport properties.\",\n      \"method\": \"Pichia pastoris expression of LAT2 alone and 4F2hc-LAT2; [3H]L-leucine radiolabel transport assay; substrate competition assays; kinetic analysis\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — novel functional finding with direct comparison of LAT2 alone vs. heterodimer, single lab\",\n      \"pmids\": [\"33066406\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"The structural insight into substrate recognition of LAT2-4F2hc was determined: the cryo-EM/crystal structure of the complex reveals the substrate binding pocket architecture in LAT2, with the 4F2hc ectodomain positioned above the LAT2 transporter domain. Structural basis for substrate selectivity of LAT2 within the heterodimeric complex was elucidated.\",\n      \"method\": \"Cryo-EM structure determination of LAT2-4F2hc; substrate binding pocket analysis\",\n      \"journal\": \"Cell discovery\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — structural determination of substrate recognition mechanism\",\n      \"pmids\": [\"33298890\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"LAT2 (Slc7a8) localizes to the CSF-facing luminal membrane of choroid plexus epithelium. Deletion of Slc7a8 in mice increases CSF levels of LAT2 substrates (leucine, valine, tryptophan) and other amino acids, demonstrating that LAT2 normally reuptakes these amino acids from CSF back into the choroid plexus, thereby participating in maintenance of the amino acid concentration gradient between plasma and CSF.\",\n      \"method\": \"qRT-PCR on isolated choroid plexus; immunofluorescence localization; LAT2 knockout mice; CSF amino acid HPLC analysis\",\n      \"journal\": \"Fluids and barriers of the CNS\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — specific localization plus knockout mouse with quantitative CSF amino acid phenotype\",\n      \"pmids\": [\"32046769\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Chemotherapy-induced macrophage secretion of IL-18 upregulates LAT2 expression in osteosarcoma tumor cells, leading to enhanced leucine and glutamine uptake, mTORC1 activation, and c-Myc-mediated CD47 transcription, resulting in tumor immune evasion. LAT2 depletion or LAT inhibitor treatment downregulates CD47, increases macrophage phagocytosis of tumor cells, and sensitizes tumors to doxorubicin.\",\n      \"method\": \"IL-18 stimulation; LAT2 depletion (siRNA/shRNA); amino acid uptake assays; mTORC1 activation (p-S6K); c-Myc ChIP; CD47 expression; macrophage phagocytosis assay; xenograft mouse model\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods linking LAT2 to specific signaling pathway with in vivo validation\",\n      \"pmids\": [\"36274066\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The cryo-EM structure of 4F2hc-LAT2 in complex with anticalin D11vs at 3.2 Å resolution reveals fixed water molecules in the LAT2 substrate binding site that may stabilize the binding region. Molecular dynamics simulations and local map resolution of 2.8-3.0 Å in the binding site provide mechanistic insight into substrate binding and selectivity of LAT2.\",\n      \"method\": \"Cryo-EM single-particle analysis at 3.2 Å; anticalin binding protein for particle alignment; molecular dynamics simulations; local resolution analysis\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution cryo-EM structure with MD simulations revealing binding site water molecules\",\n      \"pmids\": [\"36310334\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"LAT2 (encoded by SLC7A8) transports doxorubicin as a substrate. HEK293 cells overexpressing LAT2 show significantly increased doxorubicin uptake compared to controls, while cisplatin and methotrexate are not transported. This identifies LAT2 as a novel doxorubicin uptake transporter with potential relevance to osteosarcoma treatment response.\",\n      \"method\": \"HEK293 overexpression of LAT2; in vitro doxorubicin transport assay; comparison with cisplatin and methotrexate\",\n      \"journal\": \"Frontiers in pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — overexpression transport assay, single lab, single method\",\n      \"pmids\": [\"36438828\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"LAT2 (SLC7A8) is a Th2-specific amino acid transporter in the CD4 T helper compartment. Slc7a8 deficiency impairs Th2 cell proliferation and cytokine production, disrupts Th2 metabolism with reduced mTOR activation, diminished mitochondrial function, and impaired c-Myc pathway, inducing cellular stress. LAT2-deficient mice show impaired type 2 immune responses to helminth infection and allergen-induced lung inflammation.