Heterochromatin protein 1 gamma and IκB kinase alpha interdependence during tumour necrosis factor gene transcription elongation in activated macrophages

I kappa B kinase alpha (IKK alpha) is part of the cytoplasmic IKK complex regulating nuclear factor-{kappa}B (NF-kappa B) release and translocation into the nucleus in response to pro-inflammatory signals. IKK alpha can also be recruited directly to the promoter of NF-kappa B-dependent genes by NF-kappa B where it phosphorylates histone H3 at serine 10, triggering recruitment of the bromodomain-containing protein 4 and the positive transcription elongation factor b. Herein, we report that IKK alpha travels with the elongating form of ribonucleic acid polymerase II together with heterochromatin protein 1 gamma (HP1 gamma) at NF-kappa B-dependent genes in activated macrophages. IKK alpha binds to and phosphorylates HP1 gamma, which in turn controls IKK alpha binding to chromatin and phosphorylation of the histone variant H3.3 at serine 31 within transcribing regions. Downstream of transcription end sites, IKK alpha accumulates with its inhibitor the CUE-domain containing protein 2, suggesting a link between IKK alpha inactivation and transcription termination.