Induction of autophagy and inhibition of melanoma growth in vitro and in vivo by hyperactivation of oncogenic BRAF

J Invest Dermatol. 2010 Jun;130(6):1657-67. doi: 10.1038/jid.2010.26. Epub 2010 Feb 25.

Abstract

Activating mutations in NRAS and BRAF are found frequently in cutaneous melanomas. Because concurrent mutations of both BRAF and RAS are extremely rare, it is thought that transformation by RAS and BRAF occurs through a common mechanism. Also, there is evidence for a relationship of synthetic lethality between NRAS and BRAF oncogenes that leads to selection against cells with a hyperactive mitogen-activated protein kinase (MAPK) pathway. However, it is not known whether the hyperactivation of the MAPK pathway by overexpression of either oncogene alone could also inhibit melanoma tumorigenesis. Here, we show that in melanoma cells with oncogenic BRAF (mBRAF), high levels of mBRAF induce hyperactivation of ERK and senescence-like phenotype and trigger autophagy by inhibiting the mammalian target of rapamycin complex signaling. Growth inhibition and cell death caused by high mBRAF levels are partially rescued by downregulation of BRAF protein or inhibition of autophagy, but not by inhibition of the MAPK or apoptotic pathways. In nude mice, growth of mBRAF-overexpressing tumors is inhibited. Quantitative immunohistochemical analysis of human melanomas and cell lines showed a significant positive correlation between the levels of BRAF protein and autophagy marker light chain 3. Our data suggest that high oncogenic BRAF levels trigger autophagy, which may have a role in melanoma tumor progression.

Publication types

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

MeSH terms

  • Animals
  • Apoptosis / drug effects
  • Apoptosis / physiology
  • Autophagy / drug effects
  • Autophagy / physiology*
  • Cell Cycle / drug effects
  • Cell Cycle / physiology
  • Cell Line
  • Cell Line, Tumor
  • Cell Proliferation*
  • Cells, Cultured
  • Female
  • Humans
  • Intracellular Signaling Peptides and Proteins / antagonists & inhibitors
  • Intracellular Signaling Peptides and Proteins / physiology
  • Male
  • Melanoma / pathology*
  • Melanoma / physiopathology
  • Mice
  • Plasmids / genetics
  • Plasmids / pharmacology
  • Protein-Serine-Threonine Kinases / antagonists & inhibitors
  • Protein-Serine-Threonine Kinases / physiology
  • Proto-Oncogene Proteins B-raf / genetics
  • Proto-Oncogene Proteins B-raf / physiology*
  • Signal Transduction / drug effects
  • Signal Transduction / physiology
  • Skin Neoplasms / pathology*
  • Skin Neoplasms / physiopathology
  • TOR Serine-Threonine Kinases
  • Xenograft Model Antitumor Assays

Substances

  • Intracellular Signaling Peptides and Proteins
  • MTOR protein, human
  • TOR Serine-Threonine Kinases
  • mTOR protein, mouse
  • BRAF protein, human
  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins B-raf