Identification of an extended half-site motif required for the function of peroxisome proliferator-activated receptor alpha.

BACKGROUND

Peroxisome proliferator-activated receptors (PPARs) belong to the nuclear hormone receptor superfamily and regulate many genes of the proteins involved in lipid metabolism, including peroxisomal acyl-CoA oxidase (AOX). Through heterodimerization with retinoid X receptors (RXRs), PPAR was believed to recognize the sequence elements consisting of two directly repeating 6-bp half-sites spaced by one nucleotide (DR-1), located in the regulatory regions of these genes.

RESULTS

Employing the peroxisome proliferator-responsive enhancer of the rat AOX gene, we analysed the minimal sequence requirements for enhancer activity and PPARalpha/RXRalpha binding. We found that the sequence just downstream of the DR-1 motif is indispensable for both functions. By a direct selection procedure of high-affinity binding sites from a random sequence pool, we identified a consensus sequence at the four positions next to DR-1. We also suggest that PPARalpha binds to the downstream half-site, whereas RXRalpha binds to the upstream half-site of the AOX DR-1.

CONCLUSIONS

An extended half-site of 10-bp, but not a simple 6-bp half-site, is required for the PPARalpha binding, upon heterodimer formation with RXRalpha. The binding polarity of PPARalpha/RXRalpha seems to be opposite to that of other RXR-involving heterodimers.