Protein interactions underpinning pluripotency

Le résumé fourni par la source

Embryonic stem (ES) cells are maintained in an undifferentiated state by a gene \nregulatory network centred on the triumvirate of transcription factors Nanog, Oct4 \nand Sox2. Genome-wide chromatin immunoprecipitation studies indicate that in \nmany cases target genes contain closely localised binding sites for each of these \nproteins, as well as additional members of the extended pluripotency transcription \nfactor network. However, the biochemical basis of the interactions between these \nproteins is largely unknown, as are the mechanisms by which these interactions \ncontrol ES cell identity. \n \nBy purifying Nanog from ES cells and identifying co-purified proteins, we \ndetermined a Nanog interactome of over 130 proteins including transcription factors, \nchromatin modifying complexes, phosphorylation and ubiquitination enzymes, basal \ntranscriptional machinery members and RNA processing factors. Validation of \ninteractions was obtained by co-immunoprecipitation of Nanog with putative \npartners. \n \nSox2 was identified as a robust interacting partner of Nanog and the interaction was \ninvestigated further. We show that the interaction is independent of DNA binding \nand that a region of Nanog known as tryptophan repeat, in which tryptophan is \npresent every 5th residue is necessary and sufficient for the binding of Sox2. \nFurthermore, mutation of tryptophan residues within the Nanog tryptophan repeat \n(WR) abolishes the interaction with Sox2. \n \nA region of Sox2 known as serine rich region, a triple-repeat motif (S X T/S Y) \nwithin a stretch of 21 residues is required for the interaction with Nanog. Mutation of \ntyrosines to alanine within the three motifs (S X T/S Y) abrogates the Nanog–Sox2 \ninteraction. The disruption of the Nanog-Sox2 interaction results in the alteration of \nexpression of genes associated with the Nanog-Sox2 cognate sequence, and reduces \nthe ability of Sox2 to rescue ES cell differentiation induced by endogenous Sox2 \ndeletion. Substitution of the tyrosines of the motif with phenylalanine rescues both \nthe Sox2–Nanog interaction and efficient self-renewal. These results suggest that \naromatic stacking of Nanog tryptophans and Sox2 tyrosines mediates an interaction \ncentral to ES cell self-renewal. \n \nTogether these data shed light on the extent of the interactions of Nanog with protein \npartners as well as the biochemical nature of the interaction between Nanog and one \nof the most important partners Sox2, an interaction crucial for maintaining optimal \nmouse ES cell self-renewal efficiency.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.