Assembly of a membrane receptor complex: roles of the uroplakin II prosequence in regulating uroplakin bacterial receptor oligomerization.
The apical surface of the mammalian urothelium is almost completely covered by two-dimensional protein crystals (known as urothelial plaques) of hexagonally packed 16 nm particles consisting of two UP (uroplakin) heterodimers, i.e. UPs Ia/II and Ib/III pairs. UPs are functionally important as they contribute to the urothelial permeability barrier function, and UPIa may serve as the receptor for the uropathogenic Escherichia coli that causes over 90% of urinary tract infections. We study here how the UP proteins are assembled and targeted to the urothelial apical surface, paying special attention to the roles of the prosequence of UPII in UP oligomerization. We show that (i) the formation of the UPIa/UPII heterodimer, necessary for ER (endoplasmic reticulum) exit, requires disulfide formation in the prosequence domain of proUPII (the immature form of UPII still containing its prosequence); (ii) differentiation-dependent N-glycosylation of the prosequence leads to UP stabilization; (iii) a failure to form tetramers in cultured urothelial cells, in part due to altered glycosylation of the prosequence, may block two-dimensional crystal formation; and (iv) the prosequence of UPII remains attached to the mature protein complex on the urothelial apical surface even after it has been cleaved by the trans-Golgi-network-associated furin. Our results indicate that proper secondary modifications of the prosequence of UPII play important roles in regulating the oligomerization and function of the UP protein complex.
Hu
Chih-Chi Andrew
CC
Department of Pharmacology, New York University School of Medicine, New York, NY 10016, USA.
Bachmann
Thomas
T
Zhou
Ge
G
Liang
Feng-Xia
FX
Ghiso
Jorge
J
Kreibich
Gert
G
Sun
Tung-Tien
TT
D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019556:COS Cells; D002417:Cattle; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D019281:Dimerization; D006031:Glycosylation; D008565:Membrane Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D008954:Models, Biological; D008969:Molecular Sequence Data; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D060170:Uroplakin II; D019459:Urothelium / Q000166:cytology / Q000378:metabolism
D000911:Antibodies, Monoclonal; D001426:Bacterial Proteins; D008565:Membrane Proteins; D060170:Uroplakin II