ISOLATION AND ANALYSIS OF A T-CELL CLONE VARIANT EXHIBITING CONSTITUTIVELY PHOSPHORYLATED SER(133) CAMP RESPONSE ELEMENT-BINDING PROTEIN

In driving T cell proliferation, IL-2 stimulates a new program of gene expression that includes proliferating cell nuclear antigen (PCNA), a requisite processivity factor for DNA polymerase delta. PCNA transcri ption is regulated in part through tandem CRE sequences in the promote r and CRE binding proteins; IL-2 stimulates CREB phosphorylation in th e resting cloned T lymphocyte, L2. After culturing L2 cells for greate r than 91 days, we consistently isolate a stable variant that exhibits constitutive CREB phosphorylation, L2 and L2 variant cells were teste d for IL-2 responsiveness and rapamycin sensitivity with respect to sp ecific kinase activity, PCNA expression and proliferation. In L2 cells , IL-2 stimulated and rapamycin inhibited the following: cAMP-independ ent CREB kinase activity, PCNA expression and proliferation. In L2 var iant cells, CREB kinase activity was constitutively high; IL-2 stimula ted and rapamycin blocked PCNA expression and proliferation. These res ults indicate that IL-2 induces a rapamycin-sensitive, cAMP-independen t CREB kinase activity in L2 cells. However, phosphorylation of CREB a lone is not sufficient to drive PCNA expression and L2 cell proliferat ion in the absence of IL-2.