Wise Sandra S, Holmes Amie L, Xie Hong, Thompson W Douglas, Wise John Pierce
Wise Laboratory of Environmental and Genetic Toxicology, Maine Center for Toxicology and Environmental Health, University of Southern Maine, 96 Falmouth St., Portland, Maine 04104-9300, USA.
Chem Res Toxicol. 2006 Nov;19(11):1492-8. doi: 10.1021/tx0601410.
One of the hallmarks of lung cancer is chromosome instability (CIN), particularly a tetraploid phenotype, which is normally prevented by the spindle assembly checkpoint. Hexavalent chromium Cr(VI) is an established human lung carcinogen, and Cr(VI) induces tumors at lung bifurcation sites where Cr(VI) particles impact and persist. However, the effects of Cr(VI) on the spindle assembly checkpoint are unknown and little is known about prolonged exposure to particulate Cr(VI). Accordingly, we investigated particulate Cr(VI)-induced bypass of the spindle assembly checkpoint after several days of exposure in WHTBF-6 cells. We found that lead chromate indeed induces spindle assembly checkpoint bypass in human lung cells, as 72, 96, and 120 h treatments with 0.5 or 1 microg/cm2 lead chromate induced significant increases in the percentage of cells with aberrant mitotic figures. For example, treatment with 1 microg/cm2 lead chromate for 96 h induced 11, 12.3, and 14% of cells with premature anaphase, centromere spreading and premature centromere division, respectively. In addition, we found a disruption of mitosis with more cells accumulating in anaphase; cells treated for 96 h increased from 18% in controls to 31% in cells treated with lead chromate. To confirm involvement of the spindle assembly checkpoint, Mad2 expression was used as a marker. Mad2 expression was decreased in cells exposed to chronic treatments of lead chromate, consistent with disruption of the checkpoint. We also found concentration- and time-dependent increases in tetraploid cells, which continued to grow and form colonies. When cells were treated with chronic lead alone there was no increase in aberrant mitotic cells or polyploidy; however, chronic exposure to a soluble Cr(VI) showed an increase in aberrant mitotic cells and polyploidy. These data suggest that lead chromate does induce CIN and may be one mechanism in the development of Cr(VI)-induced lung cancer.
肺癌的一个标志是染色体不稳定（CIN），尤其是四倍体表型，而纺锤体组装检查点通常可防止这种情况发生。六价铬Cr(VI)是一种已确定的人类肺癌致癌物，Cr(VI)会在Cr(VI)颗粒撞击并持续存在的肺分叉部位诱发肿瘤。然而，Cr(VI)对纺锤体组装检查点的影响尚不清楚，对于长期暴露于颗粒状Cr(VI)的情况也知之甚少。因此，我们研究了在WHTBF - 6细胞中暴露数天后，颗粒状Cr(VI)诱导的纺锤体组装检查点旁路。我们发现铬酸铅确实会在人类肺细胞中诱导纺锤体组装检查点旁路，因为用0.5或1微克/平方厘米的铬酸铅处理72、96和120小时会导致有异常有丝分裂图像的细胞百分比显著增加。例如，用1微克/平方厘米的铬酸铅处理96小时分别诱导11%、12.3%和14%的细胞出现后期提前、着丝粒扩散和着丝粒分裂提前。此外，我们发现有丝分裂受到破坏，更多细胞在后期积累；处理96小时的细胞从对照组的18%增加到铬酸铅处理组的31%。为了确认纺锤体组装检查点的参与情况，使用Mad2表达作为标志物。在长期接受铬酸铅处理的细胞中，Mad2表达降低，这与检查点的破坏一致。我们还发现四倍体细胞在浓度和时间上呈依赖性增加，这些细胞继续生长并形成集落。当细胞仅用慢性铅处理时，异常有丝分裂细胞或多倍体没有增加；然而，长期暴露于可溶性Cr(VI)会导致异常有丝分裂细胞和多倍体增加。这些数据表明铬酸铅确实会诱导CIN，并且可能是Cr(VI)诱导肺癌发生的一种机制。