\",\n      \"method\": \"Slc7a8-/- mice; Th1/Th2/Th17/Treg differentiation assays; proliferation and cytokine assays; metabolic profiling; mTOR and c-Myc pathway analysis; helminth infection and allergen challenge models\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — knockout mouse with multiple immune and metabolic readouts, in vivo disease models\",\n      \"pmids\": [\"41269086\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"LAT2 ablation in skeletal muscle causes glutamine (Gln) accumulation (6.3-fold increase) intramuscularly and inhibits fasting-induced proteolysis, primarily through reduced proteasomal and autophagic activity. This is mediated by mTORC1 recruitment to the lysosome (Lamp1 colocalization), as rapamycin treatment recovers proteolysis in LAT2KO muscle. Chronic Gln accumulation and decreased proteolysis in young LAT2KO mice produce an age-related muscle phenotype.\",\n      \"method\": \"LAT2 knockout mice; metabolomics (intramuscular amino acid HPLC); proteasomal and autophagic activity assays; mTORC1 colocalization (Lamp1); rapamycin rescue; aging, cachexia, and diabetes models\",\n      \"journal\": \"Journal of cachexia, sarcopenia and muscle\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — knockout mouse with mechanistic rapamycin rescue, colocalization, and multiple disease model validation\",\n      \"pmids\": [\"40546137\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SLC7A8 (LAT2) encodes the catalytic light-chain subunit of the heterodimeric amino acid transporter 4F2hc-LAT2: it requires the 4F2hc heavy chain (SLC3A2) for plasma membrane trafficking (dependent on the 4F2hc extracellular domain) and functions as a sodium-independent obligatory antiporter with 1:1 exchange stoichiometry, broad specificity for neutral amino acids (including thyroid hormones, L-DOPA, and methylmercury-cysteine complexes), strongly asymmetric intra/extracellular affinities, and is primarily localized to the basolateral membrane of renal proximal tubules and intestinal epithelia, the CSF-facing membrane of choroid plexus, and the lens epithelium, where it drives epithelial amino acid reabsorption in functional cooperation with the aromatic amino acid uniporter TAT1; 4F2hc additionally modulates LAT2 substrate affinity and specificity beyond its trafficking role; structurally, a 3.2 Å cryo-EM structure reveals fixed water molecules in the substrate-binding site; and in vivo, loss of LAT2 causes aminoaciduria, age-related hearing loss, cataract, and in skeletal muscle causes glutamine accumulation that activates mTORC1 and suppresses fasting-induced proteolysis, while in immune cells LAT2 selectively supports Th2 cell metabolism, proliferation, and effector function via mTOR and c-Myc pathways.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"SLC7A8 (LAT2) is a sodium-independent, obligatory amino acid antiporter that heterodimerizes with 4F2hc (SLC3A2) via a disulfide bond to reach the plasma membrane, where 4F2hc both traffics and allosterically modulates LAT2 transport kinetics; LAT2 itself is the catalytic subunit that exchanges small and large neutral amino acids, thyroid hormones, L-DOPA, methylmercury-L-cysteine, S-nitrosocysteine, boronophenylalanine, and doxorubicin [PMID:10391915, PMID:10574970, PMID:33066406, PMID:12117417, PMID:15769744, PMID:36438828]. By coupling with the aromatic amino acid uniporter TAT1 (SLC16A10), LAT2 achieves net amino acid efflux at basolateral epithelial membranes, a mechanism essential for renal proximal tubule reabsorption of neutral amino acids, CSF amino acid homeostasis, lens amino acid supply, and neonatal thyroid hormone delivery to the cerebral cortex [PMID:17273864, PMID:29610403, PMID:21726201, PMID:32046769, PMID:24819605]. LAT2-mediated amino acid import—particularly of leucine and glutamine—activates mTORC1 signaling, which in skeletal muscle controls fasting-induced proteolysis, in Th2 cells supports proliferative and metabolic fitness, and in cancer cells drives c-Myc transcription and immune evasion [PMID:40546137, PMID:41269086, PMID:36274066]. Loss-of-function variants and knockout models link SLC7A8 deficiency to aminoaciduria, age-related hearing loss, and cataract [PMID:21726201, PMID:29355479, PMID:31231240].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Identification of LAT2 as a 4F2hc-dependent light chain resolved how system L amino acid transport activity arises: the light chain requires heterodimerization with 4F2hc to traffic to the plasma membrane and catalyze sodium-independent, trans-stimulated neutral amino acid exchange.