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Molecular and Cellular Biology, May 2001, p. 2991-3000, Vol. 21, No. 9
0270-7306/01/$04.00+0   DOI: 10.1128/MCB.21.9.2991-3000.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Identification of Liver X Receptor-Retinoid X Receptor as an Activator of the Sterol Regulatory Element-Binding Protein 1c Gene Promoter

Tomohiro Yoshikawa,1 Hitoshi Shimano,2,* Michiyo Amemiya-Kudo,1 Naoya Yahagi,1 Alyssa H. Hasty,1 Takashi Matsuzaka,2 Hiroaki Okazaki,1 Yoshiaki Tamura,1 Yoko Iizuka,1 Ken Ohashi,1 Jun-Ichi Osuga,1 Kenji Harada,1 Takanari Gotoda,1 Satoshi Kimura,1 Shun Ishibashi,1 and Nobuhiro Yamada2

Department of Metabolic Diseases, University of Tokyo, Bunkyo-ku, Tokyo 113-8655,1 and Department of Internal Medicine, Institute of Clinical Medicine, University of Tsukuba, Ibaraki 305-8575,2 Japan

Received 23 October 2000/Returned for modification 19 December 2000/Accepted 9 February 2001

In an attempt to identify transcription factors which activate sterol-regulatory element-binding protein 1c (SREBP-1c) transcription, we screened an expression cDNA library from adipose tissue of SREBP-1 knockout mice using a reporter gene containing the 2.6-kb mouse SREBP-1 gene promoter. We cloned and identified the oxysterol receptors liver X receptor (LXRalpha ) and LXRbeta as strong activators of the mouse SREBP-1c promoter. In the transfection studies, expression of either LXRalpha or -beta activated the SREBP-1c promoter-luciferase gene in a dose-dependent manner. Deletion and mutation studies, as well as gel mobility shift assays, located an LXR response element complex consisting of two new LXR-binding motifs which showed high similarity to an LXR response element recently found in the ABC1 gene promoter, a reverse cholesterol transporter. Addition of an LXR ligand, 22(R)-hydroxycholesterol, increased the promoter activity. Coexpression of retinoid X receptor (RXR), a heterodimeric partner, and its ligand 9-cis-retinoic acid also synergistically activated the SREBP-1c promoter. In HepG2 cells, SREBP-1c mRNA and precursor protein levels were induced by treatment with 22(R)-hydroxycholesterol and 9-cis-retinoic acid, confirming that endogenous LXR-RXR activation can induce endogenous SREBP-1c expression. The activation of SREBP-1c by LXR is associated with a slight increase in nuclear SREBP-1c, resulting in activation of the gene for fatty acid synthase, one of its downstream genes, as measured by the luciferase assay. These data demonstrate that LXR-RXR can modify the expression of genes for lipogenic enzymes by regulating SREBP-1c expression, providing a novel link between fatty acid and cholesterol metabolism.


* Corresponding author. Mailing address: Department of Internal Medicine, Institute of Clinical Medicine, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8575, Japan. Phone and fax: 81-298-63-2170. E-mail: shimano-tky{at}umin.ac.jp.


Molecular and Cellular Biology, May 2001, p. 2991-3000, Vol. 21, No. 9
0270-7306/01/$04.00+0   DOI: 10.1128/MCB.21.9.2991-3000.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.



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