STIMULATION OF TYROSINE PHOSPHORYLATION OF DISTINCT PROTEINS IN RESPONSE TO ANTIBODY-MEDIATED LIGATION AND CLUSTERING OF ALPHA(3) AND ALPHA(6) INTEGRINS

The interaction of cells with components of the extracellular matrix: through their integrin receptors results in the stimulation of tyrosin e phosphorylation of several proteins, suggesting that these receptors play a key role in signal transduction. Here we report that antibody- mediated ligation and clustering of alpha(3) beta(1) and alpha(6) beta (1)/alpha(6) beta(4) integrins resulted in the stimulation of tyrosine phosphorylation of proteins that are specific for each heterodimer. T hus, ligation and clustering of the alpha(3) beta(1) integrin on human prostate carcinoma cells (PC-3) and human umbilical vein endothelial cells (HUVEC) with anti-alpha(3) antibodies resulted in the stimulatio n of tyrosine phosphorylation of a 55 kDa protein, In contrast, ligati on and clustering of the alpha(6) beta(1) integrin on these cells with anti-alpha(6) antibody resulted in the dramatic stimulation of tyrosi ne phosphorylation of a 90 kDa protein in addition to a 52 kDa protein , and ligation and clustering of alpha(5) beta(1) on HUVEC did not res ult in the apparent stimulation of tyrosine phosphorylation of any pro teins, Clustering with anti-beta(1) antibodies triggered the tyrosine phosphorylation of all of these proteins, whereas ligation and cluster ing of PC-3 cells with an anti-beta(4) antibody resulted in the tyrosi ne phosphorylation of a distinct 62 kDa protein, Since the PC-3 cells express both alpha(6) beta(1) and alpha(6) beta(4), these data suggest that these two receptors can transduce distinct signals, All of the p hosphorylations could be inhibited by treating the cells with Genistei n, a tyrosine kinase inhibitor, Antibody-mediated ligation and cluster ing of integrins on the two types of cells did not result in the stimu lation of tyrosine phosphorylation of pp125 focal adhesion kinase, alt hough this was observed upon cell attachment and spreading on fibronec tin, laminin and anti-alpha(3) monoclonal antibody, Collectively, thes e data demonstrate that cross-linking of different integrin heterodime rs can stimulate tyrosine kinase activities, leading to the phosphoryl ation of distinct proteins, which are also different from those observ ed when cells are allowed to spread on a matrix.