THE ROLE OF PHOSPHORYLATION IN MODULATING BETA(1) INTEGRIN LOCALIZATION

The beta(1)-integrin subunit localizes to focal contacts during F9 ter atocarcinoma stem cell differentiation to parietal endoderm. Concomita ntly, this integrin subunit becomes dephosphorylated at serine 790, th e only serine in the well-conserved cytoplasmic domain of beta(1). We hypothesized that this dephosphorylation is required for this subunit to move to a focal contact. To test this, we transfected F9 stem cells with distinct cDNAs encoding three forms of chicken beta(1): the wild type, and two site-specific mutants possessing amino acid substitution s at residue 790 which included methionine and aspartate. The negative ly charged aspartate was selected to mimic the phosphorylated serine f ound at position 790 in the wildtype protein but in a form that cannot be dephosphorylated upon differentiation. The chicken beta(1) subunit s heterodimerized with endogenous mouse alpha subunits and, using a ch icken beta(1)-specific monoclonal antibody, we examined movements of t hese chimeric integrins to focal contacts using immunofluorescence mic roscopy. The chimeric integrins possessing either the wildtype or meth ionine mutant beta(1) subunits localized to focal contacts upon F9 dif ferentiation. In contrast, the aspartate chimeric integrins failed to localize. These data suggest that the dephosphorylation of serine 790 is required for the beta(1) subunit to localize to focal contacts duri ng F9 differentiation. (C) 1996 Academic Press, Inc.