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Query: UMLS:C0025202 (melanoma)
 69,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Malignant melanoma is an aggressive, heterogeneous disease where new biomarkers for diagnosis and clinical outcome are needed. We searched for chromosomal aberrations that characterize its pathogenesis using 47 different melanoma cell lines and tiling-resolution bacterial artificial chromosome-arrays for comparative genomic hybridization. Major melanoma genes, including BRAF, NRAS, CDKN2A, TP53, CTNNB1, CDK4 and PTEN, were examined for mutations. Distinct copy number alterations were detected, including loss or gain of whole chromosomes but also minute amplifications and homozygous deletions. Most common overlapping regions with losses were mapped to 9p24.3-q13, 10 and 11q14.1-qter, whereas copy number gains were most frequent on chromosomes 1q, 7, 17q and 20q. Amplifications were delineated to oncogenes such as MITF (3p14), CCND1 (11q13), MDM2 (12q15), CCNE1 (19q12) and NOTCH2 (1p12). Frequent findings of homozygous deletions on 9p21 and 10q23 confirmed the importance of CDKN2A and PTEN. Pair-wise comparisons revealed distinct sets of alterations, for example, mutually exclusive mutations in BRAF and NRAS, mutual mutations in BRAF and PTEN, concomitant chromosome 7 gain and 10 loss and concomitant chromosome 15q22.2-q26.3 gain and 20 gain. Moreover, alterations of the various melanoma genes were associated with distinct chromosomal imbalances suggestive of specific genomic programs in melanoma development.
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PMID:Genomic profiling of malignant melanoma using tiling-resolution arrayCGH. 1726 12

Despite the large body of mutational data available for melanoma and epidemiological studies linking this cancer to ultraviolet radiation (UVR), the fundamental carcinogenic mechanisms involved in melanoma remain largely unknown. To this end, we systematically reviewed, extracted, and analyzed mutational data from the extant melanoma literature in an effort to gain more insight into its early pathogenic events. We searched PubMed (1966-January 2006) using the words "mutation" AND "melanoma" in the title or abstract. Out of 2,095 returned results, there were 203 eligible studies that were subsequently analyzed. We cataloged 8,201 somatic and cultured melanoma specimens and annotated 2,041 reported somatic sequence variants. The single BRAF c.1799T>A (p.Val600Glu) alteration is the most prevalent variant while other A:T>T:A transversions were uncommon. Four highly-recurrent, non-ultraviolet B (UVB) changes account for most of the NRAS and BRAF variants. CDKN2A, PTEN/MMAC1, and TP53 harbored statistically higher rates of UVB signature changes (64.2%, 52.4%, and 69.2%, respectively) than oncogenic loci (NRAS: 15.3% and BRAF: 2.4%). More specifically, cutaneous melanomas showed a significantly higher proportion of UVB signature mutations at both TP53 and CDKN2A when compared to non-skin cancers using data from their respective locus-specific databases. Superficial spreading and nodular melanomas had the highest rates of BRAF (53.4%) and NRAS (28.0%) mutations. In melanoma, there is sufficient mutational evidence to support a role for direct UVB participation, especially at TP53 and CDKN2A. For oncogenes, the role for UVB is less clear since functionally-activating changes are uncommon and are subject to sequence constraints.
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PMID:Ultraviolet radiation and melanoma: a systematic review and analysis of reported sequence variants. 1729 41

RAS genes are mutated in approximately 30% of all human cancers. Interestingly, there exists a strong bias in favor of mutation of only one of the three major RAS genes in tumors of different cellular origins. NRAS mutations occur in approximately 20% of human melanomas, whereas HRAS and KRAS mutations are rare in this disease. To define the mechanism(s) responsible for this preference in melanocytes, we compared the transformation efficiencies of mutant NRAS and KRAS in immortal, non-transformed Ink4a/Arf-deficient melanocytes. NRAS mutation leads to increased cellular proliferation and is potently tumorigenic. In contrast, KRAS mutation does not enhance melanocyte proliferation and is only weakly tumorigenic on its own. Although both NRAS and KRAS activate mitogen-activated protein kinase signaling, only NRAS enhances MYC activity in these cells. Our data suggest that the activity of specific RAS isoforms is context-dependent and provide a possible explanation for the prevalence of NRAS mutations in melanoma. In addition, understanding this mechanism will have important implications for cancer therapies targeting RAS pathways.
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PMID:Differential oncogenic potential of activated RAS isoforms in melanocytes. 1729 68

