Rapid histone H3 phosphorylation in response to growth factors, phorbol esters, okadaic acid, and protein synthesis inhibitors

Abstract

When quiescent cells are stimulated with growth factors, phorbol esters, okadaic acid, or protein synthesis inhibitors, the early-response genes, which include c-fos and c-jun, are rapidly induced. The earliest growth factor- and phorbol ester-stimulated nuclear signaling events concomitant with proto-oncogene induction are the rapid phosphorylation of two chromatin-associated proteins, pp33 and pp15. We show here that the tumor promoter okadaic acid, which inhibits protein phosphatases 1 and 2A, and the protein synthesis inhibitors anisomycin and cycloheximide also stimulate pp33 and pp15 phosphorylation. Using transcriptional inhibitors, we show that this response is not a consequence of early gene induction. By peptide mapping and microsequencing, chromatin-associated pp15 is identified as histone H3. Upon stimulation, histone H3 is rapidly phosphorylated on serine residues within its highly charged, basic N-terminal domain. Thus, these diverse agents elicit a common early nuclear signal modulating nucleosomal structure or function, potentially contributing to conformational regulation of proto-oncogene induction.