{"gene":"TRPM6","run_date":"2026-04-28T21:43:00","timeline":{"discoveries":[{"year":2002,"finding":"TRPM6 mutations cause autosomal-recessive hypomagnesemia with secondary hypocalcemia (HSH); TRPM6 is expressed in intestinal epithelia and kidney tubules and is crucial for magnesium homeostasis, identified by positional candidate gene approach.","method":"Positional cloning, mutation analysis, expression studies","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 — independently replicated in two simultaneous papers (PMID:12032568 and PMID:12032570), foundational discovery","pmids":["12032568","12032570"],"is_preprint":false},{"year":2003,"finding":"TRPM6 is specifically localized along the apical membrane of the renal distal convoluted tubule and brush-border membrane of the small intestine; heterologous expression of wild-type but not HSH-mutant TRPM6 induces a Mg2+- and Ca2+-permeable cation channel strongly regulated by intracellular Mg2+, with 5-fold higher affinity for Mg2+ than Ca2+, outward rectification, and voltage-dependent block by ruthenium red.","method":"Immunolocalization, heterologous expression, whole-cell patch clamp, ion substitution experiments","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 — direct localization with functional consequence, electrophysiological characterization with mutagenesis, high citation count","pmids":["14576148"],"is_preprint":false},{"year":2004,"finding":"TRPM6 alone is retained intracellularly when heterologously expressed, but specifically interacts with TRPM7 to form functional TRPM6/TRPM7 heteromeric channel complexes at the cell surface; the HSH-causing S141L missense mutation abolishes oligomeric assembly of TRPM6 with TRPM7, providing a cell biological explanation for the disease.","method":"Heterologous expression in HEK293 and Xenopus oocytes, co-immunoprecipitation, confocal microscopy, two-electrode voltage clamp, whole-cell patch clamp","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal methods, mechanistic link to disease mutation confirmed","pmids":["14976260"],"is_preprint":false},{"year":2006,"finding":"TRPM6 forms functional homomeric channels with unique unitary conductance (~2-fold larger than TRPM7), distinct divalent cation permeability profile, unique pH sensitivity, and differential sensitivity to 2-APB (micromolar 2-APB maximally activates TRPM6 but inhibits TRPM7); TRPM6 also forms heteromeric TRPM6/7 complexes with intermediate pharmacological properties.","method":"Heterologous expression, whole-cell patch clamp, single-channel recordings, pharmacological profiling","journal":"The Journal of general physiology","confidence":"High","confidence_rationale":"Tier 1 — rigorous electrophysiology with multiple channel types and pharmacological discrimination","pmids":["16636202"],"is_preprint":false},{"year":2005,"finding":"TRPM6 requires TRPM7 for surface expression in HEK-293 cells; TRPM6 cross-phosphorylates TRPM7 on threonine residues (detected by phosphothreonine-specific antibody) but TRPM7 does not phosphorylate TRPM6; TRPM7 deficiency in DT40 cells cannot be complemented by heterologously expressed TRPM6, demonstrating functional non-redundancy.","method":"Complementation assay in TRPM7-deficient DT40 B-cells, surface expression assay, phosphothreonine-specific antibody","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — reciprocal functional comparison, phosphorylation-specific antibody, genetic complementation","pmids":["16150690"],"is_preprint":false},{"year":2007,"finding":"Two glutamate residues in the putative pore of TRPM6 (E1024 and E1029, corresponding to E1047 and E1052 in TRPM7) are key molecular determinants of Mg2+ and Ca2+ permeability and pH sensitivity; neutralization of E1024 (E1047 in TRPM7) largely abolished divalent permeation, converting the channel to monovalent selectivity and abolishing proton-mediated potentiation.","method":"Site-directed mutagenesis of pore residues, whole-cell patch clamp, ion substitution, pH manipulation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro mutagenesis with rigorous electrophysiological validation, multiple mutants tested","pmids":["17599911"],"is_preprint":false},{"year":2006,"finding":"A missense mutation P1017R in the putative pore-forming region of TRPM6 causes HSH; TRPM6(P1017R) suppresses TRPM7 channel activity in a dominant-negative manner when co-expressed, while not affecting TRPM6/TRPM7 assembly or co-trafficking to the cell surface, demonstrating that a pore-region functional defect alone is sufficient to impair body Mg2+ homeostasis.","method":"Two-electrode voltage clamp (Xenopus oocytes), whole-cell patch clamp (HEK293), confocal microscopy, FRET","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal methods, mechanistic insight into pore function and dominant-negative effect","pmids":["17197439"],"is_preprint":false},{"year":2006,"finding":"Neutralization of E1024 and D1031 in the TRPM6 selectivity filter (loop between TM5 and TM6, sequence GEIDVC) results in non-functional channels; E1029 neutralization increases conductance for Ba2+ and Zn2+ and alters pore diameter; I1030M reduces Ni2+ conductance — defining molecular determinants of TRPM6 cation permeation.","method":"Site-directed mutagenesis of pore residues, whole-cell patch clamp, permeability measurements","journal":"Cell calcium","confidence":"High","confidence_rationale":"Tier 1 — in vitro mutagenesis of multiple pore residues with functional electrophysiological readouts","pmids":["17098283"],"is_preprint":false},{"year":2008,"finding":"RACK1 (receptor for activated C-kinase 1) physically associates with the TRPM6 alpha-kinase domain and inhibits TRPM6 channel activity in a kinase activity-dependent manner; autophosphorylation of Thr1851 in the alpha-kinase domain is required for RACK1's inhibitory effect and is critical for Mg2+ sensitivity of TRPM6 activity; PKC activation by PMA abrogates RACK1 inhibition.","method":"Co-immunoprecipitation (Ras recruitment system), whole-cell patch clamp, siRNA knockdown, site-directed mutagenesis, PKC activation","journal":"Current biology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (pulldown, electrophysiology, siRNA, mutagenesis)","pmids":["18258429"],"is_preprint":false},{"year":2008,"finding":"TRPM6 and TRPM7 kinase domains undergo massive autophosphorylation (>30 mol/mol) predominantly in a Ser/Thr-rich region N-terminal to the catalytic domain; this autophosphorylation strongly increases the rate of substrate phosphorylation; deletion of the Ser/Thr-rich domain prevents substrate phosphorylation without affecting intrinsic catalytic activity, suggesting this domain controls substrate recognition.","method":"In vitro kinase assays, mass spectrometric phosphomapping, deletion mutagenesis, 32P autophosphorylation","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1 — in vitro biochemical assays with mass spectrometry and mutagenesis","pmids":["18365021"],"is_preprint":false},{"year":2008,"finding":"TRPM6 and TRPM7 phosphorylate the assembly domain of myosin IIA, IIB and IIC on identical residues; phosphorylation of myosin IIA is restricted to the coiled-coil domain while TRPM6 and TRPM7 also phosphorylate the non-helical tails of myosin IIB and IIC; TRPM7 does not phosphorylate eEF-2, indicating substrate specificity distinct from other alpha-kinases.","method":"In vitro kinase assay, mass spectrometry","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstituted kinase assay with mass spectrometric identification of phosphorylation sites","pmids":["18675813"],"is_preprint":false},{"year":2008,"finding":"EGF receptor stimulation increases TRPM6 (but not TRPM7) channel current via Src family tyrosine kinases and downstream effector Rac1; activated Rac1 increases TRPM6 plasma membrane mobility (FRAP) and surface abundance, thereby augmenting channel activity; dominant-negative Rac1 abolishes EGF-mediated TRPM6 activation; the TRPM6 alpha-kinase domain is not required for this EGF-mediated activation.","method":"Whole-cell patch clamp, FRAP, surface biotinylation, dominant-negative and constitutively active Rac1 constructs, Src kinase inhibitors","journal":"Journal of the American Society of Nephrology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods, specific pathway dissection with pharmacological and genetic tools","pmids":["19073827"],"is_preprint":false},{"year":2009,"finding":"REA (repressor of estrogen receptor activity) physically interacts with the 6th, 7th, and 8th beta-sheets of the TRPM6 alpha-kinase domain and inhibits TRPM6 (but not TRPM7) channel activity in a phosphorylation-dependent manner; TRPM6 kinase-dead mutant (K1804R) is not inhibited by REA despite maintained binding; PKC activation enhances REA inhibition; short-term 17β-estradiol treatment dissociates the REA-TRPM6 interaction and stimulates TRPM6-mediated current.","method":"Ras recruitment system (protein interaction), whole-cell patch clamp, co-immunoprecipitation, PKC activation, estradiol treatment","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods establishing interaction, phosphorylation dependence, and hormonal regulation","pmids":["19329436"],"is_preprint":false},{"year":2010,"finding":"MsrB1 (methionine sulfoxide reductase B1) interacts with the TRPM6 alpha-kinase domain (identified by Ras recruitment system); H2O2 decreases TRPM6 channel activity without affecting plasma membrane expression; co-expression of MsrB1 partially attenuates this inhibition; mutation of Met1755 to Ala reduces H2O2-mediated inhibition of TRPM6, indicating MsrB1 recovers TRPM6 activity by reducing oxidation of Met1755.","method":"Ras recruitment system, whole-cell patch clamp, surface biotinylation, site-directed mutagenesis, H2O2 treatment","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods including interaction screen, functional electrophysiology, and