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.

Generation of pig iPS cells: a model for cell therapy.

Reprogramming of pig somatic cells to induced pluripotent stem cells provides a tremendous advance in the field of regenerative medicine since the pig represents an ideal large animal model for the preclinical testing of emerging cell therapies. However, the current generation of pig-induced pluripotent stem cells (piPSCs) require the use of time-consuming and laborious retroviral or lentiviral transduction approaches, in order to ectopically express the pluripotency-associated transcription factors Oct4, Sox2, Klf4 and c-Myc, in the presence of feeder cells. Here, we describe a simple method to produce piPSC with a single transfection of a CAG-driven polycistronic plasmid expressing Oct4, Sox2, Klf4, c-Myc and a green fluorescent protein (GFP) reporter gene, in gelatine-coated plates, with or without feeder cells. In our system, the derivation of piPSCs from adult pig ear fibroblasts on a gelatine coating showed a higher efficiency and rate of reprogramming when compared with three consecutive retroviral transductions of a similar polycistronic construct. Our piPSCs expressed the classical embryonic stem cell markers, exhibit a stable karyotype and formed teratomas. Moreover, we also developed a simple method to generate in vitro spontaneous beating cardiomiocyte-like cells from piPSCs. Overall, our preliminary results set the bases for the massive production of xeno-free and integration-free piPSCs and provide a powerful tool for the preclinical application of iPSC technology in a large animal setting.