\",\n      \"evidence\": \"Xenopus oocyte co-expression with radiolabeled amino acid uptake, disulfide cross-linking, and subcellular localization by two independent laboratories\",\n      \"pmids\": [\"10391915\", \"10574970\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Substrate selectivity profile for LAT2 versus LAT1 was only partially resolved\", \"Structural basis of 4F2hc–LAT2 interaction unknown\", \"In vivo physiological role of LAT2 not yet demonstrated\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Demonstration that the extracellular domain of 4F2hc is specifically required for LAT2 (but not LAT1) surface trafficking revealed that 4F2hc is not a generic chaperone but differentially regulates its light-chain partners.\",\n      \"evidence\": \"Systematic 4F2hc C-terminal truncation mutants tested in Xenopus oocytes for LAT2 versus LAT1 surface expression and transport\",\n      \"pmids\": [\"11311135\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular determinants on LAT2 that recognize the 4F2hc ectodomain were undefined\", \"Whether 4F2hc modulates LAT2 kinetics beyond trafficking was unknown\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Showing that LAT2 transports methylmercury-L-cysteine as a methionine mimic expanded the substrate repertoire beyond canonical amino acids, establishing LAT2 as a toxicologically relevant transporter.\",\n      \"evidence\": \"Reconstituted transport of radiolabeled MeHg in Xenopus oocytes with kinetic characterization and trans-stimulation\",\n      \"pmids\": [\"12117417\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo contribution of LAT2 to MeHg tissue distribution not tested\", \"Whether other heavy metal conjugates are substrates was unknown\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Loss-of-function experiments in renal epithelial cells established LAT2 as the major route for trans-epithelial cystine/cysteine efflux and L-DOPA transport, assigning it a non-redundant basolateral role in proximal tubule amino acid handling.\",\n      \"evidence\": \"Antisense knockdown in OK cells with transepithelial flux assays; siRNA silencing in LLC-PK1 cells with L-DOPA uptake/efflux measurement\",\n      \"pmids\": [\"12660317\", \"15466357\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of LAT2 versus other basolateral transporters in vivo was unresolved\", \"No whole-animal genetic evidence yet\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Discovery that LAT2 stereoselectively transports S-nitrosocysteine extended its functional reach to NO signaling, while co-localization with TAT1 on basolateral membranes suggested a functional partnership for net amino acid efflux.\",\n      \"evidence\": \"Oocyte reconstitution and mammalian gain/loss-of-function for L-CSNO transport; immunohistochemistry in human kidney\",\n      \"pmids\": [\"15769744\", \"15918515\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional cooperation between LAT2 and TAT1 was inferred but not directly demonstrated\", \"Physiological impact of LAT2-mediated CSNO transport in vivo unknown\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Reconstitution of TAT1+LAT2 cooperation in oocytes proved the mechanism of net amino acid efflux: TAT1 recycles aromatic amino acids by facilitated diffusion, providing intracellular counter-substrates for LAT2-mediated obligatory exchange of other neutral amino acids.\",\n      \"evidence\": \"Xenopus oocyte co-expression with transport-inactive mutant controls, HPLC-based amino acid efflux quantification\",\n      \"pmids\": [\"17273864\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo genetic proof of cooperation was lacking\", \"Stoichiometry and directionality under physiological gradients not fully defined\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"LAT2 knockout mice exhibited specific aminoaciduria, providing the first whole-animal genetic evidence that LAT2 is required for renal reabsorption of small neutral amino acids, and linked LAT2 plasma membrane expression to mTORC1 activation in glomerular cells.\",\n      \"evidence\": \"Slc7a8 KO mouse with urine amino acid profiling; pharmacologic LAT inhibition in crescentic glomerulonephritis rat model\",\n      \"pmids\": [\"21726201\", \"21403644\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether aminoaciduria caused downstream systemic metabolic consequences was uncharacterized\", \"mTORC1 link relied partly on pharmacologic rather than genetic tools\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Structural characterization by EM and genetic epistasis in Mct8/Lat2 double-KO mice established that the 4F2hc ectodomain covers the LAT2 extracellular face to stabilize the transporter, and that LAT2 delivers thyroid hormones to the neonatal cerebral cortex.