mutagenesis","pmids":["20584906"],"is_preprint":false},{"year":2011,"finding":"PIP2 (phosphatidylinositol-4,5-bisphosphate) is required for TRPM6 channel activation and Mg2+ influx; depletion of PIP2 by PLC-coupled M1-receptor stimulation, overexpressed 5-phosphatase, or voltage-sensitive phosphatase (Ci-VSP) potently inhibits TRPM6; neutralization of basic residues in the TRP domain reduces PIP2-dependent activation, implicating TRP domain residues in PIP2 interaction.","method":"Whole-cell patch clamp, TIRF, voltage-sensitive phosphatase (Ci-VSP), receptor-mediated PLC activation, 5-phosphatase overexpression, site-directed mutagenesis","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 1–2 — multiple independent methods to deplete PIP2, mutagenesis of putative binding residues, direct channel activity measurement","pmids":["22180838"],"is_preprint":false},{"year":2012,"finding":"Insulin stimulates TRPM6 channel activity via PI3-kinase and Rac1-mediated elevation of TRPM6 cell surface expression (assessed by TIRF microscopy and patch clamp); genetic variants TRPM6(V1393I) and TRPM6(K1584E) fail to respond to insulin stimulation, likely due to inability to phosphorylate TRPM6 Thr1391 and Ser1583; these variants are associated with higher glycated hemoglobin and gestational diabetes mellitus.","method":"Patch clamp, TIRF microscopy, site-directed mutagenesis, PI3K/Rac1 pathway inhibition","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1–2 — direct functional assay with pathway dissection, mutagenesis, and clinical correlation","pmids":["22733750"],"is_preprint":false},{"year":2014,"finding":"The TRPM6 kinase domain determines Mg·ATP sensitivity of TRPM7/M6 heteromeric channels: homomeric TRPM6 is highly sensitive to intracellular free Mg2+ (unlikely active at physiological levels); heteromeric TRPM7/TRPM6 channels have altered pharmacology and are independent of intracellular Mg·ATP, uncoupling channel activity from cellular energy status; disruption of TRPM6 kinase phosphorylation activity re-introduces Mg·ATP sensitivity to the heteromeric channel.","method":"Whole-cell patch clamp, co-expression, kinase-dead TRPM6 mutant, intracellular Mg2+ and Mg·ATP manipulation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 — electrophysiology with kinase mutants and precise intracellular ion control","pmids":["24385424"],"is_preprint":false},{"year":2014,"finding":"The dimerization motif (Leu1718/Leu1721) preceding the TRPM6 kinase domain and the dimerization pocket within the kinase domain are required for both kinase activity and ion channel activity; mutations disrupting this motif/pocket abolish kinase activity and greatly diminish channel activity independently of kinase activity; one disease-causing missense mutation (S1754N) near the dimerization motif abolishes kinase activity; a peptide encompassing the dimerization motif can restore kinase activity of dimerization motif mutants.","method":"Site-directed mutagenesis, in vitro kinase assay, patch clamp, peptide rescue experiment","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 — in vitro biochemical reconstitution plus electrophysiology, mutagenesis, and peptide rescue","pmids":["24650431"],"is_preprint":false},{"year":2014,"finding":"TRPM6 kinase activity regulates TRPM7 intracellular trafficking and serine phosphorylation of TRPM7 (but TRPM7 kinase does not phosphorylate TRPM6 on serine); active TRPM6 kinase alters TRPM7 trafficking in HEK-293 and DT40 cells; co-expression of TRPM6 with intact kinase (but not kinase-dead mutant) inhibits TRPM7-dependent cell growth under hypomagnesic conditions.","method":"Phospho-specific antibodies, trafficking assays, genetic complementation in TRPM7-deficient DT40 B-cells, cell growth assay, kinase-dead mutant","journal":"Cellular and molecular life sciences","confidence":"High","confidence_rationale":"Tier 2 — multiple assays with kinase-dead control, genetic complementation in defined cell system","pmids":["24858416"],"is_preprint":false},{"year":2017,"finding":"mTRPM6 and mTRPM7 differentially regulate heteromeric mTRPM6/7 channels: mTRPM6 extreme sensitivity to Mg2+ is tuned by TRPM7 to higher concentrations, while mTRpm6 relieves mTRPM7 from tight Mg·ATP inhibition, resulting in high constitutive activity of the heteromeric complex at physiological Mg2+ and Mg·ATP levels in epithelial cells.","method":"Whole-cell patch clamp, comparative expression of mouse TRPM6 vs. TRPM7, primary cells from TRPM6- and TRPM7-deficient mice","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 — primary cell data from knockout mice combined with heterologous expression and rigorous electrophysiology","pmids":["28821869"],"is_preprint":false},{"year":2017,"finding":"Mass spectrometric analysis identified phosphorylation sites on TRPM6 including T1851 (autophosphorylation site in the kinase domain); TRPM6 transphosphorylates TRPM7 at multiple sites; phosphomimetic substitutions at TRPM7 S1777 (catalytic domain) and S1565 (exchange/dimerization domain) inactivate kinase activity through distinct mechanisms.","method":"Mass spectrometry, site-directed mutagenesis, in vitro kinase assay, molecular modeling","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 1 — MS-based phosphosite identification combined with mutagenesis and functional kinase assays","pmids":["28220887"],"is_preprint":false},{"year":2009,"finding":"Trpm6 knockout mice (Trpm6-/-) exhibit embryonic mortality by E12.5 and neural tube defects (exencephaly and spina bifida occulta), demonstrating a non-redundant role of TRPM6 in neural tube closure during development, beyond its known role in Mg2+ homeostasis.","method":"Conditional knockout mouse model, embryonic phenotyping, dietary Mg2+ supplementation rescue attempts","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 — clean knockout with specific developmental phenotype","pmids":["19692351"],"is_preprint":false},{"year":2017,"finding":"Xenopus TRPM6 (XTRPM6) is expressed in lateral mesoderm and ectoderm at neurula stage; loss of XTRPM6 (but not XTRPM7) disrupts radial intercalation cell movements during neural tube closure, establishing a non-redundant role distinct from TRPM7; a zinc-influx assay showed TRPM6 can form functional channels in the absence of TRPM7.","method":"Xenopus laevis morpholino knockdown, in situ hybridization, live imaging of cell movements, zinc-influx assay","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 — loss-of-function with specific cellular phenotype (radial vs. mediolateral intercalation), functional channel assay","pmids":["29142255"],"is_preprint":false},{"year":2014,"finding":"P2X4 receptor specifically inhibits TRPM6 (but not TRPM7) channel activity in a manner dependent on P2X4 channel activity; a P2X4 mutant with altered ATP sensitivity fails to inhibit TRPM6; P2X6 (non-functional in mammalian cells) does not inhibit TRPM6.","method":"Whole-cell patch clamp, co-expression, P2X4 mutants, RT-qPCR tissue expression","journal":"Pflugers Archiv","confidence":"Medium","confidence_rationale":"Tier 3 — single lab, electrophysiological co-expression study with functional mutant controls","pmids":["24413910"],"is_preprint":false},{"year":2018,"finding":"Uromodulin (UMOD) physically interacts with TRPM6 from the extracellular space, enhances TRPM6 cell-surface abundance by impairing dynamin-dependent TRPM6 endocytosis, and increases TRPM6 current density; Umod-/- mice show decreased apical TRPM6 staining in the DCT and increased urinary Mg2+ excretion.","method":"Co-immunoprecipitation, surface biotinylation, whole-cell patch clamp, dynamin inhibition, Umod-/- mouse model, immunofluorescence","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (pulldown, biotinylation, electrophysiology, in vivo knockout)","pmids":["30139743"],"is_preprint":false},{"year":2021,"finding":"Kidney-specific Trpm6 knockout mice show decreased blood pressure and loss of circadian blood pressure variation; renin secretion is not augmented in the active period and pharmacological β-adrenoreceptor activation fails to stimulate renin secretion; β-adrenoreceptor expression is decreased in renin-secreting cells of TRPM6-deficient kidneys, indicating TRPM6 in the DCT regulates renin secretion and circadian blood pressure.","method":"Kidney-specific conditional knockout mice, blood pressure telemetry, renin secretion assay, β-adrenoreceptor pharmacology","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — clean tissue-specific knockout with specific hemodynamic and hormonal phenotype","pmids":["34140503"],"is_preprint":false},{"year":2019,"finding":"Calmodulin (CaM) and S100A1 share a common binding site at the N-terminal TRPM6 domain (L520-R535); basic residues R526/R531/K532/R535 are critical for non-covalent interactions with both ligands; CaM and S100A1 bind via different mechanisms despite sharing the same domain.","method":"Biophysical methods (fluorescence, CD), molecular modelling, site-directed mutagenesis of N-terminal domain","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 3 — single lab, biophysical binding assays with mutagenesis but no functional channel activity data","pmids":["31505788"],"is_preprint":false},{"year":2015,"finding":"Flavaglines (natural and synthetic compounds targeting prohibitins) stimulate TRPM6 channel activity ~2-fold at nanomolar concentrations; stimulatory effect requires the presence of the TRPM6 alpha-kinase domain but not its phosphotransferase activity; TRPM6 variants with impaired insulin sensitivity (V1393I and K1584E) are not sensitive to flavagline stimulation, suggesting they act via the insulin receptor signaling pathway.","method":"Whole-cell patch clamp, kinase domain deletion/mutation, pharmacological flavagline treatment","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — electrophysiology with domain requirements and pharmacological