MAPK4 overexpression promotes tumor progression via noncanonical activation of AKT/mTOR signaling
Wei Wang, … , David D. Moore, Feng Yang
Wei Wang, … , David D. Moore, Feng Yang
Published March 1, 2019; First published January 28, 2019
Citation Information: J Clin Invest. 2019;129(3):1015-1029. https://doi.org/10.1172/JCI97712.
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Categories: Research Article Cell biology Oncology

MAPK4 overexpression promotes tumor progression via noncanonical activation of AKT/mTOR signaling

Abstract

MAPK4 is an atypical MAPK. Currently, little is known about its physiological function and involvement in diseases, including cancer. A comprehensive analysis of 8887 gene expression profiles in The Cancer Genome Atlas (TCGA) revealed that MAPK4 overexpression correlates with decreased overall survival, with particularly marked survival effects in patients with lung adenocarcinoma, bladder cancer, low-grade glioma, and thyroid carcinoma. Interestingly, human tumor MAPK4 overexpression also correlated with phosphorylation of AKT, 4E-BP1, and p70S6K, independent of the loss of PTEN or mutation of PIK3CA. This led us to examine whether MAPK4 activates the key metabolic, prosurvival, and proliferative kinase AKT and mTORC1 signaling, independent of the canonical PI3K pathway. We found that MAPK4 activated AKT via a novel, concerted mechanism independent of PI3K. Mechanistically, MAPK4 directly bound and activated AKT by phosphorylation of the activation loop at threonine 308. It also activated mTORC2 to phosphorylate AKT at serine 473 for full activation. MAPK4 overexpression induced oncogenic outcomes, including transforming prostate epithelial cells into anchorage-independent growth, and MAPK4 knockdown inhibited cancer cell proliferation, anchorage-independent growth, and xenograft growth. We concluded that MAPK4 can promote cancer by activating the AKT/mTOR signaling pathway and that targeting MAPK4 may provide a novel therapeutic approach for cancer.

Authors

Wei Wang, Tao Shen, Bingning Dong, Chad J. Creighton, Yanling Meng, Wolong Zhou, Qing Shi, Hao Zhou, Yinjie Zhang, David D. Moore, Feng Yang

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Figure 3

MAPK4 activates AKT independent of PI3K/PDK1.

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MAPK4 activates AKT independent of PI3K/PDK1. (A) H1299 and H157 cells w...
(A) H1299 and H157 cells with high endogenous MAPK4 were treated with increasing doses of PI3K inhibitor LY294002 for 24 hours. Western blots were used to detect AKT phosphorylation. The phosphorylation of AKT at T308 and S473 was analyzed using ImageJ (33). The data are from 3 (for H1299 cells) and 4 (for H157 cells) independent studies. Box and whisker plots indicate average value with the box extending from the 25th to 75th percentiles and the whisker extending from Min to Max. (B) H157 and the H157 MAPK4-KO cells (KO clone 2 and KO clone 6) were treated with 5 μM LY294002 for 2 hours. Western blots were used to detect AKT phosphorylation. (C) PTEN was ectopically overexpressed in HEK293T cells overexpressing control (293T-Ctrl) or MAPK4 (293T-MAPK4), as well as in VCaP cells. Western blots were used to detect AKT phosphorylation and confirm PTEN overexpression. (D) The FLAG-tagged AKT1 and AKT1R25C mutants were overexpressed in HEK293T-Ctrl and HEK293T-MAPK4 cells. After immunoprecipitation using anti-FLAG M2 affinity gel, phosphorylation of the overexpressed AKT1 was detected with Western blots. WCL: whole-cell lysate. (E) Three independent siRNAs against PDK1 were used to knock down PDK1 expression in VCaP cells. Western blots were used to detect AKT phosphorylation and confirm knockdown of PDK1. (F) Left, MAPK4 was ectopically overexpressed in the HCT116 PDK1-KO cells. Western blots were used to detect AKT phosphorylation. Right, Western blots were used to confirm loss of PDK1 expression in the HCT116 PDK1-KO cells. Ctrl: control. Data are representative of at least 3 independent experiments.