Clonal BRAF Mutations in Melanocytic Nevi and Initiating Role of BRAF in Melanocytic Neoplasia.
ABSTRACT BRAF(V600E) mutations are frequent in melanomas originating from intermittently sun-exposed skin and also in common acquired melanocytic nevi, suggesting that BRAF mutation is an early event in melanocytic neoplasia. All neoplastic melanocytes within such a nevus would be expected to carry the BRAF mutation, and thus we evaluated the frequency of cells with BRAF(V600E) mutations within acquired nevi by droplet digital polymerase chain reaction. In BRAF-mutant nevi the number of BRAF mutant alleles equaled the number of wild-type (WT) alleles in the neoplastic cell population, consistent with a fully clonal heterozygous BRAF mutation. The allelic ratio of BRAF(V600E) to BRAF(WT) in the eight VE1-positive nevi, adjusted for degree of stromal contamination, ranged from 0.84 to 1.12 with an average ratio of 1.01. This was confirmed by immunohistochemistry with an antibody specific for BRAF(V600E), which uniformly labeled the neoplastic cells without any evidence of heterogeneity. We found BRAF(V600E) mutations in the melanocytic nevi to be fully clonal, strongly suggesting that BRAF-activating mutations typically are early initiating events in melanocytic neoplasia.
SourceAvailable from: Toshihiko Imamura[Show abstract] [Hide abstract]
ABSTRACT: We propose Langerhans cell histiocytosis (LCH) is an inflammatory process that is prolonged by mutations. We hypothesize that Merkel cell polyomavirus (MCPyV) infection triggers an interleukin-1 (IL-1) activation loop that underlies the pathogenesis of LCH. Langerhans cells (LCs) are antigen presenting cells in the skin. When LCs encounter exogenous antigens, they migrate from the epidermis into draining lymphoid tissues to initiate T-cell activity. It has been proposed that LC migration-related factors, including E-cadherin, matrix metalloproteinase, and Notch ligand induce LCH activity. We found that the tyrosine phosphatase SHP-1, which binds IL-1 receptor-associated kinase 1, is expressed at a significantly higher level in LCH affecting multiple organ systems (MS-LCH) than in LCH affecting a single organ system (SS-LCH). IL-1 stimulates T helper 17 cells and their signature cytokine IL-17 had been a matter of controversy. We detected higher levels of IL-17A receptor expression in MS-LCH than in SS-LCH and proposed an IL-17 endocrine model that could settle the controversy. IL-1 is the first cytokine secreted in response to sensitizers and promotes LC migration from sentinel tissues. Myeloid differentiation primary response 88 (MyD88), downstream of the IL-1 receptor, has functions in both RAS signaling and inflammation, leading to human cell transformation. In 2010, an activating mutation in the B-rapidly accelerated fibrosarcoma gene (BRAF) V600E was found in LCH. This BRAF mutation induces phosphorylation of the extracellular signal-regulated kinase (ERK) that may play an important role with MyD88 in LCH pathogenesis. However, phosphorylated ERK (pERK) is rapidly dephosphorylated by dual specificity phosphatase 6 (DUSP6), and limited proliferation is predicted in BRAF mutant cells. MyD88 binds pERK via its D-domain, thereby preventing pERK–DUSP6 interaction and maintaining ERK in an active, phosphorylated state. We detected MCPyV-DNA in the peripheral blood cells of two out of three patients with LCH in high-risk organs but not in those of patients with LCH in non–high-risk organs (0/12; P = .029). MCPyV infection can trigger precursor LCH cells with BRAF mutation to produce IL-1; the IL-1 loop is amplified in all LCH subclasses. Our model indicates both BRAF mutation and IL-1 loop regulation as potential therapeutic targets.Cell Communication and Signaling 02/2015; 13(1). DOI:10.1186/s12964-015-0092-z · 4.67 Impact Factor
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ABSTRACT: The introduction of tyrosine kinase inhibitors for the treatment of malignant melanoma has led to unprecedented response rates with superior overall survival rates in patients with targetable kinase mutations. Even though targeted, the effects of these new therapies are not limited to the cancer cells and induce a wide array of different adverse events (AEs). Most toxicities are mild to moderate in severity and often only affect the skin, but quality of life of patients is still affected. To prevent dose reduction and/or interruption, a sound knowledge of potential AEs and their management is required. BRAF inhibitors should not be used in patients with known RAS-mutant tumour in the medical history. We review common AEs of BRAF, MEK and KIT inhibitors used for the treatment of malignant melanoma and their management.09/2014; 3(3):29. DOI:10.3978/j.issn.2304-3865.2014.03.03
Article: Genotyping of cutaneous melanoma.[Show abstract] [Hide abstract]
ABSTRACT: Until recently, treatment options for patients with metastatic melanoma were very limited. This landscape has evolved dramatically since the discovery of activating mutations in the BRAF gene in ~45% of cutaneous melanomas. Vemurafenib, dabrafenib, and trametinib have all received regulatory approval for the treatment of metastatic melanoma patients with a BRAF(V600) mutation. Based on the necessity to document the presence of a BRAF(V600) mutation to prescribe these agents, molecular testing is now the standard of care in this disease. However, the options and rationale for testing are evolving rapidly due to an improved understanding of the molecular drivers and heterogeneity of melanoma. Such testing may identify rational combinatorial approaches to prevent or overcome resistance for the approved BRAF inhibitors. In addition, new clinical strategies have been identified for a number of other molecular changes that are detected in this disease, including somatic changes in NRAS, PTEN, CDKN2A, and c-KIT, among others. This review summarizes the current understanding of the genetic landscape of mutations in melanoma, their associations with clinicopathological features, and their implications for clinical testing and treatment.