Cytotoxic T lymphocytes express a β₃ integrin which can induce the phosphorylation of focal adhesion kinase and the related PYK‐2

Fibronectin has been shown to stimulate tyrosine phosphorylation of a number of proteins in the 115–125 kDa range and facilitate degranulation by alloantigen‐specific cytotoxic T lymphocyte (CTL) clones in response to substimulatory amounts of anti‐CD3 or anti‐T cell receptor (TCR). The current study was initiated to further characterize integrin expression and usage by these CTL clones. We demonstrate that vitronectin and fibrinogen, but not laminin or collagen, are also able to both facilitate degranulation in the presence of substimulatory anti‐CD3 and stimulate tyrosine phosphorylation of these 115–125‐kDa proteins, with a 115‐kDa protein being the most prominently phosphorylated. These results implicate the expression and usage of the vitronectin receptor, α β 3 integrin, by these CTL clones. We demonstrate by both flow cytometry and immunoprecipitation that CTL clones do in fact express β 3 integrin. Immobilized antibody to β 3 stimulates the phosphorylation of the 115–125‐kDa proteins, suggesting that engagement of β 3 transmits the same signal into these cells as fibronectin or vitronectin. The fibronectin and vitronectin‐induced phosphorylation as well as adhesion to either fibronectin or vitronectin can be significantly inhibited with antibodies to β 3 integrins. Finally, we are able to immunoprecipitate 115‐kDa proteins with antiserum to focal adhesion kinase and a related kinase, called PYK‐2, that becomes phosphorylated in response to vitronectin or immobilized anti‐β 3 . Taken together, these results demonstrate that CTL express and use β 3 ‐integrins as signaling molecules which can augment TCR‐mediated stimulation.