Mudipalli Anuradha, Owen Russell D, Preston R Julian
Environmental Carcinogenesis Division, National Health and Environmental Effects Research Laboratory, ORD, US EPA, Research Triangle Park, NC 27711, USA.
Int J Oncol. 2005 Sep;27(3):769-78.
The molecular mechanisms mediating arsenic-induced carcinogenesis are not well understood. The role of confounding factors such as ultraviolet radiation (UV), add another level of complexity to the study of arsenic carcinogenesis and the cancer-risk assessment on humans. We hypothesized that arsenicals are capable of overriding the growth arrest caused by UV treatment and may lead to selective proliferation. To test this hypothesis, a primary normal human epidermal keratinocyte (NHEK) cell culture model was used. One group was pre-exposed to UVB (100 mJ/cm(2)) that arrested a majority ( approximately 95%) of cells in G0/G1 (+UV) and a second group was not exposed to UV (-UV). Treatment of cells with various arsenicals [0-12 microM of inorganic arsenite (iAs), 0-2 microM of methyl oxoarsine (MMAs III) and 0-3 microM of iododimethyl arsine (DMAs III)] indicated a concentration-dependent increase in proliferation at 24 h in the order of DMAs III > MMAs III > iAs. Flow-cytometric analyses revealed differential effects on cell cycle distribution. Analysis of a battery of cell cycle proteins (cyclin D1, cdk5, PCNA, cdc25A and cdc25C) indicated exposure-specific differential expression profiles. Increased activation of JNK phosphorylation (5-10-fold) in the +UV group and the synergistic increase with methyl arsenicals suggested that JNK might be involved in cell survival and proliferative signaling. Induction of EGF levels and increased phosphorylation of the EGF receptor by arsenicals (+UV) suggested that the EGF signaling pathway might mediate arsenical-induced cell proliferation of NHEK cells. Differential activation of ERK1/2 by arsenicals (+/-UV) suggested that EGF-mediated cell proliferation by arsenicals in UV-treated NHEK cells may not involve ERK activation. Taken together, the data suggest that both UV exposure and methylation status of the arsenicals dictate the participation of key cell cycle proteins and related signaling events in arsenical-induced cell proliferation.
介导砷诱导致癌作用的分子机制尚未完全明确。紫外线辐射（UV）等混杂因素的作用，给砷致癌作用的研究以及人类癌症风险评估增添了另一层面的复杂性。我们推测砷化合物能够克服紫外线处理所导致的生长停滞，并可能引发选择性增殖。为验证这一假设，我们使用了原代正常人表皮角质形成细胞（NHEK）细胞培养模型。一组预先暴露于紫外线B（100 mJ/cm²），致使大部分（约95%）细胞停滞于G0/G1期（+UV），另一组未暴露于紫外线（-UV）。用各种砷化合物[0 - 12 μM无机亚砷酸盐（iAs）、0 - 2 μM甲基氧胂（MMAs III）和0 - 3 μM碘代二甲基胂（DMAs III）]处理细胞，结果表明在24小时时增殖呈浓度依赖性增加，顺序为DMAs III > MMAs III > iAs。流式细胞术分析揭示了对细胞周期分布的不同影响。对一系列细胞周期蛋白（细胞周期蛋白D1、细胞周期蛋白依赖性激酶5、增殖细胞核抗原、细胞周期蛋白磷酸酶25A和细胞周期蛋白磷酸酶25C）的分析表明存在暴露特异性差异表达谱。+UV组中JNK磷酸化激活增加（5 - 10倍）以及与甲基砷化合物的协同增加表明JNK可能参与细胞存活和增殖信号传导。砷化合物（+UV）诱导表皮生长因子（EGF）水平升高以及EGF受体磷酸化增加，提示EGF信号通路可能介导砷化合物诱导的NHEK细胞增殖。砷化合物（+/-UV）对细胞外信号调节激酶1/2（ERK1/2）的不同激活表明，在紫外线处理的NHEK细胞中，砷化合物通过EGF介导的细胞增殖可能不涉及ERK激活。综上所述，数据表明紫外线暴露和砷化合物的甲基化状态均决定了关键细胞周期蛋白和相关信号事件在砷化合物诱导的细胞增殖中的参与情况。
