Induction of progesterone target genes requires activation of Erk and Msk kinases and phosphorylation of histone H3.

How genes are regulated in the context of chromatin is a central question of biology. Steroid hormones control gene expression via interaction of their receptors with target sequences on DNA but can also activate cytoplasmic signaling cascades. Here we report that rapid Erk activation by progestins participates in induction of target genes by preparing the chromatin for transcription. Five minutes after hormone treatment, Erk activation leads to phosphorylation of the progesterone receptor (PR), activation of Msk1, and recruitment of a complex of the three proteins to a nucleosome on the MMTV promoter. Msk1 phosphorylates histone H3, leading to displacement of HP1gamma and recruitment of Brg1 and RNA polymerase II. Cell-free experiments show a direct interaction between PR, Erk, and Msk1 and support the importance of H3 phosphorylation for nucleosome remodeling. Inhibition of Msk1 activation blocks recruitment of the kinase complex, H3 phosphorylation, and HP1gamma displacement, thus precluding remodeling and induction of the promoter.