Department of Pharmaceutical Sciences, College of Pharmacy, University of New Mexico, Albuquerque, New Mexico 87131-0001, USA.
Toxicol Sci. 2012 May;127(1):120-9. doi: 10.1093/toxsci/kfs099. Epub 2012 Mar 2.
Human arsenic exposure is associated with increased risk of skin cancer, and arsenite greatly enhances ultraviolet (UV)-induced skin tumors in a mouse model of carcinogenesis. Inhibition of DNA repair is one proposed mechanism for the observed cocarcinogenicity. We have previously demonstrated that low concentrations of arsenite inhibit poly(ADP-ribose) polymerase (PARP)-1, thus interfering with DNA repair process triggered by UV radiation. Because overactivation of PARP-1 often leads to apoptotic cell death, and unrepaired DNA lesions promote genomic instability and carcinogenesis, we hypothesized that inhibition of PARP-1 by arsenic may promote the survival of potentially "initiated carcinogenic cells," i.e., cells with unrepaired DNA lesions. In the present study, we tested this hypothesis on UV-challenged HaCat cells. Cells were pretreated with 2μM arsenite for 24 h before UV exposure. Outcome parameters included apoptotic death rate, PARP-1 activation, apoptotic molecules, and retention of DNA lesions. UV exposure induced PARP-1 activation and associated poly(ADP-ribose) production, apoptosis-inducing factor release, cytochrome C release, and caspases activation, which led to apoptotic death in HaCat cells. Pretreatment with 2μM arsenite significantly inhibited UV-induced cell death as well as the associated molecular events. Notably, knockdown of PARP-1 with small interfering RNA completely abolished the antagonism of arsenite. Furthermore, arsenite pretreatment led to long-term retention of UV-induced cyclobutane pyrimidine dimers. Together, these results suggest that low concentration of arsenite reduces UV-induced apoptosis via inhibiting PARP-1, thus promoting the survival of cells with unrepaired DNA lesions, which may be an important mechanism underlying arsenic cocarcinogenic action.
人类砷暴露与皮肤癌风险增加有关，亚砷酸盐极大地增强了致癌小鼠模型中紫外线 (UV) 诱导的皮肤肿瘤。抑制 DNA 修复是观察到的协同致癌作用的一种提出的机制。我们之前已经证明，低浓度的亚砷酸盐抑制聚 (ADP-核糖) 聚合酶 (PARP)-1，从而干扰由 UV 辐射引发的 DNA 修复过程。由于 PARP-1 的过度激活通常导致细胞凋亡，而未修复的 DNA 损伤促进基因组不稳定性和致癌作用，因此我们假设砷对 PARP-1 的抑制可能促进潜在“起始致癌细胞”的存活，即具有未修复的 DNA 损伤的细胞。在本研究中，我们在 UV 挑战的 HaCat 细胞上测试了这一假设。细胞在用 UV 暴露前用 2μM 亚砷酸盐预处理 24 小时。结果参数包括凋亡死亡率、PARP-1 激活、凋亡分子和 DNA 损伤的保留。UV 暴露诱导 PARP-1 激活和相关的聚（ADP-核糖）产生、凋亡诱导因子释放、细胞色素 C 释放和半胱天冬酶激活，导致 HaCat 细胞凋亡。用 2μM 亚砷酸盐预处理可显著抑制 UV 诱导的细胞死亡以及相关的分子事件。值得注意的是，用小干扰 RNA 敲低 PARP-1 完全消除了砷的拮抗作用。此外，亚砷酸盐预处理导致 UV 诱导的环丁烷嘧啶二聚体的长期保留。总之，这些结果表明，低浓度的亚砷酸盐通过抑制 PARP-1 减少 UV 诱导的细胞凋亡，从而促进未修复 DNA 损伤细胞的存活，这可能是砷协同致癌作用的一个重要机制。
