Constitutively activated nuclear factor kappa B (NFkappaB) contributes to the development of cancer by regulating the expression of genes involved in cell survival, metastasis, and angiogenesis. The authors have demonstrated that MEKK3 plays a critical role in cytokine-mediated NFkappaB activation, and that stable expression of MEKK3 in cultured cells leads to increased NFkappaB activity. MEKK3 expression in ovarian cancer cells or tumors was assessed by Western blotting and real-time polymerase chain reaction. NFkappaB activities were analyzed by electrophoretic mobility shift assay and luciferase reporter assays. Western blot analysis for the survival factors were also performed and correlated with MEKK3 and NFkappaB activities. Cell survival assays were used to determine the sensitivity of ovarian cancer cells to various chemotherapeutic agents. The authors found that 63% of the ovarian cancers had higher MEKK3 expression than the normal ovarian epithelial cells. Ovarian cancers with high MEKK3 showed correspondingly high IkappaB kinase and NFkappaB activity. Moreover, MEKK3 coimmunoprecipitated with Akt and cooperated with Akt to synergistically activate NFkappaB. Consistent with increased MEKK3 and NFkappaB activity in ovarian cancers, Bcl-2, Bcl-xL, survivin, and X-linked inhibitor of apoptosis levels were increased, which correlated with increased resistance to chemotherapeutic agents. Knockdown of MEKK3 with small interfering RNA significantly increased cancer cell sensitivity to paclitaxel. MEKK3 may be aberrantly expressed in ovarian cancers and plays an important role in tumors with constitutively activated NFkappaB.
