There is a growing appreciation that pancreatic cancers harbor higher numbers of bacteria & fungi compared to normal pancreatic tissue in both humans & mice. These microbes have been suggested to contribute to pancreatic carcinogenesis, & impact therapeutic sensitivity & resistance. Dual oxidase 2 (DUOX2), one of the seven NADPH oxidases, is expressed at the pancreatic cancer plasma membrane & generates extracellular hydrogen peroxide (H2O2). We previously demonstrated that DUOX protein was significantly upregulated in pancreatitis, pancreatic intra-epithelial neoplasia (PanIN), & some early stage pancreatic ductal adenocarcinomas (PDACs). Moreover, DUOX expression in these tissues was associated with H2O2-mediated DNA double strand breaks & upregulation of hypoxia markers VEGF & HIF-1α. Incidentally, we also discovered that mycoplasma-contaminated BxPC-3 human pancreatic cancer cells upregulated known oncogenes such as EGFR, MET, & VEGF-A, in concert with ~20-fold upregulation of DUOX2 mRNA. Recently, the cytosolic DNA-sensing cGAS-STING pathway has been implicated as a critical mediator of tumor-targeting immune responses. Using a panel of human colon & pancreatic cancer cell lines coupled with Western blot analysis & qPCR methods, we have demonstrated that the introduction of purified E. coli genomic DNA fragments, as well as several kinds of plasmid DNA, into the pancreatic cancer cell cytosol significantly enhanced DUOX2 RNA & protein expression, leading to an enhanced DNA damage response. For BxPC-3, CFPAC-1, & HTB134 human pancreatic cancer cells, enhanced DUOX2 expression following introduction of exogenous DNA was associated with the activation of the cGAS-STING pathway, as indicated by enhanced IRF-3 and TBK1 phosphorylation. Treatment of these cell lines with exogenous cGAMP for 24h also activated the cGAS-STING pathway and significantly increased DUOX2 expression. Correspondingly, in BxPC-3 cells treated with human cGAS-specific small interfering RNAs, we observed the significant suppression of cGAS RNA and protein expression & related downstream signaling, along with the significant attenuation of DNA-induced DUOX2 RNA & protein. In contrast, exogenous DNA did not upregulate DUOX2 in colon cancer cell lines. In summary, our data suggest that, in pancreatic cancers, a bacteria-containing microenvironment is likely to promote DUOX2-related H2O2 production as a consequence of the bacterial DNA-induced activation of the cGAS-STING innate immunity pathway, which, in turn, could enhance the oxidative milieu, augment leukocyte recruitment, & increase genetic instability, thus contributing to the molecular evolution of pancreatic tumors.
Citation Format: Yongzhong Wu, Stephen L. Wang, Smitha Antony, Jennifer L. Meitzler, Jiamo Lu, Guojian Jiang, Becky Diebold, Mallick David, Mariam M. Konate, Roy Krishnendu, James H. Doroshow. E. coli genomic DNA fragments induce cGAS-STING-mediated DUOX2 expression in human pancreatic cancer cells that is associated with H2O2-related DNA damage [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1755.