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Spatial and Temporal Control of Murine Melanoma Initiation from Mutant Melanocyte Stem Cells
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Oncogenic BRAF(V600E) inhibits BIM expression to promote melanoma cell survival

Robert A Cartlidge1, G R Thomas, Sebastien Cagnol

  • 1Cancer Research Institute and Department of Cellular and Molecular Pharmacology, University of California, San Francisco, Helen Diller Family Comprehensive Cancer Center, San Francisco, CA, USA.

Pigment Cell & Melanoma Research
|August 22, 2008
PubMed

Insights

BRAF mutations drive melanoma by inhibiting BIM, a cell death protein. Blocking BRAF or MEK reactivates BIM, suggesting a new therapeutic target for melanoma treatment.

Area of Science:

  • Oncology
  • Molecular Biology
  • Cell Signaling

Background:

  • Somatic activating BRAF mutations are key early events in melanoma development.
  • The precise mechanisms by which BRAF signaling promotes melanoma cell survival and proliferation are not fully understood.
  • BIM, a pro-apoptotic protein, is a critical regulator of cell death.

Purpose of the Study:

  • To investigate the role of BRAF signaling in regulating BIM expression in melanocytes and melanoma cells.
  • To elucidate the signaling pathway involved in BRAF-mediated BIM inhibition.
  • To explore the therapeutic potential of targeting this pathway in melanoma.

Main Methods:

  • Utilized mouse and human melanocytes, and human melanoma cell lines.
  • Investigated the effects of trophic factor deprivation and re-addition on BIM expression.
  • Examined the impact of BRAF(V600E) activation and pharmacological inhibitors (PLX4720, CI-1040) on BIM levels.
  • Assessed the role of MEK1/2 activity and proteasomal degradation in BIM regulation.
  • Employed RNA interference to inhibit BIM expression.

Main Results:

  • BRAF-->MEK-->ERK signaling inhibits BIM expression in melanocytes and melanoma cells.
  • Trophic factor deprivation increases BIM expression, while re-addition or BRAF(V600E) activation decreases it.
  • BIM inhibition is dependent on MEK1/2 activity and proteasomal degradation.
  • Pharmacological inhibition of BRAF or MEK increases BIM expression.
  • BRAF signaling phosphorylates BIM-EL, leading to its degradation.
  • Endogenous BIM levels are insufficient to induce apoptosis alone but protect against it when BIM expression is inhibited.

Conclusions:

  • BRAF-->MEK-->ERK signaling suppresses BIM expression, contributing to melanoma cell survival.
  • Regulation of BIM by oncogenic BRAF(V600E) is a key mechanism in melanoma pathogenesis.
  • Targeting the BRAF-MEK-ERK pathway can restore BIM expression and potentially induce apoptosis in melanoma cells.

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