Role of membrane proteins in permeability barrier function: uroplakin ablation elevates urothelial permeability.
Although water, small nonelectrolytes, and gases are freely permeable through most biological membranes, apical membranes of certain barrier epithelia exhibit extremely low permeabilities to these substances. The role of integral membrane proteins in this barrier function has been unclear. To study this problem, we have ablated the mouse gene encoding uroplakin III (UPIII), one of the major protein subunits in urothelial apical membranes, and measured the permeabilities of these membranes. Ablation of the UPIII gene greatly diminishes the amounts of uroplakins on the apical urothelial membrane (Hu P, Deng FM, Liang FX, Hu CM, Auerbach AB, Shapiro E, Wu XR, Kachar B, and Sun TT. J Cell Biol 151: 961-972, 2000). Our results indicate that normal mouse urothelium exhibits high transepithelial resistance and low urea and water permeabilities. The UPIII-deficient urothelium exhibits a normal transepithelial resistance (normal 2,024 +/- 122, knockout 2,322 +/- 114 Omega. cm(2); P > 0.5). However, the UPIII-deficient apical membrane has a significantly elevated water permeability (normal 0.91 +/- 0.06, knockout 1.83 +/- 0.14 cm/s x 10(-5); P < 0.05). The urea permeability of the UPIII-deficient membrane also increased, although to a lesser extent (normal 2.22 +/- 0.24, knockout 2.93 +/- 0.31 cm/s x 10(-6); P = 0.12). These results indicate that reduced targeting of uroplakins to the apical membrane does not significantly alter the tight junctional barrier but does double the water permeability. We provide the first demonstration that integral membrane proteins contribute to the apical membrane permeability barrier function of urothelium.
Hu
Ping
P
Ronald O. Perelman Department of Dermatology, Kaplan Comprehensive Cancer Center, New York University School of Medicine, New York, NY 10016, USA.
Meyers
Susan
S
Liang
Feng-Xia
FX
Deng
Fang-Ming
FM
Kachar
Bechara
B
Zeidel
Mark L
ML
Sun
Tung-Tien
TT
D000818:Animals; D002463:Cell Membrane Permeability / Q000187:drug effects*; D007668:Kidney / Q000502:physiology; D008562:Membrane Glycoproteins / Q000235:genetics / Q000502:physiology*; D008565:Membrane Proteins / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout / Q000235:genetics; D008854:Microscopy, Electron; D008855:Microscopy, Electron, Scanning; D012016:Reference Values; D001743:Urinary Bladder / Q000033:anatomy & histology / Q000378:metabolism* / Q000648:ultrastructure; D060171:Uroplakin III; D019459:Urothelium / Q000378:metabolism
D008562:Membrane Glycoproteins; D008565:Membrane Proteins; C554661:Upk3a protein, mouse; D060171:Uroplakin III