Abstract 1150: Downregulation of Hedgehog signaling via Sirt6 activation is important to docosahexaenoic acid-induced cell death in human EGFR mutant non-small cell lung cancer
Authors: Jeong Soyeon , Jing Kaipeng , Shin Soyeon , Han Seung-Hyeon , Yoo Yoon-Seon , Silwal Prashanta , Jeon Young-Joo , Heo Jun-Young , Kweon Gi-Ryang , Park Seung-Kiel , Park Jong-Il , Wu Tong , Lim Kyu 
Published: July 2017

Abstract
Docosahexaenoic acid (DHA) induces apoptotic cell death through several mechanisms in cancer cells. Here we report that DHA-induced apoptotic cell death is related to the inhibition of Hedgehog signaling via SIRT6 activation in human PC9 and H1975 nonsmall cell lung cancer (NSCLC). DHA-induced cell death was confirmed increase of the protein levels of cleaved PARP and caspase-3 Bax as well as the number of TUNEL positive cells and the Sub-G1 proportion in PC9 and H1975. DHA significantly increased the SIRT6 levels. Knockdown of SIRT6 by siRNAs inhibited apoptosis induced by DHA, while SIRT6 overexpression increased apoptotic cell death, indicating that DHA-induced SIRT6 activation results in apoptosis. In addition, SIRT6 activation by DHA treatment was associated with downregulation of Hh signaling and knockdown of SIRT6 resulted in augmentation of Hh signaling, suggesting elevation of SIRT6 levels in DHA-treated NSCLC cells leads to downregulate the Hh signaling. Smo activator SAG increased the protein levels of Hh signaling molecules by DHA, and SAG plus DHA treatment decreased cleaved PARP levels, implying that DHA-inhibited Hh signaling is related to apoptotic cell death. To unveil the effects of endogenous DHA on apoptosis via SIRT6-mediated Hh signaling downregulation, we used PC9 stable cell lines of fat-1 (ω3-desaturase) gene. The SIRT6 levels were significantly increased and Hh signaling molecules were diminished in fat-1 stable PC9 (f-PC9) cells, compared with the cells transfected with the control vector (c-PC9). Moreover, SIRT6 expression was elevated and Gli and smo levels were inhibited in tumor tissues from f-PC9 cells-injected mice, demonstrating that DHA regulates SIRT6 and Hh signaling in vivo. Taken together, these results suggest that DHA may induce apoptotic cell death through SIRT6-modulated Hh signaling suppression in human NSCLC cells. These findings implicate that ω3-PUFAs may represent a potential effective therapy for the chemoprevention and treatment of human NSCLC. [This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (2007-0054932, NRF-2015R1D1A1A01056887) and by the framework of international cooperation program managed by National Research Foundation of Korea (2015K2A2A6002008)].
Citation Format: Soyeon Jeong, Kaipeng Jing, Soyeon Shin, Seung-Hyeon Han, Yoon-Seon Yoo, Prashanta Silwal, Young-Joo Jeon, Jun-Young Heo, Gi-Ryang Kweon, Seung-Kiel Park, Jong-Il Park, Tong Wu, Kyu Lim. Downregulation of Hedgehog signaling via Sirt6 activation is important to docosahexaenoic acid-induced cell death in human EGFR mutant non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1150. doi:10.1158/1538-7445.AM2017-1150