\",\n      \"evidence\": \"Transmission EM single-particle analysis with proteoliposome reconstitution; Mct8/Lat2 double-KO mouse with brain thyroid hormone and gene expression analysis\",\n      \"pmids\": [\"24516142\", \"24819605\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic-resolution structure was unavailable\", \"Relative contributions of LAT2 versus other thyroid hormone transporters in adult brain undefined\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"In vivo LAT2+TAT1 double-knockout mice showed greater aminoaciduria than either single KO—including cationic amino acid loss—confirming functional cooperation and revealing compensatory upregulation of y+LAT1; simultaneously, SLC7A8 ablation was linked to age-related hearing loss via cochlear degeneration, with patient variants showing reduced transport activity.\",\n      \"evidence\": \"LAT2/TAT1 double-KO mouse urine amino acid profiling; Slc7a8 KO auditory phenotyping plus in vitro functional characterization of human variants in HeLa cells\",\n      \"pmids\": [\"29610403\", \"29355479\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of cochlear degeneration (amino acid deprivation vs. oxidative stress) was not delineated\", \"Transporter compensation mechanisms at the molecular level were uncharacterized\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"LAT2 knockout mice developed cataracts and a human homozygous SLC7A8 deletion co-segregated with familial cataract, establishing SLC7A8 loss-of-function as a cause of cataract through impaired lens amino acid supply.\",\n      \"evidence\": \"Slc7a8 KO mouse lens phenotyping with amino acid measurement; patient variant functional assay in HeLa cells\",\n      \"pmids\": [\"31231240\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which specific amino acid deficiencies drive lens opacification was not fully resolved\", \"Penetrance and genetic modifiers in human populations unknown\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"LAT2 was shown to be the catalytic subunit of the heterodimer—functional without 4F2hc albeit with altered kinetics—while 4F2hc acts as an allosteric modulator; separately, LAT2 localization to the choroid plexus luminal membrane with KO-induced CSF amino acid elevation revealed a role in CSF amino acid homeostasis.\",\n      \"evidence\": \"Pichia pastoris expression of LAT2 alone versus 4F2hc-LAT2 with comparative kinetics; LAT2 KO mouse CSF amino acid profiling with choroid plexus immunofluorescence\",\n      \"pmids\": [\"33066406\", \"32046769\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether 4F2hc allosteric effects differ across tissues was unexplored\", \"How CSF amino acid imbalance affects neurological function was not assessed\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"A 3.2 Å cryo-EM structure of human 4F2hc-LAT2 provided atomic-level insight into the substrate binding pocket including fixed water molecules, while functional studies revealed doxorubicin as a LAT2 substrate and elucidated an IL-18→LAT2→mTORC1→c-Myc→CD47 pathway enabling tumor immune evasion.\",\n      \"evidence\": \"Single-particle cryo-EM with MD simulations; HEK293 overexpression drug transport assays; LAT2 KD/inhibitor plus ChIP and in vivo osteosarcoma model\",\n      \"pmids\": [\"36310334\", \"36438828\", \"36274066\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Substrate-bound conformational states (inward-open, occluded) not captured structurally\", \"Clinical relevance of LAT2-mediated doxorubicin transport versus other uptake routes unresolved\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"LAT2 was identified as a critical glutamine efflux transporter in fasting skeletal muscle and a Th2-specific amino acid transporter: LAT2 KO causes intramuscular glutamine accumulation that activates lysosomal mTORC1 and suppresses proteolysis, while in Th2 cells LAT2 loss impairs mTOR activation, mitochondrial function, and cytokine production.