TMEM147

TMEM147 is an ER- and nuclear envelope-resident multi-pass transmembrane protein that functions in membrane protein biogenesis, cholesterol homeostasis, and ER/nuclear envelope organization. It is a core subunit of the Nicalin-NOMO complex, assembled hierarchically with Nicalin stabilizing both NOMO and TMEM147, and participates in the ribosome-bound TMCO1 translocon complex to facilitate co-translational insertion of nascent multi-pass membrane proteins (PMID:20538592, PMID:36044892). TMEM147 anchors lamin B receptor (LBR) at the inner nuclear membrane via the LBR sterol-reductase domain, physically interacts with DHCR7, and regulates cholesterol biosynthesis; its loss causes LBR mislocalization, reduced DHCR7 levels, altered cholesterol/cholesteryl ester profiles, ER expansion toward flat sheets, and accelerated protein degradation through the autophagy-lysosomal pathway (PMID:32694168, PMID:34638576, PMID:36044892). Bi-allelic loss-of-function variants in TMEM147 cause syndromic intellectual disability with pseudo-Pelger-Huët anomaly (PMID:36044892).

1. 2010 High

   Identification of TMEM147 as a novel stable subunit of the ER-resident Nicalin-NOMO complex established it as a participant in a gamma-secretase-like assembly, revealing that the complex has a previously unrecognized third component whose stability depends on Nicalin.

   Evidence Affinity purification/mass spectrometry, reciprocal co-IP, and siRNA/overexpression in cultured cells

   PMID:20538592

   Open questions at the time

   • Enzymatic or signaling activity of the Nicalin-NOMO-TMEM147 complex remains undefined
   • Substrates or client proteins of the complex are unknown
   • Structural basis of hierarchical assembly not resolved
2. 2020 High

   Demonstrating that TMEM147 physically interacts with LBR and DHCR7 and is required for LBR inner nuclear membrane retention and cholesterol homeostasis connected an ER transmembrane protein to sterol metabolism and nuclear envelope organization.

   Evidence Co-IP, domain-deletion mapping, siRNA silencing, lipidomics, and immunofluorescence in HeLa cells

   PMID:32694168

   Open questions at the time

   • Whether TMEM147 directly chaperones LBR insertion or acts indirectly through complex formation is unresolved
   • How TMEM147 loss reduces DHCR7 transcription is not mechanistically explained
   • Relative contributions of LBR mislocalization versus DHCR7 loss to cholesterol phenotype are unclear
3. 2021 Medium

   Showing that TMEM147 depletion causes ER expansion toward flat sheets and reduced DNA condensation linked TMEM147 to ER morphology control and chromatin organization, extending its role beyond protein complex stability.

   Evidence siRNA knockdown with quantitative immunofluorescence of CLIMP-63 and RTN4 ER markers

   PMID:34638576

   Open questions at the time

   • Causal chain between ER sheet expansion and chromatin decondensation is not established
   • Whether ER shape change is secondary to LBR loss or an independent TMEM147 function is unclear
   • Pathway enrichment analysis is partly computational and not functionally validated
4. 2022 High

   Discovery that bi-allelic TMEM147 loss-of-function variants cause syndromic intellectual disability with pseudo-Pelger-Huët anomaly, together with evidence that TMEM147 participates in the TMCO1 translocon and that its loss accelerates autophagy-lysosomal protein degradation, established TMEM147 as essential for multi-pass membrane protein biogenesis in humans.

   Evidence Patient-derived fibroblasts, in silico structural modeling of translocon assembly, protein degradation assays, neutrophil morphology, immunofluorescence

   PMID:36044892

   Open questions at the time

   • Direct biochemical reconstitution of TMEM147 within the TMCO1 translocon is lacking
   • Specific client proteins whose biogenesis depends on TMEM147-translocon function are not catalogued
   • Neuronal-specific mechanisms underlying intellectual disability are unexplored
5. 2023 Medium

   Demonstrating that TMEM147 promotes DHCR7 expression via STAT2 transcriptional activation and that the resulting cholesterol/27-hydroxycholesterol axis confers ferroptosis resistance and drives macrophage M2 polarization in hepatocellular carcinoma extended TMEM147's cholesterol-regulatory role to tumor immune evasion.

   Evidence Co-IP/MS, RNA-seq, lipidomics, ferroptosis assays, flow cytometry, and in vivo xenograft models in HCC cells

   PMID:37891677

   Open questions at the time

   • Mechanism by which TMEM147 enhances STAT2 transcriptional activity is not defined
   • Whether the TMEM147-DHCR7-27HC axis operates outside HCC contexts is unknown
   • Single-lab study; independent replication in additional tumor types needed

• Key unresolved questions include the precise structural organization of TMEM147 within both the Nicalin-NOMO complex and the TMCO1 translocon, the identity of specific client proteins whose biogenesis depends on TMEM147, and how TMEM147 loss in neurons produces intellectual disability.
• No high-resolution structure of TMEM147 in any complex context
• Full client/substrate repertoire of TMEM147-containing translocon undefined
• Tissue-specific functions in brain and hematopoietic lineages not characterized