Contribution of NADPH oxidase to the retention of UVR-induced DNA damage by arsenic

DSB-induced oxidative stress: Uncovering crosstalk between DNA damage response and cellular metabolism

While that ROS causes DNA damage is well documented, there has been limited investigation into whether DNA damages and their repair processes can conversely induce oxidative stress. By generating a site-specific DNA double strand break (DSB) via I-SceI endonuclease expression in S. cerevisiae without damaging other cellular components, this study demonstrated that DNA repair does trigger oxidative stress. Deleting genes participating in the initiation of the resection step of homologous recombination (HR), like the MRX complex, resulted in stimulation of ROS. In contrast, deleting genes acting downstream of HR resection suppressed ROS levels. Additionally, blocking non-homologous end joining (NHEJ) also suppressed ROS. Further analysis identified Rad53 as a key player that relays DNA damage signals to alter redox metabolism in an HR-specific manner. These results suggest both HR and NHEJ can drive metabolism changes and oxidative stress, with NHEJ playing a more prominent role in ROS stimulation. Further analysis revealed a correlation between DSB-induced ROS increase and enhanced activity of NADPH oxidase Yno1 and various antioxidant enzymes. Deleting the antioxidant gene SOD1 induced synthetic lethality in HR-deficient mutants like mre11Δ and rad51Δ upon DSB induction. These findings uncover a significant interplay between DNA repair mechanisms and cellular metabolism, providing insights into understanding the side effects of genotoxic therapies and potentially aiding development of more effective cancer treatment strategies.

Arsenic is a potent co-mutagen of ultraviolet light

Arsenic enhances the carcinogenicity of ultraviolet radiation (UVR). However, the mechanisms of arsenic-driven oncogenesis are not well understood. Here, we utilize experimental systems to investigate the carcinogenic and mutagenic properties of co-exposure to arsenic and UVR. In vitro and in vivo exposures indicate that, by itself, arsenic is not mutagenic. However, in combination with UVR, arsenic exposure has a synergistic effect leading to an accelerated mouse skin carcinogenesis and to more than 2-fold enrichment of UVR mutational burden. Notably, mutational signature ID13, previously found only in UVR-associated human skin cancers, is observed exclusively in mouse skin tumors and cell lines jointly exposed to arsenic and UVR. This signature was not observed in any model system exposed purely to arsenic or purely to UVR, making ID13, to the best of our knowledge, the first co-exposure signature to be reported using controlled experimental conditions. Analysis of existing skin cancer genomics data reveals that only a subset of cancers harbor ID13 and these exhibit an elevated UVR mutagenesis. Our results report a unique mutational signature caused by a co-exposure to two environmental carcinogens and provide comprehensive evidence that arsenic is a potent co-mutagen and co-carcinogen of UVR.

Arsenic is a potent co-mutagen of ultraviolet light

Environmental co-exposures are widespread and are major contributors to carcinogenic mechanisms. Two well-established environmental agents causing skin cancer are ultraviolet radiation (UVR) and arsenic. Arsenic is a known co-carcinogen that enhances UVR's carcinogenicity. However, the mechanisms of arsenic co-carcinogenesis are not well understood. In this study, we utilized primary human keratinocytes and a hairless mouse model to investigate the carcinogenic and mutagenic properties of co-exposure to arsenic and UVR. In vitro and in vivo exposures revealed that, on its own, arsenic is neither mutagenic nor carcinogenic. However, in combination with UVR, arsenic exposure has a synergistic effect leading to an accelerated mouse skin carcinogenesis as well as to more than 2-fold enrichment of UVR mutational burden. Notably, mutational signature ID13, previously found only in UVR-associated human skin cancers, was observed exclusively in mouse skin tumors and cell lines jointly exposed to arsenic and UVR. This signature was not observed in any model system exposed purely to arsenic or purely to UVR, making ID13 the first co-exposure signature to be reported using controlled experimental conditions. Analysis of existing genomics data from basal cell carcinomas and melanomas revealed that only a subset of human skin cancers harbor ID13 and, consistent with our experimental observations, these cancers exhibited an elevated UVR mutagenesis. Our results provide the first report of a unique mutational signature caused by a co-exposure to two environmental carcinogens and the first comprehensive evidence that arsenic is a potent co-mutagen and co-carcinogen of UVR. Importantly, our findings suggest that a large proportion of human skin cancers are not formed purely due to UVR exposure but rather due to a co-exposure of UVR and other co-mutagens such as arsenic.

New Insights into How Melatonin Ameliorates Bisphenol A-Induced Colon Damage: Inhibition of NADPH Oxidase

Bisphenol A (BPA) is an endocrine disruptor, widely employed, and detected in many consumer products and food items. Oral intake poses a great threat to intestinal health. Melatonin (MT) stands out as an endogenous, dietary, and therapeutic molecule with potent antioxidant capacity. To explore the protective effect of MT against BPA-induced colon damage and the role of NADPH oxidase (NOX) in this process, we established mice and colonic epithelial cell (NCM460) models of BPA exposure and treated with MT. In vitro and in vivo results showed that MT ameliorated BPA-induced oxidative stress, DNA damage, and the G2/M cell cycle arrest. MT also downregulated the expression of NOX family-related genes, reversed the inhibition of the base excision repair (BER) pathway, promoted the activation of non-homologous end-joining (NHEJ) pathway, and suppressed the mRNA and protein expression of ATM, Chk1/2, and p53. Diphenyleneiodonium chloride (DPI), a NOX-specific inhibitor, also attenuated the toxic effects of BPA on NCM460 cells. Furthermore, molecular docking revealed that MT could bind to NOX. Conclusively, our finding suggested that MT can ameliorate BPA-induced colonic DNA damage by scavenging NOX-derived ROS, which further attenuates G2/M cell cycle arrest dependent on the ATM-Chk1/2-p53 axis.

Arsenic and cancer: Evidence and mechanisms

Arsenic is a potent carcinogen and poses a significant health concern worldwide. Exposure occurs through ingestion of drinking water and contaminated foods and through inhalation due to pollution. Epidemiological evidence shows arsenic induces cancers of the skin, lung, liver, and bladder among other tissues. While studies in animal and cell culture models support arsenic as a carcinogen, the mechanisms of arsenic carcinogenesis are not fully understood. Arsenic carcinogenesis is a complex process due its ability to be metabolized and because of the many cellular pathways it targets in the cell. Arsenic metabolism and the multiple forms of arsenic play distinct roles in its toxicity and contribute differently to carcinogenic endpoints, and thus must be considered. Arsenic generates reactive oxygen species increasing oxidative stress and damaging DNA and other macromolecules. Concurrently, arsenic inhibits DNA repair, modifies epigenetic regulation of gene expression, and targets protein function due its ability to replace zinc in select proteins. While these mechanisms contribute to arsenic carcinogenesis, there remain significant gaps in understanding the complex nature of arsenic cancers. In the future improving models available for arsenic cancer research and the use of arsenic induced human tumors will bridge some of these gaps in understanding arsenic driven cancers.