Rozengurt E, Sinnett-Smith J W
J Cell Physiol. 1987 May;131(2):218-25. doi: 10.1002/jcp.1041310211.
Bombesin is a potent mitogen for Swiss 3T3 cells and acts synergistically with insulin and other growth factors. We show here that addition of bombesin to quiescent Swiss 3T3 cells causes a striking increase in the levels of c-fos and c-myc mRNAs. Enhanced expression of c-fos (122 +/- 14-fold) occurred within minutes of peptide addition followed by increased expression of c-myc (82 +/- 16-fold). The concentrations of peptide required for half-maximal increase in the levels of c-fos and c-myc mRNAs were 1.0 and 0.9 nM, respectively. The peptide [D-Arg1, D-Pro2, D-Trp7,9, Leu11] substance P which inhibits the binding of bombesin to its receptor and bombesin-stimulated DNA synthesis in Swiss 3T3 cells blocked the increase in c-fos and c-myc mRNA levels promoted by bombesin. Down-regulation of protein kinase C by long-term exposure to phorbol esters prevented c-fos and c-myc induction by bombesin. This and other results indicate that the induction of these proto-oncogenes by bombesin could be mediated by the coordinated effects of protein kinase C activation and Ca2+ mobilization. The marked synergistic effect between bombesin and insulin was used to assess whether the increase in the induction of c-fos and c-myc is an obligatory event in cell activation. In the presence of insulin, bombesin stimulated DNA synthesis at subnanomolar concentrations but had only a small effect on c-fos and c-myc mRNA levels. This apparent dissociation of mitogenesis from proto-oncogene induction was even more dramatic in 3T3 cells with down-regulated protein kinase C. In these cells bombesin stimulated DNA synthesis in the presence of insulin but failed to enhance c-fos and c-myc mRNA levels at comparable concentrations. Thus, the induction of c-fos and c-myc may be a necessary step in the mitogenic response initiated by ligands that act through activation of protein kinase C but the expression of these proto-oncogenes may not be an obligatory event in the stimulation of mitogenesis in 3T3 cells by mitogens that utilise other signalling pathways.
蛙皮素是瑞士3T3细胞的一种强效促有丝分裂原，可与胰岛素及其他生长因子协同发挥作用。我们在此表明，向静止的瑞士3T3细胞中添加蛙皮素会导致c-fos和c-myc mRNA水平显著升高。添加肽后数分钟内，c-fos表达增强（122±14倍），随后c-myc表达增加（82±16倍）。c-fos和c-myc mRNA水平增加至最大值一半时所需的肽浓度分别为1.0和0.9 nM。肽[D-Arg1, D-Pro2, D-Trp7,9, Leu11]P物质可抑制蛙皮素与其受体的结合以及瑞士3T3细胞中蛙皮素刺激的DNA合成，它能阻断蛙皮素促进的c-fos和c-myc mRNA水平升高。长期暴露于佛波酯导致蛋白激酶C下调，可阻止蛙皮素诱导c-fos和c-myc。这一结果及其他结果表明，蛙皮素对这些原癌基因的诱导可能由蛋白激酶C激活和Ca2+动员的协同作用介导。利用蛙皮素与胰岛素之间显著的协同效应来评估c-fos和c-myc诱导增加是否是细胞激活中的必要事件。在有胰岛素存在的情况下，蛙皮素在亚纳摩尔浓度下刺激DNA合成，但对c-fos和c-myc mRNA水平影响较小。在蛋白激酶C下调的3T3细胞中，有丝分裂原生成与原癌基因诱导之间的这种明显分离更为显著。在这些细胞中，蛙皮素在有胰岛素存在的情况下刺激DNA合成，但在相当浓度下未能增强c-fos和c-myc mRNA水平。因此，c-fos和c-myc的诱导可能是由通过激活蛋白激酶C发挥作用的配体引发的有丝分裂反应中的必要步骤，但这些原癌基因的表达可能不是利用其他信号通路的有丝分裂原刺激3T3细胞有丝分裂中的必要事件。
