Isolation of PBP165 as a cofactor of peroxisome proliferator activated receptor(PPAR)gamma

Peroxisomc proliferalor-activated receptor (PPAR)gamma a member of the nuclear receptor suporfamily involved in the adipocytc differentiation. In an attempt to isolate proteins that bind PPAR gamma and influence PPAR gamma transcriptional activity, we used yeast two hybrid system. Gal4 PPAR gamma was used as the bait to screen the mouse liver r I) N A library. In an earlier study we identified mSRC-1 as the PPAR gamma coactivator (/Chu et al., (lene Expression, 6:185-195, 1996), and here we report the isolation of a cDNA encoding a protein with an estimated molecular weight of 165 kDa which we designated as PPAR gamma binding protein (PBP1Ö5). The interaction between PPAR gamma and PBP165 was confirmed by in vitro binding assay. PBP165 also binds to RXR alpha, TR beta. RAR alpha and PPAR alpha in vitro and their ligands increase this interaction. The mRNA of PBP165 was detected as an 8 kb band in all tissue of mouse examined with highest expression in testis. The PBP165 moderately increases the transcriptional activity of PPAR gamma. The binding domain of the PUP165 for PPAR gamma acts as a strong dominant negative-form with concomitant decrease in the transcriptional activity of PPAR gamma.