Abstract 4495: Role of base excision repair (BER) pathway in regulation of KRAS expression in pancreatic cancer

Abstract

Activating mutations in KRAS proto-oncogene, a signature event driving the development, progression and therapeutic resistance of pancreatic ductal adenocarcinoma (PDAC), remains undruggable. The occurrence of guanine oxidation (8-oxoguanine) in the KRAS promoter and up-regulation of KRAS gene transcription under oxidative stress has been shown to be associated with KRAS expression and cancer development and progression. However, the molecular mechanism by which 8-oxoguanine damage regulates KRAS expression is largely unknown. Here, we show that the base excision repair (BER) pathway, a fundamental DNA damage repair pathway that processes most of the endogenous damages including oxidative base damage is involved in regulation of KRAS expression and survival of PDAC. We show that Apurinic/apyrimidinic endonuclease (APE1), a key enzyme of the BER pathway, is highly elevated in pancreatic cancer tissue samples. To elucidate the role of active BER pathway in the regulation of KRAS expression, we used real-time PCR (RT-PCR) analysis. Inflicting cells with oxidative damage using glucose oxidase increased KRAS gene expression in control cells but not in APE1 downregulated cells. ChIP assay showed enhanced occupancy of APE1 in KRAS promoter upon oxidative stress. Consistent with this, using synthetic oligonucleotide containing the KRAS promoter region, we showed that APE1 could bind and cleave AP site in KRAS promoter. Further, ChIP-qPCR analysis showed decreased occupancy of MAZ, a transcription factor, to the KRAS promoter in APE1 downregulated cells. Down-regulation of APE1 also resulted in decreased KRAS expression and increased sensitivity of pancreatic cancer cells to routinely used chemotherapeutic agents such as Gemcitabine, 5-Fluorouracil, Oxaliplatin, etc., suggesting that targeting APE1 and in turn, BER can sensitize pancreatic cancer cells. Our study suggests that BER pathway or APE1 plays a significant role in the tumor-selective regulation of gene expression and sensitization of cancer cells to chemotherapy, and supports the further investigation of novel treatments that target this pathway for cancer therapy.

Citation Format: Suravi Pramanik, Shrabasti Roychoudhury, Hannah Harris, Heyu Song, Kishor K. Bhakat. Role of base excision repair (BER) pathway in regulation of KRAS expression in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4495.