REGULATION OF CAMP-RESPONSIVE ENHANCER-BINDING PROTEINS DURING CELL-CYCLE PROGRESSION IN T-LYMPHOCYTES STIMULATED BY IL-2

IL-2 stimulates the proliferative response of various lymphoid cells. Previous studies showed an increase in intracellular levels of cAMP co ncomitant with an increase in phosphorylation of discrete proteins by protein kinase A at late G1 phase in mitogen-stimulated lymphocytes. T hus, experiments were undertaken to study nuclear proteins that bind t o the the cAMP-responsive enhancer (CRE) in cloned T lymphocytes stimu lated with IL-2. With the use of a P-32-labeled CRE consensus sequence in a DNA binding gel mobility shift assay, we showed that IL-2 stimul ation resulted in the induction of two major DNA-protein complexes at late G1/S during the cell cycle. This binding was competed in a dose-d ependent manner by a nonlabeled CRE oligonucleotide but was not compet ed by a nonlabeled AP-1 oligonucleotide. Rapamycin, a potent immunosup pressant, which arrest IL-2-stimulated T lymphocytes at G1/S, inhibite d the IL-2-induced CRE binding activities concomitantly wit inhibition of DNA synthesis. By using specific Abs in a gel mobility shift assay , we identified two known CREB/ATF transcription factors in the IL-2-i nduced CRE complexes: the CRE binding factor (CREB), and ATF1. The ind uction of CREB binding by IL-2 was not associated with an increase in its abundance but was associated with a major increase in CREB phospho rylation that was particularly prominent at late G1/S. However, we fou nd that G1/S progression induced by IL-2 was not associated with an in crease in the intracellular levels of cAMP. These results suggest that 1) the transcription factors CREB and ATF1 and possibly other CRE bin ding proteins may have an important role in the modulation of specific gene expression at G1/S during cell cycle progression induced by IL-2 . 2) The involvement of these CRE binding transcription factors in IL- 2-stimulated cells is regulated via a mechanism that is not cAMP depen dent.