Activated sterol regulatory element-binding protein-2 (srebp-2) suppresses hapatocyte nuclear factor-4-mediated cyp3a11 gene expression in mouse liver

PREGNANE X RECEPTOR MEDIATED INDUCTION OF MDR1A IS DIFFERENT FROM CYP3A11 IN TISSUE-, REGIONAND TIME-DEPENDENCIES IN MICE Yuki Yamasaki, Kaoru Kobayashi, Naoya Kameyama, Mika Endo and Kan Chiba Laboratory of Pharmacology and Toxicology, Graduate School of Pharmaceutical Sciences, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba 260-8675, Japan [Purpose] SREBP-2 is a key transcription factor for the cholesterol homeostasis. Recent studies have suggested the association of CYP3A, major drug-metabolizing enzymes, with cholesterol metabolism. We previously found that SREBP-2 inhibits HNF-4α-mediated Cyp3a11 expression in reporter gene assays. However, the mechanism remains unknown. In the present study, we have investigated a mechanism for the SREBP-2-mediated inhibition of hepatic Cyp3a11 expression. [Methods] Pull-down assays were performed with GST-fused HNF-4α or SREBP-2, and in vitro synthesized SREBP-2 and PGC-1α. Reporter assays were performed with Cyp3a11 reporter plasmids containing 5’ -flanking regions of Cyp3a11, and SREBP-2 and PGC-1α expression plasmid. Chromatin immunoprecipitation (ChIP) assays were performed with mouse livers. [Results and Discussion] SREBP-2 showed the interaction with HNF-4α in pull-down assays, but was unable to interact with HNF-4α bound to DNA in the assays. Furthermore, SREBP-2 inhibited the interaction of HNF4α with PGC-1α through the binding to PGC-1α. PGC-1α overexpression relieved the SREBP-2-mediated reduction of Cyp3a11 expression in reporter assays. ChIP assays demonstrated that the extent of PGC-1α binding to the Cyp3a11 promoter was reduced in mouse livers by feeding a low-cholesterol diet, which activates hepatic SREBP-2. [Conclusions] Activated SREBP-2 is suggested to interact with PGC-1α in mouse livers at a condition of reduced cholesterol intake. This may result in the reduced PGC-1α recruitment to HNF-4α on the Cyp3a11 promoter and the subsequent down-regulation of Cyp3a11 expression.