Isolation and characterization of peroxisome proliferator-activated receptor (PPAR) interacting protein (PRIP) as a coactivator for PPAR

We previously isolated and identified steroid receptor coactivator-1 (SRC-1 ) and peroxisome proliferator-activated receptor (PPAR)-binding protein (PB P/PPARBP) as coactivators for PPAR, using the ligand-binding domain of PPAR gamma as bait in a yeast two-hybrid screening. As part of our continuing e ffort to identify cofactors that influence the transcriptional activity of PPARs, we now report the isolation of a novel coactivator from mouse, desig nated PRIP (peroxisome proliferator-activated receptor interacting protein) , a nuclear protein with 2068 amino acids and encoded by 13 exons. Northern analysis showed that PRIP mRNA is ubiquitously expressed in many tissues o f adult mice. PRIP contains two LXXLL signature motifs. The amino-terminal LXYLL motif (amino acid position 892 to 896) of PRIP was found to be necess ary for nuclear receptor interaction, but the second LXYLL motif (amino aci d position 1496 to 1500) appeared unable to bind PPAR gamma. Deletion of th e last 12 amino acids from the carboxyl terminus of PPAR gamma resulted in the abolition of the interaction between PRIP and PPAR gamma, PRIP also bin ds to PPAR alpha; RAR alpha; RXR alpha, ER, and TR beta 1, and this binding is increased in the presence of specific ligands. PRIP acts as a strong co activator for PPAR gamma in the yeast and also potentiates the transcriptio nal activities of PPAR gamma and RXR alpha in mammalian cells. A truncated form of PRIP (amino acids 786-1132) acts as a dominant-negative repressor, suggesting that PRIP is a genuine coactivator.