Preponderance of the oncogenic V599E and V599K mutations in B-raf kinase domain is enhanced in melanoma cutaneous/subcutaneous metastases

BMC Cancer. 2005 Jun 3;5:58. doi: 10.1186/1471-2407-5-58.

Abstract

Background: Downstream of Ras, the serine/threonine kinase B-raf has been reported to be mutated, among other carcinomas, in a substantial subset of primary melanomas with a preponderance of mutations within the kinase domain including the activating V599E and V599K transitions.

Methods: We here investigated a representative series of 60 resection specimens of cutaneous and subcutaneous melanoma metastases for the presence of mutations within the activation segment (exon 15) of the B-raf kinase domain by polymerase chain reaction (PCR) and single-strand conformation polymorphism (SSCP) gel electrophoresis.

Results: Sequencing of cloned PCR-SSCP amplicons resulted in 24 (40%) samples harbouring somatic mutations which is not exceeding the mutation frequency in recently investigated primary melanomas. The activating mutation T1796A was present in 24/60 (40%) resection specimens, followed in frequency by the oncogenic g1795A mutation in 8/60 (13%) cases. As to the B-raf protein sequence, the acidic amino acid transitions V599E and V599K were predicted in 19/60 (32%) and 6/60 (10%) cases, respectively, but were not associated with enhanced risk for subsequent metastasis in patients' follow up. In comparison to the primary melanomas that we recently investigated, the spectrum of predicted B-raf protein mutations narrowed significantly in the cutaneous/subcutaneous metastases. Unexpectedly, V599 and V599E mutations were absent in cutaneous/subcutaneous metastases derived from acrolentiginous melanomas as preceding primary tumours.

Conclusion: During transition from primary melanomas towards cutaneous/subcutaneous metastases, the spectrum of predicted B-raf mutations narrows significantly. Focusing on the V599E and V599K, these oncogenic mutations are likely to affect melanocyte-specific pathways controlling proliferation and differentiation.

MeSH terms

  • Cell Differentiation
  • Cell Proliferation
  • Exons
  • Humans
  • Melanocytes / metabolism*
  • Melanoma / genetics*
  • Melanoma / pathology*
  • Models, Statistical
  • Mutation*
  • Neoplasm Metastasis
  • Paraffin / chemistry
  • Plasmids / metabolism
  • Point Mutation
  • Polymerase Chain Reaction
  • Polymorphism, Single-Stranded Conformational
  • Protein Structure, Tertiary
  • Proto-Oncogene Proteins B-raf / chemistry*
  • Proto-Oncogene Proteins B-raf / genetics*
  • Risk
  • Sequence Analysis, DNA
  • Signal Transduction
  • Skin Neoplasms / genetics*
  • Skin Neoplasms / pathology*
  • Time Factors
  • Treatment Outcome

Substances

  • Paraffin
  • Proto-Oncogene Proteins B-raf