The peroxisome proliferator-activated receptor interacts with the retinoid X receptor in vivo

The peroxisome proliferator-activated receptor (PPAR) binds cooperatively to cognate peroxisome proliferator-responsive elements (PPRE) in vitro through heterodimerization with retinoid X receptors (RXR). We used the yeast two-hybrid system to determine whether these two nuclear receptors physically interact in vivo. Mouse (m) PPAR and human (h) RXR alpha were synthesized as fusion proteins to either the DNA-binding domain (GBD) or the transactivation domain (GAD) of the yeast GAL4 transcription-activator protein, and were tested for their ability to activate expression of a GAL1::lacZ reporter gene. Strong activation was observed only in yeast transformed with combinations of GBD::mPPAR and GAD::hRXR alpha or with GAD::mPPAR and GBD::hRXR alpha. Homodimeric interaction by mPPAR was not detected. These results provide evidence for the interaction of PPAR and RXR alpha in vivo in the absence of a PPRE target site or exogenously added ligands.