Plays a role in the transport of cargos that are too large to fit into COPII-coated vesicles and require specific mechanisms to be incorporated into membrane-bound carriers and exported from the endoplasmic reticulum ( , ). Plays a role in the secretion of lipoproteins, pre-chylomicrons and pre-VLDLs, by participating in their export from the endoplasmic reticulum . Thereby, may play a role in cholesterol and triglyceride homeostasis (By similarity). Required for collagen VII (COL7A1) secretion by loading COL7A1 into transport carriers and recruiting PREB/SEC12 at the endoplasmic reticulum exit sites ( ).
Subcellular locations: Endoplasmic reticulum membrane
Localizes to endoplasmic reticulum exit sites (ERES), also known as transitional endoplasmic reticulum (tER).
Highly expressed in liver and weakly in testis. Expression was higher in patients with severe fibrosis or inflammation and chronic hepatitis . Isoform 1 is specifically expressed in lung, testis, small intestine, colon, pancreas, kidney, liver and prostate . Isoform 8 is expressed only in testis (at the protein level). Isoform 8 (at protein level) and isoform 9 are expressed in cutaneous T-cell lymphoma (CTCL) cell lines, colorectal carcinomas, breast carcinomas and melanoma. Isoform 9, but not isoform 5A, is expressed in head and neck squamous cell carcinoma .