Prolactin activation of IRF-1 transcription involves changes in histone acetylation.

In response to prolactin (PRL) signaling, transcription of the interferon regulatory factor-1 gene (IRF-1) is rapidly induced during early G(1), declines in mid G(1), and rises again over the G(1)/S transition phase of the cell cycle in Nb2 T cells. Using chromatin immunoprecipitation assays, we show that histone H4 acetylation increases over a 1.7 kb region of the IRF-1 promoter in early G(1) and again at the G(1)/S transition in response to PRL stimulation. These results demonstrate a correlation between histone H4 hyperacetylation at the IRF-1 promoter and biphasic transcription of IRF-1 in response to PRL signaling in vivo.