Abstract B54: The role of fatty acid synthase in regulation of autophagy in colorectal cancer

Fatty Acid Synthase (FASN), a key enzyme of de novo lipid synthesis, is significantly up regulated in colorectal cancer (CRC) and its activity is associated with worse prognosis. Recent studies suggest that up regulation of FASN provides a survival advantage to cancer cells by reprogramming metabolic pathways and maintaining energy homeostasis. Autophagy is an adaptive survival mechanism induced under conditions of stress. However, the interconnection between de novo lipogenesis and autophagy has not been studied. Therefore, the purpose of our study was to determine the role of FASN in regulation of autophagy in vitro and in human CRC. Methods: Expression of p62, LC3, and Beclin1 (autophagy markers) and pAMPK was assessed in CRC cell lines with altered expression of FASN cultured in normal, serum free medium and/or detached conditions by western blot and confocal microscopy. Human specimens, including matching cancer, normal colon and liver metastasis tissues from 19 patients were analyzed for expression of FASN, p62, and pAMPK by immunohistochemistry (IHC). The effect of stable knockdown of p62 on proliferation and apoptosis was analyzed in CRC cell lines by cell counting, cell death ELISA and western blot analysis. Results: We demonstrated that under metabolic stress conditions overexpression of FASN is associated with a decrease in autophagy as shown by accumulation of p62, a marker of inhibition of autophagy, and a decrease in LC3, an autophagosome marker, in CRC cell lines. Under energy stress conditions, overexpression of FASN is also associated with a decrease in activation of pAMPK. Statistical analysis of IHC staining showed that expression of FASN and p62 are significantly higher in cancer and metastatic tissues as compared to normal colon tissues. A significant moderate correlation between expression of FASN and p62 was determined in human primary CRCs. Stable knockdown of p62 in CRC cell lines demonstrated that an increased level of p62 is associated with increased cellular proliferation and decreased cell death. Conclusions: We have identified a novel link between FASN and autophagy, and showed that, under metabolic stress conditions, overexpression of FASN is associated with inhibition of autophagy. Furthermore, for the first time, we showed the significant correlation between expression of FASN and p62 in human CRC. The effects of p62 on cellular proliferation and apoptosis suggest that p62 may also play a role independent of autophagy; therefore, further studies are require to understand how FASN-mediated up regulation of p62 contributes to tumorigenesis. The differential expression of FASN in normal versus cancer cells makes de novo lipogenesis a desirable target for therapeutic intervention. Understanding the role of FASN in regulation of survival mechanisms of cancer cells including autophagy will reveal new therapeutic approaches in CRC. Citation Format: Yekaterina Zaytseva, Jennifer Harris, Ji Tae Kim, Eun Lee, Heidi Weiss, Tianyan Gao, Mark Evers. The role of fatty acid synthase in regulation of autophagy in colorectal cancer. [abstract]. In: Proceedings of the AACR Special Conference: Metabolism and Cancer; Jun 7-10, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(1_Suppl):Abstract nr B54.