REGULATION OF INTERFERON-GAMMA MESSENGER-RNA IN A CYTOLYTIC T-CELL CLONE - CA2-INDUCED TRANSCRIPTION FOLLOWED BY MESSENGER-RNA STABILIZATION THROUGH ACTIVATION OF PROTEIN-KINASE-C OR INCREASE IN CAMP()

Activation pathways inducing the expression of the interferon (IFN)-ga mma gene in a cytotoxic T lymphocyte (CTL) clone were studied for thei r effects on transcription and on mRNA stability. IFN-gamma was secret ed by the CTL clone in response to the Ca2+ ionophore ionomycin when u sed in conjunction with either protein kinase C (PKC)-activating phorb ol 12-myristate 13-acetate (PMA) or with agents increasing cAMP includ ing prostaglandin E(2). We describe that ionomycin induced IFN-gamma g ene transcription, which was totally inhibited in the presence of cycl osporin A (CSA), an immunosuppress ant forming a calcine urin-inhibiti ng complex with cyclophilin. Ionomycin did not, however, permit accumu lation of IFN-gamma, mRNA. Activation of PKC by PMA or of cAMP-depende nt protein kinase through increase in cAMP had no transcription-induci ng effect; either alone or in conjunction with ionomycin, as measured in run on assays of the IFN-gamma gene. When transcription of the IFN- gamma gene, initiated in the presence of ionomycin and an agent increa sing intracellular cAMP, was inhibited by CSA in the absence of PKC or cAMP-dependent protein kinase activation, the IFN-gamma mRNA was rapi dly degraded (half-life = 30 min). When either PKC was activated or in tracellular cAMP was increased at the time of inhibition with CSA, a s tabilizing effect was observed on IFN-gamma mRNA, which led to an incr ease in secreted IFN-gamma. These effects were selective, they did not affect the rate of transcription of the actin gene, nor the accumulat ion of actin mRNA. These results show that (i) post-transcriptional ev ents can be critical for IFN-gamma expression in activated lymphocytes , and (ii) specific stabilization of IFN-gamma mRNA can be mediated by activation of two different protein kinases involved in T cell activa tion.