Activated sterol regulatory element-binding protein-2 suppresses hepatocyte nuclear factor-4-mediated Cyp3a11 expression in mouse liver.

摘要

Sterol regulatory element-binding protein-2 (SREBP-2) is a key transcription factor for the cholesterol homeostasis. Recent studies have suggested the association of CYP3A enzymes, major drug-metabolizing enzymes, with cholesterol metabolism. In the present study, we have investigated a possible involvement of SREBP-2 in hepatic Cyp3a11 expression. Feeding a low-cholesterol diet (LCD) to mice activated hepatic SREBP-2 whereas it attenuated hepatic Cyp3a11 expression. These phenomena were reversed by cholesterol supplementation to LCD. In reporter assays, the overexpression of constitutively active SREBP-2 reduced Cyp3a11 reporter activity through the region from -1581 to -1570 of Cyp3a11. This region contained a putative hepatocyte nuclear factor-4alpha (HNF-4alpha) binding motif, and HNF-4alpha, but not SREBP-2, bound to the motif in in vitro binding assays. With the mutation or deletion of this motif, the SREBP-2-dependent suppression of Cyp3a11 expression disappeared in reporter assays. In pull-down assays and coimmunoprecipitation assays, SREBP-2 bound to peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha), a major coactivator for HNF-4alpha, via its transactivation domain and inhibited the interaction between HNF-4alpha and PGC-1alpha in vitro. A mutant SREBP-2 lacking the transactivation domain consistently failed to reduce Cyp3a11 reporter activity. Furthermore, PGC-1alpha overexpression relieved the SREBP-2-mediated reduction of Cyp3a11 reporter activity. Finally, chromatin immunoprecipitation assays demonstrated that the extent of PGC-1alpha binding to the Cyp3a11 promoter was reduced by LCD-feeding in mouse livers. In conclusion, activated SREBP-2 interacts with PGC-1alpha in mouse livers at reduced cholesterol intake. This results in the reduced PGC-1alpha recruitment to HNF-4alpha on the Cyp3a11 promoter and the subsequent down-regulation of Cyp3a11 expression.