C-Raf antagonizes apoptosis induced by IFN-alpha in human lung cancer cells by phosphorylation and increase of the intracellular content of elongation factor 1A

Cell Death Differ. 2007 May;14(5):952-62. doi: 10.1038/sj.cdd.4402102. Epub 2007 Mar 2.

Abstract

Interferon alpha (IFNalpha) induces both apoptosis and a counteracting epidermal growth factor Erk-dependent survival response in cancer cells. In this report, IFNalpha increased eukaryotic elongation factor 1A (eEF-1A) protein expression by inhibition of eEF-1A degradation via a proteasome-dependent pathway. The reduction of the expression level of eEF-1A by RNA interference enhanced the apoptosis induced by IFNalpha on the same cells. Moreover, IFNalpha induced the phosphorylation of both serine and threonine in eEF-1A. These effects were paralleled by an increased co-immunoprecipitation and colocalization of eEF-1A with C-Raf. The suppression of C-Raf kinase activity with the inhibitor BAY 43-9006 completely antagonized the increase of both eEF-1A phosphorylation and expression and of C-Raf/eEF-1A colocalization induced by IFNalpha and enhanced apoptosis and eEF-1A ubiquitination. Cell transfection with the mutated K48R ubiquitin increased EF-1A expression and desensitized tumor cells to the modulating effects of IFNalpha. The dynamic simulation of 3Dstructure of eEF-1A identified putative serine and threonine phosphorylation sites. In conclusion, the interaction between eEF-1A and C-Raf increases eEF-1A stability and induces a survival activity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis / drug effects*
  • Cell Line, Tumor
  • Humans
  • Immunoprecipitation
  • Interferon-alpha / pharmacology*
  • Lung Neoplasms / metabolism
  • Lung Neoplasms / pathology*
  • Oncogene Proteins / metabolism*
  • Peptide Elongation Factor 1 / metabolism*
  • Phosphorylation / drug effects
  • Phosphoserine / metabolism
  • Phosphothreonine / metabolism
  • Proteasome Endopeptidase Complex / metabolism
  • Protein Binding / drug effects
  • Protein Processing, Post-Translational / drug effects
  • Protein Transport / drug effects
  • Proto-Oncogene Proteins c-raf / metabolism*
  • RNA, Small Interfering / metabolism
  • Ubiquitin / metabolism

Substances

  • EEF1A1 protein, human
  • Interferon-alpha
  • Oncogene Proteins
  • Peptide Elongation Factor 1
  • RNA, Small Interfering
  • Ubiquitin
  • Phosphothreonine
  • Phosphoserine
  • Proto-Oncogene Proteins c-raf
  • Proteasome Endopeptidase Complex