TMEM74

TMEM74 is a multi-pass transmembrane protein that acts as a positive regulator of autophagy and, independently, modulates apoptosis and neuronal excitability (PMID:18294959, PMID:29048433, PMID:30886335). Localized to lysosomes and autophagosomes, its overexpression drives autophagic vacuolization and LC3-II accumulation, while its loss abolishes starvation-induced autophagy (PMID:18294959). Mechanistically, TMEM74 increases autophagic flux by physically interacting with the autophagy machinery components ATG16L1 and ATG9A, doing so independently of the BECN1/PI3KC3 complex and ULK1; it is itself degraded through autophagy, defining a self-limiting loop, and this activity promotes tumor cell survival under metabolic stress (PMID:29048433). TMEM74 also restrains apoptosis: it co-localizes with and binds the pro-apoptotic protein BIK through a direct TM domain–BH3 domain interaction, and this inhibition of BIK-induced apoptosis is at least partly autophagy-independent (PMID:28412412). In the nervous system, TMEM74 couples with HCN1 channels to support their surface expression and sustain hyperpolarization-activated Ih current, suppressing pyramidal neuron excitability via its TM1 domain; loss of Tmem74 in prefrontal cortical neurons disrupts PL→dorsal-striatum and PL→BLA circuit activity to produce autism- and anxiety-like behaviors (PMID:30886335, PMID:36690791).

1. 2008 Medium

   Established TMEM74 as an autophagy-active transmembrane protein by localizing it to lysosomes/autophagosomes and showing both gain- and loss-of-function effects on LC3 conversion.

   Evidence Subcellular localization, GFP-LC3/MDC assays, LC3-II immunoblot, wortmannin inhibition and siRNA knockdown in HeLa cells

   PMID:18294959

   Open questions at the time

   • No binding partners or molecular mechanism identified
   • Single-lab characterization
2. 2009 Medium

   Independently confirmed TMEM74 as an autophagy-inducing gene in an unbiased functional screen, reducing the chance the earlier effect was an overexpression artifact.

   Evidence High-throughput GFP-LC3 cell-based functional screen with cDNA library cotransfection

   PMID:19029833

   Open questions at the time

   • Screen readout only; no mechanism for TMEM74 specifically
   • Does not address endogenous physiological role
3. 2017 High

   Defined how TMEM74 engages the autophagy machinery, showing it binds ATG16L1 and ATG9A and induces flux bypassing the canonical BECN1/PI3KC3 and ULK1 steps.

   Evidence Reciprocal Co-IP, autophagic flux assays, pharmacological inhibitors, and knockdown across multiple tumor cell lines

   PMID:29048433

   Open questions at the time

   • Structural basis of ATG16L1/ATG9A binding unresolved
   • Mechanism of TMEM74 self-degradation not detailed
4. 2017 High

   Identified a distinct anti-apoptotic function via direct TMEM74 TM domain–BIK BH3 domain interaction, separating apoptosis suppression from the autophagy role.

   Evidence Co-IP, fluorescence co-localization, TM-deletion mutants, and autophagosome-formation inhibitor in cell lines

   PMID:28412412

   Open questions at the time

   • Quantitative contribution of autophagy-dependent vs -independent inhibition unclear
   • No structural model of the TM–BH3 interface
5. 2019 High

   Revealed an unanticipated neuronal function in which TMEM74 couples with HCN1 to control Ih current and excitability, linking the protein to behavior.

   Evidence Tmem74-/- and BLA-targeted knockdown, whole-cell Ih electrophysiology, HCN1 surface-expression assay, TM1 mutant, viral rescue, behavioral assays in mice

   PMID:30886335

   Open questions at the time

   • Whether TMEM74 binds HCN1 directly is not established
   • Connection between autophagy/apoptosis roles and HCN1 regulation unknown
6. 2023 High

   Mapped TMEM74-dependent prefrontal circuits, showing distinct PL→dSTR and PL→BLA projections separately mediate autism- and anxiety-like behaviors.

   Evidence Conditional/global knockout, optogenetics, DREADD chemogenetics, excitability recordings, viral rescue, and behavioral assays

   PMID:36690791

   Open questions at the time

   • Molecular effector linking TMEM74 loss to PL PN hyperexcitability not pinned to HCN1 here
   • Human relevance of the autism-like phenotype untested
7. 2026 Low

   Placed TMEM74 as a candidate downstream effector of SIRT7-mediated H3K79 desuccinylation governing autophagy and survival in granulosa cells.

   Evidence siRNA knockdown, autophagy-marker immunoblot, viability/apoptosis assays, and transcriptomics in goat ovarian granulosa cells

   PMID:42061017

   Open questions at the time

   • Single-method knockdown with limited mechanistic follow-up; TMEM74 is a candidate, not the focus
   • Direct regulation of TMEM74 by SIRT7 not demonstrated
   • Not validated in mammalian/human cells

• How TMEM74's autophagy-promoting, apoptosis-inhibiting, and HCN1-coupling activities are mechanistically integrated within a single transmembrane protein remains unresolved.
• No structural data on TMEM74 or its membrane topology
• Whether HCN1 trafficking depends on autophagy is unknown
• No reported human disease-causing mutation