Thivierge M, Alami N, Müller E, de Brum-Fernandes A J, Rola-Pleszczynski M
Department of Pediatrics, Faculty of Medicine, University of Sherbrooke, Québec, Canada.
J Biol Chem. 1993 Aug 15;268(23):17457-62.
We examined the effects of increasing intracellular cyclic AMP levels on the expression of human PAF receptor (hPAF-R). Peripheral blood monocytes constitutively expressed hPAF-R mRNA transcripts. A transiently elevated intracellular concentration of AMP induced with prostaglandin E2, cholera toxin, or forskolin was a sufficient signal to inhibit PAF-R expression. To determine the mechanisms of this inhibition, human monocytes were treated with dibutyryl cAMP, a cell-permeable cAMP analogue. cAMP reduced the expression of hPAF-R in a concentration- and a time-dependent manner. The effect was seen as early as 1 h and was essentially total by 4 h. Stability of hPAF-R mRNA was not markedly decreased by cAMP, as assessed by measuring the half-lives of the transcripts. Moreover, the nuclear transcription rate of the hPAF-R gene was reduced as early as 30 min after stimulation with cAMP. The inhibition of hPAF-R mRNA accumulation was associated with diminished responsiveness to PAF, as assayed by intracellular Ca2+ fluxes, decreased number of binding sites, and decreased hPAF-R protein expression on the cell surface, as assessed by flow cytometry using a polyclonal anti-hPAF-R antibody. These data indicate that PAF-R expression can be regulated at the transcriptional and possibly post-transcriptional levels by elevation of intracellular cAMP.
我们研究了细胞内环磷酸腺苷（cAMP）水平升高对人血小板活化因子受体（hPAF-R）表达的影响。外周血单核细胞组成性表达hPAF-R mRNA转录本。用前列腺素E2、霍乱毒素或福斯可林诱导细胞内AMP短暂升高是抑制PAF-R表达的充分信号。为了确定这种抑制的机制，用人单核细胞处理二丁酰cAMP，一种可透过细胞的cAMP类似物。cAMP以浓度和时间依赖性方式降低hPAF-R的表达。这种效应早在1小时就可见，到4小时基本完全显现。通过测量转录本的半衰期评估，cAMP并未显著降低hPAF-R mRNA的稳定性。此外，cAMP刺激后最早30分钟，hPAF-R基因的核转录率就降低了。通过细胞内Ca2+通量测定、结合位点数量减少以及使用多克隆抗hPAF-R抗体通过流式细胞术评估细胞表面hPAF-R蛋白表达，发现hPAF-R mRNA积累的抑制与对PAF的反应性降低有关。这些数据表明，细胞内cAMP升高可在转录水平以及可能的转录后水平调节PAF-R的表达。
