The cytoplasmic domains of a β1 integrin mediate polarization in Madin-Darby canine kidney cells by selective basolateral stabilization

In Madin-Darby canine kidney cells, newly synthesized apical and basolateral membrane proteins are gen erally transported directly to their respective cell surface domain due to targeting determinants that mediate sorting in the Golgi complex. In several basolateral membrane proteins, these targeting determinants reside in the cytoplasmic domains. We show here that basolateral expression of the human alpha(5)beta(1) integrin in stably transfected Madin-Darby canine kidney cells is also mediated by the cytoplasmic domains. Distinct regions in both cytoplasmic domains were found to be sufficient to mediate basolateral expression independently from one another. Unexpectedly, newly synthesized wild-type alpha(5)beta(1) and basolaterally expressed chimeras containing the cytoplasmic domain of either alpha(5) or beta(1) were integrated into both cell surface domains, preferentially apically, during biosynthesis, The apical pools of wild-type integrin and chimeric subunits were found to become quickly degraded, whereas the basolateral pools were stabilized. Thus, the cytoplasmic domains of the alpha(5)beta(1) integrin are independently sufficient to mediate sorting by selective basolateral stabilization.