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Isolation and Analysis of a T Cell Clone Variant Exhibiting Constitutively Phosphorylated Ser¹³³ cAMP Response Element-Binding Protein¹

Stanley M. Belkowski^*, Charles S. Rubin and Michael B. Prystowsky^2,*

Departments of ^* Pathology and Pharmacology, Albert Einstein College of Medicine, Bronx, NY 10461

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 . PCNA transcription is regulated in part through tandem CRE sequences in the promoter and CRE binding proteins; IL-2 stimulates CREB phosphorylation in the resting cloned T lymphocyte, L2. After culturing L2 cells for greater than 91 days, we consistently isolate a stable variant that exhibits constitutive CREB phosphorylation. L2 and L2 variant cells were tested for IL-2 responsiveness and rapamycin sensitivity with respect to specific kinase activity, PCNA expression and proliferation. In L2 cells, IL-2 stimulated and rapamycin inhibited the following: cAMP-independent CREB kinase activity, PCNA expression and proliferation. In L2 variant cells, CREB kinase activity was constitutively high; IL-2 stimulated and rapamycin blocked PCNA expression and proliferation. These results indicate that IL-2 induces a rapamycin-sensitive, cAMP-independent CREB kinase activity in L2 cells. However, phosphorylation of CREB alone is not sufficient to drive PCNA expression and L2 cell proliferation in the absence of IL-2.

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