The Role of BRAF Mutation and p53 Inactivation During Transformation of a Subpopulation of Primary Human Melanocytes

Am J Pathol. 2009 Jun;174(6):2367-77. doi: 10.2353/ajpath.2009.081057. Epub 2009 Apr 23.

Abstract

Melanocytic nevi frequently harbor oncogenic BRAF mutations, but only a minority progress to melanoma. In human melanocytes, persistent BRAF(V600E) expression triggers oncogene-induced senescence, which implies that bypass of oncogene-induced senescence is necessary for malignant transformation of melanocytes. We show that a subpopulation of primary human melanocytes with persistent expression of BRAF(V600E) do not enter oncogene-induced senescence, but instead survive despite heightened MAPK activity. Disruption of the p53 pathway using short-hairpin RNA initiated rapid growth of these V600E(+) melanocytes in vitro. The resultant V600E(+)/p53(sh) melanocytes grew anchorage-independently in soft agar, formed pigmented lesions reminiscent of in situ melanoma in artificial skin reconstructs, and were weakly tumorigenic in vivo. Array comparative genomic hybridization analysis demonstrated that the transformed melanocytes acquired a substantial deletion in chromosome 13, which encodes the Rb1 tumor suppressor gene. Gene expression profiling study of nevi and melanomas showed that p53 target genes were differentially expressed in melanomas compared with nevi, suggesting a dysfunctional p53 pathway in melanoma in vivo. In summary, these data demonstrate that a subpopulation of melanocytes possesses the ability to survive BRAF(V600E)-induced senescence, and suggest that p53 inactivation may promote malignant transformation of these cells.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Blotting, Western
  • Cell Transformation, Neoplastic / genetics*
  • Cell Transformation, Neoplastic / metabolism*
  • Cells, Cultured
  • Cellular Senescence / genetics
  • Comparative Genomic Hybridization
  • Gene Expression
  • Gene Expression Profiling
  • Humans
  • Immunohistochemistry
  • Melanocytes / metabolism
  • Melanocytes / pathology*
  • Melanoma / genetics
  • Melanoma / metabolism
  • Mice
  • Mice, SCID
  • Mutation
  • Oligonucleotide Array Sequence Analysis
  • Polymerase Chain Reaction
  • Proto-Oncogene Proteins B-raf / genetics*
  • Retinoblastoma Protein / genetics
  • Skin Neoplasms / genetics
  • Skin Neoplasms / metabolism
  • Tumor Suppressor Protein p53 / metabolism*

Substances

  • Retinoblastoma Protein
  • Tumor Suppressor Protein p53
  • BRAF protein, human
  • Proto-Oncogene Proteins B-raf