INSULIN AND OTHER GROWTH-FACTORS INDUCE BINDING OF THE TERNARY COMPLEX AND A NOVEL PROTEIN COMPLEX TO THE C-FOS SERUM RESPONSE ELEMENT

Rapid, transient induction of c-fos transcription follows treatment of cells with insulin and other growth factors. This is mediated through the serum response element (SRE), which binds the serum response fact or (SRF), as well as accessory factors such as p62 ternary complex fac tor. Using a gel shift assay we found that formation of the ternary co mplex increased transiently within 2 min of insulin or phorbol ester t reatment of several insulin-sensitive cell lines. However, mutations t hat prevented formation of this ternary complex did not inhibit insuli n- or phorbol ester-stimulated induction of c-fos transcription in the se cell Lines. We also identified a novel SRF-containing multiprotein complex that forms on the SRE within 2 min following insulin, phorbol ester, or other growth factor treatment. Formation of this novel compl ex, called band 3, occurred rapidly and transiently, with a time cours e parallel to the induction of c-fos transcription. Band 3 also formed with gamma-actin and zif268/3 SRE probes. Methylation and carboxy eth ylation interference analysis, as well as extensive SRE mutagenesis, s uggest that only the SRF directly contacts the SRF in forming band 3. Formation of this novel complex appears to involve protein-protein int eractions between SRF and other nuclear protein(s) that may play a rol e in growth factor stimulation of c-fos transcription.