Activated 4E-BP1 represses tumourigenesis and IGF-I-mediated activation of the eIF4F complex in mesothelioma

Our plain-English summary of Activated 4E-BP1 represses tumourigenesis and IGF-I-mediated activation of the eIF4F complex in mesothelioma, by B.A. Jacobson, A. De, M.G. Kratzke, et al (British Journal of Cancer, 2009).

The study

• Authors: B.A. Jacobson, A. De, M.G. Kratzke, M.R. Patel, J. Jay-Dixon, B.A. Whitson, A.A. Sadiq, P.B. Bitterman, V.A. Polunovsky, R.A. Kratzke
• Journal: British Journal of Cancer
• Published: 2009;101(3):424-31
• Cited by: 23 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Insulin-like growth factor (IGF)-I signalling stimulates proliferation, survival, and invasion in malignant mesothelioma and other tumour types. Studies have found that tumourigenesis is linked to dysregulation of cap-dependent protein translation.

Methods: The effect of IGF stimulation on cap-mediated translation activation in mesothelioma cell lines was studied using binding assays to a synthetic 7-methyl GTP-cap analogue. In addition, cap-mediated translation was genetically repressed in these cells with a dominant active motive of 4E-BP1.

Results: In most mesothelioma cell lines, IGF-I stimulation resulted in a hyperphosphorylation-mediated inactivation of 4E-BP1 compared with that in normal mesothelial cells. An inhibitor of Akt diminished IGF-I-mediated phosphorylation of 4E-BP1, whereas inhibiting MAPK signalling had no such effect. IGF-I stimulation resulted in the activation of the cap-mediated translation complex as indicated by an increased eIF4G/eIF4E ratio in cap-affinity assays. Akt inhibition reversed the eIF4G/eIF4E ratio. Mesothelioma cells transfected with an activated 4E-BP1 protein (4E-BP1(A37/A46)) were resistant to IGF-I-mediated growth, motility, and colony formation. In a murine xenograft model, mesothelioma cells expressing the dominant active 4E-BP1(A37/A46) repressor protein showed abrogated tumourigenicity compared with control tumours.

Conclusion: IGF-I signalling in mesothelioma cells drives cell proliferation, motility, and tumourigenesis through its ability to activate cap-mediated protein translation complex through PI3K/Akt/mTOR signalling.

In plain English

This laboratory study examined cap-dependent protein translation in malignant mesothelioma, using five human mesothelioma cell lines (H513, H2052, H2373, H2461, H2596), the non-transformed mesothelial line LP9, and mouse xenografts. Stimulation with IGF-I (5 nM) phosphorylated IGF1R, Akt and MAPK in the mesothelioma lines and in LP9 cells, though the authors reported a weaker response in LP9 cells, and led to sustained hyperphosphorylation (inactivation) of the translation repressor 4E-BP1 in most mesothelioma lines; the PI3K inhibitor LY294002 reduced this phosphorylation, while the MEK inhibitor U0126 did not. In cap-affinity assays, IGF-I increased the eIF4G/eIF4E ratio 1.5- to 3.5-fold over untreated cells, and the same PI3K inhibitor lowered the ratio. Cells made to express a phosphorylation-defective 4E-BP1(A37/A46) showed reduced eIF4F assembly (66.7% inhibition in H2373 to 51% in H2461), fewer colonies, less proliferation, and less IGF-I-driven motility, which the authors noted did not reach statistical significance. In nude mice, H2373 cells expressing 4E-BP1(A37/A46) formed tumours one-third the size of controls and H2596 cells formed none.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory (in vitro) study of human mesothelioma cell lines with a mouse xenograft experiment
• Who was studied: Five human mesothelioma cell lines (H513, H2052, H2373, H2461, H2596) and the non-transformed human mesothelial line LP9; five nude mice per cell line for the xenograft experiments
• Exposure: Insulin-like growth factor-I (5 nM) stimulation, with or without the PI3K inhibitor LY294002 (20 µM) or the MEK inhibitor U0126 (10 µM); and transfection with the dominant active repressor 4E-BP1(A37/A46)
• Main results:
  • IGF-I for 20 minutes phosphorylated IGF1R in both mesothelioma cells and control LP9 mesothelial cells
  • The normal mesothelial LP9 cells responded less strongly to IGF-I than the mesothelioma lines
  • Akt inhibition reduced phosphorylation of Akt and of 4E-BP1 in all five mesothelioma cell lines and in LP9 control cells
  • MAPK inhibition suppressed MAPK phosphorylation but not 4E-BP1 phosphorylation
  • IGF-I raised the eIF4G/eIF4E ratio 1.5- to 3.5-fold in treated mesothelioma cells versus untreated cells
  • The PI3K inhibitor (printed as LY249002 in the results section) lowered the eIF4G/eIF4E ratio in IGF-I-stimulated cells in all mesothelioma lines
  • Expression of 4E-BP1(A37/A46) inhibited eIF4F complex formation by 66.7% in H2373 to 51% in H2461
  • Motility: H2461 parental and empty-vector cells increased migration 4-fold and 2.6-fold with IGF-I, while cells expressing 4E-BP1(A37/A46) showed no increase; the authors state the motility results were not statistically significant
  • Xenografts: H2373 cells with 4E-BP1(A37/A46) made tumours one-third the size of parental controls; H2596 cells with 4E-BP1(A37/A46) made no tumours in any mouse
• The authors' conclusion: The authors concluded that IGF-I signalling drives mesothelioma cell proliferation, motility and tumourigenesis by activating the cap-mediated translation complex through PI3K/Akt/mTOR signalling
• Limitations the authors state:
  • The authors state the reduction in IGF-I-stimulated motility with 4E-BP1(A37/A46) did not reach statistical significance
  • The authors note that expression of the transfected 4E-BP1(A37/A46) protein fell to nearly undetectable levels in H2373 xenograft tumours, suggesting selection of cells with minimal expression
  • The authors note eIF4G levels fell with the PI3K inhibitor in some lines and offer caspase-mediated cleavage only as a possible explanation

Topics

The National Library of Medicine indexes this study under subjects our site covers: Mesothelioma.

Medical terms in this study, explained in our Lexicon: Mesothelioma, Mesothelial Cells.

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