Late induction of CREB/ATF binding and a concomitant increase in cAMP levels in T and B lymphocytes stimulated via the antigen receptor.

Abstract

Transcription factors of the cAMP-responsive element (CRE) binding protein/activating transcription factor (CREB/ATF) family were implicated in the expression of T cell-specific genes and in the expression of oncogenic retroviruses associated with leukemia in T and B lymphocytes. To study the regulation of CREB/ATF transcription factors during lymphocyte activation, studies were pursued in primary cultures of resting murine splenic T and B lymphocytes stimulated via the Ag receptor. Using consensus/CRE and proliferating cell nuclear Ag (PCNA)/CRE as probes in the DNA binding assay, we showed that a marked induction of CRE binding is associated with activation of splenic T lymphocytes with anti-CD3 Ab. CRE binding was markedly induced after 48 h; it gradually declined at 72 h, but remained elevated above control levels after 120 h. Most significant, activation by anti-CD3 was associated with a marked induction of cAMP levels that preceded the onset of DNA synthesis and the induction of IL-2 secretion and reached a peak after 48 h (9.5- to 11-fold), concomitant with the peak in CRE binding. Rapamycin, a potent immunosuppressant, inhibited the induction of cAMP levels by anti-CD3 concomitant with inhibition of CRE binding activity and arrest of DNA synthesis. A marked induction in CRE binding after 48 h was also found in splenic B lymphocytes stimulated by LPS and anti-Ig and was correlated with a 3- to 4-fold increase in the intracellular levels of cAMP. Two inducible CRE complexes were found to bind to consensus/CRE and PCNA/CRE; the major complex contained primarily CREB homodimers and was constitutively expressed in resting lymphocytes. Conversely, stimulation of lymphocytes was associated with formation of a new, slow migrating CRE complex that demonstrated high inducibility in both consensus/CRE and PCNA/CRE. We show that this de novo inducible CRE complex contains CREB and ATF2, but not ATF1. Taken collectively, these results suggest that recruitment of CREB and ATF2 to the promoter of genes is tightly regulated during activation of T and B lymphocytes and implicate a cross-talk of cAMP and non-cAMP pathways in the regulation of transcriptional processes at late stages of activation in T and B lymphocytes stimulated via the Ag receptor.