mutant analysis, single lab","pmids":["25774985"],"is_preprint":false},{"year":2022,"finding":"Iloperidone and ifenprodil selectively inhibit TRPM6 channel activity (IC50 0.73 and 3.33 µM respectively) without affecting TRPM7; VER155008 selectively suppresses TRPM7 (IC50 0.11 µM) without affecting TRPM6; effects confirmed on endogenous channels in native mouse and human cell models.","method":"Patch clamp, Ca2+ imaging, pharmacological analysis in native cell models","journal":"Cell calcium","confidence":"High","confidence_rationale":"Tier 2 — rigorous electrophysiology with confirmed selectivity in native cells, multiple compounds","pmids":["36030694"],"is_preprint":false},{"year":2022,"finding":"The nuclear receptor FXR (farnesoid X receptor) directly controls transcription of intestinal Trpm6 by binding an inverted repeat 1 (IR1) response element in an intronic FXR binding peak as a FXR-RXRα heterodimer; intestinal FXR is required for basal and GW4064-induced Trpm6 expression in mice.","method":"FXR ChIP-seq analysis, reporter assay with IR1 response element, FXR-knockout mice, GW4064 (FXR agonist) treatment, RT-qPCR","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP-seq with functional reporter assay and in vivo knockout validation, single lab","pmids":["35216094"],"is_preprint":false},{"year":2020,"finding":"Deletion of transcription factor Prox-1 specifically in the DCT causes hypomagnesemia with profound downregulation of TRPM6 and NCC at both mRNA and protein levels, establishing Prox-1 as a transcriptional regulator of TRPM6 expression in the adult kidney.","method":"DCT-specific conditional knockout mice (NCCcre:Prox-1flox/flox), RT-qPCR, immunohistochemistry, Western blot, plasma electrolyte measurements","journal":"Pflugers Archiv","confidence":"High","confidence_rationale":"Tier 2 — tissue-specific knockout with specific molecular and physiological phenotype","pmids":["33200256"],"is_preprint":false},{"year":2024,"finding":"Intestine-specific TRPM6 knockout (Vill1-TRPM6-/-) mice show significantly lower 25Mg2+ absorption, lower serum Mg2+ levels, and lower urinary Mg2+ excretion compared to controls; compensatory upregulation of renal Slc41a3, Trpm6, and Trpm7 gene expression is observed, demonstrating that intestinal TRPM6 is essential for Mg2+ absorption in the intestine.","method":"Intestine-specific conditional knockout mice, 25Mg2+ isotope absorption assay, RNA sequencing, RT-qPCR","journal":"Pflugers Archiv","confidence":"High","confidence_rationale":"Tier 2 — tissue-specific knockout with isotope-based functional absorption measurement","pmids":["39266724"],"is_preprint":false}],"current_model":"TRPM6 is a bifunctional channel-kinase localized to the apical membrane of intestinal and renal epithelial cells, where it forms Mg2+/Ca2+-permeable cation channels (primarily as TRPM6/TRPM7 heteromers) that mediate active transepithelial Mg2+ transport regulated by intracellular Mg2+, Mg·ATP, PIP2, and multiple hormonal inputs (EGF via Src/Rac1, insulin via PI3K/Rac1, estrogen via REA displacement), while its fused alpha-kinase domain autophosphorylates, transphosphorylates TRPM7, and interacts with regulatory proteins (RACK1, REA, MsrB1, uromodulin) to modulate channel gating and surface expression; loss-of-function mutations cause hereditary hypomagnesemia with secondary hypocalcemia in humans, and complete knockout in mice additionally causes embryonic lethality and neural tube defects."},"narrative":{"teleology":[{"year":2002,"claim":"Positional cloning resolved the genetic basis of hypomagnesemia with secondary hypocalcemia (HSH), establishing that TRPM6 mutations are causative and that the gene is expressed in intestinal and renal epithelia critical for Mg²⁺ homeostasis.","evidence":"Positional cloning and mutation analysis in HSH families, expression profiling in two independent studies","pmids":["12032568","12032570"],"confidence":"High","gaps":["Channel properties unknown","Subcellular localization not resolved","Mechanism by which loss causes hypocalcemia unclear"]},{"year":2003,"claim":"Immunolocalization and electrophysiology established that TRPM6 resides at the apical membrane of DCT and intestinal brush border and forms a Mg²⁺/Ca²⁺-permeable cation channel with strong intracellular Mg²⁺ sensitivity, directly linking the genetic finding to a defined ion transport mechanism.","evidence":"Immunolocalization in kidney and intestine, whole-cell patch clamp of heterologously expressed TRPM6","pmids":["14576148"],"confidence":"High","gaps":["Whether TRPM6 functions as a homomer or heteromer in vivo unknown","Pore determinants of selectivity unresolved"]},{"year":2004,"claim":"The discovery that TRPM6 requires TRPM7 for surface expression and forms TRPM6/TRPM7 heteromers—disrupted by the HSH-causing S141L mutation—provided a cell biological explanation for the disease and established heteromerization as the physiologically relevant channel configuration.","evidence":"Co-immunoprecipitation, confocal microscopy, and electrophysiology in HEK293 and Xenopus oocytes","pmids":["14976260"],"confidence":"High","gaps":["Whether TRPM6 can form functional homomeric channels remained debated","Stoichiometry of heteromeric complex unknown"]},{"year":2005,"claim":"Functional non-redundancy of TRPM6 and TRPM7 was demonstrated: TRPM6 cannot complement TRPM7-deficient cells, and TRPM6 cross-phosphorylates TRPM7 but not vice versa, establishing an asymmetric kinase relationship.","evidence":"Genetic complementation in TRPM7-deficient DT40 cells, phosphothreonine-specific antibody detection","pmids":["16150690"],"confidence":"High","gaps":["Functional consequences of TRPM6→TRPM7 transphosphorylation unknown","Sites of transphosphorylation not mapped"]},{"year":2006,"claim":"Biophysical characterization revealed that TRPM6 homomers have distinct conductance, pharmacology (2-APB activation), and pH sensitivity from TRPM7, while pore-region mutations (P1017R) act dominant-negatively on TRPM7, defining the channel pore as a critical functional locus.","evidence":"Single-channel recordings, pharmacological profiling, pore mutagenesis with electrophysiology and FRET in multiple expression systems","pmids":["16636202","17197439","17098283"],"confidence":"High","gaps":["Structural basis of pore selectivity not resolved at atomic level","Relative contribution of homomers vs. heteromers in native tissue unknown"]},{"year":2007,"claim":"Mutagenesis of pore glutamates E1024 and E1029 defined the molecular determinants of divalent cation permeation and pH-dependent potentiation, converting the channel to monovalent selectivity upon neutralization.","evidence":"Site-directed mutagenesis with whole-cell patch clamp and ion substitution","pmids":["17599911"],"confidence":"High","gaps":["No high-resolution pore structure available","How pore residues contribute to Mg²⁺ vs. Ca²⁺ discrimination at physiological levels not fully resolved"]},{"year":2008,"claim":"Multiple regulatory mechanisms converging on the α-kinase domain were uncovered: RACK1 inhibits channel activity through kinase-dependent T1851 autophosphorylation; massive autophosphorylation of a Ser/Thr-rich region controls substrate recognition; and myosin II heavy chains were identified as shared kinase substrates with TRPM7.","evidence":"Co-immunoprecipitation, patch clamp with siRNA and mutagenesis (RACK1); MS-based phosphomapping and deletion mutagenesis (autophosphorylation); in vitro kinase assay with MS (myosin substrates)","pmids":["18258429","18365021","18675813"],"confidence":"High","gaps":["Physiological relevance of myosin phosphorylation by TRPM6 in epithelial Mg²⁺ transport not tested","How RACK1 inhibition integrates with other regulatory inputs unclear"]},{"year":2008,"claim":"EGF receptor signaling was shown to specifically increase TRPM6 surface abundance and channel activity via Src and Rac1, independent of kinase domain activity, establishing a hormonal pathway for regulated Mg²⁺ reabsorption.","evidence":"Patch clamp, FRAP, surface biotinylation with pharmacological and dominant-negative Rac1 constructs","pmids":["19073827"],"confidence":"High","gaps":["Direct phosphorylation targets linking Rac1 to TRPM6 trafficking unknown","Whether EGF acts in vivo on DCT TRPM6 not directly tested"]},{"year":2009,"claim":"Two new regulatory axes were identified: REA inhibits TRPM6 in a kinase-dependent manner and is displaced by estradiol (linking sex hormones to Mg²⁺ handling), while Trpm6 knockout mice revealed embryonic lethality and neural tube defects, demonstrating developmental functions beyond ion homeostasis.","evidence":"Ras recruitment system, patch clamp, estradiol treatment (REA); global Trpm6 knockout mouse embryonic phenotyping (NTDs)","pmids":["19329436","19692351"],"confidence":"High","gaps":["Mechanism by which TRPM6 regulates neural tube closure not identified","Whether estrogen-TRPM6 axis operates in vivo in kidney/intestine unresolved"]},{"year":2010,"claim":"MsrB1 was identified as a redox-responsive regulator that protects TRPM6 channel activity from oxidative inhibition by reducing Met1755, linking oxidative stress to Mg²⁺ transport.","evidence":"Ras recruitment system, patch clamp, M1755A mutagenesis, H₂O₂ treatment","pmids":["20584906"],"confidence":"High","gaps":["Whether oxidative regulation of TRPM6 is physiologically relevant in DCT or intestine not tested in vivo"]},{"year":2011,"claim":"PIP₂ was established as an essential gating cofactor for TRPM6, with basic residues in the TRP domain mediating PIP₂-dependent activation, adding lipid signaling to the regulatory framework.","evidence":"Multiple PIP₂ depletion strategies (PLC, 5-phosphatase, Ci-VSP), patch clamp, TRP domain mutagenesis","pmids":["22180838"],"confidence":"High","gaps":["Direct PIP₂ binding to TRPM6 not demonstrated by structural or biophysical methods","Contribution of