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Molecular and Cellular Biology, June 2007, p. 4238-4247, Vol. 27, No. 12
0270-7306/07/$08.00+0 doi:10.1128/MCB.00317-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.
Peroxisome Proliferator-Activated Receptor
Regulates a MicroRNA-Mediated Signaling Cascade Responsible for Hepatocellular Proliferation
,
Yatrik M. Shah,
Keiichirou Morimura,
Qian Yang,
Tomotaka Tanabe,
Mitsuhiro Takagi, and
Frank J. Gonzalez*
Laboratory of Metabolism, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland
Received 21 February 2007/
Returned for modification 29 March 2007/
Accepted 5 April 2007
Activation of peroxisome proliferator-activated receptor
(PPAR
) leads to hepatocellular proliferation and liver carcinomas. The early events mediating these effects are unknown. A novel mechanism by which PPAR
regulates gene expression and hepatocellular proliferation was uncovered. MicroRNA (miRNA) expression profiling demonstrated that activated PPAR
was a major regulator of hepatic miRNA expression. Of particular interest, let-7C, an miRNA important in cell growth, was inhibited following 4-h treatment and 2-week and 11-month sustained treatment with the potent PPAR
agonist Wy-14,643 in wild-type mice. let-7C was shown to target c-myc via direct interaction with the 3' untranslated region of c-myc. The PPAR
-mediated induction of c-myc via let-7C subsequently increased expression of the oncogenic mir-17-92 cluster; these events did not occur in Ppar
-null mice. Overexpression of let-7C decreased c-myc and mir-17 and suppressed the growth of Hepa-1 cells. Furthermore, using the human PPAR
-expressing mouse model, which is responsive to Wy-14,643 effects on ß-oxidation and serum triglycerides but resistant to hepatocellular proliferation and tumorigenesis, we demonstrated a critical role for let-7C in liver oncogenesis. Wy-14,643 treatment did not inhibit let-7C or induce c-myc and mir-17 expression. These observations reveal a let-7C signaling cascade critical for PPAR
agonist-induced liver proliferation and tumorigenesis.
* Corresponding author. Mailing address: Building 37, Room 3106, National Cancer Institute, Bethesda, MD 20892. Phone: (301) 496-9067. Fax: (301) 496-8419. E-mail:
fjgonz{at}helix.nih.gov
Published ahead of print on 16 April 2007.
Supplemental material for this article may be found at http://mcb.asm.org/.
Molecular and Cellular Biology, June 2007, p. 4238-4247, Vol. 27, No. 12
0270-7306/07/$08.00+0 doi:10.1128/MCB.00317-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.
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