title: Bombesin induction of c-fos and c-myc proto-oncogenes in Swiss 3T3 cells: significance for the mitogenic response.
abstract: 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.
mesh_terms: D000818:Animals; D001839:Bombesin / Q000494:pharmacology*; D000001:Calcimycin / Q000494:pharmacology; D002460:Cell Line; D004261:DNA Replication; D004305:Dose-Response Relationship, Drug; D005786:Gene Expression Regulation / Q000187:drug effects*; D007399:Interphase; D051379:Mice; D015240:Phorbol 12,13-Dibutyrate; D010703:Phorbol Esters / Q000494:pharmacology; D011519:Proto-Oncogenes; D012333:RNA, Messenger / Q000378:metabolism; D013329:Structure-Activity Relationship; D013997:Time Factors
chemical_list: D010703:Phorbol Esters; D012333:RNA, Messenger; D015240:Phorbol 12,13-Dibutyrate; D000001:Calcimycin; D001839:Bombesin