Calcium control of actin-myosin-based contraction in Triton-treated murine bladder tumor cells.

Using mouse bladder tumor cells (MBT-2 cells) and epithelial cells, the present study evaluated the functional characteristics of the actomyosin system in bladder cancer cells. An immunofluorescence study demonstrated the presence of contractile proteins (actin and myosin) in MBT-2 cells as well as bladder epithelial cells. Triton-treated MBT-2 cells and epithelial cells showed a Ca(2+)-dependent contraction. This was inhibited by N-ethylmaleimide-modified myosin subfragment 1 (NEM-S1), demonstrating that the interaction between actin and myosin is responsible for the contraction of Triton-treated cells. The extent of Ca(2+)-dependent contraction was much greater in MBT-2 cells than in epithelial cells. These results suggest that MBT-2 cells possess a locomotive apparatus consisting of actin and myosin, and that Ca2+ can activate this actomyosin system, leading to the contraction or active locomotory movement of tumor cells.