Carnitine palmitoyltransferase 1A functions to repress FoxO transcription factors to allow cell cycle progression in ovarian cancer
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Huanjie Shao1,4, Esraa M. Mohamed1, Guoyan G. Xu2, Michael Waters1, Kai Jing1, Yibao Ma1, Yan Zhang2, Sarah Spiegel1, Michael O. Idowu3, Xianjun Fang1
1Departments of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, VA 23298, USA
2Department of Medicinal Chemistry, Virginia Commonwealth University, Richmond, VA 23298, USA
3Department of Pathology, Virginia Commonwealth University, Richmond, VA 23298, USA
4Institute of Biological Sciences, Shaanxi Normal University, Xi’an, China
Xianjun Fang, e-mail: firstname.lastname@example.org
Keywords: fatty acid β-oxidation, ovarian cancer, CPT1A, FoxO, p21
Received: July 31, 2015 Accepted: November 26, 2015 Published: December 24, 2015
Cancer cells rely on hyperactive de novo lipid synthesis for maintaining malignancy. Recent studies suggest involvement in cancer of fatty acid oxidation, a process functionally opposite to lipogenesis. A mechanistic link from lipid catabolism to oncogenic processes is yet to be established. Carnitine palmitoyltransferase 1 (CPT1) is a rate-limiting enzyme of fatty acid β-oxidation (FAO) that catalyzes the transfer of long-chain acyl group of the acyl-CoA ester to carnitine, thereby shuttling fatty acids into the mitochondrial matrix for β-oxidation. In the present study, we demonstrated that CPT1A was highly expressed in most ovarian cancer cell lines and primary ovarian serous carcinomas. Overexpression of CPT1A correlated with a poor overall survival of ovarian cancer patients. Inactivation of CPT1A decreased cellular ATP levels and induced cell cycle arrest at G0/G1, suggesting that ovarian cancer cells depend on or are addicted to CPT1A-mediated FAO for cell cycle progression. CPT1A deficiency also suppressed anchorage-independent growth and formation of xenografts from ovarian cancer cell lines. The cyclin-dependent kinase inhibitor p21WAF1 (p21) was identified as most consistently and robustly induced cell cycle regulator upon inactivation of CPT1A. Furthermore, p21 was transcriptionally upregulated by the FoxO transcription factors, which were in turn phosphorylated and activated by AMP-activated protein kinase and the mitogen-activated protein kinases JNK and p38. Our results established the oncogenic relevance of CPT1A and a mechanistic link from lipid catabolism to cell cycle regulation, suggesting that CPT1A could be a prognostic biomarker and rational target for therapeutic intervention of cancer.
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