PIP₂ regulation in heteromeric TRPM6/7 context not assessed"]},{"year":2012,"claim":"Insulin was shown to stimulate TRPM6 via PI3K/Rac1-mediated surface trafficking, and specific TRPM6 variants (V1393I, K1584E) that abolish insulin responsiveness were linked to gestational diabetes, connecting channel regulation to metabolic disease.","evidence":"Patch clamp, TIRF microscopy, PI3K/Rac1 inhibition, mutagenesis, clinical association","pmids":["22733750"],"confidence":"High","gaps":["Causal relationship between TRPM6 variants and diabetes not established by Mendelian genetics","Identity of kinases phosphorylating T1391 and S1583 not determined"]},{"year":2014,"claim":"The physiological rationale for TRPM6/TRPM7 heteromerization was clarified: TRPM6 relieves TRPM7 from Mg·ATP inhibition through its kinase domain, while TRPM7 tunes TRPM6's extreme Mg²⁺ sensitivity, yielding constitutively active channels at physiological ion concentrations; separately, the kinase dimerization motif was shown to be essential for both kinase and channel activity.","evidence":"Patch clamp with kinase-dead mutants and intracellular ion manipulation; dimerization motif mutagenesis with peptide rescue and in vitro kinase assay","pmids":["24385424","24650431","24858416"],"confidence":"High","gaps":["Stoichiometry and architecture of the heteromeric complex not structurally resolved","How kinase dimerization controls the channel pore conformationally is unknown"]},{"year":2017,"claim":"Studies in primary cells from TRPM6- and TRPM7-knockout mice confirmed that the heteromeric channel is the physiologically active species in epithelial cells, while mass spectrometry mapped transphosphorylation sites on TRPM7 and identified phosphomimetic substitutions that inactivate TRPM7 kinase, and Xenopus studies demonstrated TRPM6's non-redundant role in radial intercalation during neural tube closure.","evidence":"Patch clamp on primary knockout cells; MS phosphomapping with mutagenesis; Xenopus morpholino knockdown with live imaging","pmids":["28821869","28220887","29142255"],"confidence":"High","gaps":["How TRPM6 governs cell intercalation movements mechanistically is unknown","Whether transphosphorylation of TRPM7 occurs in vivo in DCT"]},{"year":2018,"claim":"Uromodulin was identified as an extracellular stabilizer of apical TRPM6 that impairs dynamin-dependent endocytosis, with Umod⁻/⁻ mice showing reduced DCT TRPM6 and Mg²⁺ wasting, establishing a paracrine/extracellular regulatory axis.","evidence":"Co-immunoprecipitation, surface biotinylation, patch clamp, dynamin inhibition, Umod⁻/⁻ mouse model","pmids":["30139743"],"confidence":"High","gaps":["Binding interface between uromodulin and TRPM6 extracellular domains not mapped","Whether uromodulin acts on heteromeric TRPM6/7 specifically not tested"]},{"year":2020,"claim":"Transcriptional control of TRPM6 was established: Prox-1 deletion in the DCT causes hypomagnesemia with loss of TRPM6 expression, identifying a critical upstream transcription factor.","evidence":"DCT-specific Prox-1 conditional knockout mice with RT-qPCR and immunohistochemistry","pmids":["33200256"],"confidence":"High","gaps":["Whether Prox-1 directly binds the Trpm6 promoter not shown","Other transcription factors cooperating with Prox-1 not identified"]},{"year":2021,"claim":"Kidney-specific TRPM6 deletion revealed an unexpected role in circadian blood pressure regulation through control of renin secretion and β-adrenoreceptor expression in renin-secreting cells, extending TRPM6 function beyond Mg²⁺ transport.","evidence":"Kidney-specific conditional knockout mice, blood pressure telemetry, renin secretion assay, β-adrenoreceptor pharmacology","pmids":["34140503"],"confidence":"High","gaps":["Mechanism linking DCT Mg²⁺ transport to renin-secreting cell β-adrenoreceptor expression unknown","Whether this is a direct or Mg²⁺-mediated effect not distinguished"]},{"year":2024,"claim":"Intestine-specific TRPM6 knockout with ²⁵Mg isotope tracing definitively proved that TRPM6 is essential for active intestinal Mg²⁺ absorption and cannot be compensated by other transporters despite compensatory upregulation of renal Trpm6, Trpm7, and Slc41a3.","evidence":"Intestine-specific Trpm6 knockout mice, ²⁵Mg²⁺ isotope absorption, RNA-seq","pmids":["39266724"],"confidence":"High","gaps":["Whether compensatory renal upregulation is sufficient long-term not assessed","Role of intestinal TRPM6 in Ca²⁺ absorption not evaluated"]},{"year":null,"claim":"No high-resolution structure of TRPM6 (homomeric or heteromeric with TRPM7) has been reported, leaving the structural basis of heteromeric assembly, pore selectivity, kinase-channel coupling, and the mechanism by which TRPM6 controls neural tube closure and renin secretion unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No cryo-EM or crystal structure of full-length TRPM6 or TRPM6/7 heteromer","Mechanism linking TRPM6 to neural tube closure cell movements unknown","Signal from DCT TRPM6 to juxtaglomerular renin cells not identified"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[1,3,5,6,7,14]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[8,9,10,17,20]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[9,10,20]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1,2,11,15,24]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[11,12,15]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[21,22]}],"complexes":["TRPM6/TRPM7 heteromeric channel"],"partners":["TRPM7","RACK1","REA","MSRB1","UMOD","RAC1","P2X4"],"other_free_text":[]},"mechanistic_narrative":"TRPM6 is a bifunctional channel-kinase that serves as the principal gatekeeper of transcellular Mg²⁺ absorption in the intestine and Mg²⁺ reabsorption in the renal distal convoluted tubule, with additional non-redundant roles in neural tube closure and circadian blood pressure regulation. The channel pore, whose divalent cation selectivity is determined by glutamate residues E1024 and E1029 in the selectivity filter, conducts Mg²⁺ and Ca²⁺ and is gated by intracellular Mg²⁺, PIP₂, and Mg·ATP; TRPM6 predominantly functions at the cell surface as a heteromer with TRPM7, which confers physiologically appropriate Mg·ATP insensitivity, while the fused C-terminal α-kinase domain autophosphorylates, transphosphorylates TRPM7, and scaffolds regulatory proteins including RACK1, REA, MsrB1, and uromodulin to modulate channel trafficking and gating [PMID:14576148, PMID:14976260, PMID:24385424, PMID:16636202, PMID:30139743]. Channel surface abundance is dynamically controlled by EGF/Src/Rac1, insulin/PI3K/Rac1, and estrogen signaling pathways, and uromodulin stabilizes apical TRPM6 by impairing dynamin-dependent endocytosis [PMID:19073827, PMID:22733750, PMID:19329436, PMID:30139743]. Loss-of-function mutations in TRPM6 cause autosomal-recessive hypomagnesemia with secondary hypocalcemia in humans, and complete knockout in mice causes embryonic lethality with neural tube defects [PMID:12032568, PMID:12032570, PMID:19692351]."},"prefetch_data":{"uniprot":{"accession":"Q9BX84","full_name":"Transient receptor potential cation channel subfamily M member 6","aliases":["Channel kinase 2","Melastatin-related TRP cation channel 6"],"length_aa":2022,"mass_kda":231.7,"function":"Bifunctional protein that combines an ion channel with an intrinsic kinase domain, enabling it to modulate cellular functions either by conducting ions through the pore or by phosphorylating downstream proteins via its kinase domain (PubMed:14576148, PubMed:16636202, PubMed:18258429, PubMed:18365021). Crucial for Mg(2+) homeostasis. Has an important role in epithelial Mg(2+) transport and in the active Mg(2+) absorption in the gut and kidney (PubMed:14576148). However, whether TRPM6 forms functional homomeric channels by itself or functions primarily as a subunit of heteromeric TRPM6-TRPM7 channels, is still under debate (PubMed:14576148, PubMed:16636202, PubMed:24385424) The C-terminal kinase domain can be cleaved from the channel segment in a cell-type-specific fashion. The cleaved kinase fragments can translocate to the nucleus, and bind chromatin-remodeling complex proteins to ultimately phosphorylate specific Ser/Thr residues of histones known to be functionally important for cell differentiation and development","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/Q9BX84/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/TRPM6","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/TRPM6","total_profiled":1310},"omim":[{"mim_id":"618314","title":"HYPOMAGNESEMIA, SEIZURES, AND IMPAIRED INTELLECTUAL DEVELOPMENT 2; HOMGSMR2","url":"https://www.omim.org/entry/618314"},{"mim_id":"610803","title":"SOLUTE CARRIER FAMILY 41, MEMBER 3; SLC41A3","url":"https://www.omim.org/entry/610803"},{"mim_id":"607009","title":"TRANSIENT RECEPTOR POTENTIAL CATION CHANNEL, SUBFAMILY M, MEMBER 6; TRPM6","url":"https://www.omim.org/entry/607009"},{"mim_id":"602014","title":"HYPOMAGNESEMIA 1, INTESTINAL; HOMG1","url":"https://www.omim.org/entry/602014"},{"mim_id":"176260","title":"POTASSIUM CHANNEL, VOLTAGE-GATED, SHAKER-RELATED SUBFAMILY, MEMBER 1; KCNA1","url":"https://www.omim.org/entry/176260"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"intestine","ntpm":15.6}],"url":"https://www.proteinatlas.org/search/TRPM6"},"hgnc":{"alias_symbol":["CHAK2","FLJ22628"],"prev_symbol":["HOMG","HSH"]},"alphafold":{"accession":"Q9BX84","domains":[{"cath_id":"3.40.50.450","chopping":"98-421","consensus_level":"medium","plddt":84.3456,"start":98,"end":421},{"cath_id":"-","chopping":"961-1117","consensus_level":"medium","plddt":83.1475,"start":961,"end":1117}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BX84","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BX84-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BX84-F1-predicted_aligned_error_v6.png","plddt_mean":64.62},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=TRPM6","jax_strain_url":"https://www.jax.org/strain/search?query=TRPM6"},"sequence":{"accession":"Q9BX84","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9BX84.