Oncogenic Activation of AKT by MAPK6

Abstract Mitogen-activated protein kinase 6 (MAPK6) is an atypical MAPK closely related to MAPK4. We recently reported that MAPK4 can promote cancer by activating the Protein Kinase B (PKB/AKT) pathway of cell growth and survival. Here we report that MAPK6 overexpression also activates AKT to induce oncogenic outcomes, including transforming “normal” human epithelial cells into anchorage-independent growth and enhancing cancer cell growth. Knockdown of MAPK6 inhibited cancer cell growth and xenograft growth, supporting the tumor-promoting activities of endogenous MAPK6. Unlike MAPK4, which binds AKT through its kinase domain and phosphorylates AKT at T308, MAPK6 interacts with AKT through its C34 region and the unique C-terminal tail and phosphorylates AKT at S473 independent of mTORC2, the major AKT S473 kinase. MAPK6 overexpression is associated with decreased overall survival and the survival of lung adenocarcinoma, mesothelioma, uveal melanoma, and breast cancer patients. We conclude that MAPK6 can promote cancer by activating AKT and that targeting MAPK6 may be effective in human cancers.