Animal studies have shown that chemical carcinogenesis consists of a three-stage process: initiation, promotion, and progression. However, because of the lack of a suitable tissue model, the molecular mechanisms of cell-cell interactions involved in those processes remain unclear. We have established a human intraepidermal carcinoma skin equivalent with organotypic culture-consisting of keratinocytes, fibroblasts, and peripheral blood mononuclear cells - induced by arsenic treatment. This SE shows the pathognomonic characteristics of arsenic-induced Bowen's disease, including acanthosis, dysplasia, and dyskeratosis. Using this SE model, we showed that arsenic initiated SUV39H2-mediated epigenetic modification of E2F1, which induced centrosome amplification in keratinocytes in 2 days; this, however, led to caspase-8-mediated apoptosis in 10 days. In parallel, arsenic stimulated tumor necrosis factor-α release mainly from peripheral blood mononuclear cells. Tumor necrosis factor-α triggered anti-apoptotic signals via FLIP-associated caspase-8 inactivation in arsenic-treated keratinocytes, which in turn contributed to cell survival and aneuploidy. The interaction between arsenic-induced epigenetic modification and inflammatory promotion resulted in the development of the pathognomonic features of arsenic-induced Bowen's disease in this model.
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