Low dose arsenite confers resistance to UV induced apoptosis via p53-MDM2 pathway in ketatinocytes

Abstract

Chronic arsenite and ultraviolet (UV) exposure are associated with skin tumor. To investigate the details by low concentrations of arsenite and UV induced carcinogenesis in skin, hTERT-immortalized human keratinocytes were used as a cellular model with exposure to low concentrations of sodium arsenite and UV. The effect of NaAsO2 on UV treatment-induced apoptosis was measured by flow cytometry and Hoechst staining. We found that the cell apoptosis induced by UV exposure was significantly attenuated after exposure to low-dose arsenite, and knockdown of p53 could block UV-induced apoptosis indicating that this phenomenon depended on p53. Interestingly, the expression of murine double minute 2 (MDM2), including its protein and transcriptional levels, was remarkably high after exposure to low-dose arsenite. Moreover, low-dose arsenite treatment dramatically decreased the MDM2 gene promoter activity, suggesting that this effect has been mediated through transcription. In addition, treatment of PD98059 reversed low-dose arsenite-induced MDM2 expression, and the inhibition of ERK2 expression could significantly block MDM2 expression as a consequence, and p53 expression automatically was increased. To validate the role of p53 in exposure to low-dose arsenite, the expression of p53 was examined by immunohistochemistry in the skin of Sprague−Dawley rats model by chronic arsenite exposure for 6 months and in patients with arsenic keratosis, and the results showed that the expression of p53 was decreased in those samples. Taken together, our results demonstrated that low-dose arsenite-induced resistance to apoptosis through p53 mediated by MDM2 in keratinocytes.

The Role of Reactive Oxygen Species in Arsenic Toxicity

“…however, haCaT cells are immortalized with SV40, which are known to interfere with p53 expression. In human telomerase reverse transcriptase (hTERT)-immortalized human keratinocytes, exposure to low-dose arsenite inhibited p53 expression by transcriptionally upregulating murine double minute 2 (MDM2) or ERK2-mediated overexpression of MDM2 [172]. In arsenic-exposed MCF-7 cells, an S-phase cell cycle arrest was found to depend on activation of p53 downstream cellular defense enzymes (i.e., sestrin 1 (SESN1) and activating transcription factor 3 (ATF3)) that was triggered by ROS generation in the early stage [93].…”

Apoptotic resistance,cell cycle dysregulation and autophagy activation contribute to arsenic carcinogenesis

“…Cultures were maintained at 37 ℃ in a humidified 5% CO2 atmosphere. For chronic arsenic exposure, cells were maintained continuously in medium containing 100 nM of arsenic trioxide (Sigma, St. Louis, MO) for 28 weeks [20,21]. All the materials for cell culture were purchased from Thermo Scientific HyClone (Logan,UT, USA).…”