Dissection of T cell antigen receptor signaling using protein tyrosine kinase inhibitors.

T cell antigen receptor (TcR) recognition of appropriately presented antigen results in the rapid activation of protein tyrosine kinases. Subsequent events include activation of protein kinase C and increased intracellular free calcium which lead to the activation of transcription factors involved in regulating interleukin-2 gene expression. We have assayed the ability of a panel of protein tyrosine kinase (PTK) inhibitors to interfere with activation of the NF-AT transcription factor by TcR ligation or treatment with phorbol ester and calcium ionophore which bypass many of the early events of TcR signal transduction. The results indicate that PTK are involved in early and late stages of TcR signaling. Moreover, one inhibitor (genistein) revealed the existence of a PTK which down-regulates specifically calcium-mediated signaling at a point downstream of the PTK p56lck but upstream of calcium mobilization.