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9BX84/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BX84"}},"corpus_meta":[{"pmid":"12032568","id":"PMC_12032568","title":"Hypomagnesemia 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TRPM6 is expressed in intestinal epithelia and kidney tubules and is crucial for magnesium homeostasis, identified by positional candidate gene approach.\",\n      \"method\": \"Positional cloning, mutation analysis, expression studies\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — independently replicated in two simultaneous papers (PMID:12032568 and PMID:12032570), foundational discovery\",\n      \"pmids\": [\"12032568\", \"12032570\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"TRPM6 is specifically localized along the apical membrane of the renal distal convoluted tubule and brush-border membrane of the small intestine; heterologous expression of wild-type but not HSH-mutant TRPM6 induces a Mg2+- and Ca2+-permeable cation channel strongly regulated by intracellular Mg2+, with 5-fold higher affinity for Mg2+ than Ca2+, outward rectification, and voltage-dependent block by ruthenium red.\",\n      \"method\": \"Immunolocalization, heterologous expression, whole-cell patch clamp, ion substitution experiments\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct localization with functional consequence, electrophysiological characterization with mutagenesis, high citation count\",\n      \"pmids\": [\"14576148\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"TRPM6 alone is retained intracellularly when heterologously expressed, but specifically interacts with TRPM7 to form functional TRPM6/TRPM7 heteromeric channel complexes at the cell surface; the HSH-causing S141L missense mutation abolishes oligomeric assembly of TRPM6 with TRPM7, providing a cell biological explanation for the disease.\",\n      \"method\": \"Heterologous expression in HEK293 and Xenopus oocytes, co-immunoprecipitation, confocal microscopy, two-electrode voltage clamp, whole-cell patch clamp\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods, mechanistic link to disease mutation confirmed\",\n      \"pmids\": [\"14976260\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"TRPM6 forms functional homomeric channels with unique unitary conductance (~2-fold larger than TRPM7), distinct divalent cation permeability profile, unique pH sensitivity, and differential sensitivity to 2-APB (micromolar 2-APB maximally activates TRPM6 but inhibits TRPM7); TRPM6 also forms heteromeric TRPM6/7 complexes with intermediate pharmacological properties.\",\n      \"method\": \"Heterologous expression, whole-cell patch clamp, single-channel recordings, pharmacological profiling\",\n      \"journal\": \"The Journal of general physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — rigorous electrophysiology with multiple channel types and pharmacological discrimination\",\n      \"pmids\": [\"16636202\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"TRPM6 requires TRPM7 for surface expression in HEK-293 cells; TRPM6 cross-phosphorylates TRPM7 on threonine residues (detected by phosphothreonine-specific antibody) but TRPM7 does not phosphorylate TRPM6; TRPM7 deficiency in DT40 cells cannot be complemented by heterologously expressed TRPM6, demonstrating functional non-redundancy.\",\n      \"method\": \"Complementation assay in TRPM7-deficient DT40 B-cells, surface expression assay, phosphothreonine-specific antibody\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal functional comparison, phosphorylation-specific antibody, genetic complementation\",\n      \"pmids\": [\"16150690\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Two glutamate residues in the putative pore of TRPM6 (E1024 and E1029, corresponding to E1047 and E1052 in TRPM7) are key molecular determinants of Mg2+ and Ca2+ permeability and pH sensitivity; neutralization of E1024 (E1047 in TRPM7) largely abolished divalent permeation, converting the channel to monovalent selectivity and abolishing proton-mediated potentiation.\",\n      \"method\": \"Site-directed mutagenesis of pore residues, whole-cell patch clamp, ion substitution, pH manipulation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro mutagenesis with rigorous electrophysiological validation, multiple mutants tested\",\n      \"pmids\": [\"17599911\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"A missense mutation P1017R in the putative pore-forming region of TRPM6 causes HSH; TRPM6(P1017R) suppresses TRPM7 channel activity in a dominant-negative manner when co-expressed, while not affecting TRPM6/TRPM7 assembly or co-trafficking to the cell surface, demonstrating that a pore-region functional defect alone is sufficient to impair body Mg2+ homeostasis.\",\n      \"method\": \"Two-electrode voltage clamp (Xenopus oocytes), whole-cell patch clamp (HEK293), confocal microscopy, FRET\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods, mechanistic insight into pore function and dominant-negative effect\",\n      \"pmids\": [\"17197439\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Neutralization of E1024 and D1031 in the TRPM6 selectivity filter (loop between TM5 and TM6, sequence GEIDVC) results in non-functional channels; E1029 neutralization increases conductance for Ba2+ and Zn2+ and alters pore diameter; I1030M reduces Ni2+ conductance — defining molecular determinants of TRPM6 cation permeation.\",\n      \"method\": \"Site-directed mutagenesis of pore residues, whole-cell patch clamp, permeability measurements\",\n      \"journal\": \"Cell calcium\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro mutagenesis of multiple pore residues with functional electrophysiological readouts\",\n      \"pmids\": [\"17098283\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"RACK1 (receptor for activated C-kinase 1) physically associates with the TRPM6 alpha-kinase domain and inhibits TRPM6 channel activity in a kinase activity-dependent manner; autophosphorylation of Thr1851 in the alpha-kinase domain is required for RACK1's inhibitory effect and is critical for Mg2+ sensitivity of TRPM6 activity; PKC activation by PMA abrogates RACK1 inhibition.\",\n      \"method\": \"Co-immunoprecipitation (Ras recruitment system), whole-cell patch clamp, siRNA knockdown, site-directed mutagenesis, PKC activation\",\n      \"journal\": \"Current biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (pulldown, electrophysiology, siRNA, mutagenesis)\",\n      \"pmids\": [\"18258429\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"TRPM6 and TRPM7 kinase domains undergo massive autophosphorylation (>30 mol/mol) predominantly in a Ser/Thr-rich region N-terminal to the catalytic domain; this autophosphorylation strongly increases the rate of substrate phosphorylation; deletion of the Ser/Thr-rich domain prevents substrate phosphorylation without affecting intrinsic catalytic activity, suggesting this domain controls substrate recognition.\",\n      \"method\": \"In vitro kinase assays, mass spectrometric phosphomapping, deletion mutagenesis, 32P autophosphorylation\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro biochemical assays with mass spectrometry and mutagenesis\",\n      \"pmids\": [\"18365021\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"TRPM6 and TRPM7 phosphorylate the assembly domain of myosin IIA, IIB and IIC on identical residues; phosphorylation of myosin IIA is restricted to the coiled-coil domain while TRPM6 and TRPM7 also phosphorylate the non-helical tails of myosin IIB and IIC; TRPM7 does not phosphorylate eEF-2, indicating substrate specificity distinct from other alpha-kinases.\",\n      \"method\": \"In vitro kinase assay, mass spectrometry\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstituted kinase assay with mass spectrometric identification of phosphorylation sites\",\n      \"pmids\": [\"18675813\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"EGF receptor stimulation increases TRPM6 (but not TRPM7) channel current via Src family tyrosine kinases and downstream effector Rac1; activated Rac1 increases TRPM6 plasma membrane mobility (FRAP) and surface abundance, thereby augmenting channel activity; dominant-negative Rac1 abolishes EGF-mediated TRPM6 activation; the TRPM6 alpha-kinase domain is not required for this EGF-mediated activation.\",\n      \"method\": \"Whole-cell patch clamp, FRAP, surface biotinylation, dominant-negative and constitutively active Rac1 constructs, Src kinase inhibitors\",\n      \"journal\": \"Journal of the American Society of Nephrology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods, specific pathway dissection with pharmacological and genetic tools\",\n      \"pmids\": [\"19073827\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"REA (repressor of estrogen receptor activity) physically interacts with the 6th, 7th, and 8th beta-sheets of the TRPM6 alpha-kinase domain and inhibits TRPM6 (but not TRPM7) channel activity in a phosphorylation-dependent manner; TRPM6 kinase-dead mutant (K1804R) is not inhibited by REA despite maintained binding; PKC activation enhances REA inhibition; short-term 17β-estradiol treatment dissociates the REA-TRPM6 interaction and stimulates TRPM6-mediated current.