Human NPC1L1 expression is positively regulated by PPARα.
OBJECTIVE
Niemann-Pick C1-like 1 (NPC1L1), a pharmacological target of ezetimibe, is responsible for cholesterol absorption in enterocytes and hepatocytes. In the present study, the involvement of peroxisome proliferator-activated receptor α (PPARα) and its cofactor, PPARγ coactivator 1α (PGC1α) in the transcriptional regulation of human NPC1L1 was analyzed.


METHODS
Reporter gene assays and electrophoretic mobility shift assays (EMSAs) were performed with the 5'-flanking region of the human NPC1L1 gene and the effect of siPPARα was examined.


RESULTS
PPARα-mediated transactivation was observed with human NPC1L1 promoter constructs. Detailed analyses using deletion- and mutated-promoter constructs revealed the presence of a functional PPARα-response element (PPRE) upstream of the human NPC1L1 gene (-846/-834), a direct binding of PPARα and RXRα to which was confirmed by EMSAs. Moreover, PPARα-specific knockdown resulted in a significant decrease in the endogenous expression of NPC1L1 mRNA and protein in human-derived HepG2 cells. Furthermore, cotransfection of PGC1α stimulated the SREBP2/HNF4α- and PPARα/RXRα-mediated activation of the human NPC1L1 promoter.


CONCLUSIONS
We found that PPARα positively regulates human NPC1L1 transcription via direct binding to a PPRE. Additionally, PGC1α stimulates the SREBP2/HNF4α- and PPARα/RXRα-mediated transactivation of human NPC1L1. These findings may provide new insights into the close relationship of glucose, fatty acids and cholesterol homeostasis.
Iwayanagi
Yuki
Y
Department of Pharmacy, The University of Tokyo Hospital Faculty of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8655, Japan.
Takada
Tappei
T
Tomura
Fumiya
F
Yamanashi
Yoshihide
Y
Terada
Tomohiro
T
Inui
Ken-ichi
K
Suzuki
Hiroshi
H
D001384:Azetidines / Q000494:pharmacology; D002784:Cholesterol / Q000235:genetics / Q000378:metabolism; D024202:Electrophoretic Mobility Shift Assay; D020895:Enterocytes / Q000378:metabolism; D000069438:Ezetimibe; D011345:Fenofibrate / Q000494:pharmacology; D005786:Gene Expression Regulation; D056945:Hep G2 Cells; D006801:Humans; D007408:Intestinal Absorption / Q000187:drug effects / Q000235:genetics; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000187:drug effects; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D026901:Membrane Transport Proteins; D009542:Niemann-Pick Diseases / Q000235:genetics / Q000378:metabolism; D047493:PPAR alpha / Q000235:genetics / Q000378:metabolism*; D047495:PPAR gamma / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D020218:Response Elements / Q000235:genetics
D001384:Azetidines; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; C410800:NPC1L1 protein, human; D047493:PPAR alpha; D047495:PPAR gamma; D002784:Cholesterol; D000069438:Ezetimibe; D011345:Fenofibrate