ENTR1

ENTR1 (SDCCAG3) is a multifunctional trafficking and protein-stability regulator that operates at the primary cilium, in metabolic and immune signaling, and in cancer cell metabolism (PMID:27767179, PMID:40058593). At the ciliary basal body it interacts with the intraflagellar transport protein IFT88 through its N-terminus and is required for normal ciliary length, ciliation, and the ciliary delivery of the membrane protein polycystin-2 (PMID:27767179); it acts within a DLG1-dependent pathway, forming a complex with IFT20 that associates with DLG1 to control ciliary trafficking of polycystin-2, a pathway disrupted by a CAKUT-associated DLG1 variant (PMID:38849673, PMID:37987012). In metabolism, ENTR1 binds PPARγ and enhances its abundance, stabilizing PPARγ by antagonizing SMURF1-mediated ubiquitin-proteasome degradation within a reciprocal feedback loop that drives adipogenesis, with adipose-specific loss causing pathological adipose expansion and metabolic dysfunction (PMID:38810405, PMID:40058593). ENTR1 also acts as a positive regulator of innate signaling: it interacts with AMPK and enhances its activating phosphorylation to suppress macrophage M1 polarization (PMID:40054733), and it stabilizes mitochondrial MAVS by suppressing NIX-mediated mitophagy to sustain type I interferon responses and restrict viral replication (PMID:41494271). A recurring theme across these roles is control of partner protein stability and intracellular localization.

1. 2016 Medium

   Established ENTR1/SDCCAG3 as a basal-body component required for ciliogenesis and selective ciliary cargo delivery, answering whether the protein has a defined role at the cilium.

   Evidence Immunofluorescence localization, siRNA knockdown with ciliary quantification, and reciprocal Co-IP/domain mapping with IFT88 in cultured cells

   PMID:27767179

   Open questions at the time

   • Mechanism by which the SDCCAG3-IFT88 interaction promotes polycystin-2 trafficking not resolved
   • Single-lab Co-IP without orthogonal interaction validation
   • No structural detail of the N-terminus/TPR-repeat contact
2. 2024 High

   Placed SDCCAG3 within an upstream-to-downstream trafficking hierarchy, showing DLG1 governs SDCCAG3/IFT20/polycystin-2 ciliary delivery and linking the pathway to disease via a CAKUT variant.

   Evidence Conditional Dlg1 knockout mouse, BioID proximity proteomics, Co-IP, AlphaFold modelling, and genetic rescue with DLG1 wild-type vs variant

   PMID:37987012 PMID:38849673

   Open questions at the time

   • SDCCAG3-DLG1 association shown only as indirect/at least partially indirect
   • Direct molecular bridge between the SDCCAG3-IFT20 complex and DLG1 not defined
3. 2024 Medium

   Identified a metabolic role by showing ENTR1 binds PPARγ and enhances its expression to drive adipogenic differentiation, and demonstrated druggability.

   Evidence Co-IP, bidirectional gain/loss-of-function in BMSCs with lipid droplet staining, and a small-molecule ENTR1 ligand tested in a hyperlipidemia mouse model

   PMID:38810405

   Open questions at the time

   • Mechanism by which both gain and loss of function enhance lipid droplet formation not reconciled
   • Direct vs indirect nature of PPARγ regulation not resolved at this stage
4. 2025 Medium

   Defined the molecular basis of ENTR1-PPARγ regulation as stabilization against SMURF1-dependent degradation within a reciprocal feedback loop, advancing from correlation to mechanism.

   Evidence Adipose-specific conditional knockout and overexpression mice on high-fat diet, PPARγ ubiquitination/degradation Western blots, SDCCAG3-SMURF1-PPARγ Co-IP, and transcriptional assays

   PMID:40058593

   Open questions at the time

   • Whether ENTR1 acts as a direct SMURF1 competitor or scaffold not established
   • Single-lab mechanism
5. 2025 Medium

   Extended ENTR1 to inflammatory signaling by showing it interacts with AMPK and enhances its activating phosphorylation to suppress macrophage M1 polarization and bone loss.

   Evidence Co-IP, AMPK phosphorylation Westerns, overexpression/knockdown in macrophages, Compound C epistasis, and a ligature-induced periodontitis mouse model

   PMID:40054733

   Open questions at the time

   • How ENTR1 binding enhances AMPK phosphorylation mechanistically unknown
   • Direct vs indirect kinase activation not distinguished
6. 2025 Medium

   Established an antiviral role by showing ENTR1 stabilizes mitochondrial MAVS through suppression of NIX-mediated mitophagy to sustain type I interferon responses.

   Evidence ENTR1 knockout cells, BPIV3/VSV infection assays, mitophagy flux readouts, and NIX-knockdown epistasis rescue of MAVS levels and viral titers

   PMID:41494271

   Open questions at the time

   • How ENTR1 restrains NIX accumulation on mitochondria not defined
   • Single-lab loss-of-function model
7. 2025 Low

   Linked ENTR1 to cancer cell metabolism, showing its loss reduces colon cancer proliferation and glycolytic enzyme expression.

   Evidence CRISPR knockout in HCT-116 cells with proliferation assays and glycolytic enzyme Westerns

   PMID:40462015

   Open questions at the time

   • No mechanistic pathway placement beyond enzyme expression change
   • Single cell line, single lab
   • Whether the glycolytic effect is direct or downstream of another ENTR1 function unknown

• Whether ENTR1's diverse roles (ciliary trafficking, PPARγ/AMPK regulation, MAVS stabilization, glycolysis) reflect a single unifying biochemical activity remains unresolved.
• No defined enzymatic or core biochemical activity shared across functions
• No structural model of the protein
• Tissue-specific determinants of which pathway ENTR1 engages are unknown