期刊
JOURNAL OF CELL SCIENCE
卷 119, 期 24, 页码 5077-5086出版社
COMPANY BIOLOGISTS LTD
DOI: 10.1242/jcs.03285
关键词
uroplakins; tetraspanins; endoplasmic reticulum; membrane proteins
类别
资金
- NIDDK NIH HHS [DK52206, DK39753] Funding Source: Medline
The surface of the mammalian urinary bladder is covered by a crystalline, asymmetric unit membrane (AUM) structure that contains the four major uroplakins (UPs): Ia, Ib, II and IIIa. UPIa and UPIb belong to the family of tetraspanins. Although UPIa and UPIb are structurally conserved, only UPIb could exit from the endoplasmic reticulum (ER) and reach the cell surface when expressed alone in 293T cells. Modifications of the large extracellular loop of UPIb, such as mutation of the N-glycosylation site or the cysteines involved in the formation of three disulfide bridges, or exchanging the large luminal loop of UPIb with that of UPIa did not affect the ability of UPIb to reach the cell surface. However, modifications of any of the four transmembrane domains of UPIb led to ER retention, suggesting that the proper formation of helical bundles consisting of the tetraspanin transmembrane domains is a prerequisite for UPIb to exit from the ER. Results of sedimentation analysis suggested that aggregate formation is a mechanism for ER retention.
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