Dynamic association of IκBα to chromatin is regulated by acetylation and cleavage of histone H4

Abstract

I{kappa}Bs exert a principal function as cytoplasmic inhibitors of the NF-kB transcription factors. Additional functions for I{kappa}B homologues have been described including association to chromatin and transcriptional regulatioin. Phosphorylated and SUMOylated I{kappa}B (pS-I{kappa}B) binds histones H2A and H4 in the stem and progenitor compartment of skin and intestine, but the mechanisms controlling its recruitment to chromatin are largely unstudied. We here show that serine 32-36 phosphorylation of I{kappa}B favors its binding with nucleosomes and demonstrated that p-I{kappa}B association to H4 is favored by acetylation at specific H4 lysine residues. N-terminal tail of H4 is lost during intestinal cell differentiation by proteolytic cleavage at residues 17-19 imposed ny trypsin or chymotrypsin, which interferes p-I{kappa}B binding. Paradoxically, inhibition of trypsin and chymotrypsin activity in HT29 cells increased p-I{kappa}B chromatin binding and impaired goblet cell differentiation, comparable to I{kappa}B deletion. Together our results indicate that dynamic binding of I{kappa}B to chromatin is a requirement for intestinal cell differentiation and provide a molecular base for the restricted nuclear distribution of p-I{kappa}B at specific stem cell compartments.