Peroxisome proliferator-activated receptor alpha induces rat sterol carrier protein x promoter activity through two peroxisome proliferator-response elements.

Sterol carrier protein x (SCPx) plays a critical role in the peroxisomal oxidation of fatty acids. It has been previously demonstrated in streptozotocin-induced diabetic rats that SCPx expression is induced in association with an elevation in serum fatty acid and triglyceride levels. To elucidate the mechanisms underlying the expression of this gene during diabetes, the rat SCPx promoter was cloned and analyzed for regulatory motifs. Sequence analysis of this TATA-less promoter revealed two putative peroxisomal-proliferator-response element (PPRE) binding motifs at positions -134 and -869 relative to the translation start site. To examine peroxisomal-proliferator-activated receptor alpha (PPARalpha) effects on this gene, 935 bp of the SCPx promoter containing both PPRE motifs was cloned in front of the chloramphenicol acetyl-transferase gene or the luciferase gene and co-transfected into HTB-9 cells with vectors that encoded for PPARalpha and retinoid X receptor (RXR). The results indicate that PPARalpha was able to induce SCPx promoter activity in both cases, an effect that was enhanced by RXR and clofibrate. In addition, mutational analysis studies demonstrated that both PPREs contributed to the PPARalpha/RXRalpha-dependent activation of the SCPx promoter. Mobility shift assays and supershift analysis showed that nuclear extracts containing PPARalpha bound to the two PPRE motifs. This investigation indicates that similar to other genes involved in beta-oxidation, SCPx transcription may be controlled by fatty acid levels via PPARalpha.