Mitogen-activated protein kinase kinase-4 promotes cell survival by decreasing PTEN expression through an NFκB-dependent pathway

Mitogen-activated protein kinase kinase-4 (MKK4/SEK1) cooperates with phosphatidylinositol 3-kinase to maintain the survival of non-small cell lung cancer (NSCLC) cells, but the biochemical basis of this phenomenon has not been elucidated. Here we used genetic approaches to modulate MKK4 expression in mouse embryo fibroblasts (MEF cells) and NSCLC cells to identify prosurvival signals downstream of MKK4. Relative to wild-type MEF cells, MKK4-null MEF cells were highly susceptible to apoptosis by LY294002, paclitaxel, or serum starvation. MKK4 promoted the survival of MEF cells by decreasing the expression of phosphatase and tensin homologue deleted from chromosome 10 (PTEN). MKK4 inhibited PTEN transcription by activating NF kappa B, a transcriptional suppressor of PTEN. MKK4 was required for nuclear translocation of RelA/p65 and processing of the NF kappa B2 precursor (p100) into the mature form (p52). Studies on a panel of NSCLC cell lines revealed a subset with high MKK4/high NF kappa B/low PTEN that was relatively resistant to apoptosis. Thus, MKK4 promotes cell survival by activating phosphatidylinositol 3-kinase through an NF kappa B/PTEN-dependent pathway.