Sterol regulatory element-binding protein-2 interacts with hepatocyte nuclear factor-4 to enhance sterol isomerase gene expression in hepatocytes.
In the course of an effort to identify unknown targets genes for sterol regulatory element-binding proteins (SREBPs) by PCR, the gene for ATP citrate-lyase was determined to be one such gene. (Sato, R., Okamoto, A., Inoue, J., Miyamoto, W., Sakai, Y., Emoto, N., Shimano, H., and Maeda, M. (2000) J. Biol. Chem. 275, 12497-12502). We here report that gene expression of sterol Delta8-isomerase (SI), which catalyzes the conversion of the 8-ene isomer into the 7-ene isomer in the last steps of the cholesterol biosynthetic pathway, is regulated by SREBPs, mainly by SREBP-2. Luciferase assays using the promoter of the human SI gene revealed that a 200-base pair segment upstream region from the transcription start site contains functional elements required for the activity of the SREBPs, Sp1 and NF-Y. Interestingly, SI gene expression was well regulated by sterols in Caco-2 and HepG2 cells, in contrast with HEK293 and HeLa cells. Overexpression of hepatocyte nuclear factor (HNF)-4 in HEK293 cells augmented expression of SREBP-responsive genes including the SI gene, whereas inactivation of HNF-4 by small interfering RNAs in HepG2 cells reduced the SI gene promoter activity. The in vitro pull-down and in vivo co-immunoprecipitation experiments showed the direct interaction between SREBP-2 and HNF-4. These data provide a novel pathway by which HNF-4 potentiates the SREBP functions and stimulates expression of SREBP-responsive genes in enterohepatic cells.
Misawa
Koichi
K
Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan.
Horiba
Taro
T
Arimura
Naoto
N
Hirano
Yuko
Y
Inoue
Jun
J
Emoto
Noriaki
N
Shimano
Hitoshi
H
Shimizu
Makoto
M
Sato
Ryuichiro
R
D000818:Animals; D001483:Base Sequence; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D015152:Blotting, Northern; D016466:CHO Cells; D002460:Cell Line; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism; D006224:Cricetinae; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D005982:Glutathione Transferase / Q000378:metabolism; D006367:HeLa Cells; D051557:Hepatocyte Nuclear Factor 4; D022781:Hepatocytes / Q000378:metabolism*; D006801:Humans; D008156:Luciferases / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D010750:Phosphoproteins / Q000378:metabolism*; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D034741:RNA, Small Interfering / Q000378:metabolism; D013251:Steroid Isomerases / Q000096:biosynthesis* / Q000737:chemistry; D051782:Sterol Regulatory Element Binding Protein 2; D014157:Transcription Factors / Q000378:metabolism*
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins; D051557:Hepatocyte Nuclear Factor 4; C403128:MLX protein, human; D010750:Phosphoproteins; D034741:RNA, Small Interfering; C497390:SREBF2 protein, human; C497391:Srebf2 protein, mouse; D051782:Sterol Regulatory Element Binding Protein 2; C501970:Tcfl4 protein, mouse; D014157:Transcription Factors; D002784:Cholesterol; D008156:Luciferases; D005982:Glutathione Transferase; D013251:Steroid Isomerases; C022669:delta(8)-delta(7)-sterol isomerase