[Show abstract][Hide abstract] ABSTRACT: Ochratoxin A (OTA), a mycotoxin produced by ubiquitous Aspergilli, is carcinogenic, teratogenic, and nephrotoxic in both humans and animals. Our previous study found that OTA induced DNA double-strand breaks (DSBs) and resulted in G2 phase arrest in human gastric epithelium immortalized (GES-1) cells. DSBs can cause genomic instability, mutations, and neoplastic transformations, and improper repair of DSBs may lead to the development of cancer. Rad51 is a key protein in the homologous recombination (HR) pathway of DSBs repair. The roles of Rad51 in the repair of DNA damage vary in response to different types of cytotoxic agents. The effect of OTA on Rad51 expression and its putative role in the OTA-induced DSBs in GES-1 cells are still not clear enough. The aim of the current study is to elucidate the role of Rad51 in OTA-induced DSBs in GES-1 cells. The results showed that OTA treatment decreased Rad51 expression in a dose- and time-dependent manner. Specific downregulation of Rad51 by siRNA induced DSBs and G2 phase arrest. Rad51 overexpression by transfection with a Rad51-expressing plasmid partly rescued the DSBs and G2 phase arrest in OTA-treated cells. The findings indicate that downregulation of Rad51 contributes to OTA-induced DNA damage in GES-1 cells. Knockdown of p53 with siRNA for 48h effectively reversed the downregulation of Rad51, and decreased the OTA-induced DSBs in GES-1 cells. In addition, the downregulation of Rad51 induced by OTA could be significantly attenuated with specific ERK inhibitor PD98059 or specific p38 MAPK inhibitor SB203580 pre-treatment in GES-1 cells. Thus, the results suggest that downregulation of Rad51 participates in OTA-induced DNA double-strand breaks in GES-1 cells in vitro. And p53, ERK and p38 signaling pathways are all involved in the process.
No preview · Article · Feb 2014 · Toxicology Letters
[Show abstract][Hide abstract] ABSTRACT: Our previous studies showed that Aflatoxin G1 (AFG1) could induce lung adenocarcinoma, and that the cancer cells originated from alveolar type II cells (AT-II cells). Recently, we found AFG1 induced structural impairment in rat AT-II cells, which may account for an early event in lung tumorigenesis. However, the mechanism of AFG1-induced AT-II cell damage remains unclear. DNA damage and apoptosis induced by oxidative stress are well accepted causes of cell damage. Thus, we explore whether AFG1 activates the reactive oxygen species (ROS)/MAPK/apoptosis pathway to cause cell damage in human AT-II cells like the cell line (A549). We found AFG1 induced oxidative stress by increasing ROS generation and caused DNA double-strand breaks (DSBs) by up-regulating γH2AX expression. AFG1 also triggered apoptosis in A549 cells by regulating Fas/FasL, caspase-8, Bax, Bcl-2, and activating caspase-3. Pre-treatment with antioxidant N-acetyl- L-cysteine (NAC) reduced ROS generation and DNA DSBs, inhibited apoptosis, and increased cell viability in AFG1-treated cells. Furthermore, we found AFG1 activated ROS-mediated JNK and p38 pathways to induce cell apoptosis in A549 cells. In conclusion, our results indicate that AFG1 induces oxidative DNA damage and triggers apoptosis through ROS-mediated JNK and p38 signaling pathways in A549 cells, which may contribute to AFG1-induced AT-II cell damage.
No preview · Article · Sep 2013 · Food and chemical toxicology: an international journal published for the British Industrial Biological Research Association
[Show abstract][Hide abstract] ABSTRACT: Ochratoxin A is one of the most abundant food-contaminating mycotoxins worldwide, and its immunosuppressive effects in human caused more and more concern in biomedical field. In the present study, the toxicity of OTA on human peripheral blood mononuclear cells (hPBMC) was explored by analyzing the involvement of oxidative pathway. It was found that OTA treatment led to the release of reactive oxygen species (ROS) and the increase of 8-hydroxydeoxyguanosine (8-OHdG), an important biomarker of oxidative DNA stress. Moreover, we found that OTA treatment induced DNA strand breaks in hPBMC as evidenced by DNA comet tails formation and increased γ-H2AX expression. In addition, OTA could induce cell cycle arrest at G1 phase by down-regulating the expression of CDK4 and cyclinD1 protein, as well as apoptosis in hPBMC in vitro. Pre-treatment of hPBMC with antioxidant, N-acetyl-L-cysteine (NAC), could reduce OTA-induced ROS release and DNA damage, thus confirming the involvement of oxidative DNA damage in the OTA genotoxicity in hPBMC. NAC pre-treatment could also significantly prevent OTA-induced down-regulation of CDK4 and cyclinD1 expression in hPBMC. All the results demonstrated the involvement of oxidative pathway in OTA mediated cytotoxicity in human immune cells, which including the ROS accumulation-oxidative DNA damage-G1 arrest and apoptosis. Our results provide new insights into the molecular mechanisms by which OTA might promote immunotoxicity.
No preview · Article · Apr 2012 · Toxicology Letters