Mutant B-RAF mediates resistance to anoikis via Bad and Bim

Oncogene. 2008 May 22;27(23):3301-12. doi: 10.1038/sj.onc.1211003. Epub 2008 Feb 4.


Normal cells undergo anoikis when they lose adhesion to or encounter an inappropriate extracellular matrix. By contrast, oncogenic signaling in tumor cells enables resistance to anoikis, a trait that contributes to tumor progression. The B-RAF serine-threonine kinase is mutated in multiple cancers and functions as an oncogene in melanoma. Previously, we demonstrated that B-RAF and downstream mitogen-activated protein/extracellular signal-regulated kinase kinase (MEK) signaling are necessary for protection from anoikis in mutant B-RAF-expressing melanoma cells. Regulation of Bcl-2 family members in melanoma and their role in B-RAF-mediated survival is poorly defined. Here, we provide evidence that B-RAF-MEK signaling protects against anoikis through alterations in two proapoptotic Bcl-2 family proteins: Bcl-xL/Bcl-2-associated death promoter (Bad) and Bcl-2-interacting mediator of cell death (Bim). B-RAF-MEK signaling regulates phosphorylation of the inhibitory serine-75 residue of Bad, and decreases Bad mRNA expression. RNA interference and overexpression experiments demonstrate that Bad contributes to the susceptibility of B-RAF-depleted cells to anoikis. Additionally, B-RAF-MEK signaling regulates the expression of Bim(EL), mainly through control of protein turnover. Increased Bim(EL) levels induce apoptosis in suspended cells and are required for anoikis in B-RAF-depleted cells. Depletion of Bim together with Bad has an additive effect on protecting B-RAF knockdown cells from anoikis. Together, our data show that Bad and Bim are major B-RAF responsive proteins regulating apoptosis in melanoma cells.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Anoikis / genetics*
  • Apoptosis Regulatory Proteins / metabolism
  • Apoptosis Regulatory Proteins / physiology*
  • Bcl-2-Like Protein 11
  • Cell Adhesion / genetics
  • Cell Adhesion / physiology
  • Gene Expression Regulation, Neoplastic
  • Humans
  • MAP Kinase Kinase Kinases / physiology
  • Melanoma / genetics
  • Membrane Proteins / metabolism
  • Membrane Proteins / physiology*
  • Mutant Proteins / physiology
  • Phosphorylation
  • Proteasome Endopeptidase Complex / metabolism
  • Proto-Oncogene Proteins / metabolism
  • Proto-Oncogene Proteins / physiology*
  • Proto-Oncogene Proteins B-raf / antagonists & inhibitors
  • Proto-Oncogene Proteins B-raf / genetics
  • Proto-Oncogene Proteins B-raf / physiology*
  • RNA, Small Interfering / pharmacology
  • Signal Transduction / physiology
  • Tumor Cells, Cultured
  • bcl-Associated Death Protein / genetics
  • bcl-Associated Death Protein / metabolism
  • bcl-Associated Death Protein / physiology*


  • Apoptosis Regulatory Proteins
  • BCL2L11 protein, human
  • Bcl-2-Like Protein 11
  • Membrane Proteins
  • Mutant Proteins
  • Proto-Oncogene Proteins
  • RNA, Small Interfering
  • bcl-Associated Death Protein
  • BRAF protein, human
  • Proto-Oncogene Proteins B-raf
  • MAP Kinase Kinase Kinases
  • Proteasome Endopeptidase Complex