Rab27b is associated with fusiform vesicles and may be involved in targeting uroplakins to urothelial apical membranes.
The terminally differentiated umbrella cells of bladder epithelium contain unique cytoplasmic organelles, the fusiform vesicles, which deliver preassembled crystalline arrays of uroplakin proteins to the apical cell surface of urothelial umbrella cells. We have investigated the possible role of Rab proteins in this delivery process, and found Rab27b to be expressed at an extraordinary high level (0.1% of total protein) in urothelium, whereas Rab27b levels were greatly reduced (to <5% of normal urothelium) in cultured urothelial cells, which synthesized only small amounts of uroplakins and failed to form fusiform vesicles. Immuno-electron microscopy showed that Rab27b was associated with the cytoplasmic face of the fusiform vesicles, but not with that of the apical plasma membrane. The association of Rab27b with fusiform vesicles and its differentiation-dependent expression suggest that this Rab protein plays a role in regulating the delivery of fusiform vesicles to the apical plasma membrane of umbrella cells.
Chen
Yanru
Y
Department of Cell Biology, New York University School of Medicine, 550 First Avenue, New York, NY 10016, USA.
Guo
Xuemei
X
Deng
Fang-Ming
FM
Liang
Feng-Xia
FX
Sun
Wenyu
W
Ren
Mindong
M
Izumi
Tetsuro
T
Sabatini
David D
DD
Sun
Tung-Tien
TT
Kreibich
Gert
G
D000818:Animals; D001483:Base Sequence; D001693:Biological Transport, Active; D002417:Cattle; D002478:Cells, Cultured; D018076:DNA, Complementary / Q000235:genetics; D015536:Down-Regulation; D006367:HeLa Cells; D006801:Humans; D008562:Membrane Glycoproteins / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D019459:Urothelium / Q000166:cytology / Q000378:metabolism*; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D000075745:rab27 GTP-Binding Proteins
D018076:DNA, Complementary; D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D000075745:rab27 GTP-Binding Proteins; C512958:Rab27b protein, mouse; C066694:RAB27A protein, human; C512960:Rab27B protein, human; C512962:Rab27a protein, mouse; D020691:rab GTP-Binding Proteins