Journal
MOLECULAR AND CELLULAR BIOLOGY
Volume 27, Issue 12, Pages 4238-4247Publisher
AMER SOC MICROBIOLOGY
DOI: 10.1128/MCB.00317-07
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- Intramural NIH HHS Funding Source: Medline
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Activation of peroxisome proliferator-activated receptor alpha (PPARot) leads to hepatocellular proliferation and liver carcinomas. The early events mediating these effects are unknown. A novel mechanism by which PPARot regulates gene expression and hepatocellular proliferation was uncovered. MicroRNA (miRNA) expression profiling demonstrated that activated PPARot 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 alpha 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 alpha-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 alpha-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 alpha-expressing mouse model, which is responsive to Wy-14,643 effects on beta-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 PPARot agonist-induced liver proliferation and tumorigenesis.
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