Myosin light chain kinase plays a role in the regulation of epithelial cell survival

Myosin II activation is essential for stress fiber and focal adhesion formation, and is implicated in integrin-mediated signaling events. In this study we investigated the role of acto-myosin contractility, and its main regulators, i. e. myosin light chain kinase (MLCK) and Rho-kinase ( ROCK) in cell survival in normal and Ras- transformed MCF-10A epithelial cells. Treatment of cells with pharmacological inhibitors of MLCK ( ML-7 and ML-9), or expression of dominant- negative MLCK, led to apoptosis in normal and transformed MCF- 10A cells. By contrast, treatment of cells with a ROCK inhibitor ( Y- 27632) did not induce apoptosis in these cells. Apoptosis following inhibition of myosin II activation by MLCK is probably meditated through the death receptor pathway because expression of dominant- negative FADD blocked apoptosis. The apoptosis observed after MLCK inhibition is rescued by pre- treatment of cells with integrin- activating antibodies. In addition, this rescue of apoptosis is dependent on FAK activity, suggesting the participation of an integrin- dependent signaling pathway. These studies demonstrate a newly discovered role for MLCK in the generation of pro- survival signals in both untransformed and transformed epithelial cells and supports previous work suggesting distinct cellular roles for Rho- kinase- and MLCK- dependent regulation of myosin II.