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alphaB-crystallin is mutant B-RAF regulated and contributes to cyclin D1 turnover in melanocytic cells

Rong Hu1, Andrew E Aplin

  • 1Department of Cancer Biology, Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, PA, USA.

Pigment Cell & Melanoma Research
|January 14, 2010
PubMed

Insights

Mutant BRAF in melanoma down-regulates alphaB-crystallin, a protein that normally degrades cyclin D1. Restoring alphaB-crystallin in melanoma cells enhances cyclin D1 turnover after DNA damage.

Area of Science:

  • Cell Biology
  • Molecular Oncology
  • Biochemistry

Background:

  • The serine/threonine kinase B-RAF is a key regulator of cell proliferation, frequently mutated in melanoma.
  • Cell cycle progression is controlled by proteasomal degradation of cyclins and inhibitors, mediated by E3 ubiquitin ligases.
  • Alpha-crystallin, a co-factor for Fbx4, promotes cyclin D1 degradation.

Purpose of the Study:

  • To investigate the role of alphaB-crystallin in melanoma.
  • To determine the relationship between B-RAF signaling and alphaB-crystallin expression.
  • To elucidate the impact of alphaB-crystallin re-expression on cyclin D1 turnover in melanoma cells.

Main Methods:

  • Western blotting to assess protein levels.
  • Pharmacological inhibition of MEK and proteasome.
  • Gene knockdown experiments.
  • Cellular assays to evaluate cyclin D1 turnover.

Main Results:

  • Alpha-crystallin is down-regulated in B-RAF-mutant melanoma cells compared to melanocytes, dependent on B-RAF and MEK signaling.
  • MEK inhibition increased alpha-crystallin levels in some cell lines, while others required combined MEK and proteasome inhibition.
  • Alpha-crystallin knockdown partially stabilized cyclin D1 in melanocytes.
  • Re-expression of alpha-crystallin in melanoma cells enhanced cyclin D1 turnover specifically after DNA damage.

Conclusions:

  • Alpha-crystallin is expressed in melanocytes and contributes to cyclin D1 turnover.
  • Alpha-crystallin expression is suppressed in a B-RAF-dependent manner in melanoma.
  • Re-expressing alpha-crystallin in melanoma cells can restore regulation of cyclin D1 turnover, particularly following DNA damage.
Keywords:
B-RAFFbx4cyclin D1melanomaαB-crystallin

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