1880-P: The Protein-Tyrosine Phosphatase Shp1 Interacts with PPAR Gamma and Regulates Its Transcriptional Activity through Dephosphorylation of Selected Tyrosine Sites

Src homology region 2 domain-containing phosphatase-1 (Shp1) plays an important role in modulating insulin signaling and thereby glucose homeostasis. Our laboratory has demonstrated that despite being more prone to hepatic steatosis, mice with a liver specific Shp1 knock out (Shp1^H-KO) on high-fat diet (HFD) exhibit improved fasting glycaemia, reduced insulin resistance and lower inflammation than their flox/flox littermates. Microarray analysis of HFD-fed Shp1^H-KO versus Shp1^fl/fl livers revealed elevated levels of peroxisome proliferator-activated receptor gamma (PPARγ), an important transcription factor controlling adipogenesis. In addition, overexpression of Shp1 decreased PPARγ activity in vitro. The aim of this study was to investigate the mechanism of regulation of PPARγ by Shp1. Molecular modeling analyses suggested that Shp1 interaction with PPARγ depends on the tyrosine phosphorylation status of PPARγ. We found, by co-immunoprecipitation, that Shp1 N-terminal SH2-domains binds to PPARγ. We confirmed PPARγ tyrosine-phosphorylation and demonstrated that this phosphorylation could be reduced by Shp1 in vitro. Using mass spectrometry, we identified 5 phosphorylated tyrosine residues in PPARγ. Mutagenesis experiments showed that PPARγ significantly lost its activity when two of these sites were selectively and independently mutated to the non-phosphorylatable phenylalanine but did not interfere with the nuclear localization of PPARγ. Additionally, we generated Shp1 knockout HepG2 cells using CRISPR-Cas9 technology. We found that expression of several PPARγ regulated transcripts was upregulated in Shp1-KO cells as compared to control cells. Altogether, we show that PPARγ is a novel substrate of Shp1. Our results reveal a fine regulation of PPARγ tyrosine phosphorylation by Shp1, which might lead to novel therapeutic approaches for treating metabolic disorders related to obesity.