PPAR gamma S273 Phosphorylation Modifies the Dynamics of Coregulator Proteins Recruitment

The nuclear receptor PPAR gamma is essential to maintain whole-body glucose homeostasis and insulin sensitivity, acting as a master regulator of adipogenesis, lipid, and glucose metabolism. Its activation through natural or synthetic ligands induces the recruitment of coactivators, leading to transcription of target genes such as cytokines and hormones. More recently, post translational modifications, such as PPAR gamma phosphorylation at Ser273 by CDK5 in adipose tissue, have been linked to insulin resistance trough the dysregulation of expression of a specific subset of genes. Here, we investigate how this phosphorylation may disturb the interaction between PPAR gamma and some coregulator proteins as a new mechanism that may leads to insulin resistance. Through cellular and in vitro assays, we show that PPAR gamma phosphorylation inhibition increased the activation of the receptor, therefore the increased recruitment of PGC1-alpha and TIF2 coactivators, whilst decreases the interaction with SMRT and NCoR corepressors. Moreover, our results show a shift in the coregulators interaction domains preferences, suggesting additional interaction interfaces formed between the phosphorylated PPAR gamma and some coregulator proteins. Also, we observed that the CDK5 presence disturb the PPAR gamma-coregulator's synergy, decreasing interaction with PGC1-alpha, TIF2, and NCoR, but increasing coupling of SMRT. Finally, we conclude that the insulin resistance provoked by PPAR gamma phosphorylation is linked to a differential coregulators recruitment, which may promote dysregulation in gene expression. (AU)