Mammalian uroplakins. A group of highly conserved urothelial differentiation-related membrane proteins (original) (raw)

1994, Journal of Biological Chemistry

The asymmetric unit membrane (AUM) forms the apical plaques of mammalian urothelium and is believed to play a role in strengthening the urothelial apical surface thus preventing the cells from rupturing during bladder distention. W e have shown previously that purified bovine GUMS contain four major integral membrane proteins: the uroplakins Ia (27 m a) , Ib (28 ma), I1 (16 ma), and I11 (47 m a). This contradicts some previous reports indicating that some of these proteins are absent in AUMs of several species. Using an improved procedure, we isolated AUMs from, in addition to cattle, eight mammalian species (human, monkey, sheep, pig, dog, rabbit, rat, and mouse). The AUMs of these species appear morphologically similar bearing crystalline patches of 12-nm protein particles with a center-to-center spacing of 16.6 nm. Using antibodies raised against synthetic oligopeptides or individual bovine uroplakins, we established by immunoblotting that the four uroplakins are present in AUMs of all these species. The DNA-deduced amino acid sequences of bovine and mouse uroplakin I1 revealed 83% identity. These results indicate that uroplakins la, Ib, 11, and I11 are the mGor protein components of probably all mammalian urothelial plaques, and that the sequence and three-dimensional structure of uroplakin molecules are highly conserved during mammalian evolution. Ultrastructural studies have established that mammalian urothelia elaborate a highly specialized plasma membrane during an advanced stage of cellular differentiation. This membrane forms numerous rigid-looking plaques covering the apical surface of the urothelium. They exhibit a thickened luminal leaflet (8 nm) and a regular looking cytoplasmic leaflet (4 nm), hence the term asymmetric unit membrane (AUM)' (Porter and Bonneville, 1963; Hicks, 1965; Koss, 1969). Negative staining of plaques purified from several species revealed densely packed, hexagonal protein particles (12 nm in diameter) that form crystalline patches associated with the outer leaflet of the * T h s work was supported in part by National Institutes of Health Grants DK39753, DK47529, and AR39749 (to T.-T. S.), Grant 31-30129.90 from the Swiss National Science Foundation (to U. A.), a predoctoral fellowship from the Roche Research Foundation (to T. W.), Education of the Kanton Basel-Stadt. The computing was supported by the M. E. Muller Foundation of Switzerland, and the Department of National Science Foundation Grant DIR-8908095. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "aduertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.