MSK1 and MSK2 mediate mitogen- and stress-induced phosphorylation of histone H3: a controversy resolved.

It is well established that mitogen- and stress-activated signal transduction pathways result in the rapid phosphorylation (Ser10 and Ser28) and acetylation of mammalian histone H3 associated with immediate-early genes. However, the prerequisite of H3 phosphorylation for the acetylation event and the identity of the mitogen-activated H3 kinase as RSK2 or MSK1 were controversial. A recent study with mouse embryonic fibroblasts lacking MSK1 and/or MSK2 demonstrated that MSK2 and MSK1 were the stimulus-induced H3 kinases and that neither of these enzyme activities was required for acetylation of H3 bound to immediate-early genes to occur.