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


CONCLUSIONS
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.
Deichmann
Martin
M
Department of Dermatology, Heidelberg University Clinics, Vossbstrasse 2, 69115 Heidelberg, Germany. martin_deichmann@web.de
Thome
Marianne
M
Benner
Axel
A
Kirschner
Martin
M
Hassanzadeh
Judith
J
Kurzen
Hjalmar
H
D002454:Cell Differentiation; D049109:Cell Proliferation; D005091:Exons; D006801:Humans; D008544:Melanocytes / Q000378:metabolism*; D008545:Melanoma / Q000235:genetics* / Q000473:pathology*; D015233:Models, Statistical; D009154:Mutation; D009362:Neoplasm Metastasis; D010232:Paraffin / Q000737:chemistry; D010957:Plasmids / Q000378:metabolism; D017354:Point Mutation; D016133:Polymerase Chain Reaction; D018807:Polymorphism, Single-Stranded Conformational; D017434:Protein Structure, Tertiary; D048493:Proto-Oncogene Proteins B-raf / Q000737:chemistry* / Q000235:genetics*; D012306:Risk; D017422:Sequence Analysis, DNA; D015398:Signal Transduction; D012878:Skin Neoplasms / Q000235:genetics* / Q000473:pathology*; D013997:Time Factors; D016896:Treatment Outcome
D010232:Paraffin; D048493:Proto-Oncogene Proteins B-raf