Arsenite Disrupts Mitosis and Induces Apoptosis in SV40-Transformed Human Skin Fibroblasts

Abstract

Chronic ingestion of arsenite-contaminated drinking water causes skin, bladder, and liver cancer. The mechanism of arsenite-induced carcinogenesis is unknown. Arsenite is known to disrupt mitosis and to delay transit through M phase in normal diploid fibroblasts. SV40-transformed human fibroblasts were observed to be hypersensitive to the cytotoxic and cytostatic effects of NaAsO2 compared with normal diploid fibroblasts in concentration–response experiments. Five to 20 μM NaAsO2 induced cytostasis in cycling normal diploid fibroblasts but not overt lethality in quiescent normal diploid fibroblasts. High concentrations of arsenite were overtly lethal in both cycling and quiescent cells. The IC50 for cycling SV40-transformed fibroblasts was 3.8 and 4.8 μM for the SV40-transformed lines GM4429 and GM0637, respectively, whereas, in cycling normal diploid fibroblasts (GM0024), the IC50 was 24.7 μM. Microscopic examination of NaAsO2-treated SV40-transformed fibroblasts suggested a concentration-dependent accumulation of cells in mitosis undergoing apoptosis. Treatment of SV40-transformed fibroblasts with 0–10 μM NaAsO2 caused a concentration-dependent inhibition of cell proliferation, accumulation of cells having G2/M DNA contents, and increases in the mitotic index. Phase microscopy, annexin V binding, and electron microscopy demonstrated that arrested mitotic cells underwent apoptosis. These results indicate that SV40-transformation sensitizes cells to arsenite-induced mitotic arrest and induction of apoptosis in the mitotic cells.