Camp dependent protein kinase activity in IL2-stimulated T lymphocytes

Interieukin 2 stimulates a new program of gene expression which drives T lymphocytes through the cell cycle. Proliferating cell nuclear antigen (PCNA) functions as a requisite processivity factor for DNA porymerase. PCNA expression is regulated transcriptionally in part though tandem CRE sequences in the promoter and CRE binding proteins. IL2 stimulates CREB phosphorylation in T lymphocytes. The most commonly identified mechanism for CREB phosphorylation is through the cAMP dependent protein kinase, PKA. Therefore, we examined PKA activity in the cloned T lymphocyte L2 following IL2 stimulation. Using a radioactive assay method with the phosphate receptor LRRASLG as a substrate, we observed an increase during the first six hours of stimulation followed by a decrease at the time of entry into S phase. A second ELISA-based assay system employing the phosphate receptor RRRVTSAARRS as a substrate yielded results that showed both a small early and larger late rise in PKA levels throughout the 48 hour time period assayed. The ELISA-based assay conditions employed revealed that most of the PKA was in an inactive form at the time of harvest and that all enzyme activity was inhibited by Pl6-22 a PKA specific inhibitor. However, the radioactive assay method showed a much higher level of PKA in an active form which was also inhibited by the Pl6-22. The different results obtained with the two assay systems suggest that there are two cAMP-inducible enzymes phosphorylating the peptide substrates which account for the activities in IL2-stimulated T cell lysates.