\",\n      \"evidence\": \"LAT2 KO mouse fasting studies with rapamycin rescue and mTORC1–LAMP1 colocalization; Slc7a8 KO T helper cell differentiation, metabolic profiling, helminth infection and allergen challenge models\",\n      \"pmids\": [\"40546137\", \"41269086\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How LAT2 is transcriptionally or post-translationally regulated in skeletal muscle during catabolic stress is unknown\", \"Whether LAT2-driven mTORC1 activation in Th2 cells is leucine- or glutamine-dependent was not dissected\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis of substrate-bound conformational transitions (inward-open, occluded states), the mechanism of tissue-specific transcriptional regulation of SLC7A8, and whether LAT2 loss-of-function contributes to broader neurological or metabolic phenotypes beyond aminoaciduria, hearing loss, and cataract.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No substrate-bound or inward-open cryo-EM structures published\", \"Transcriptional regulation of SLC7A8 across tissues is poorly characterized\", \"Comprehensive clinical phenotyping of human SLC7A8 loss-of-function is lacking\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 1, 4, 5, 7, 9, 10, 15, 16, 21, 24, 26, 27]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 1, 3, 5, 8, 13, 22]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [0, 1, 4, 5, 7, 9, 10, 15, 16, 24, 26]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [12, 17, 23, 26, 27]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [27]}\n    ],\n    \"complexes\": [\n      \"4F2hc-LAT2 (SLC3A2-SLC7A8) heterodimer\"\n    ],\n    \"partners\": [\n      \"SLC3A2\",\n      \"SLC16A10\",\n      \"ICAM1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"SLC7A8 (LAT2) is the catalytic light-chain subunit of a heterodimeric sodium-independent amino acid antiporter that, upon disulfide-linked heterodimerization with the heavy chain 4F2hc (SLC3A2), traffics to the plasma membrane and mediates obligatory 1:1 exchange of neutral amino acids with strongly asymmetric intra- and extracellular affinities [PMID:10391915, PMID:11847106]. Localized to the basolateral membrane of renal proximal tubules, intestinal epithelia, choroid plexus, and lens epithelium, LAT2 drives reabsorption of neutral amino acids in functional cooperation with the aromatic amino acid uniporter TAT1 (SLC16A10), and its loss causes aminoaciduria, age-related hearing loss, and cataract in mice and humans [PMID:21726201, PMID:29610403, PMID:29355479, PMID:31231240]. Beyond canonical amino acids, LAT2 transports thyroid hormone metabolites, L-DOPA, S-nitroso-L-cysteine, methylmercury-cysteine conjugates, and doxorubicin [PMID:15466357, PMID:12117417, PMID:15769744, PMID:26601072]. In skeletal muscle, LAT2 ablation causes glutamine accumulation that constitutively activates lysosomal mTORC1 and suppresses fasting-induced proteolysis, while in CD4+ T cells LAT2 selectively supports Th2 metabolism, proliferation, and effector function via mTOR and c-Myc pathways [PMID:40546137, PMID:41269086].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"The identity of LAT2 as a broad-specificity neutral amino acid transporter requiring 4F2hc for surface expression was established, resolving how a second L-type system with distinct substrate preference operates as a disulfide-linked heterodimer at renal and intestinal basolateral membranes.\",\n      \"evidence\": \"Xenopus oocyte co-expression with 4F2hc; subcellular localization; radiolabeled amino acid uptake kinetics; immunofluorescence on kidney/intestine sections\",\n      \"pmids\": [\"10391915\", \"10574970\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Exchange stoichiometry and asymmetric affinity not yet quantified\",\n        \"Structural basis of 4F2hc requirement for LAT2 trafficking unknown\",\n        \"In vivo physiological role not yet demonstrated by genetic loss-of-function\"\n      ]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Quantitative demonstration that LAT2-4F2hc is an obligatory 1:1 antiporter with millimolar intracellular Km versus micromolar extracellular Km resolved the asymmetric affinity model that explains how intracellular amino acid pools drive net substrate exchange.\",\n      \"evidence\": \"Xenopus oocyte co-expression; simultaneous HPLC quantification of influx and efflux; intracellular substrate injection\",\n      \"pmids\": [\"11847106\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural determinants of affinity asymmetry unknown\",\n        \"How 4F2hc contributes to asymmetric kinetics not addressed\"\n      ]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"The requirement for the 4F2hc extracellular domain in LAT2 surface trafficking—distinct from LAT1—established that the heavy chain plays a light-chain-specific chaperoning role beyond disulfide linkage.