PEROXISOME PROLIFERATOR-ACTIVATED RECEPTOR-ALPHA INHIBITS HEPATIC S14GENE-TRANSCRIPTION - EVIDENCE AGAINST THE PEROXISOME PROLIFERATOR-ACTIVATED RECEPTOR A AS THE MEDIATOR OF POLYUNSATURATED FATTY-ACID REGULATION OF S14 GENE-TRANSCRIPTION

The peroxisome proliferator-activated receptor (PPAR alpha) has been i mplicated in fatty acid regulation of gene transcription, Lipogenic ge ne transcription is inhibited by polyunsaturated fatty acids (PUFA), W e have used the PUFA-sensitive rat liver S14 gene as a model to examin e the role PPAR alpha plays in fatty acid regulation of hepatic lipoge nic gene transcription, Both PPAR alpha and the potent peroxisome prol iferator, WY14643, inhibit S14CAT activity in transfected primary hepa tocytes. WY14643 and PPAR alpha target the S14 T-3 regulatory region ( TRR, -2.8 to -2.5 kilobases), a region containing 3 T-3 response eleme nts (TRE). Transfer of the TRR to the thymidine kinase (TK) promoter c onferred negative control to the TKCAT gene following WY14643 and PPAR alpha treatment, Gel shift analysis showed that PPAR alpha, either al one or with RXR alpha, did not bind the S14TRR. However, PPAR alpha in terfered with TR beta/RXR alpha binding to a TRE (DR+4). Functional st udies showed that co-transfected RXR alpha, but not T-3 receptor beta( 1) (TR beta 1), abrogated the inhibitory effect of PPAR alpha on S14 g ene transcription. These results suggest that WY14643 and PPAR alpha f unctionally interfere with T-3 regulation of S14 gene transcription by inhibiting TR beta 1/RXR binding to S14 TREs. Previous studies had es tablished that the cis-regulatory targets of PUFA control were located within the proximal promoter region of the S14 gene, i.e. between -22 0 and -80 bp. Finding that the cis-regulatory elements for WY14643/PPA R alpha and PUFA are functionally and spatially distinct argues agains t PPAR alpha as the mediator of PUFA suppression of S14 gene transcrip tion.