Genetic studies of melanocytic tumors have mainly demonstrated activation of oncogenes such as NRAS or BRAF through point mutations. In two cases of large congenital melanocytic nevi, we observed a chromosomal translocation involving the BRAF oncogene on chromosome 7q34, resulting in both cases in removal of the auto-inhibitory N-terminal regulatory domain (hence the Ras-guanosine triphosphate binding domain) of BRAF from its protein kinase domain. This is early evidence of BRAF activation through chromosomal translocation in melanocytic tumors. Because BRAF point mutations are rather rare in congenital melanocytic nevi and melanoma arising in non-sun-exposed area, the molecular mechanism of oncogenic activation as described here could be a recurrent molecular feature in these groups of melanocytic tumors.
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PMID:Chromosomal translocations as a mechanism of BRAF activation in two cases of large congenital melanocytic nevi. 1730 36

Although a number of genes related to melanoma development have been identified through candidate gene screening approaches, few studies have attempted to conduct such analyses on a genome-wide scale. Here we use Illumina 317K whole-genome single-nucleotide polymorphism arrays to define a comprehensive allelotype of melanoma based on loss of heterozygosity (LOH) and copy number changes in a panel of 76 melanoma cell lines. In keeping with previous reports, we found frequent LOH on chromosome arms 9p (72%), 10p (55%), 10q (55%), 9q (49%), 6q (43%), 11q (43%), and 17p (41%). Tumor suppressor genes (TSGs) can be identified through homozygous deletion (HD). We detected 174 HDs, the most common of which targeted CDKN2A (n = 33). The second highest frequency of HD occurred in PTEN (n = 8), another well known melanoma TSG. HDs were also common for PTPRD (n = 7) and HDAC4 (n = 3), TSGs recently found to be mutated or deleted in other cancer types. Analysis of other HDs and regions of LOH that we have identified might lead to the characterization of further melanoma TSGs. We noted 197 regional amplifications, including some centered on the melanoma oncogenes MITF (n = 9), NRAS (n = 3), BRAF (n = 3), and CCND1 (n = 3). Other amplifications potentially target novel oncogenes important in the development of a subset of melanomas. The numerous focal amplifications and HDs we have documented here are the first step toward identifying a comprehensive catalog of genes involved in melanoma development, some of which may be useful prognostic markers or targets for therapies to treat this disease.
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PMID:Genome-wide loss of heterozygosity and copy number analysis in melanoma using high-density single-nucleotide polymorphism arrays. 1736 83

We established a novel melanoma cell line, SMYM-PRGP, which was non-tumorigenic in vivo, from an acral melanoma in radial growth phase under a low-oxygen environment. SMYM-PRGP was wild-type for known mutation sites in the BRAF and NRAS genes, and showed focal amplification of the human telomerase reverse transcriptase and cyclin D1 genes as well as the fibroblast growth factor-3 and fibroblast growth factor-4 genes. Neither mutation nor copy number loss of the CDKN2A gene was observed. The p16(INK4A) protein was expressed at a level equal to that in normal melanocytes. Among the various melanocyte growth factors added to the culture of SMYM-PRGP cells, endothelin-1 was the strongest growth stimulator, the effect of which was significantly augmented by the addition of calcium chloride. The growth stimulatory effect of endothelin-1 was shown to be mediated via the endothelin B receptor. The protein level of cyclin D1 in SMYM-PRGP cells was approximately 10 times higher than that in normal melanocytes. Although the stimulation with endothelin-1 plus calcium chloride increased cyclin D1 protein levels after 4-6 h, the level of phosphorylated retinoblastoma protein did not increase, suggesting that overexpression of cyclin D1 protein may have little effect on cell cycle progression but rather act as a pro-survival factor. SMYM-PRGP is an excellent tool for investigating the development and progression of acral melanoma.
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PMID:Establishment of a novel melanoma cell line SMYM-PRGP showing cytogenetic and biological characteristics of the radial growth phase of acral melanomas. 1748 38

Malignant melanomas often contain BRAF or NRAS mutations, but the relationship of these mutations to ambient UV exposure in combination with phenotypic characteristics is unknown. In a population-based case series from North Carolina, 214 first primary invasive melanoma patients in the year 2000 were interviewed regarding their risk factors. Ambient solar UV exposures were estimated using residential histories and a satellite-based model. Cases were grouped on the basis of BRAF and NRAS somatic mutations, determined using single-strand conformation polymorphism analysis and radiolabeled DNA sequencing, and the risk profiles of these groups were compared. Mutually exclusive BRAF-mutant and NRAS-mutant cases occurred at frequencies of 43.0% and 13.6% with mean ages at diagnosis of 47.3 and 62.1 years, respectively. Tumors from patients with >14 back nevi were more likely to harbor either a BRAF mutation [age-adjusted odds ratio (OR), 3.2; 95% confidence interval (95% CI), 1.4-7.0] or an NRAS mutation (age-adjusted OR, 1.7; 95% CI, 0.6-4.8) compared with patients with 0 to 4 back nevi. However, BRAF-mutant and NRAS-mutant tumors were distinctive in that BRAF-mutant tumors were characteristic of patients with high early-life ambient UV exposure (adjusted OR, 2.6; 95% CI, 1.2-5.3). When ambient UV irradiance was analyzed by decadal age, high exposure at ages 0 to 20 years was associated with BRAF-mutant cases, whereas high exposure at ages 50 and 60 years was characteristic of NRAS-mutant cases. Our results suggest that although nevus propensity is important for the occurrence of both BRAF and NRAS-mutant melanomas, ambient UV irradiance influences risk differently based on the age of exposure. The association of BRAF mutations with early-life UV exposure provides evidence in support of childhood sun protection for melanoma prevention.
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PMID:Number of nevi and early-life ambient UV exposure are associated with BRAF-mutant melanoma. 1750 27

