Polyploidy in malignant melanoma

Effect of stress-induced polyploidy on melanoma reprogramming and therapy resistance

Melanomas and their precursors, the melanocytes, are frequently exposed to UV due to their anatomic location, leading to DNA damage and reactive oxygen stress related harm. Such damage can result in multinucleation or polyploidy, in particularly in presence of mitotic or cell division failure. As a consequence, the cell encounters either of two fates: mitotic catastrophe, resulting in cell death, or survival and recovery, the latter occurring less frequently. However, when cells manage to recover in an polyploid state, they have often acquired new features, which allow them to tolerate and adapt to oncogene- or therapy induced stress. This review focuses on polyploidy inducers in melanoma and their effects on transcriptional reprogramming and phenotypic adaptation as well as the relevance of polyploid melanoma cells for therapy resistance.

Human endogenous retroviral K element encodes fusogenic activity in melanoma cells

INTRODUCTION AND HYPOTHESIS

Nuclear atypia with features of multi nuclei have been detected in human melanoma specimens. We found that the K type human endogenous retroviral element (HERV K) is expressed in such cells. Since cellular syncytia can form when cells are infected with retroviruses, we hypothesized that HERV K expressed in melanoma cells may contribute to the formation of multinuclear atypia cells in melanoma.

EXPERIMENTS AND RESULTS

We specifically inhibited HERV K expression using RNA interference (RNAi) and monoclonal antibodies and observed dramatic reduction of intercellular fusion of cultured melanoma cells. Importantly, we identified loss of heterozygosity (LOH)of D19S433 in a cell clone that survived and proliferated after cell fusion.

CONCLUSION

Our results support the notion that proteins encoded by HERV K can mediate intercellular fusion of melanoma cells, which may generate multinuclear cells and drive the evolution of genetic changes that provide growth and survival advantages.

Martini: using literature keywords to compare gene sets

Life scientists are often interested to compare two gene sets to gain insight into differences between two distinct, but related, phenotypes or conditions. Several tools have been developed for comparing gene sets, most of which find Gene Ontology (GO) terms that are significantly over-represented in one gene set. However, such tools often return GO terms that are too generic or too few to be informative. Here, we present Martini, an easy-to-use tool for comparing gene sets. Martini is based, not on GO, but on keywords extracted from Medline abstracts; Martini also supports a much wider range of species than comparable tools. To evaluate Martini we created a benchmark based on the human cell cycle, and we tested several comparable tools (CoPub, FatiGO, Marmite and ProfCom). Martini had the best benchmark performance, delivering a more detailed and accurate description of function. Martini also gave best or equal performance with three other datasets (related to Arabidopsis, melanoma and ovarian cancer), suggesting that Martini represents an advance in the automated comparison of gene sets. In agreement with previous studies, our results further suggest that literature-derived keywords are a richer source of gene-function information than GO annotations. Martini is freely available at http://martini.embl.de.

Malignant melanoma--its precursors and its topography of proliferation. DNA-Feulgen-cytophotometry and mitosis index

DNA-content and size of the nuclear areas in different zones of malignant melanomas of different histological types and in dysplastic naevi were measured in order to provide information on the histogenesis and proliferative behaviour of human malignant melanoma. The results were compared with those from normal epidermis, common naevi, and reactive melanocytic hyperplasias. The mitotic index of melanomas--divided into different topographic zones in an analogous way--was also determined. The DNA-histographs of all naevi and reactive melanocytic hyperplasias showed a diploid maximum, but the dysplastic naevi had a larger proportion of nuclei with hyperdiploid and tetraploid DNA-content, indicating an increased proliferative activity. The mean values (X) of nuclear areas in dysplastic naevi (DN) were about the same as in common naevi (CN) and slightly lower than in superficial spreading melanomas (SSM). The coefficient of variability (cv) as an indicator of anisokaryosis was markedly higher in DN (27.8) and SSM (29.3) than in CN (20.2). In DNA-content we found similar results: almost no difference in mean values, but DN taking an intermediate position between CN and SSM with respect to cv (CN: 12.3; DN: 21.0; SSM: 36.6). There was no unequivocal evidence in these data for DN being a precancerous stage. Superficial melanomas with a nodular component ("SSM/NM") differed from SSM and NM by increased DNA-content and greater variability of nuclear areas and showed the clearest features of malignancy in their DNA-histographs. The mitotic indices had rather low values in SSM and intraepidermal marginal zones of "SSM/NM" on one hand and markedly higher values in NM and nodular parts of "SSM/NM" on the other. The highest mitotic counts were found in the three investigated metastases.

DNA ploidy-characteristics of human malignant melanoma analysed by flow cytometry and compared with histology and clinical course

Flow cytometric analysis of nuclear DNA content is valuable for indicating ploidy- and proliferation abnormalities in surgically removed human malignant melanomas. In 35 primary cutaneous melanomas, 20 metastases of melanoma in skin and lymph nodes, and 16 nevi the DNA distribution was analyzed by flow cytometry and compared with a variety of histological parameters and the subsequent clinical course. Heteroploid DNA distributions with increased polyploid or aneuploid fractions were found in 26 primary melanomas (74%), 14 metastases (70%), and 4 nevi (25%) indicating tumor clones with an abnormal nuclear DNA content. Three or more cell clones in a single biopsy was found in 10 primary melanomas, 2 metastases, and 1 nevus. The frequency of heteroploidy was significantly higher in primary and secondary melanomas than in nevi (p less than 0.001) and was correlated significantly with a high mitotic activity (p less than 0.002), marked nuclear pleomorphism (p less than 0.01), large nucleoli (p less than 0.01) and a thickness of the primary melanoma of more than 2.25 mm (p less than 0.02). Such histologic findings in malignant melanomas have been shown previously to be correlated with a bad prognosis. No significant correlation was found between heteroploidy and the histologic type of melanoma or the level of invasion. A 2-year clinical follow-up showed that more patients died from melanoma if the DNA distribution in the primary or secondary melanoma was heteroploid (6/26; 23% and 8/13; 62% respectively) than if it was diploid (0/9; 0% and 2/5; 40% respectively). However, the differences were not statistically significant. It is concluded that heteroploidy 1) is not an absolute criterion of malignancy, 2) is significantly correlated with histologic features indicating marked cellular anaplasia, and 3) is apparently correlated with a bad prognosis.

Tumor cell karyotypes in malignant melanoma

Fifteen malignant melanomas were subjected to chromosomal analysis, in order to determine whether the number of chromosomes in a tumor cell could be correlated to a clinical prognosis. The protocol involved a direct technique which utilized a Colcemid blockade of spindle formation in mitosis to allow study of metaphase chromosomes. The direct method was chosen to reveal chromosome changes in the tumor cell in situ rather than changes in the cultured cell. Two tumors yielded chromosome spreads which could be counted and correlated with a clinical prognosis. Failure to obtain other adequate chromosome spreads were accounted for by the presence of tissue necrosis and the absence of viable tumor cells.

Sex chromatin positive metastatic melanoma in a male with a favourable prognosis

The presence of sex chromatin in a metastatic malignant melanoma from a male patient aged 26 who showed no evidence of any constitutional chromosome anomaly is described. A possible association between the apparently "female" origin of the tumour and the good response to therapy is considered.