HNF4α is a crucial modulator of the cholesterol-dependent regulation of NPC1L1

Purpose. Niemann-Pick C1-like 1 (NPC1L1) has been identified as a target of ezetimibe and found to be responsible for intestinal cholesterol absorption. Although, it was recently demonstrated that sterol responsive element binding protein 2 (SREBP2) is responsible for the cholesterol-dependent down-regulation of NPC1L1, the molecular mechanism of NPC1L1 expression is not fully understood. In the present study, we examined the involvement of hepatocyte nuclear factor 4 alpha (HNF4 alpha), a key modulator of lipid metabolism, in the transcriptional regulation of human NPC1L1 gene. Methods. Reporter gene assays and EMSAs were performed using human NPC1L1 promoter constructs and the effect of siHNF4 alpha was examined. Results. Transfection of SREBP2 induced the transcriptional activities of NPC1L1 and additional transfection of HNF4 alpha results in a marked stimulation of the activities. Studies with deletion mutants indicated that important elements are located within 264 nt upstream in the human NPC1L1 promoter. In addition, studies with mutations in putative binding sites of HNF4 alpha indicated the existence of binding sites in -209 to -197 and -52 to -40. Moreover, HNF4 alpha knockdown resulted in the reduced expression and regulation by cholesterol. Conclusions. It is concluded that HNF4 alpha plays a crucial role in the expression and regulation of human NPC1L1 gene.