MTMR7

MTMR7 is a myotubularin-family 3-phosphatase that dephosphorylates phosphatidylinositol 3-phosphate and the soluble inositol substrate Ins(1,3)P2, with a distinctive preference for the water-soluble substrate, and that broadly restrains proliferative and survival signaling by lowering cellular phosphoinositide levels (PMID:12890864, PMID:27409167). Catalytic output is set by complex formation with the inactive paralog MTMR9: MTMR9 binds MTMR7 through coiled-coil/CC-domain interactions and enhances its phosphatase activity, and the reconstituted complex acts on both PI(3)P and PI(3,5)P2 (PMID:12890864, PMID:22647598, PMID:39614773). Through this lipid-phosphatase activity MTMR7 functions as a negative regulator of PI3K/AKT signaling in diverse cell types, suppressing AKT phosphorylation and proliferation in T cells, myoblasts, spermatogonial stem cells, and colorectal cancer cells, where it also dampens insulin-driven ERK1/2 signaling (PMID:23630283, PMID:27409167, PMID:28153733, PMID:31478454). MTMR7 is recruited via direct STIM1 binding to ER–plasma membrane contact sites, where its catalytic activity alters local PI(3,5)P2 and PI(4,5)P2 to promote ORAI1 fast inactivation and limit store-operated Ca2+ entry (PMID:40327889, PMID:42004029). Beyond its phosphatase function, MTMR7 acts through its charged coiled-coil domain to directly bind and inhibit K-RAS (including the G12V mutant), reducing RAS GTPase activity and downstream ERK1/2 signaling (PMID:38462034), complexes with PPARγ to enhance its transcriptional activity by blocking ERK1/2-dependent PPARγ phosphorylation (PMID:32522977), suppresses VSMC phenotypic switching via dephosphorylation and dissociation of p62 from mTORC1 (PMID:38342025), inhibits PASMC proliferation through an ERK1/2→STAT3 axis (PMID:39918745), and promotes FLNB ubiquitination and degradation to restrain β-catenin signaling in spermatogonial stem cells (PMID:40638605).

1. 2003 High

   Establishing MTMR7's enzymatic identity answered what biochemical reaction it catalyzes, defining it as a 3-phosphatase with an unusual preference for a soluble inositol substrate distinct from other MTM members.

   Evidence In vitro phosphatase assay with recombinant MTMR7 on PI3P and Ins(1,3)P2

   PMID:12890864

   Open questions at the time

   • Physiological relevance of soluble Ins(1,3)P2 dephosphorylation versus lipid dephosphorylation in cells not resolved
   • No structural basis for substrate preference
2. 2003 High

   Identifying MTMR9 as a binding partner answered how MTMR7 catalytic activity is regulated, showing the inactive paralog acts as an activating subunit via its coiled-coil domain.

   Evidence Anti-MTMR7 Co-IP with mass-spec identification, domain mapping, and in vitro activity assay in N1E-115 cells

   PMID:12890864

   Open questions at the time

   • Stoichiometry of the complex not defined here
   • How MTMR9 binding alters active-site chemistry unknown
3. 2012 High

   Reconstituting the complex answered which lipid substrates MTMR7/MTMR9 acts on, extending activity to PI(3,5)P2 and confirming MTMR9 modulates both specificity and rate.

   Evidence In vitro phosphatase assays with recombinant complexes and cellular PIP measurement

   PMID:22647598

   Open questions at the time

   • Quantitative fold-changes focused on other MTMR/R9 pairs
   • In vivo substrate prioritization unresolved
4. 2013 Medium

   Loss-of-function in T cells answered whether MTMR7 has a cellular signaling role, establishing it as a negative regulator of AKT controlling T-helper lineage decisions.

   Evidence shRNA knockdown with T-cell differentiation assay and phospho-AKT readout

   PMID:23630283

   Open questions at the time

   • Direct link between phosphatase activity and AKT suppression not isolated
   • Single lab, no catalytic-dead rescue
5. 2017 Medium

   Knockdown across colorectal cancer cells, myoblasts, and stem cells answered whether AKT suppression is a general MTMR7 function, showing it restrains proliferation by lowering phosphoinositides in multiple lineages.

