MYC BUT NOT FOS RESCUE OF PDGF SIGNALING BLOCK CAUSED BY KINASE INACTIVE SRC

GROWTH factors such as platelet-derived growth factor (PDGF) elicit th e transcriptional activation of a large number of immediate early gene s (many of which encode transcription factors), and ultimately DNA syn thesis(1). Both AP1 and Myc are activated in fibroblasts in response t o growth factor stimulation(2-5), and various experiments suggest thei r importance in proliferation(6-10). Src family kinases are required f or PDGF (and other growth factors) to induce DNA synthesis(11,12). We have examined which transcription factors, when constitutively express ed, 'rescue' the block elicited by dominant negative Src. We report he re 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 domin ant negative Ras. Our data suggest that Src kinases control the transc riptional activation of Myc.