Myc but not Fos rescue of PDGF signalling block caused by kinase-inactive Src

Growth factors such as platelet-derived growth factor (PDGF) elicit the transcriptional activation of a large number of immediate early genes (many of which encode transcription factors), and ultimately DNA synthesis. Both AP1 and Myc are activated in fibroblasts in response to growth factor stimulation, and various experiments suggest their importance in proliferation. Src family kinases are required for PDGF (and other growth factors) to induce DNA synthesis. We have examined which transcription factors, when constitutively expressed, 'rescue' the block elicited by dominant negative Src. We report here that Myc, but not Fos and/or Jun, was able to rescue the block. In contrast, Fos and Jun, but not Myc, rescued the block induced by dominant negative Ras. Our data suggest that Src kinases control the transcriptional activation of Myc.