Mazer B D, Domenico J, Szepesi A, Lucas J J, Gelfand E W
Department of Pediatrics, National Jewish Center for Immunology and Respiratory Medicine, Denver, CO.
J Lipid Mediat Cell Signal. 1994 Sep;10(3):269-81.
Platelet-activating factor (PAF) is a powerful stimulator of a wide variety of cells. In transformed human B-lymphoblastoid cell lines, PAF increases intracellular Ca2+ concentrations ([Ca2+]i) and induces the expression of the proto-oncogenes c-fos and early growth response gene-2 (EGR2). Here, we present data that evaluates the role of Ca2+ in the PAF-dependent induction of these cell-cycle activated genes. PAF (10(-7) M) increased c-fos and EGR2 mRNA levels in cells suspended in Ca(2+)-containing medium by 6-10-fold. In PAF-stimulated cells suspended in medium depleted of Ca2+, eliminating Ca2+ influx but not intracellular store release of Ca2+, the induction of gene expression was reduced by approx. 50%. In contrast, buffering of Ca2+ released from intracellular stores but maintaining transmembrane Ca2+ uptake had little effect on gene expression. When both sources of Ca2+ were eliminated, PAF-stimulated expression of these genes was completely prevented. This was not due to any toxicity to the cells since the response to phorbol ester under identical conditions was unaffected. The regulation of c-fos mRNA expression was paralleled by changes in levels of FOS protein. These data indicate that changes in [Ca2+]i, primarily from stimulated entry across the plasma membrane and to a lesser extent release of Ca2+ from sequestered intracellular stores, play an essential role in PAF-dependent triggering of c-fos and EGR2 mRNA expression.
血小板活化因子（PAF）是多种细胞的强效刺激剂。在转化的人B淋巴细胞系中，PAF可增加细胞内钙离子浓度（[Ca2+]i），并诱导原癌基因c-fos和早期生长反应基因2（EGR2）的表达。在此，我们展示了评估钙离子在PAF依赖性诱导这些细胞周期激活基因中的作用的数据。PAF（10^(-7) M）使悬浮于含Ca(2+)培养基中的细胞中c-fos和EGR2 mRNA水平增加6至10倍。在悬浮于去除Ca2+的培养基中的PAF刺激细胞中，消除Ca2+内流但不消除细胞内钙库释放的Ca2+，基因表达的诱导降低约50%。相反，缓冲从细胞内钙库释放的Ca2+但维持跨膜Ca2+摄取对基因表达影响很小。当两种钙源都被消除时，PAF刺激的这些基因的表达被完全抑制。这并非由于对细胞有任何毒性，因为在相同条件下对佛波酯的反应未受影响。c-fos mRNA表达的调节与FOS蛋白水平的变化平行。这些数据表明，[Ca2+]i的变化，主要来自刺激后跨质膜的进入，在较小程度上来自隔离的细胞内钙库释放的Ca2+，在PAF依赖性触发c-fos和EGR2 mRNA表达中起重要作用。
