TMEM237

TMEM237 is a transmembrane protein of the ciliary transition zone (TZ) that maintains TZ architecture, ciliogenesis, and Wnt signaling control, with loss-of-function producing defective ciliogenesis and deregulated Wnt signaling across mammalian, zebrafish, and C. elegans models (PMID:22152675). Within the TZ, TMEM237 functions in the MKS module: its proper TZ localization requires RPGRIP1L/MKS5 (PMID:22152675), it is recruited within an intermediate TZ subdomain layer organized by TMEM107 (PMID:26595381), and it genetically interacts with NPHP4 and other MKS-module components to control basal body–TZ membrane anchoring (PMID:22152675). A splice-site variant causing exon skipping establishes TMEM237 loss-of-function as a cause of Joubert syndrome (PMID:34839509). Beyond the cilium, TMEM237 has context-specific roles: in intestinal epithelium it binds and stabilizes the riboflavin transporter RFVT-3 to promote riboflavin uptake (PMID:30892938), and under HIF-1α–driven hypoxia—where HIF-1α transactivates its promoter—it interacts with NPHP1 to strengthen the NPHP1–Pyk2 interaction and drive Pyk2/ERK1/2 phosphorylation, promoting hepatocellular carcinoma proliferation, migration, invasion, and EMT (PMID:37041420). In the retina, TMEM237 localizes to photoreceptor outer segments and the outer-segment plasma membrane, where it associates with cytoskeletal and motor proteins (PMID:20375344, PMID:33933680).

1. 2011 High

   Established TMEM237 as a transition-zone protein whose loss disrupts ciliogenesis and Wnt signaling, and placed it epistatically within the MKS/NPHP TZ network downstream of RPGRIP1L/MKS5.

   Evidence Immunofluorescence localization plus loss-of-function in mammalian cells; C. elegans genetic epistasis with nphp-4 and MKS-module genes; RPGRIP1L knockdown; zebrafish morpholino

   PMID:22152675

   Open questions at the time

   • Molecular mechanism by which TMEM237 maintains the diffusion barrier is not defined
   • Direct physical (vs. genetic) interactions among TZ components not mapped
   • How TMEM237 loss deregulates Wnt mechanistically is unresolved
2. 2015 High

   Resolved where TMEM237 sits in TZ subdomain architecture, showing TMEM107 organizes its recruitment to an intermediate MKS-module layer.

   Evidence C. elegans genetics and super-resolution fluorescence localization of TZ proteins in tmem-107 mutants, with mammalian validation

   PMID:26595381

   Open questions at the time

   • Direct binding interface between TMEM107 and TMEM237 not characterized
   • Stoichiometry and assembly order of the full MKS module remain incomplete
3. 2010 Medium

   Demonstrated a retinal localization for TMEM237 (photoreceptor outer segments, ciliary complex, horizontal cells) and catalogued candidate cytoskeletal/motor interactors.

   Evidence Immunohistochemistry, immunoelectron microscopy, and Co-IP/mass spectrometry in mouse retina

   PMID:20375344

   Open questions at the time

   • Co-IP/MS interactors (vimentin, actin, myosins, kinesin 1, lamin B-1) lack reciprocal validation
   • Functional consequence of motor-protein association is untested
4. 2019 High

   Revealed a non-ciliary function: TMEM237 binds and stabilizes the intestinal riboflavin transporter RFVT-3 to regulate vitamin uptake.

   Evidence Yeast two-hybrid, reciprocal co-IP in HuTu-80 cells, confocal colocalization, siRNA knockdown with riboflavin uptake assay, and protein half-life assay

   PMID:30892938

   Open questions at the time

   • Mechanism of RFVT-3 stabilization (e.g., trafficking vs. degradation protection) not defined
   • Whether this function depends on TMEM237 transmembrane topology is unknown
5. 2021 Medium

   Confirmed TMEM237 as a unique component of the photoreceptor outer-segment plasma membrane and a disease-causing splicing target in Joubert syndrome.

   Evidence Label-free quantitative MS / protein correlation profiling of OS plasma membrane; RT-PCR on patient RNA demonstrating exon skipping from a splice-site variant

   PMID:33933680 PMID:34839509

   Open questions at the time

   • OS plasma-membrane function of TMEM237 is not established
   • Patient/splicing evidence is from a single family
6. 2023 High

   Defined a hypoxia-driven oncogenic axis: HIF-1α transactivates TMEM237, which binds NPHP1 to potentiate NPHP1–Pyk2 coupling and Pyk2/ERK1/2 signaling driving hepatocellular carcinoma progression.

   Evidence ChIP and luciferase reporter assays, IP-MS, Co-IP, and gain/loss-of-function in vitro and in mouse tumor models

   PMID:37041420

   Open questions at the time

   • Whether this signaling role requires ciliary localization is unclear
   • Structural basis of TMEM237 enhancement of NPHP1–Pyk2 binding unknown
7. 2025 Medium

   Linked TMEM237/Wnt function to neuronal maintenance, showing its loss sensitizes dopaminergic neurons to toxicant-induced degeneration.

   Evidence RNAi knockdown of the Drosophila ortholog CG14186, DGRP association with DA neuron viability, and Wnt-pathway perturbation

   PMID:40644377

   Open questions at the time

   • Direct relevance to mammalian neurodegeneration untested
   • Mechanistic link between TMEM237, Wnt, and DA neuron survival not resolved

• How TMEM237's distinct activities—TZ barrier maintenance, RFVT-3 stabilization, and NPHP1/Pyk2 signaling—relate to a single biochemical function remains unknown.
• No structural model or defined molecular activity for TMEM237
• Whether ciliary and non-ciliary roles share a common mechanism is undetermined