Abstract 1428 The Role of Mitochondrial Fission in Regulating DNA Damage Response in Colorectal Cancer

Colorectal cancer (CRC) ranks fourth in the United States for both incidence and mortality rates. Previous studies have shown that dysregulation of mitochondrial fission and fusion homeostasis contributes to tumorigenesis in CRC. We have shown recently that disruption of mitochondrial fission blocks Wnt signaling activation by inhibiting fatty acid metabolism. The purpose of this study is to determine the functional interaction between mitochondrial dynamics and DNA damage response in CRC cells. The expression of Drp1, a key regulator of mitochondrial fission, was silenced in human CRC cell lines SW480 and HT29 using lentivirus-mediated RNAi. To induce DNA damage response, control and Drp1 knockdown cells were treated with irinotecan (1 μM), a chemotherapy drug commonly used in the treatment of CRC. The extent of DNA damage as well as the activation of DNA repair pathways were analyzed by western blot, RT-qPCR, and confocal microscopy. We show that knockdown of Drp1 increases the expression of gamma-H2AX, a DNA damage marker, both basally and in irinotecan-treated CRC cells. In addition, knockdown of Drp1 alters the activation of DNA repair pathway proteins (e.g., ATM and ATR). Functionally, silencing Drp1 renders CRC cells more sensitive to irinotecan treatment as shown by reduced survival compared to control cells. Taken together, our results suggest that inhibition of mitochondrial fission may exacerbate the genotoxic effects of chemotherapy drugs and improve the efficacy of current treatment options. These findings establish a possible link between mitochondrial fission and DNA damage response in CRC cells. This research is funded by the following grant: R01CA133429.