   Evidence Overexpression/knockdown in CRC and C2C12 cells with PIP quantification, AKT/ERK1/2 immunoblotting, and proliferation assays

   PMID:27409167 PMID:28153733

   Open questions at the time

   • Causality between specific lipid pools and each signaling output not dissected
   • Differentiation effects mechanistically separate from proliferation effects unclear
6. 2019 Medium

   In vivo testis knockdown answered whether MTMR7 governs stem-cell homeostasis, showing it maintains spermatogonial stem cells by inhibiting PI3K/AKT.

   Evidence Morpholino knockdown in neonatal mouse testis and SSC culture with proliferation and PI3K/AKT analysis

   PMID:31478454

   Open questions at the time

   • Phosphatase-dependence not tested by catalytic mutant
   • Long-term spermatogenesis consequences not assessed
7. 2020 Medium

   Discovery of the PPARγ interaction answered whether MTMR7 has phosphatase-independent functions, revealing a CC-domain-dependent role enhancing PPARγ transcription by blocking ERK1/2-mediated phosphorylation.

   Evidence Co-IP, PPARγ reporter assays, CC peptide treatment in mice, and docking simulations

   PMID:32522977

   Open questions at the time

   • Direct versus indirect effect on ERK1/2 not separated from lipid activity
   • Single lab
8. 2024 Medium

   Direct K-RAS inhibition answered how MTMR7 suppresses oncogenic RAS signaling, defining the charged CC domain as a binding module that reduces RAS GTPase activity even for the G12V mutant.

   Evidence Co-IP, molecular modeling, RAS GTPase assays, ERK1/2 immunoblotting, and CC-peptide tumor models in mice

   PMID:38462034

   Open questions at the time

   • High-resolution structure of the MTMR7-CC/K-RAS interface lacking
   • Relationship between CC binding and lipid-phosphatase function unresolved
9. 2024 Medium

   VSMC and CC-domain studies answered how MTMR7 controls cell phenotype beyond AKT, linking it to mTORC1 inhibition via p62 dephosphorylation and providing structural detail on CC oligomerization.

   Evidence Mtmr7-transgenic carotid injury model, mTORC1/p62 Co-IP and glycolysis assays with rescue; biophysical CC-domain oligomerization analysis

   PMID:38342025 PMID:39614773

   Open questions at the time

   • Whether p62 dephosphorylation is direct MTMR7 catalysis not shown
   • CC oligomerization measured in isolation, not in full-length complex
10. 2025 Medium

    STIM1 interaction and FLNB/STAT3 studies answered how MTMR7 is spatially targeted and what additional effectors it controls, placing it at the ER as a STIM1 partner and linking it to FLNB degradation/β-catenin and an ERK1/2→STAT3 axis.

    Evidence Yeast two-hybrid, Co-IP and imaging for STIM1; MS/Co-IP/ubiquitination for FLNB in human SSCs; transgenic PH model with epistasis for ERK1/2/STAT3 in PASMCs

    PMID:39918745 PMID:40327889 PMID:40638605

    Open questions at the time

    • Mechanism of FLNB ubiquitination (E3 partner) unidentified
    • How STIM1 recruitment integrates with cytosolic signaling roles unclear
11. 2026 High

    Functional dissection at ER-PM contact sites answered how MTMR7 connects phosphoinositide turnover to calcium signaling, showing STIM1-anchored MTMR7 tunes local PI(3,5)P2/PI(4,5)P2 to promote ORAI1 inactivation and limit SOCE.

    Evidence Phosphatase-dead and STIM1-interaction-disruption mutants, PM lipid measurement, and electrophysiology/SOCE assays

    PMID:42004029

    Open questions at the time

    • Quantitative contribution of MTMR7 to physiological Ca2+ responses in tissue not established
    • Interplay between STIM1-anchored and cytosolic MTMR7 pools unresolved

• Whether MTMR7's lipid-phosphatase activity and its phosphatase-independent CC-domain protein interactions (K-RAS, PPARγ, STIM1) operate as a single integrated mechanism or as separable functions remains unresolved.
• No unified structural model of full-length MTMR7
• No genetic separation-of-function across all reported effectors in one system
• No Mendelian disease association established in the corpus