YIPF6

YIPF6 is a five-transmembrane Golgi protein that controls secretory granule biogenesis, cargo sorting in the early secretory pathway, and Golgi membrane homeostasis. It forms stable complexes with YIPF1 and YIPF2 in the medial-/trans-Golgi and is required for their protein stability, while also interacting with TVP23B to maintain the Golgi glycosylation enzyme complement needed for proper mucin glycosylation and Paneth cell antimicrobial peptide secretion (PMID:28286305, PMID:37339972). In the endoplasmic reticulum, YIPF6 binds FGF21 to restrict its loading into COPII vesicles, thereby limiting FGF21 secretion; loss of YIPF6 elevates circulating FGF21 and protects mice from diet-induced metabolic syndrome in an FGF21-dependent manner (PMID:31289229). Yipf6-null mice exhibit defective large secretory granule formation in intestinal Paneth and goblet cells, leading to impaired antimicrobial secretion and spontaneous intestinal inflammation (PMID:22802641).

1. 2006 Medium

   Establishing the ancestral pathway context: yeast homologs of YIPF6-family proteins were shown to physically associate with TVP23-family proteins at the late Golgi and to function genetically in the Ypt6/Rab6 pathway, placing the Yip1/TVP23 module in Golgi-to-endosome trafficking.

   Evidence Co-IP plus synthetic-lethal genetic epistasis with ypt6/ric1 in yeast

   PMID:17178117

   Open questions at the time

   • Mammalian YIPF6–TVP23B interaction not yet demonstrated at this time
   • Precise cargo or membrane trafficking step controlled by the module was undefined
2. 2012 High

   A forward genetic screen revealed that YIPF6 is essential for the biogenesis and secretion of large secretory granules in intestinal Paneth and goblet cells, linking it to mucosal defense and demonstrating that its loss causes spontaneous intestinal inflammation.

   Evidence ENU-derived Yipf6-null mice analyzed by electron microscopy, immunocytochemistry, DSS colitis challenge

   PMID:22802641

   Open questions at the time

   • Whether the granule defect reflects a Golgi sorting, maturation, or trafficking failure was unresolved
   • Direct protein partners of YIPF6 were unknown
3. 2016 Medium

   Determination of YIPF6 membrane topology and pan-Golgi distribution clarified that it spans the Golgi membrane five times with a cytosolic N-terminus and lumenal C-terminus, and that its depletion alters Golgi morphology.

   Evidence Protease-accessibility topology assay, immunofluorescence, siRNA knockdown in cultured cells

   PMID:27999994

   Open questions at the time

   • Single-study topology determination; no structural data
   • Which Golgi functions depend on YIPF6 remained unclear
4. 2017 Medium

   Identification of YIPF1 and YIPF2 as stable Golgi-resident binding partners of YIPF6 showed that YIPF6 is required for their stability and Golgi retention, and that free YIPF6 can dominantly interfere with post-BFA Golgi reassembly, establishing YIPF6 as a scaffold within YIPF-family complexes.

   Evidence Reciprocal co-IP, siRNA knockdown with protein-level readout, BFA washout Golgi reassembly assay

   PMID:28286305

   Open questions at the time

   • Stoichiometry and structural basis of the YIPF6–YIPF1/YIPF2 complexes unknown
   • How these complexes relate to secretory granule formation was not addressed
5. 2017 Medium

   Overexpression studies in prostate cancer cells demonstrated that YIPF6 can suppress proliferation and enhance extracellular vesicle secretion, extending its role beyond conventional secretory granules to broader vesicular trafficking.

   Evidence Stable overexpression and siRNA in 22Rv1 cells; proliferation, colony formation, NTA, and EV proteomics

   PMID:28144969

   Open questions at the time

   • Single cancer cell line; generalizability to other cell types uncertain
   • Mechanism connecting YIPF6 to EV biogenesis versus conventional secretion not delineated
6. 2019 High

   YIPF6 was found to act as a cargo-selective gatekeeper in the ER, binding FGF21 and restricting its loading into COPII vesicles; genetic epistasis proved that the metabolic protection observed in Yipf6-mutant mice depends entirely on elevated FGF21 secretion.

   Evidence Co-IP of YIPF6–FGF21 in ER fraction, hepatocyte secretion assay, liver-specific FGF21 knockout epistasis, high-fat diet metabolic phenotyping

   PMID:31289229

   Open questions at the time

   • Whether YIPF6 acts as a direct retention receptor or an indirect sorting factor for FGF21 is unresolved
   • Other ER-to-Golgi cargo regulated by YIPF6 not identified
7. 2023 High

   Physical interaction between YIPF6 and TVP23B was demonstrated, and Golgi proteomics of their respective knockout colonocytes converged on a shared loss of glycosylation enzymes, unifying the secretory granule and glycosylation defects into a common Golgi quality-control mechanism for intestinal homeostasis.

   Evidence Co-IP of YIPF6–TVP23B, Golgi proteomics from YIPF6- and TVP23B-deficient mouse colonocytes, intestinal phenotyping

   PMID:37339972

   Open questions at the time

   • How the YIPF6–TVP23B complex retains glycosylation enzymes in the Golgi is mechanistically undefined
   • Relationship between the YIPF6–YIPF1/2 and YIPF6–TVP23B complexes (overlapping or distinct) is unknown

• The structural basis for YIPF6 complex assembly, how it discriminates between ER and Golgi cargo, and whether it functions as a direct retention receptor versus a trafficking adaptor remain open questions.
• No high-resolution structure of YIPF6 or any of its complexes
• Full repertoire of ER-exit and Golgi-resident cargo regulated by YIPF6 is unknown
• Mechanism by which the YIPF6–TVP23B complex maintains Golgi glycosylation enzyme composition is undefined