Activated Sterol Regulatory Element-Binding Protein-2 Suppresses Hepatocyte Nuclear Factor-4-Mediated Cyp3a11 Expression in Mouse Liver

Abstract

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 Ϫ1581 to Ϫ1570 of Cyp3a11. This region contained a putative hepatocyte nuclear factor-4␣ (HNF-4␣) binding motif, and HNF-4␣, 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 ␥ coactivator-1␣ (PGC-1␣), a major coactivator for HNF-4␣, via its transactivation domain and inhibited the interaction between HNF-4␣ and PGC-1␣ in vitro. A mutant SREBP-2 lacking the transactivation domain consistently failed to reduce Cyp3a11 reporter activity. Furthermore, PGC-1␣ overexpression relieved the SREBP-2-mediated reduction of Cyp3a11 reporter activity. Finally, chromatin immunoprecipitation assays demonstrated that the extent of PGC-1␣ binding to the Cyp3a11 promoter was reduced by LCD-feeding in mouse livers. In conclusion, activated SREBP-2 interacts with PGC-1␣ in mouse livers at reduced cholesterol intake. This results in the reduced PGC-1␣ recruitment to HNF-4␣ on the Cyp3a11 promoter and the subsequent downregulation of Cyp3a11 expression.

Knockout of mouse Cyp3a gene enhances synthesis of cholesterol and bile acid in the liver

“…In summary, the results of the present study showed that expression of genes encoding enzymes involved in cholesterol biosynthesis is enhanced via the activation of SREBP-2 in the livers of Cyp3a Ϫ / Ϫ mice, possibly due to the decreased formation of oxysterols. Because dietary cholesterol has been reported to affect gene expression of CYP3A enzymes (49)(50)(51), the present observations suggest that CYP3A enzymes play a role in maintaining cholesterol levels at a constant level in the liver. The results of the present study also showed that total cholesterol levels were also decreased by 20% in the livers of Cyp3a Ϫ / Ϫ mice, possibly due to enhanced bile acid synthesis by elevation of CYP7A1 in Cyp3a Ϫ / Ϫ mice.…”

“…Interestingly, it has been reported that feeding a low-cholesterol diet to mice attenuates hepatic Cyp3a11 expression by activating hepatic SREBP-2 ( 49 ). Activated SREBP-2 has been suggested to interact with peroxisome proliferator-activated receptor ␥ coactivator 1 ␣ (PGC1 ␣ ) in the mouse liver, resulting in reduced PGC1 ␣ recruitment to hepatocyte nuclear factor-4 ␣ on the Cyp3a11 promoter and subsequent downregulation of Cyp3a11 expression ( 49 ). Conversely, feeding high-cholesterol diets to rats has been reported to increase expression and activity of CYP3A ( 50 ).…”

Involvement of multiple elements in FXR-mediated transcriptional activation of FGF19

“…Chromatin immunoprecipitation coupled with massively parallel sequencing was used to detect several FXR-binding sites in mouse FXR target genes such as Shp and Ost˛/ˇ [27]. This report suggested that Shp consists of two FXR-responsive elements located in the promoter region and downstream enhancer.…”

“…Sixty-seven hours after transfection, the cells were treated with 0.1 M GW4064 for 5 h. Chromatin immunoprecipitation (ChIP) assays were performed as described previously [27,28] with minor modifications. After crosslinking with 1% formaldehyde and sonication of the cells, supernatant was obtained by centrifugation, and a portion of the supernatant was retained as the input sample.…”

Hepatic nuclear corepressor 1 regulates cholesterol absorption through a TRβ1-governed pathway

“…While CYP3A11 is mainly known as a major drug-metabolizing P450 enzyme, there is evidence that it also plays a role in cholesterol and bile acid metabolism (33,34). It has also been shown that highcholesterol feeding as well as LXRα or LXRα/β deficiency lead to dramatic upregulation of Cyp3a11 expression in mouse liver and overall Cyp3a11 mRNA levels correlate with the liver cholesterol content, suggesting that Cyp3a11 may mediate a compensatory response to cholesterol overload (35,54). These data strongly suggest that upregulation of Cyp27a1 and Cyp3a11 expression in L-ΔID animals is likely responsible for the observed changes in the bile acid pool composition and improved cholesterol tolerance.…”