Melanocytic lesions, including Spitz nevi (SN), common benign nevi (CBN) and cutaneous metastatic melanoma (CMM), were analyzed for activating mutations in NRAS, HRAS and BRAF oncogenes, which induce cellular proliferation via the MAP kinase pathway. One of 22 (4.5%) SN tested showed an HRAS G61L mutation. Another lesion, a 'halo' SN, showed a BRAF V600E (T1796A) mutation. BRAF V600E mutations were found in two thirds (20/31) of CBN, while a further 19% (6/31) showed NRAS codon 61 mutations. One third of CMM (10/30) had various BRAF mutations of codon 600, and a further 6% (2/31) showed NRAS codon 61 mutations. Seventeen SN tested for loss of heterozygosity (LOH) at 9p and 10q regions, known to be frequently deleted in melanoma, showed LOH at the 9p loci D9S942 and IFNA. A further lesion was found with low-level microsatellite instability at one locus, D10S214. The low rate of RAS-RAF mutations (2/22, 9.1%) observed in SN suggests that these lesions harbor as yet undetected activating mutations in other components of the RAS-RAF-MEK-ERK-MAPK pathway. Germline DNA from members of 111 multiple-case melanoma families, representing a range of known (CDKN2A) and unknown predisposing gene defects, was analyzed for germline BRAF mutations, but none was found.
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PMID:Low prevalence of RAS-RAF-activating mutations in Spitz melanocytic nevi compared with other melanocytic lesions. 1751 71

Inactivation of the p53 pathway represents the most common molecular defect of human cancer. But in the setting of melanoma, a highly aggressive and invariably fatal malignancy in its advanced disseminated form, mutation/deletion of p53 is relatively rare, whereas its positive regulator ARF is often lost. Here, we show that genetic deficiency in Arf but not p53 facilitates rapid development of melanoma in a genetically engineered mouse model. This difference is accounted for, at least in part, by the unanticipated observation that, unlike fibroblasts, senescence control in melanocytes is strongly regulated by Arf and not p53. Moreover, oncogenic NRAS collaborates with deficiency in Arf, but not p53, to fully transform melanocytes. Our data demonstrate that ARF and p53, although linked in a common pathway, suppress tumorigenesis through distinct, lineage-dependent mechanisms and suggest that ARF helps restrict melanoma progression by executing the oncogene-induced senescence program in benign nevi. Thus, therapeutics designed to restore wild-type p53 function may be insufficient to counter melanoma and other malignancies in which ARF holds p53-independent tumor suppressor activity.
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PMID:ARF functions as a melanoma tumor suppressor by inducing p53-independent senescence. 1757 30

Tumor progression is a multistep process in which proproliferation mutations must be accompanied by suppression of senescence. In melanoma, proproliferative signals are provided by activating mutations in NRAS and BRAF, whereas senescence is bypassed by inactivation of the p16(Ink4a) gene. Melanomas also frequently exhibit constitutive activation of the Wnt/beta-catenin pathway that is presumed to induce proliferation, as it does in carcinomas. We show here that, contrary to expectations, stabilized beta-catenin reduces the number of melanoblasts in vivo and immortalizes primary skin melanocytes by silencing the p16(Ink4a) promoter. Significantly, in a novel mouse model for melanoma, stabilized beta-catenin bypasses the requirement for p16(Ink4a) mutations and, together with an activated N-Ras oncogene, leads to melanoma with high penetrance and short latency. The results reveal that synergy between the Wnt and mitogen-activated protein (MAP) kinase pathways may represent an important mechanism underpinning the genesis of melanoma, a highly aggressive and increasingly common disease.
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PMID:Beta-catenin induces immortalization of melanocytes by suppressing p16INK4a expression and cooperates with N-Ras in melanoma development. 1800 87


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