CNIH4

CNIH4 is an ER-resident cargo-sorting receptor that couples transmembrane cargo to the COPII machinery for ER-to-Golgi export (PMID:24405750). It localizes to the early secretory pathway, binds Class 3 GPCRs, and co-immunoprecipitates with the COPII coat components Sec23 and Sec24, recruiting GPCRs into COPII vesicles; both overexpression and knockdown cause intracellular receptor retention, and low-level CNIH4 rescues surface expression of a trafficking-defective β2-adrenergic receptor, indicating that an optimal CNIH4 level is required for export (PMID:24405750). As a member of the cornichon family, CNIH4 also functions in the biogenesis and secretion of the EGFR ligand TGFα, acting within a TMED9-dependent loop that promotes colon cancer metastasis (PMID:31253868) and amplifying TGFα secretion to drive EGFR–AKT–ERK signaling in hepatocellular carcinoma (PMID:39885395). Across cancer contexts CNIH4 is a transcriptional and post-transcriptional node: FOXM1 directly binds the CNIH4 enhancer to activate its transcription in response to macrophage-derived glutamine in oral squamous cell carcinoma (PMID:41715179), its protein levels are raised by a circUCK2-driven miR-149-5p sponge (PMID:39885395), and it suppresses ferroptosis in cervical cancer by upregulating SLC7A11 to boost cystine import, glutathione synthesis, and GPX4 activity (PMID:37716418). CNIH4 is dispensable for fertility in mice, where loss is buffered by compensatory upregulation of Cnih3 (PMID:36657507).

1. 2014 High

   Established CNIH4's core molecular function: whether the cornichon homologue acts in cargo export was unknown, and this work showed it is an ER cargo-sorting receptor linking GPCRs to the COPII coat.

   Evidence BRET interaction screen, reciprocal Co-IP with Sec23/Sec24, knockdown/overexpression trafficking assays and mutant receptor rescue in cultured cells

   PMID:24405750

   Open questions at the time

   • No structure of the CNIH4–cargo or CNIH4–COPII interface
   • Cargo selectivity beyond Class 3 GPCRs not defined
   • Stoichiometry and regulation of the optimal expression level unresolved
2. 2019 Medium

   Extended CNIH4's cargo repertoire to TGFα and linked it to disease: it was unclear whether CNIH4 contributes to growth-factor secretion, and epistasis placed it in a TMED9/TGFα/GLI1 feedback loop driving colon cancer metastasis.

   Evidence RNAi knockdown, migration rescue and transcriptional/epistasis analysis in colon cancer cell lines

   PMID:31253868

   Open questions at the time

   • CNIH4's direct role in TGFα export inferred, not biochemically reconstituted
   • Mechanism of TMED9/TMED3 antagonism on CNIH4 unclear
   • Relationship between TGFα export and the COPII function from 2014 not directly connected
3. 2023 Medium

   Defined a redox/metabolic role: whether CNIH4 influences cell death was unknown, and this work showed it suppresses ferroptosis through SLC7A11-dependent cystine import.

   Evidence Lentiviral gain/loss-of-function, ferroptosis and viability assays, transcriptomics and SLC7A11 knockdown epistasis in cervical cancer cells

   PMID:37716418

   Open questions at the time

   • No reconstitution of how CNIH4 regulates SLC7A11
   • Unclear whether the effect requires CNIH4 trafficking activity
   • Single lab, single cancer context
4. 2023 Medium

   Tested physiological essentiality: it was unknown whether CNIH4 is required in vivo, and a knockout showed it is dispensable for fertility owing to cornichon-family redundancy.

   Evidence Cnih4 knockout mice with histology, sperm analysis, fertility testing and detection of compensatory Cnih3 upregulation

   PMID:36657507

   Open questions at the time

   • Phenotypes outside the reproductive system not examined
   • Extent of Cnih3 functional substitution not quantified at the molecular level
   • No tissue-specific or compound knockout
5. 2025 Medium

   Resolved post-transcriptional control of CNIH4: it was unclear how CNIH4 levels are elevated in tumors, and a circUCK2/miR-149-5p sponge axis was shown to raise CNIH4 and feed TGFα–EGFR–AKT/ERK signaling.

   Evidence RIP, RNA pulldown, dual luciferase, CRISPR-Cas9, polysome fractionation and medium transfer in hepatocellular carcinoma cells

   PMID:39885395

   Open questions at the time

   • CNIH4's direct TGFα-secretion step not reconstituted here
   • Generality of the circUCK2 axis beyond HCC unknown
   • Quantitative contribution of CNIH4 versus other miR-149-5p targets unclear
6. 2026 Medium

   Resolved transcriptional control of CNIH4: how CNIH4 is induced by the tumor microenvironment was unknown, and FOXM1 was shown to bind the CNIH4 enhancer in response to macrophage-derived glutamine.

   Evidence ChIP-qPCR for FOXM1 and H3K27ac, SLC38A5 knockdown, conditioned-medium transfer and FOXM1-knockdown rescue by CNIH4 in oral squamous cell carcinoma

   PMID:41715179

   Open questions at the time

   • Whether glutamine acts solely through FOXM1 is not established
   • Connection between FOXM1-driven CNIH4 and its trafficking/secretory output not shown
   • Single lab, no independent replication

• How CNIH4's biochemical cargo-export activity mechanistically connects to its downstream effects on TGFα/EGFR signaling, ferroptosis suppression via SLC7A11, and metastasis remains unresolved.
• No reconstitution linking COPII-dependent cargo sorting to the cancer phenotypes
• Whether SLC7A11 is a trafficking cargo of CNIH4 untested
• No structural basis for cargo selectivity