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.