Mcl-1 is required for melanoma cell resistance to anoikis

Mol Cancer Res. 2009 Apr;7(4):549-56. doi: 10.1158/1541-7786.MCR-08-0358.

Abstract

Melanoma is a particularly aggressive tumor type that exhibits a high level of resistance to apoptosis. The serine/threonine kinase B-RAF is mutated in 50% to 70% of melanomas and protects melanoma cells from anoikis, a form of apoptosis induced by lack of adhesion or adhesion to an inappropriate matrix. Mutant B-RAF down-regulates two BH3-only proapoptotic proteins, Bim(EL) and Bad. BH3-only proteins act, at least in part, by sequestering prosurvival Bcl-2 family proteins and preventing them from inhibiting the mitochondrial apoptotic pathway. Several Bcl-2 proteins are up-regulated in melanoma; however, the mechanisms of up-regulation and their role in melanoma resistance to anoikis remain unclear. Using RNA interference, we show that depletion of Mcl-1 renders mutant B-RAF melanoma cells sensitive to anoikis. By contrast, minor effects were observed following depletion of either Bcl-2 or Bcl-(XL). Mcl-1 expression is enhanced in melanoma cell lines compared with melanocytes and up-regulated by the B-RAF-MEK-extracellular signal-regulated kinase 1/2 pathway through control of Mcl-1 protein turnover. Similar to B-RAF knockdown cells, adhesion to fibronectin protected Mcl-1 knockdown cells from apoptosis. Finally, expression of Bad, which does not sequester Mcl-1, further augmented apoptosis in nonadherent Mcl-1 knockdown cells. Together, these data support the notion that BH3 mimetic compounds that target Mcl-1 may be effective for the treatment of melanoma in combinatorial strategies with agents that disrupt fibronectin-integrin signaling.

Publication types

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

MeSH terms

  • Anoikis*
  • Cell Adhesion / physiology
  • Extracellular Signal-Regulated MAP Kinases / metabolism
  • Fibronectins / metabolism
  • Humans
  • Melanocytes / metabolism
  • Melanoma / metabolism
  • Melanoma / pathology*
  • Mitogen-Activated Protein Kinase Kinases / metabolism
  • Myeloid Cell Leukemia Sequence 1 Protein
  • Phosphorylation
  • Proto-Oncogene Proteins B-raf / metabolism
  • Proto-Oncogene Proteins c-bcl-2 / metabolism
  • Proto-Oncogene Proteins c-bcl-2 / physiology*
  • RNA Interference
  • RNA, Small Interfering / pharmacology
  • Signal Transduction
  • Skin Neoplasms / genetics
  • Skin Neoplasms / metabolism
  • Skin Neoplasms / pathology
  • Tumor Cells, Cultured
  • bcl-Associated Death Protein / metabolism
  • bcl-X Protein / metabolism

Substances

  • BAD protein, human
  • BCL2L1 protein, human
  • Fibronectins
  • Myeloid Cell Leukemia Sequence 1 Protein
  • Proto-Oncogene Proteins c-bcl-2
  • RNA, Small Interfering
  • bcl-Associated Death Protein
  • bcl-X Protein
  • BRAF protein, human
  • Proto-Oncogene Proteins B-raf
  • Extracellular Signal-Regulated MAP Kinases
  • Mitogen-Activated Protein Kinase Kinases