\",\n      \"method\": \"Ras recruitment system (protein interaction), whole-cell patch clamp, co-immunoprecipitation, PKC activation, estradiol treatment\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods establishing interaction, phosphorylation dependence, and hormonal regulation\",\n      \"pmids\": [\"19329436\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"MsrB1 (methionine sulfoxide reductase B1) interacts with the TRPM6 alpha-kinase domain (identified by Ras recruitment system); H2O2 decreases TRPM6 channel activity without affecting plasma membrane expression; co-expression of MsrB1 partially attenuates this inhibition; mutation of Met1755 to Ala reduces H2O2-mediated inhibition of TRPM6, indicating MsrB1 recovers TRPM6 activity by reducing oxidation of Met1755.\",\n      \"method\": \"Ras recruitment system, whole-cell patch clamp, surface biotinylation, site-directed mutagenesis, H2O2 treatment\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods including interaction screen, functional electrophysiology, and mutagenesis\",\n      \"pmids\": [\"20584906\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PIP2 (phosphatidylinositol-4,5-bisphosphate) is required for TRPM6 channel activation and Mg2+ influx; depletion of PIP2 by PLC-coupled M1-receptor stimulation, overexpressed 5-phosphatase, or voltage-sensitive phosphatase (Ci-VSP) potently inhibits TRPM6; neutralization of basic residues in the TRP domain reduces PIP2-dependent activation, implicating TRP domain residues in PIP2 interaction.\",\n      \"method\": \"Whole-cell patch clamp, TIRF, voltage-sensitive phosphatase (Ci-VSP), receptor-mediated PLC activation, 5-phosphatase overexpression, site-directed mutagenesis\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple independent methods to deplete PIP2, mutagenesis of putative binding residues, direct channel activity measurement\",\n      \"pmids\": [\"22180838\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Insulin stimulates TRPM6 channel activity via PI3-kinase and Rac1-mediated elevation of TRPM6 cell surface expression (assessed by TIRF microscopy and patch clamp); genetic variants TRPM6(V1393I) and TRPM6(K1584E) fail to respond to insulin stimulation, likely due to inability to phosphorylate TRPM6 Thr1391 and Ser1583; these variants are associated with higher glycated hemoglobin and gestational diabetes mellitus.\",\n      \"method\": \"Patch clamp, TIRF microscopy, site-directed mutagenesis, PI3K/Rac1 pathway inhibition\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct functional assay with pathway dissection, mutagenesis, and clinical correlation\",\n      \"pmids\": [\"22733750\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The TRPM6 kinase domain determines Mg·ATP sensitivity of TRPM7/M6 heteromeric channels: homomeric TRPM6 is highly sensitive to intracellular free Mg2+ (unlikely active at physiological levels); heteromeric TRPM7/TRPM6 channels have altered pharmacology and are independent of intracellular Mg·ATP, uncoupling channel activity from cellular energy status; disruption of TRPM6 kinase phosphorylation activity re-introduces Mg·ATP sensitivity to the heteromeric channel.\",\n      \"method\": \"Whole-cell patch clamp, co-expression, kinase-dead TRPM6 mutant, intracellular Mg2+ and Mg·ATP manipulation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — electrophysiology with kinase mutants and precise intracellular ion control\",\n      \"pmids\": [\"24385424\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The dimerization motif (Leu1718/Leu1721) preceding the TRPM6 kinase domain and the dimerization pocket within the kinase domain are required for both kinase activity and ion channel activity; mutations disrupting this motif/pocket abolish kinase activity and greatly diminish channel activity independently of kinase activity; one disease-causing missense mutation (S1754N) near the dimerization motif abolishes kinase activity; a peptide encompassing the dimerization motif can restore kinase activity of dimerization motif mutants.\",\n      \"method\": \"Site-directed mutagenesis, in vitro kinase assay, patch clamp, peptide rescue experiment\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro biochemical reconstitution plus electrophysiology, mutagenesis, and peptide rescue\",\n      \"pmids\": [\"24650431\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"TRPM6 kinase activity regulates TRPM7 intracellular trafficking and serine phosphorylation of TRPM7 (but TRPM7 kinase does not phosphorylate TRPM6 on serine); active TRPM6 kinase alters TRPM7 trafficking in HEK-293 and DT40 cells; co-expression of TRPM6 with intact kinase (but not kinase-dead mutant) inhibits TRPM7-dependent cell growth under hypomagnesic conditions.\",\n      \"method\": \"Phospho-specific antibodies, trafficking assays, genetic complementation in TRPM7-deficient DT40 B-cells, cell growth assay, kinase-dead mutant\",\n      \"journal\": \"Cellular and molecular life sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple assays with kinase-dead control, genetic complementation in defined cell system\",\n      \"pmids\": [\"24858416\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"mTRPM6 and mTRPM7 differentially regulate heteromeric mTRPM6/7 channels: mTRPM6 extreme sensitivity to Mg2+ is tuned by TRPM7 to higher concentrations, while mTRpm6 relieves mTRPM7 from tight Mg·ATP inhibition, resulting in high constitutive activity of the heteromeric complex at physiological Mg2+ and Mg·ATP levels in epithelial cells.\",\n      \"method\": \"Whole-cell patch clamp, comparative expression of mouse TRPM6 vs. TRPM7, primary cells from TRPM6- and TRPM7-deficient mice\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — primary cell data from knockout mice combined with heterologous expression and rigorous electrophysiology\",\n      \"pmids\": [\"28821869\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Mass spectrometric analysis identified phosphorylation sites on TRPM6 including T1851 (autophosphorylation site in the kinase domain); TRPM6 transphosphorylates TRPM7 at multiple sites; phosphomimetic substitutions at TRPM7 S1777 (catalytic domain) and S1565 (exchange/dimerization domain) inactivate kinase activity through distinct mechanisms.\",\n      \"method\": \"Mass spectrometry, site-directed mutagenesis, in vitro kinase assay, molecular modeling\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — MS-based phosphosite identification combined with mutagenesis and functional kinase assays\",\n      \"pmids\": [\"28220887\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Trpm6 knockout mice (Trpm6-/-) exhibit embryonic mortality by E12.5 and neural tube defects (exencephaly and spina bifida occulta), demonstrating a non-redundant role of TRPM6 in neural tube closure during development, beyond its known role in Mg2+ homeostasis.\",\n      \"method\": \"Conditional knockout mouse model, embryonic phenotyping, dietary Mg2+ supplementation rescue attempts\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean knockout with specific developmental phenotype\",\n      \"pmids\": [\"19692351\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Xenopus TRPM6 (XTRPM6) is expressed in lateral mesoderm and ectoderm at neurula stage; loss of XTRPM6 (but not XTRPM7) disrupts radial intercalation cell movements during neural tube closure, establishing a non-redundant role distinct from TRPM7; a zinc-influx assay showed TRPM6 can form functional channels in the absence of TRPM7.\",\n      \"method\": \"Xenopus laevis morpholino knockdown, in situ hybridization, live imaging of cell movements, zinc-influx assay\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function with specific cellular phenotype (radial vs. mediolateral intercalation), functional channel assay\",\n      \"pmids\": [\"29142255\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"P2X4 receptor specifically inhibits TRPM6 (but not TRPM7) channel activity in a manner dependent on P2X4 channel activity; a P2X4 mutant with altered ATP sensitivity fails to inhibit TRPM6; P2X6 (non-functional in mammalian cells) does not inhibit TRPM6.\",\n      \"method\": \"Whole-cell patch clamp, co-expression, P2X4 mutants, RT-qPCR tissue expression\",\n      \"journal\": \"Pflugers Archiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single lab, electrophysiological co-expression study with functional mutant controls\",\n      \"pmids\": [\"24413910\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Uromodulin (UMOD) physically interacts with TRPM6 from the extracellular space, enhances TRPM6 cell-surface abundance by impairing dynamin-dependent TRPM6 endocytosis, and increases TRPM6 current density; Umod-/- mice show decreased apical TRPM6 staining in the DCT and increased urinary Mg2+ excretion.\",\n      \"method\": \"Co-immunoprecipitation, surface biotinylation, whole-cell patch clamp, dynamin inhibition, Umod-/- mouse model, immunofluorescence\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (pulldown, biotinylation, electrophysiology, in vivo knockout)\",\n      \"pmids\": [\"30139743\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Kidney-specific Trpm6 knockout mice show decreased blood pressure and loss of circadian blood pressure variation; renin secretion is not augmented in the active period and pharmacological β-adrenoreceptor activation fails to stimulate renin secretion; β-adrenoreceptor expression is decreased in renin-secreting cells of TRPM6-deficient kidneys, indicating TRPM6 in the DCT regulates renin secretion and circadian blood pressure.\",\n      \"method\": \"Kidney-specific conditional knockout mice, blood pressure telemetry, renin secretion assay, β-adrenoreceptor pharmacology\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean tissue-specific knockout with specific hemodynamic and hormonal phenotype\",\n      \"pmids\": [\"34140503\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Calmodulin (CaM) and S100A1 share a common binding site at the N-terminal TRPM6 domain (L520-R535); basic residues R526/R531/K532/R535 are critical for non-covalent interactions with both ligands; CaM and S100A1 bind via different mechanisms despite sharing the same domain.