\",\n      \"evidence\": \"C-terminal truncation mutants of 4F2hc co-expressed with LAT2 in oocytes; surface biotinylation; transport assays\",\n      \"pmids\": [\"11311135\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether 4F2hc ectodomain also modulates LAT2 substrate specificity was untested\",\n        \"No structural model of the ectodomain-LAT2 interface\"\n      ]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Identification of methylmercury-cysteine as a LAT2 substrate acting as a methionine mimic expanded the transporter's known cargo beyond canonical amino acids to environmentally relevant toxicants.\",\n      \"evidence\": \"Xenopus oocyte expression; [14C]MeHg-L-cysteine uptake with Km/Vmax determination; trans-stimulation\",\n      \"pmids\": [\"12117417\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"In vivo relevance for mercury toxicity not tested\",\n        \"No structural basis for molecular mimicry\"\n      ]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"siRNA knockdown established LAT2 as the primary L-DOPA transporter in renal epithelial cells, extending its physiological substrate repertoire to catecholamine precursors.\",\n      \"evidence\": \"siRNA knockdown in LLC-PK1 cells; [14C]-L-DOPA uptake and efflux; qRT-PCR\",\n      \"pmids\": [\"15466357\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Contribution relative to other transporters in vivo unknown\",\n        \"Relevance to L-DOPA pharmacokinetics not established\"\n      ]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Demonstration that TAT1 and LAT2 functionally cooperate without physical interaction—TAT1 recycling aromatic amino acids to fuel LAT2-mediated net efflux—provided the mechanistic model for basolateral amino acid reabsorption in kidney.\",\n      \"evidence\": \"Xenopus oocyte co-expression; HPLC efflux quantification; functionally inactive surface mutants; negative co-IP and crosslinking\",\n      \"pmids\": [\"17273864\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"In vivo validation by double knockout not yet performed\",\n        \"Whether this cooperation operates in other epithelia unknown\"\n      ]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Targeted Slc7a8 knockout in mice confirmed the in vivo requirement for LAT2 in renal neutral amino acid reabsorption (aminoaciduria phenotype) and revealed an unexpected role in neonatal cortical thyroid hormone supply via genetic epistasis with Mct8.\",\n      \"evidence\": \"Slc7a8−/− mice; urine amino acid analysis; Mct8/Lat2 double knockout; cerebral cortex T3 measurements and target gene expression\",\n      \"pmids\": [\"21726201\", \"24819605\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Intestinal and placental transport roles not confirmed by knockout\",\n        \"Mechanism of LAT2's thyroid hormone transport contribution limited to early postnatal window\"\n      ]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Electron microscopy and biochemical reconstitution revealed the architecture of the 4F2hc-LAT2 heterodimer, showing the ectodomain covers LAT2's extracellular face and stabilizes it, establishing the structural framework for understanding heavy-chain modulation.\",\n      \"evidence\": \"Negative-stain TEM single-particle analysis; Pichia pastoris purification; proteoliposome reconstitution; crosslinking\",\n      \"pmids\": [\"24516142\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Atomic-resolution structure not available\",\n        \"Substrate-bound conformational states not captured\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"LAT2 loss-of-function was linked to age-related hearing loss—both in Slc7a8−/− mice showing cochlear damage and in human patients carrying transport-defective SLC7A8 variants—establishing a Mendelian-type disease connection.\",\n      \"evidence\": \"Slc7a8−/− mice; ABR testing; cochlear histology; in vitro transport assays of human patient variants\",\n      \"pmids\": [\"29355479\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Specific amino acid(s) whose deficiency drives ototoxicity unknown\",\n        \"Whether cochlear phenotype is cell-autonomous not determined\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Double knockout of LAT2 and TAT1 in vivo confirmed their functional cooperation for renal amino acid reabsorption and revealed compensatory upregulation of y+LAT1, demonstrating transporter network plasticity at the basolateral membrane.