MYLK promotes hepatocellular carcinoma progression through regulating cytoskeleton to enhance epithelial-mesenchymal transition

Myosin light chain kinase (MYLK) is found to catalyze the phosphorylation of myosin light chains (MLC) and regulate invasion and metastasis in some malignancies. However, there is little knowledge on the role of MYLK in hepatocellular carcinoma (HCC), and no studies have been conducted to investigate the mechanisms underlying MYLK-mediated promotion of HCC invasion and metastasis until now. In this study, we investigated the expression of MYLK in 50 pairs of human HCC and adjacent liver specimens. High MYLK expression was significantly correlated with aggressive clinicopathological features including tumor encapsulation, microvascular invasion and metastasis. In vitro assays showed that shRNA-induced MYLK knockdown significantly inhibited the wound-healing ability of HCC cells and the ability to migrate and invade through Matrigel. We next uncovered that MYLK knockdown resulted in a reduction in the number of F-actin stress fibers, disorganization of F-actin architectures and morphological alterations of HCC cells. Phosphorylated MLC, rather than total MLC, was found to be markedly reduced in response to downregulation of MYLK expression, and MYLK-regulated actin cytoskeleton through phosphorylating MLC in HCC cells. In addition, Western blotting assay revealed downregulation of the epithelial marker E-cadherin and upregulation of mesenchymal markers Vimentin, N-cadherin and Snail. Taken together, our findings indicate that MYLK promotes HCC progression by altering cytoskeleton to enhance epithelial-mesenchymal transition (EMT).