title: Exon 15 BRAF mutations are uncommon in canine oral malignant melanomas.
abstract: An activating mutation in codon 599 of BRAF has been identified in approximately 60% of human cutaneous nevi and melanomas, but not melanomas of mucosal origin. The purpose of this study was to determine if BRAF mutations occur in canine oral malignant melanomas. The canine BRAF gene was first cloned from normal canine testicular cDNA, and a novel previously unreported splice variant involving exon 5 was identified during this process. To screen canine melanoma samples for BRAF mutation in codon 599, cDNA and genomic DNA were isolated from canine malignant melanoma cell lines and primary tumor samples respectively, all from cases seen at the Veterinary Medical Teaching Hospital at the University of California, Davis. Polymerase chain reaction (PCR) was performed for exon 15 using primers based at the 5' end of exon 15 and the 5' end of intron 15 and the resultant products were directly sequenced. No mutations in codon 599 or exon 15 were identified in any of the 17 samples evaluated. However, all of the melanoma cell lines expressed BRAF and demonstrated high levels of basal ERK phosphorylation suggesting that dysregulation of this pathway is present. Therefore, similar to the case with human mucosal melanomas, canine oral malignant melanomas do not possess codon 599 BRAF mutations commonly identified in human cutaneous melanomas. This finding supports the notion that melanomas arising from non-sun-exposed sites exhibit distinct mechanisms of molecular transformation.
authors.affiliation: Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, 2112 Tupper Hall,One Shields Ave., California, 95616, USA.
authors.forename: Suzanne
authors.initials: S
authors.lastname: Shelly
authors.forename: May B
authors.initials: MB
authors.lastname: Chien
authors.forename: Becky
authors.initials: B
authors.lastname: Yip
authors.forename: Michael S
authors.initials: MS
authors.lastname: Kent
authors.forename: Alain P
authors.initials: AP
authors.lastname: Theon
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: McCallan
authors.forename: Cheryl A
authors.initials: CA
authors.lastname: London
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D045744:Cell Line, Tumor; D004283:Dog Diseases / Q000235:genetics*; D004285:Dogs; D005091:Exons; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D008545:Melanoma / Q000235:genetics / Q000378:metabolism / Q000662:veterinary*; D009061:Mouth Mucosa; D009062:Mouth Neoplasms / Q000235:genetics / Q000662:veterinary*; D009154:Mutation; D048493:Proto-Oncogene Proteins B-raf / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism
chemical_list: D048493:Proto-Oncogene Proteins B-raf; D048049:Extracellular Signal-Regulated MAP Kinases