Kaldy P, Schmitt-Verhulst A M
Centre d'Immunologie, INSERM-CNRS de Marseille-Luminy, France.
Eur J Immunol. 1995 Apr;25(4):889-95. doi: 10.1002/eji.1830250405.
Activation pathways inducing the expression of the interferon (IFN)-gamma gene in a cytotoxic T lymphocyte (CTL) clone were studied for their effects on transcription and on mRNA stability. IFN-gamma was secreted by the CTL clone in response to the Ca2+ ionophore ionomycin when used in conjunction with either protein kinase C (PKC)-activating phorbol 12-myristate 13-acetate (PMA) or with agents increasing cAMP, including prostaglandin E2. We describe that ionomycin induced IFN-gamma gene transcription, which was totally inhibited in the presence of cyclosporin A (CSA), an immunosuppressant forming a calcineurin-inhibiting complex with cyclophilin. Ionomycin did not, however, permit accumulation of IFN-gamma mRNA. Activation of PKC by PMA or of cAMP-dependent protein kinase through increase in cAMP had no transcription-inducing 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 increasing intracellular cAMP, was inhibited by CSA in the absence of PKC or cAMP-dependent protein kinase activation, the IFN-gamma mRNA was rapidly degraded (half-life = 30 min). When either PKC was activated or intracellular cAMP was increased at the time of inhibition with CSA, a stabilizing effect was observed on IFN-gamma mRNA, which led to an increase in secreted IFN-gamma. These effects were selective, they did not affect the rate of transcription of the actin gene, nor the accumulation of actin mRNA. These results show that (i) post-transcriptional events 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 activation.
研究了细胞毒性T淋巴细胞（CTL）克隆中诱导干扰素（IFN）-γ基因表达的激活途径对转录和mRNA稳定性的影响。当与蛋白激酶C（PKC）激活剂佛波醇12-肉豆蔻酸酯13-乙酸酯（PMA）或增加cAMP的试剂（包括前列腺素E2）联合使用时，钙离子载体离子霉素可使CTL克隆分泌IFN-γ。我们发现离子霉素可诱导IFN-γ基因转录，而环孢素A（CSA）（一种与亲环蛋白形成钙调神经磷酸酶抑制复合物的免疫抑制剂）可完全抑制该转录。然而，离子霉素不能使IFN-γ mRNA积累。如在IFN-γ基因的连续分析中所测，单独或与离子霉素联合使用时，PMA激活PKC或通过增加cAMP激活cAMP依赖性蛋白激酶均无转录诱导作用。当在不存在PKC或cAMP依赖性蛋白激酶激活的情况下，CSA抑制在离子霉素和增加细胞内cAMP的试剂存在时启动的IFN-γ基因转录时，IFN-γ mRNA会迅速降解（半衰期 = 30分钟）。当在用CSA抑制时激活PKC或增加细胞内cAMP，可观察到对IFN-γ mRNA有稳定作用，这导致分泌的IFN-γ增加。这些作用具有选择性，它们不影响肌动蛋白基因的转录速率，也不影响肌动蛋白mRNA的积累。这些结果表明：（i）转录后事件对于活化淋巴细胞中IFN-γ的表达可能至关重要；（ii）参与T细胞活化的两种不同蛋白激酶的激活可介导IFN-γ mRNA的特异性稳定。
