ACTIVATION OF THE CAMP-DEPENDENT SIGNALING PATHWAY DOWN-REGULATES THEEXPRESSION OF INTERLEUKIN-3 AND GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR IN ACTIVATED HUMAN T-LYMPHOCYTES

Expression of cytokines by T lymphocytes is a highly balanced process, involving stimulatory and inhibitory intracellular signaling pathways . We have examined the modulating effects of the cAMP-dependent signal ing pathway on the expression of interleukin-3 (IL-3) and granulocyte- macrophage colony-stimulating factor (GM-CSF) in activated human T lym phocytes. 2'-O-dibutyryl-cAMP (db-cAMP), prostaglandin E(2) (PGE(2)), isoproterenol (ISO), and isobutyl methyl-xantin (IBMX) costimulated wi th concanavalin A (Con A) or Con A plus the phorbolester phorbol myris tate acetate (PMA) inhibited IL-3 and GM-CSF mRNA accumulation compare d to the effects of Con A or Con A plus PMA alone. Nuclear run-on expe riments revealed that the inhibitory effect of db-cAMP could partially be ascribed to a five-fold reduction in transcription rate of both th e IL-3 and GM-CSF gene in the presence of Con A or Con A plus PMA. mRN A stability studies demonstrated that PMA increased the stability of b oth transcripts. db-cAMP did not affect the stability of IL-3 and GM-C SF mRNAs in Con A activated cells. In contrast, in Con A plus PMA acti vated cells, db-cAMP significantly reduced the half-life of both trans cripts: IL-3 >240 minutes vs. 90 minutes and GM-CSF 90 minutes vs. 60 minutes. Finally, in accordance with the mRNA data, db-cAMP, PGE(2), a nd ISO reduced the secretion of IL-3 and GM-CSF protein in Con A and C on A plus PMA activated cells. In conclusion, these data demonstrate t hat the protein kinase A (PKA)-dependent signaling pathway is an impor tant regulatory mechanism in controlling IL-3 and GM-CSF gene expressi on in activated human T lymphocytes.