Mitogen-activated Protein Kinase Kinase-4 Promotes Cell Survival by Decreasing PTEN Expression through an NFκB-dependent Pathway

Dianren Xia,Harish Srinivas,Young-Ho Ahn,Gautam Sethi,Xiaoyang Sheng,W.K Alfred Yung,Qianghua Xia,Paul J Chiao,Heetae Kim,Powel H Brown,Ignacio I Wistuba,Bharat B Aggarwal,Jonathan M Kurie

doi:10.1074/jbc.m610141200

Abstract

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 NFkappaB, a transcriptional suppressor of PTEN. MKK4 was required for nuclear translocation of RelA/p65 and processing of the NFkappaB2 precursor (p100) into the mature form (p52). Studies on a panel of NSCLC cell lines revealed a subset with high MKK4/high NFkappaB/low PTEN that was relatively resistant to apoptosis. Thus, MKK4 promotes cell survival by activating phosphatidylinositol 3-kinase through an NFkappaB/PTEN-dependent pathway.

Highlights

PI[3,4,5]P3 [1]
We hypothesized that mitogen-activated protein kinase kinase-4 (MKK4) promotes cell survival through interactions with phosphatidylinositol 3-kinase (PI3K)-dependent signaling, which we addressed by using genetic approaches to modulate MKK4 expression in mouse embryo fibroblasts (MEF cells) and non-small cell lung cancer (NSCLC) cells
MKK4 Loss Enhances Sensitivity to Apoptosis—We showed previously that MKK4-null MEF cells are more sensitive than wild-type MEF cells to apoptosis caused by LY294002, a PI3K inhibitor [14]

Summary

Introduction

PI[3,4,5]P3 [1]. Endogenous PI[3,4,5]P3 levels are regulated by phosphatidylinositol 3-kinase (PI3K), which phosphorylates the D3 position of phosphatidylinositol (PI) on PI[4]P and PI[4,5]P2 to produce PI[3,4]P2 and PI[3,4,5]P3. PTEN expression and AKT expression and phosphorylation by Western blotting following serum deprivation overnight in wild-type (ϩ/ϩ) and MKK4-null (Ϫ/Ϫ) MEF cells are shown. Because PTEN negatively regulates intracellular levels of PIP3, which is required for the activation of downstream effectors of PI3K, such as AKT, based on the above results we predicted that MKK4-null and wild-type MEF cells would differ with respect to the expression and activity of these downstream effectors basally or in response to LY294002.

Results

Conclusion