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

IκBs exert principal functions as cytoplasmic inhibitors of NF-kB transcription factors. Additional roles for IκB homologues have been described, including chromatin association and transcriptional regulation. Phosphorylated and SUMOylated IκBα (pS-IκBα) binds to histones H2A and H4 in the stem cell and progenitor cell compartment of skin and intestine, but the mechanisms controlling its recruitment to chromatin are largely unknown. Here, we show that serine 32-36 phosphorylation of IκBα favors its binding to nucleosomes and demonstrate that p-IκBα association with H4 depends on the acetylation of specific H4 lysine residues. The N-terminal tail of H4 is removed during intestinal cell differentiation by proteolytic cleavage by trypsin or chymotrypsin at residues 17-19, which reduces p-IκBα binding. Inhibition of trypsin and chymotrypsin activity in HT29 cells increases p-IκBα chromatin binding but, paradoxically, impaired goblet cell differentiation, comparable to IκBα deletion. Taken together, our results indicate that dynamic binding of IκBα to chromatin is a requirement for intestinal cell differentiation and provide a molecular basis for the understanding of the restricted nuclear distribution of p-IκBα in specific stem cell compartments.We want to thank the Bigas’ and Espinosa’s lab members for constructive discussions and suggestions and technical support. This work has been funded by Instituto de Salud Carlos III FEDER (PI19/0013), Agencia Estatal de Investigación, Spain (PID2019-104695RB-I00) to A.B., NIH/GM085490 to G.G., BIO2017-83650-P to JVF and Generalitat de Catalunya 2017SGR135. LM is a predoctoral fellow of 2015FI-B00806 and 2016FI-B1 00110 and MF has financial support by the Universitat de Vic-Universitat Central de Catalunya PhD fellowships program. The authors thankfully acknowledge the computer resources at Pirineus and the technical support provided by the Spanish Supercomputer Network (BCV-2020-1-0001)