CRAF inhibition induces apoptosis in melanoma cells with non-V600E BRAF mutations

Oncogene. 2009 Jan 8;28(1):85-94. doi: 10.1038/onc.2008.362. Epub 2008 Sep 15.


Here, we identify a panel of melanoma lines with non-V600E mutations in BRAF. These G469E- and D594G-mutated melanomas were found to exhibit constitutive levels of phospho-extracellular signal-regulated kinase (pERK) and low levels of phospho-mitogen-activated protein kinase/ERK kinase (pMEK) and were resistant to MEK inhibition. Upon treatment with the CRAF inhibitor sorafenib, these lines underwent apoptosis and associated with mitochondrial depolarization and relocalization of apoptosis-inducing factor, whereas the BRAF-V600E-mutated melanomas did not. Studies have shown low-activity mutants of BRAF (G469E/D594G) instead signal through CRAF. Unlike BRAF, CRAF directly regulates apoptosis through mitochondrial localization where it binds to Bcl-2 and phosphorylates BAD. The CRAF inhibitor sorafenib was found to induce a time-dependent reduction in both BAD phosphorylation and Bcl-2 expression in the D594G/G469E lines only. Knockdown of CRAF using a lentiviral shRNA suppressed both Bcl-2 expression and induced apoptosis in the D594G melanoma line but not in a V600E-mutated line. Finally, we showed in a series of xenograft studies that sorafenib was more potent at reducing the growth of tumors with the D594G mutation than those with the V600E mutation. In summary, we have identified a group of melanomas with low-activity BRAF mutations that are reliant upon CRAF-mediated survival activity.

MeSH terms

  • Apoptosis* / genetics
  • Benzenesulfonates / pharmacology
  • Cell Line, Tumor
  • Drug Resistance, Neoplasm / genetics*
  • Gene Knockdown Techniques
  • Glutamic Acid / genetics
  • Glutamic Acid / metabolism
  • Humans
  • Melanoma / enzymology*
  • Melanoma / genetics
  • Mitogen-Activated Protein Kinase Kinases / metabolism
  • Mutation
  • Niacinamide / analogs & derivatives
  • Phenylurea Compounds
  • Protein Kinase Inhibitors / pharmacology
  • Proto-Oncogene Proteins B-raf / genetics*
  • Proto-Oncogene Proteins c-raf / antagonists & inhibitors*
  • Proto-Oncogene Proteins c-raf / genetics
  • Pyridines / pharmacology
  • RNA, Small Interfering / genetics
  • Signal Transduction
  • Sorafenib
  • Valine / genetics
  • Valine / metabolism


  • Benzenesulfonates
  • Phenylurea Compounds
  • Protein Kinase Inhibitors
  • Pyridines
  • RNA, Small Interfering
  • Niacinamide
  • Glutamic Acid
  • Sorafenib
  • BRAF protein, human
  • Proto-Oncogene Proteins B-raf
  • Proto-Oncogene Proteins c-raf
  • Mitogen-Activated Protein Kinase Kinases
  • Valine