Effects of epidermal growth factor and platelet-derived growth factor on c-fos and c-myc mRNA levels in normal human fibroblasts.
The mRNA levels of two proto-oncogenes, c-fos and c-myc, were determined in human foreskin fibroblasts exposed to epidermal growth factor (EGF) or platelet-derived growth factor (PDGF) in a serum-free, defined medium (MCDB 104). Untreated, quiescent cells were found to have low or undetectable levels of c-fos and c-myc mRNA. Within 10 min after the addition of EGF or PDGF the c-fos mRNA level increased, reached a peak at 30 min, and then declined to the control level after 60 min. The level of c-myc mRNA increased somewhat later and peaked after 8 h in cultures treated with either of the growth factors. The c-myc mRNA level remained elevated throughout the 24 h of investigation. The concentrations of EGF and PDGF required for a maximal effect on c-fos or c-myc expression were found to be similar to those that give maximal effect on cell proliferation. Both c-fos and c-myc mRNA expression were super-induced by the addition of cycloheximide. The addition of neutralizing PDGF antibodies to cultures that had received PDGF 4 h earlier inhibited the subsequent increase in the c-myc mRNA level, indicating that the effect of PDGF on c-myc expression is not caused by a "hit and run," mechanism. Density-inhibited cells responded to EGF and PDGF by an increase in c-fos and c-myc mRNA levels in the absence of any mitogenic response. The present results conform to the view that the c-fos and c-myc proto-oncogenes may be important (or necessary) but not sufficient for the initiation of DNA synthesis. Moreover, the finding that both EGF and PDGF increase c-fos and c-myc expression supports our previous suggestion that these two growth factors may in part act via a common intracellular pathway in the prereplicative phase of human fibroblasts.
D000906:Antibodies; D002455:Cell Division; D002478:Cells, Cultured; D003260:Contact Inhibition; D003513:Cycloheximide / Q000494:pharmacology; D004247:DNA / Q000096:biosynthesis; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D005347:Fibroblasts; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D010982:Platelet-Derived Growth Factor / Q000276:immunology / Q000494:pharmacology*; D011519:Proto-Oncogenes; D012333:RNA, Messenger / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic
D000906:Antibodies; D010982:Platelet-Derived Growth Factor; D012333:RNA, Messenger; D004815:Epidermal Growth Factor; D004247:DNA; D003513:Cycloheximide