Objective  To analyze the effect of knocking down MAP4K4 expression on the proliferation and migration of cancer cells, and to explore its underlining molecular mechanisms.

  Methods  A stable knockdown MAP4K4 cell line was constructed and the subcellular localization of the cells was determined with immunofluorescence, cell proliferation assay and cell migration assay. In addition, the effects of down-regulated MAP4K4 expression were analyzed by examining the difference between the proliferation and migration of cancer cells in the knockdown group and those of the control group.

  Results  MAP4K4 was localized in focal adhesion and cell edges in A549 cells. Stable knockdown of MAP4K4 expression induced cancer cells to grow in clusters and arrested the progression of the cell cycle and cell migration. Further analysis found that knocking down MAP4K4 expression in A549 cells induced the accumulation of epithelial cell marker E-cadherin, and subsequently, the down-regulation of N-cadherin, a mesenchymal cell marker, thereby disrupting the "cadherin switch" and the epithelial-mesenchymal conversion. Then, the control group and the knockdown group both received the combined treatment of cisplatin at a final concentration of 5 μmol/L and paclitaxel at a final concentration of 20 nmol/L. The stably knocked down MAP4K4 expressing cells showed significantly enhanced toxicity of chemotherapeutic drugs to cancer cells.

  Conclusion  The study shows that MAP4K4 regulates the malignant phenotypes of cancer cells and chemoresistance by regulating "cadherin switch" to promote epithelial-mesenchymal transition in A549 cells.