ACTIVATION OF TYPE-I PROTEIN-KINASE-A DURING RECEPTOR-MEDIATED HUMAN T-LYMPHOCYTE ACTIVATION

The experiments reported herein have characterized the signaling pathw ay leading to stimulation of type I protein kinase A isozyme (PKA-I) a ctivity during the early events of Ag receptor-mediated T cell activat ion, Inhibitor studies demonstrated that receptor-initiated activation of nonreceptor protein tyrosine kinases, phosphorylation and activati on of phospholipase C-gamma l, and activation of protein kinase C occu r temporally and precede PKA-I activation, Bypass of both the TCR/CD3 complex and IL-1R and direct activation of protein kinase C by a phorb ol ester can also activate PKA-I. To confirm that PKA-I activation via the TCR/CD3 complex and IL-1R requires antecedent protein tyrosine ki nase-catalyzed phosphorylation of phospholipase C-gamma 1, we used wil d-type and CD45-deficient (mutant J45.01) jurkat T cell lines. Unlike wild-type jurkat T cells, the absence of CD45 tyrosine phosphatase res ulted in the failure of receptor-mediated activation of PKA-I activity and of IL-2 mRNA transcription in the mutant J45.01 Jurkat cell line. In conclusion, our data support the concept that a signal derived fro m ligand binding to both the TCR/CD3 complex and IL-1R receptor mediat es rapid activation of the PKA-I isozyme in primary T lymphocytes by s equential activation of an intracellular pathway comprised of CD45 pho sphatase/protein tyrosine kinase/polyphosphoinositide/Ca2+/protein kin ase C pathway rather than via the conventional surface receptor/stimul atory C protein system.