Abstract 1142: COP1 functions as a sensor of cellular lipids and regulator of lipogenesis in human cancer cells

Abstract

Abstract Background Constitutive photomorphogenesis protein 1 (COP1; also known as Rfwd2), an evolutionally conserved E3 ubiquitin ligase, has been defined to mediate the degradation of several important proteins, such as p53, c-Jun, ETS, FOXO1 and ACC1, being involved in tumorigenesis. In response to DNA damage, COP1 is autodegraded in the context of ATM, which is triggered by 14-3-3σ. However, the biological function and expression regulation of COP1 remain to be fully understood. This study reports a novel function of COP1 in lipid metabolism. Methods We targeted COP1 expression in cancer cells MCF-7 and HepG2 with COP1 shRNA lentivirus and COP1 overexpression lentivirus, respectively. We investigated the lipid synthesis, glucose oxidation and conversion into lipids in these cells using radiolabeled acetate and glucose and lipid complex analysis. Quantitative real-time PCR and Western blot were used to examine gene expression. Acetyl CoA carboxylase-1 (ACC1) siRNA and TOFA, an inhibitor of ACC1, were used to modulate the intracellular lipid synthesis. Results Lipid depletion induced by acetyl CoA carboxylase-1 (ACC1) knockdown or the inhibition of ACC1 by TOFA induced COP1 expression, but palmatic acid, the end-product of de novo fatty acid synthesis pathway, reversed TOFA-induced COP1 expression. In addition, U73122, an inhibitor of phospholipase C that cleaves PIP2 into DAG and IP3, triggered COP1 expression. These data suggest that COP1 expression is mediated by cellular lipid state, and the lipid second messengers (PIP2 and DAG) are involved in the expression regulation of COP1. In contrast, the ectopic expression of COP1 greatly reduced pAMPK and pACC1 levels, but elevated fatty acid synthase (FASN) expression, leading to the increase of fatty acid (FA)/lipid synthesis. In sharp contrast, siRNA-mediated COP1 knockdown in cancer cells significantly increased pACC1 and pAMPK levels and reduced FASN expression, leading to decrease of lipid synthesis. The cell growth and proliferation was accordingly changed in response to the alterations of lipid synthesis. Altogether our data suggest that COP1 expression is regulated through the lipid second messenger mediated signaling, and the upregulated COP1 in turn enhances lipid synthesis, functioning as a positive feedback. Conclusion COP1 functions as a sensor of cellular lipid state and promoter of lipogenesis, facilitating tumorigenesis. Note: This abstract was not presented at the meeting. Citation Format: Chenfei Huang, Yiwen Bu, Deliang Cao. COP1 functions as a sensor of cellular lipids and regulator of lipogenesis in human cancer cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1142. doi:10.1158/1538-7445.AM2015-1142