Silencing of EEF2K (eukaryotic elongation factor-2 kinase) reveals AMPK-ULK1-dependent autophagy in colon cancer cells

Autophagy. 2014 Sep;10(9):1495-508. doi: 10.4161/auto.29164. Epub 2014 Jun 19.

Abstract

EEF2K (eukaryotic elongation factor-2 kinase), also known as Ca (2+)/calmodulin-dependent protein kinase III, functions in downregulating peptide chain elongation through inactivation of EEF2 (eukaryotic translation elongation factor 2). Currently, there is a limited amount of information on the promotion of autophagic survival by EEF2K in breast and glioblastoma cell lines. However, the precise role of EEF2K in carcinogenesis as well as the underlying mechanism involved is still poorly understood. In this study, contrary to the reported autophagy-promoting activity of EEF2K in certain cancer cells, EEF2K is shown to negatively regulate autophagy in human colon cancer cells as indicated by the increase of LC3-II levels, the accumulation of LC3 dots per cell, and the promotion of autophagic flux in EEF2K knockdown cells. EEF2K negatively regulates cell viability, clonogenicity, cell proliferation, and cell size in colon cancer cells. Autophagy induced by EEF2K silencing promotes cell survival and does not potentiate the anticancer efficacy of the AKT inhibitor MK-2206. In addition, autophagy induced by silencing of EEF2K is attributed to induction of protein synthesis and activation of the AMPK-ULK1 pathway, independent of the suppression of MTOR activity and ROS generation. Knockdown of AMPK or ULK1 significantly abrogates EEF2K silencing-induced increase of LC3-II levels, accumulation of LC3 dots per cell as well as cell proliferation in colon cancer cells. In conclusion, silencing of EEF2K promotes autophagic survival via activation of the AMPK-ULK1 pathway in colon cancer cells. This finding suggests that upregulation of EEF2K activity may constitute a novel approach for the treatment of human colon cancer.

Keywords: AMPK; ATG; MTOR; ROS; ULK1; autophagy; cancer growth; cell survival; colon cancer; elongation factor-2 kinase.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • AMP-Activated Protein Kinases / metabolism*
  • Autophagy / drug effects
  • Autophagy / genetics*
  • Autophagy-Related Protein-1 Homolog
  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Cell Proliferation / physiology
  • Cell Survival / drug effects
  • Cell Survival / genetics
  • Colonic Neoplasms / drug therapy
  • Colonic Neoplasms / genetics*
  • Colonic Neoplasms / metabolism
  • Elongation Factor 2 Kinase / genetics*
  • Gene Silencing / physiology*
  • Heterocyclic Compounds, 3-Ring / pharmacology
  • Humans
  • Intracellular Signaling Peptides and Proteins / metabolism*
  • Protein-Serine-Threonine Kinases / metabolism*
  • Signal Transduction / genetics

Substances

  • Heterocyclic Compounds, 3-Ring
  • Intracellular Signaling Peptides and Proteins
  • MK 2206
  • Autophagy-Related Protein-1 Homolog
  • Protein-Serine-Threonine Kinases
  • ULK1 protein, human
  • Elongation Factor 2 Kinase
  • AMP-Activated Protein Kinases