\",\n      \"evidence\": \"LAT2/TAT1 double-knockout mice; urine amino acid analysis; Western blot for compensatory transporter expression\",\n      \"pmids\": [\"29610403\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Molecular signals driving compensatory transporter upregulation unknown\",\n        \"Functional consequences in non-renal epithelia not assessed\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"LAT2 ablation caused cataract in mice with depleted lens amino acids, and a human homozygous SLC7A8 frameshift abolished transport and segregated with congenital cataract, establishing a second Mendelian phenotype.\",\n      \"evidence\": \"Slc7a8−/− and double Slc7a8/Slc16a10 KO mice; slit-lamp; lens amino acid HPLC; in vitro transport of human variants in HeLa cells\",\n      \"pmids\": [\"31231240\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Which specific amino acid deficit is cataractogenic not pinpointed\",\n        \"Whether lens-specific rescue would prevent cataract untested\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Multiple cryo-EM structures at improving resolution (sub-nanometer to 3.2 Å) defined the substrate binding pocket of LAT2 within the 4F2hc heterodimer and revealed that 4F2hc modulates LAT2 substrate affinity beyond its trafficking role, fundamentally redefining heavy-chain function.\",\n      \"evidence\": \"Cryo-EM at 3.2 Å with anticalin; molecular dynamics; Pichia pastoris expression of LAT2 alone vs. heterodimer with comparative kinetics\",\n      \"pmids\": [\"33298890\", \"36310334\", \"33066406\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Outward-open conformation structure not captured\",\n        \"Substrate-bound structures at atomic resolution for multiple substrates lacking\",\n        \"Mechanism by which 4F2hc ectodomain allosterically tunes LAT2 selectivity not resolved\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"LAT2-mediated amino acid uptake was shown to activate mTORC1 and downstream c-Myc in osteosarcoma cells, linking transporter activity to immune evasion via CD47 upregulation, thereby placing LAT2 in the signaling interface between amino acid import and tumor immunity.\",\n      \"evidence\": \"siRNA/shRNA LAT2 depletion; mTORC1/c-Myc ChIP; CD47 expression; macrophage phagocytosis assay; xenograft model\",\n      \"pmids\": [\"36274066\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether LAT2's signaling role is cell-type specific or generalizable unknown\",\n        \"Direct LAT2-mTORC1 signaling mechanism (sensing vs. substrate supply) not dissected\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Two independent studies revealed tissue-specific metabolic consequences of LAT2 loss: in skeletal muscle, glutamine accumulation constitutively activates lysosomal mTORC1 and blocks fasting-induced proteolysis; in CD4+ T cells, LAT2 selectively supports Th2 metabolism and effector function via mTOR/c-Myc.\",\n      \"evidence\": \"Slc7a8−/− mice; intramuscular amino acid metabolomics; mTORC1-Lamp1 colocalization; rapamycin rescue; Th2 differentiation assays; helminth and allergen models\",\n      \"pmids\": [\"40546137\", \"41269086\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether glutamine is the sole mTORC1-activating metabolite in LAT2-deficient muscle not proven\",\n        \"Mechanism of Th2-selective LAT2 dependence vs. other T helper lineages not resolved\",\n        \"Translational relevance of LAT2 as a therapeutic target in muscle wasting or allergy unexplored\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis for the outward-open conformation and full substrate translocation cycle, the precise mechanism by which LAT2-imported amino acids activate mTORC1 across different tissues, and whether pharmacological modulation of LAT2 can be exploited therapeutically for hearing loss, cataract, or immune disorders.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No outward-open or occluded-state structure available\",\n        \"Direct sensing mechanism linking LAT2 transport to lysosomal mTORC1 recruitment not identified\",\n        \"No selective LAT2 inhibitor or activator tool compounds reported\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 1, 3, 5, 6, 9, 11, 13, 17, 21, 22, 23, 27, 30, 35, 36]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 1, 4, 7, 12, 15, 32]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [0, 1, 5, 6, 7, 9, 13, 14, 26, 27, 32]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [15, 25, 33, 37]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [36]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [5, 6, 21, 25, 37]}\n    ],\n    \"complexes\": [\n      \"4F2hc-LAT2 (SLC3A2-SLC7A8) heterodimer\"\n    ],\n    \"partners\": [\n      \"SLC3A2\",\n      \"SLC16A10\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}