Dynamic association of IκBα to chromatin during intestinal differentiation is regulated by Acetylation and N-terminal cleavage of histone H4

IκBs exert a principal function as cytoplasmic inhibitors of the NF-kB transcription factors. Additional functions for specific IκB homologues have also been described including their association to chromatin to directly regulate gene transcription. Phosphorylated and SUMOylated IκBα (pS-IκBα) specifically binds histones H2A and H4 in the stem and progenitor compartment of skin and intestine, but the mechanisms that control the recruitment of nuclear pS-IκBα to the chromatin are largely unstudied. We here show thatserine 32-36 phosphorylation of IκBα favors its binding with nucleosomes and demonstrated that p-IκBαassociation to H4 is favored by acetylation at specific H4 lysine (K) residues. Acetylated N-terminal tail of H4 is lost during intestinal cell differentiation due to histone cleavage at amino acids 17-19 by the action of trypsin or chymotrypsin, which interferes p-IκBα association to chromatin. Paradoxically, pharmacologic or genetic inhibition of trypsin and chymotrypsin activity in HT29 cells increased p-IκBα chromatin binding, associated to impaired goblet cell differentiation, which was comparable to IκBα deletion. Together our results indicate that dynamic binding of IκBα to chromatin is a requirement for intestinal cell differentiation and provide a molecular base for the restricted nuclear distribution of p-IκBα at specific stem cell compartments. HCT116 ChIP-seq with various antibodies. 5 analyzed samples.