Cap-dependent mRNA translation and the ubiquitin-proteasome system cooperate to promote ERBB2-dependent esophageal cancer phenotype

Cancer Gene Ther. 2012 Sep;19(9):609-18. doi: 10.1038/cgt.2012.39. Epub 2012 Jul 6.

Abstract

Pathological post-transcriptional control of the proteome composition is a central feature of malignancy. Two steps in this pathway, eIF4F-driven cap-dependent mRNA translation and the ubiquitin-proteasome system (UPS), are deregulated in most if not all cancers. We tested a hypothesis that eIF4F is aberrantly activated in human esophageal adenocarcinoma (EAC) and requires elevated rates of protein turnover and proteolysis and thereby activated UPS for its pro-neoplastic function. Here, we show that 80% of tumors and cell lines featuring amplified ERBB2 display an aberrantly activated eIF4F. Direct genetic targeting of the eIF4F in ERBB2-amplified EAC cells with a constitutively active form of the eIF4F repressor 4E-BP1 decreased colony formation and proliferation and triggered apoptosis. In contrast, suppression of m-TOR-kinase activity towards 4E-BP1with rapamycin only modestly inhibited eIF4F-driven cap-dependent translation and EAC malignant phenotype; and promoted feedback activation of other cancer pathways. Our data show that co-treatment with 2 FDA-approved agents, the m-TOR inhibitor rapamycin and the proteasome inhibitor bortezomib, leads to strong synergistic growth-inhibitory effects. Moreover, direct targeting of eIF4F with constitutively active 4E-BP1 is significantly more potent in collaboration with bortezomib than rapamycin. These data support the hypothesis that a finely tuned balance between eIF4F-driven protein synthesis and proteasome-mediated protein degradation is required for the maintenance of ERBB2-mediated EAC malignant phenotype. Altogether, our study supports the development of pharmaceuticals to directly target eIF4F as most efficient strategy; and provides a clear rationale for the clinical evaluation of combination therapy with m-TOR inhibitors and bortezomib for EAC treatment.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / genetics
  • Adaptor Proteins, Signal Transducing / metabolism
  • Apoptosis
  • Boronic Acids / pharmacology
  • Bortezomib
  • Case-Control Studies
  • Cell Cycle Proteins
  • Cell Line, Tumor
  • Cell Proliferation
  • Drug Synergism
  • Enzyme Activation
  • Esophageal Neoplasms / drug therapy
  • Esophageal Neoplasms / metabolism
  • Esophageal Neoplasms / therapy*
  • Eukaryotic Initiation Factor-4F / genetics
  • Eukaryotic Initiation Factor-4F / metabolism*
  • Feedback, Physiological
  • Gene Expression Regulation, Neoplastic
  • Gene Silencing
  • Gene Targeting / methods
  • Humans
  • Phenotype
  • Phosphoproteins / genetics
  • Phosphoproteins / metabolism
  • Phosphorylation
  • Proteasome Endopeptidase Complex / drug effects
  • Proteasome Endopeptidase Complex / metabolism
  • Proteasome Inhibitors / pharmacology
  • Protein Biosynthesis*
  • Proteolysis
  • Pyrazines / pharmacology
  • RNA Caps / genetics
  • RNA Caps / metabolism*
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • RNA, Small Interfering / genetics
  • RNA, Small Interfering / metabolism
  • Receptor, ErbB-2 / genetics
  • Receptor, ErbB-2 / metabolism*
  • Repressor Proteins / genetics
  • Repressor Proteins / metabolism
  • Sirolimus / pharmacology
  • Ubiquitin / genetics
  • Ubiquitin / metabolism

Substances

  • Adaptor Proteins, Signal Transducing
  • Boronic Acids
  • Cell Cycle Proteins
  • EIF4EBP1 protein, human
  • Eukaryotic Initiation Factor-4F
  • Phosphoproteins
  • Proteasome Inhibitors
  • Pyrazines
  • RNA Caps
  • RNA, Messenger
  • RNA, Small Interfering
  • Repressor Proteins
  • Ubiquitin
  • Bortezomib
  • ERBB2 protein, human
  • Receptor, ErbB-2
  • Proteasome Endopeptidase Complex
  • Sirolimus