\",\n      \"method\": \"Biophysical methods (fluorescence, CD), molecular modelling, site-directed mutagenesis of N-terminal domain\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single lab, biophysical binding assays with mutagenesis but no functional channel activity data\",\n      \"pmids\": [\"31505788\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Flavaglines (natural and synthetic compounds targeting prohibitins) stimulate TRPM6 channel activity ~2-fold at nanomolar concentrations; stimulatory effect requires the presence of the TRPM6 alpha-kinase domain but not its phosphotransferase activity; TRPM6 variants with impaired insulin sensitivity (V1393I and K1584E) are not sensitive to flavagline stimulation, suggesting they act via the insulin receptor signaling pathway.\",\n      \"method\": \"Whole-cell patch clamp, kinase domain deletion/mutation, pharmacological flavagline treatment\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — electrophysiology with domain requirements and pharmacological mutant analysis, single lab\",\n      \"pmids\": [\"25774985\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Iloperidone and ifenprodil selectively inhibit TRPM6 channel activity (IC50 0.73 and 3.33 µM respectively) without affecting TRPM7; VER155008 selectively suppresses TRPM7 (IC50 0.11 µM) without affecting TRPM6; effects confirmed on endogenous channels in native mouse and human cell models.\",\n      \"method\": \"Patch clamp, Ca2+ imaging, pharmacological analysis in native cell models\",\n      \"journal\": \"Cell calcium\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — rigorous electrophysiology with confirmed selectivity in native cells, multiple compounds\",\n      \"pmids\": [\"36030694\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The nuclear receptor FXR (farnesoid X receptor) directly controls transcription of intestinal Trpm6 by binding an inverted repeat 1 (IR1) response element in an intronic FXR binding peak as a FXR-RXRα heterodimer; intestinal FXR is required for basal and GW4064-induced Trpm6 expression in mice.\",\n      \"method\": \"FXR ChIP-seq analysis, reporter assay with IR1 response element, FXR-knockout mice, GW4064 (FXR agonist) treatment, RT-qPCR\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP-seq with functional reporter assay and in vivo knockout validation, single lab\",\n      \"pmids\": [\"35216094\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Deletion of transcription factor Prox-1 specifically in the DCT causes hypomagnesemia with profound downregulation of TRPM6 and NCC at both mRNA and protein levels, establishing Prox-1 as a transcriptional regulator of TRPM6 expression in the adult kidney.\",\n      \"method\": \"DCT-specific conditional knockout mice (NCCcre:Prox-1flox/flox), RT-qPCR, immunohistochemistry, Western blot, plasma electrolyte measurements\",\n      \"journal\": \"Pflugers Archiv\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — tissue-specific knockout with specific molecular and physiological phenotype\",\n      \"pmids\": [\"33200256\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Intestine-specific TRPM6 knockout (Vill1-TRPM6-/-) mice show significantly lower 25Mg2+ absorption, lower serum Mg2+ levels, and lower urinary Mg2+ excretion compared to controls; compensatory upregulation of renal Slc41a3, Trpm6, and Trpm7 gene expression is observed, demonstrating that intestinal TRPM6 is essential for Mg2+ absorption in the intestine.\",\n      \"method\": \"Intestine-specific conditional knockout mice, 25Mg2+ isotope absorption assay, RNA sequencing, RT-qPCR\",\n      \"journal\": \"Pflugers Archiv\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — tissue-specific knockout with isotope-based functional absorption measurement\",\n      \"pmids\": [\"39266724\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TRPM6 is a bifunctional channel-kinase localized to the apical membrane of intestinal and renal epithelial cells, where it forms Mg2+/Ca2+-permeable cation channels (primarily as TRPM6/TRPM7 heteromers) that mediate active transepithelial Mg2+ transport regulated by intracellular Mg2+, Mg·ATP, PIP2, and multiple hormonal inputs (EGF via Src/Rac1, insulin via PI3K/Rac1, estrogen via REA displacement), while its fused alpha-kinase domain autophosphorylates, transphosphorylates TRPM7, and interacts with regulatory proteins (RACK1, REA, MsrB1, uromodulin) to modulate channel gating and surface expression; loss-of-function mutations cause hereditary hypomagnesemia with secondary hypocalcemia in humans, and complete knockout in mice additionally causes embryonic lethality and neural tube defects.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"TRPM6 is a bifunctional channel-kinase that serves as the principal gatekeeper of transcellular Mg²⁺ absorption in the intestine and Mg²⁺ reabsorption in the renal distal convoluted tubule, with additional non-redundant roles in neural tube closure and circadian blood pressure regulation. The channel pore, whose divalent cation selectivity is determined by glutamate residues E1024 and E1029 in the selectivity filter, conducts Mg²⁺ and Ca²⁺ and is gated by intracellular Mg²⁺, PIP₂, and Mg·ATP; TRPM6 predominantly functions at the cell surface as a heteromer with TRPM7, which confers physiologically appropriate Mg·ATP insensitivity, while the fused C-terminal α-kinase domain autophosphorylates, transphosphorylates TRPM7, and scaffolds regulatory proteins including RACK1, REA, MsrB1, and uromodulin to modulate channel trafficking and gating [PMID:14576148, PMID:14976260, PMID:24385424, PMID:16636202, PMID:30139743]. Channel surface abundance is dynamically controlled by EGF/Src/Rac1, insulin/PI3K/Rac1, and estrogen signaling pathways, and uromodulin stabilizes apical TRPM6 by impairing dynamin-dependent endocytosis [PMID:19073827, PMID:22733750, PMID:19329436, PMID:30139743]. Loss-of-function mutations in TRPM6 cause autosomal-recessive hypomagnesemia with secondary hypocalcemia in humans, and complete knockout in mice causes embryonic lethality with neural tube defects [PMID:12032568, PMID:12032570, PMID:19692351].\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Positional cloning resolved the genetic basis of hypomagnesemia with secondary hypocalcemia (HSH), establishing that TRPM6 mutations are causative and that the gene is expressed in intestinal and renal epithelia critical for Mg²⁺ homeostasis.\",\n      \"evidence\": \"Positional cloning and mutation analysis in HSH families, expression profiling in two independent studies\",\n      \"pmids\": [\"12032568\", \"12032570\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Channel properties unknown\", \"Subcellular localization not resolved\", \"Mechanism by which loss causes hypocalcemia unclear\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Immunolocalization and electrophysiology established that TRPM6 resides at the apical membrane of DCT and intestinal brush border and forms a Mg²⁺/Ca²⁺-permeable cation channel with strong intracellular Mg²⁺ sensitivity, directly linking the genetic finding to a defined ion transport mechanism.\",\n      \"evidence\": \"Immunolocalization in kidney and intestine, whole-cell patch clamp of heterologously expressed TRPM6\",\n      \"pmids\": [\"14576148\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether TRPM6 functions as a homomer or heteromer in vivo unknown\", \"Pore determinants of selectivity unresolved\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"The discovery that TRPM6 requires TRPM7 for surface expression and forms TRPM6/TRPM7 heteromers—disrupted by the HSH-causing S141L mutation—provided a cell biological explanation for the disease and established heteromerization as the physiologically relevant channel configuration.\",\n      \"evidence\": \"Co-immunoprecipitation, confocal microscopy, and electrophysiology in HEK293 and Xenopus oocytes\",\n      \"pmids\": [\"14976260\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether TRPM6 can form functional homomeric channels remained debated\", \"Stoichiometry of heteromeric complex unknown\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Functional non-redundancy of TRPM6 and TRPM7 was demonstrated: TRPM6 cannot complement TRPM7-deficient cells, and TRPM6 cross-phosphorylates TRPM7 but not vice versa, establishing an asymmetric kinase relationship.\",\n      \"evidence\": \"Genetic complementation in TRPM7-deficient DT40 cells, phosphothreonine-specific antibody detection\",\n      \"pmids\": [\"16150690\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequences of TRPM6→TRPM7 transphosphorylation unknown\", \"Sites of transphosphorylation not mapped\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Biophysical characterization revealed that TRPM6 homomers have distinct conductance, pharmacology (2-APB activation), and pH sensitivity from TRPM7, while pore-region mutations (P1017R) act dominant-negatively on TRPM7, defining the channel pore as a critical functional locus.\",\n      \"evidence\": \"Single-channel recordings, pharmacological profiling, pore mutagenesis with electrophysiology and FRET in multiple expression systems\",\n      \"pmids\": [\"16636202\", \"17197439\", \"17098283\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of pore selectivity not resolved at atomic level\", \"Relative contribution of homomers vs. heteromers in native tissue unknown\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Mutagenesis of pore glutamates E1024 and E1029 defined the molecular determinants of divalent cation permeation and pH-dependent potentiation, converting the channel to monovalent selectivity upon neutralization.