S. Biffo et al., ISOLATION OF A NOVEL BETA(4) INTEGRIN-BINDING PROTEIN (P27(BBP)) EXPRESSED IN EPITHELIAL-CELLS, The Journal of biological chemistry, 272(48), 1997, pp. 30314-30321
The integrin beta(4) has a long cytodomain necessary for hemidesmosome
formation. A yeast two-hybrid screen using beta(4) cytodomain uncover
ed a protein called p27(BBP) that represents a beta(4) interactor. Bot
h in yeast and in vitro, p27(BBP) binds the two NH2-terminal fibronect
in type III modules of beta(4), a region required for signaling and he
midesmosome formation, Sequence analysis of p27(BBP) revealed that p27
(BBP) was not previously known and has no homology with any isolated m
ammalian protein, bat 85% identical to a yeast gene product of unknown
function, Expression studies by Northern analysis and in situ hybridi
zation showed that, in vivo, p27(BBP) mRNA is highly expressed in epit
helia and proliferating embryonic epithelial cells, An antibody raised
against p27(BBP) COOH-terminal domain showed that all beta(4)-contain
ing epithelial cell lines expressed p27(BBP). The p27(BBP) protein is
insoluble and present in the intermediate filament pool, Furthermore,
subcellular fractionation indicated the presence of p27(BBP) both in t
he cytoplasm and in the nucleus, Confocal analysis of cultured cells s
howed that part of p27(BBP) immunoreactivity was both nuclear and in t
he membrane closely apposed to beta(4). These results suggest that the
p27(BBP) is an in vivo interactor of beta(4), possibly linking beta(4
) to the intermediate filament cytoskeleton.