Chronic exposure to particulate chromate induces spindle assembly checkpoint bypass in human lung cells.
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.
Wise
Sandra S
SS
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.
Holmes
Amie L
AL
Xie
Hong
H
Thompson
W Douglas
WD
Wise
John Pierce
JP
D002135:Calcium-Binding Proteins / Q000378:metabolism; D002453:Cell Cycle / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000378:metabolism; D002460:Cell Line; D002840:Chromates / Q000378:metabolism / Q000633:toxicity*; D043171:Chromosomal Instability / Q000187:drug effects*; D003078:Colchicine / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects; D006801:Humans; D007854:Lead / Q000378:metabolism / Q000633:toxicity*; D008168:Lung / Q000166:cytology* / Q000187:drug effects; D064246:Mad2 Proteins; D052638:Particulate Matter / Q000378:metabolism / Q000633:toxicity*; D011123:Polyploidy; D012097:Repressor Proteins / Q000378:metabolism; D012995:Solubility; D008941:Spindle Apparatus / Q000187:drug effects*; D013997:Time Factors
D002135:Calcium-Binding Proteins; D018797:Cell Cycle Proteins; D002840:Chromates; C577697:MAD2L1 protein, human; D064246:Mad2 Proteins; D052638:Particulate Matter; D012097:Repressor Proteins; D007854:Lead; C031895:lead chromate; D003078:Colchicine