\",\n      \"evidence\": \"Site-directed mutagenesis with whole-cell patch clamp and ion substitution\",\n      \"pmids\": [\"17599911\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No high-resolution pore structure available\", \"How pore residues contribute to Mg²⁺ vs. Ca²⁺ discrimination at physiological levels not fully resolved\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Multiple regulatory mechanisms converging on the α-kinase domain were uncovered: RACK1 inhibits channel activity through kinase-dependent T1851 autophosphorylation; massive autophosphorylation of a Ser/Thr-rich region controls substrate recognition; and myosin II heavy chains were identified as shared kinase substrates with TRPM7.\",\n      \"evidence\": \"Co-immunoprecipitation, patch clamp with siRNA and mutagenesis (RACK1); MS-based phosphomapping and deletion mutagenesis (autophosphorylation); in vitro kinase assay with MS (myosin substrates)\",\n      \"pmids\": [\"18258429\", \"18365021\", \"18675813\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological relevance of myosin phosphorylation by TRPM6 in epithelial Mg²⁺ transport not tested\", \"How RACK1 inhibition integrates with other regulatory inputs unclear\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"EGF receptor signaling was shown to specifically increase TRPM6 surface abundance and channel activity via Src and Rac1, independent of kinase domain activity, establishing a hormonal pathway for regulated Mg²⁺ reabsorption.\",\n      \"evidence\": \"Patch clamp, FRAP, surface biotinylation with pharmacological and dominant-negative Rac1 constructs\",\n      \"pmids\": [\"19073827\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct phosphorylation targets linking Rac1 to TRPM6 trafficking unknown\", \"Whether EGF acts in vivo on DCT TRPM6 not directly tested\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Two new regulatory axes were identified: REA inhibits TRPM6 in a kinase-dependent manner and is displaced by estradiol (linking sex hormones to Mg²⁺ handling), while Trpm6 knockout mice revealed embryonic lethality and neural tube defects, demonstrating developmental functions beyond ion homeostasis.\",\n      \"evidence\": \"Ras recruitment system, patch clamp, estradiol treatment (REA); global Trpm6 knockout mouse embryonic phenotyping (NTDs)\",\n      \"pmids\": [\"19329436\", \"19692351\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which TRPM6 regulates neural tube closure not identified\", \"Whether estrogen-TRPM6 axis operates in vivo in kidney/intestine unresolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"MsrB1 was identified as a redox-responsive regulator that protects TRPM6 channel activity from oxidative inhibition by reducing Met1755, linking oxidative stress to Mg²⁺ transport.\",\n      \"evidence\": \"Ras recruitment system, patch clamp, M1755A mutagenesis, H₂O₂ treatment\",\n      \"pmids\": [\"20584906\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether oxidative regulation of TRPM6 is physiologically relevant in DCT or intestine not tested in vivo\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"PIP₂ was established as an essential gating cofactor for TRPM6, with basic residues in the TRP domain mediating PIP₂-dependent activation, adding lipid signaling to the regulatory framework.\",\n      \"evidence\": \"Multiple PIP₂ depletion strategies (PLC, 5-phosphatase, Ci-VSP), patch clamp, TRP domain mutagenesis\",\n      \"pmids\": [\"22180838\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct PIP₂ binding to TRPM6 not demonstrated by structural or biophysical methods\", \"Contribution of PIP₂ regulation in heteromeric TRPM6/7 context not assessed\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Insulin was shown to stimulate TRPM6 via PI3K/Rac1-mediated surface trafficking, and specific TRPM6 variants (V1393I, K1584E) that abolish insulin responsiveness were linked to gestational diabetes, connecting channel regulation to metabolic disease.\",\n      \"evidence\": \"Patch clamp, TIRF microscopy, PI3K/Rac1 inhibition, mutagenesis, clinical association\",\n      \"pmids\": [\"22733750\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Causal relationship between TRPM6 variants and diabetes not established by Mendelian genetics\", \"Identity of kinases phosphorylating T1391 and S1583 not determined\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"The physiological rationale for TRPM6/TRPM7 heteromerization was clarified: TRPM6 relieves TRPM7 from Mg·ATP inhibition through its kinase domain, while TRPM7 tunes TRPM6's extreme Mg²⁺ sensitivity, yielding constitutively active channels at physiological ion concentrations; separately, the kinase dimerization motif was shown to be essential for both kinase and channel activity.\",\n      \"evidence\": \"Patch clamp with kinase-dead mutants and intracellular ion manipulation; dimerization motif mutagenesis with peptide rescue and in vitro kinase assay\",\n      \"pmids\": [\"24385424\", \"24650431\", \"24858416\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and architecture of the heteromeric complex not structurally resolved\", \"How kinase dimerization controls the channel pore conformationally is unknown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Studies in primary cells from TRPM6- and TRPM7-knockout mice confirmed that the heteromeric channel is the physiologically active species in epithelial cells, while mass spectrometry mapped transphosphorylation sites on TRPM7 and identified phosphomimetic substitutions that inactivate TRPM7 kinase, and Xenopus studies demonstrated TRPM6's non-redundant role in radial intercalation during neural tube closure.\",\n      \"evidence\": \"Patch clamp on primary knockout cells; MS phosphomapping with mutagenesis; Xenopus morpholino knockdown with live imaging\",\n      \"pmids\": [\"28821869\", \"28220887\", \"29142255\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How TRPM6 governs cell intercalation movements mechanistically is unknown\", \"Whether transphosphorylation of TRPM7 occurs in vivo in DCT\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Uromodulin was identified as an extracellular stabilizer of apical TRPM6 that impairs dynamin-dependent endocytosis, with Umod⁻/⁻ mice showing reduced DCT TRPM6 and Mg²⁺ wasting, establishing a paracrine/extracellular regulatory axis.\",\n      \"evidence\": \"Co-immunoprecipitation, surface biotinylation, patch clamp, dynamin inhibition, Umod⁻/⁻ mouse model\",\n      \"pmids\": [\"30139743\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Binding interface between uromodulin and TRPM6 extracellular domains not mapped\", \"Whether uromodulin acts on heteromeric TRPM6/7 specifically not tested\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Transcriptional control of TRPM6 was established: Prox-1 deletion in the DCT causes hypomagnesemia with loss of TRPM6 expression, identifying a critical upstream transcription factor.\",\n      \"evidence\": \"DCT-specific Prox-1 conditional knockout mice with RT-qPCR and immunohistochemistry\",\n      \"pmids\": [\"33200256\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Prox-1 directly binds the Trpm6 promoter not shown\", \"Other transcription factors cooperating with Prox-1 not identified\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Kidney-specific TRPM6 deletion revealed an unexpected role in circadian blood pressure regulation through control of renin secretion and β-adrenoreceptor expression in renin-secreting cells, extending TRPM6 function beyond Mg²⁺ transport.\",\n      \"evidence\": \"Kidney-specific conditional knockout mice, blood pressure telemetry, renin secretion assay, β-adrenoreceptor pharmacology\",\n      \"pmids\": [\"34140503\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism linking DCT Mg²⁺ transport to renin-secreting cell β-adrenoreceptor expression unknown\", \"Whether this is a direct or Mg²⁺-mediated effect not distinguished\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Intestine-specific TRPM6 knockout with ²⁵Mg isotope tracing definitively proved that TRPM6 is essential for active intestinal Mg²⁺ absorption and cannot be compensated by other transporters despite compensatory upregulation of renal Trpm6, Trpm7, and Slc41a3.\",\n      \"evidence\": \"Intestine-specific Trpm6 knockout mice, ²⁵Mg²⁺ isotope absorption, RNA-seq\",\n      \"pmids\": [\"39266724\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether compensatory renal upregulation is sufficient long-term not assessed\", \"Role of intestinal TRPM6 in Ca²⁺ absorption not evaluated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"No high-resolution structure of TRPM6 (homomeric or heteromeric with TRPM7) has been reported, leaving the structural basis of heteromeric assembly, pore selectivity, kinase-channel coupling, and the mechanism by which TRPM6 controls neural tube closure and renin secretion unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No cryo-EM or crystal structure of full-length TRPM6 or TRPM6/7 heteromer\", \"Mechanism linking TRPM6 to neural tube closure cell movements unknown\", \"Signal from DCT TRPM6 to juxtaglomerular renin cells not identified\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [1, 3, 5, 6, 7, 14]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [8, 9, 10, 17, 20]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [9, 10, 20]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 2, 11, 15, 24]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0382551\", \"supporting_discovery_ids\": [0, 1, 15, 31]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [11, 12, 15]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [21, 22]}\n    ],\n    \"complexes\": [\n      \"TRPM6/TRPM7 heteromeric channel\"\n    ],\n    \"partners\": [\n      \"TRPM7\",\n      \"RACK1\",\n      \"REA\",\n      \"MsrB1\",\n      \"UMOD\",\n      \"RAC1\",\n      \"P2X4\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}