| The immunoprecipitation of PPARalpha in mouse liver cytosol using mAb 3B6 / PPAR has resulted in the detection of two co immunoprecipitated proteins , which are heat shock protein 90 ( hsp 90 ) and the hepatitis B virus 10 associated protein 2 ( XAP 2 ) . ^^^ Complex formation between XAP 2 and PPARalpha / FLAG was also demonstrated in an in vitro translation binding assay . hsp 90 interacts with PPARalpha in a mammalian two hybrid assay and binds to the E / F domain . ^^^ Transient expression of XAP 2 co expressed with PPARalpha resulted in down regulation of a peroxisome proliferator response element driven reporter gene activity . ^^^ Taken together , these results indicate that PPARalpha is in a complex with hsp 90 and XAP 2 , and XAP 2 appears to function as a repressor . ^^^ |