Clinical implications of cytogenetic abnormalities in melanoma

Loss of Heterozygosity on Chromosome 1 and 9 and Hormone Receptor Analysis of Metastatic Malignant Melanoma Presenting in Breast

Malignant melanoma (MM), the most common metastatic solid tumor to involve the breast, may present as a diagnostic problem, frequently requiring the use of ancillary studies for accurate diagnosis. The implication of hormonal interplay is strong since metastatic MM to the breast is seen nearly always in women. However, the role of hormonal status as a predisposing factor in the development of this entity is largely unresolved. A number of chromosomal loci, including ip36 and 9p2l-22, appear to harbor critical genes important to melanoma tumorigenesis, and additionally chromosome 9q22.3-31. We wanted to know if metastatic MM in breast showed chromosome lp and 9p genetic alterations (loss of heterozygosity) similar to those that occur in primary cutaneous MM, and whether additional 9q LOH changes are present. Hormonal receptor status of the metastatic MM was also determined. We identified 20 patients with known MM metastatic to the breast, which we analyzed with the following genetic markers: D9S12 (9q22.3), D9S171 (9p21), IFNA (9p22), and DlS450 (ip). Visually directed microdissection was performed on archival histologic slides containing both tumor and adjacent normal breast epithelium, followed by single-step DNA extraction and polymerase chain reaction (PCR) amplification for evaluation of loss of heterozygosity (LOH) for the above-listed markers. Immunohistochemical (IHC) stains for estrogen receptor (ER) and progesterone receptor (PR) was performed on 10 of the cases. Twelve of the 20 cases contained DNA suitable for PCR amplification following direct visualization microdissection. Four of 8 (50%) informative cases showed LOH at 9p21 with D9S171. Ten cases were heterozygous for IFNA, with 2 cases (20%) showing LOH at this locus. These particular cases also showed LOH at 9p21. One of 9 (11%) informative cases showed LOH for DlS450 (Ip36). Five cases were heterozygous for D9S12, and 2 1-22 (50%) and lp36 (11%), as previously described in primary cutaneous MM. Additional LOH was observed at the 9q22.3-31 locus (40%). We suggest this locus to be investigated for harboring potential genes important in the tumorigenesis of cutaneous MM.

Gene Expression Profile Changes between Melanoma Metastases and their Daughter Cell Lines: Implication for Vaccination Protocols

Vaccination protocols based on autologous tumor material often require in vitro culturing of tumor cells to obtain enough cellular material for the production of the vaccine. Cancer cells and particularily melanoma cells are known for their genomic instability. Therefore, it can be assumed that melanoma cells acquire genomic changes and thereby changes in the transcriptome during in vitro culturing. This may lead to a shift of epitopes expressed on the tumor cells. We analyzed the transcriptome of in vitro cultured melanoma cells prepared from melanoma metastases. Comparing the gene expression changes between the tumors and their offspring cell lines, we demonstrate that with increasing passage numbers, gene expression changes increase drastically.

Isolation and characterization of the human Cdc2L1 gene promoter

CDK11 (cyclin-dependent kinase 11, formerly known as PITSLRE) is a member of the p34cdc2-related kinases. It has been previously shown to be involved in a variety of different cellular processes including RNA processing, apoptosis, and cell cycle progression. It is encoded by two different but highly similar genes, Cdc2L1 (cell division control 2 like 1) and Cdc2L2 (cell division control 2 like 2). Previous studies from our group identified and characterized the transcriptional regulation of the human Cdc2L2 gene promoter. The current studies identify and characterize the Cdc2L1 gene promoter. We cloned the promoter and elucidated the different transcriptional regulatory elements that reside within the 5' region of the gene. Deletion analysis of the promoter showed a region of nucleotides -152 to +11 to be necessary for basal transcription of the Cdc2L1 gene. Sequencing analysis found this region of the promoter to be highly GC-rich but is lacking both TATA and CAAT boxes. There are several different transcription factor binding sites that are consensus or near consensus found within this region. The potential binding sites include two Ets-1 sites, one Skn-1 site, and one E2F-1 site. Transfection studies of various site-directed mutagenesis clones for these different sites revealed that both Ets-1 sites play critical roles in sustained transcriptional activity as well as Skn-1. Chromatin immunoprecipitation of the endogenous promoter with Ets-1 and Skn-1 verified an in vivo association of Ets-1 and Skn-1 transcription factors with the endogenous promoter. These results, in addition to our Cdc2L2 results, lead to the further comprehension of the fundamental mechanisms dictating CDK11 gene expression through the Cdc2L1 gene promoter.

Cytogenetic analysis of melanoma cell lines: subclone selection in long-term melanoma cell cultures

We employed G-banding cytogenetic analysis to follow the clonal constitution of short-term cultures of metastatic malignant melanoma compared to their long-term cultures. Eight metastatic melanoma cell lines were analyzed. No long-term culture was found to be identical to its line of origin. In all cultures there was a selection of one subclone and emergence of its own subclones. In the majority of cultured tumors (5/8), this process was associated with a decrease in the number of subclones composing the line. We suggest that subclone selection in long-term tumor cultures can be associated with a change in phenotype. Therefore, caution is required when employing long-term cultures for research and therapy.

Chromosomal imbalances in primary and metastatic melanomas revealed by comparative genomic hybridization

Characteristic genetic changes underlying the metastatic progression of malignant melanoma is incompletely understood. The goal of our study was to explore specific chromosomal alterations associated with the aggressive behavior of this neoplasm. Comparative genomic hybridization was performed to screen and compare genomic imbalances present in primary and metastatic melanomas. Sixteen primary and 12 metastatic specimens were analyzed. We found that the pattern of chromosomal aberrations is similar in the two subgroups; however, alterations present only in primary and/or metastatic tumors were also discovered. The mean number of genetic changes was 6.3 (range 1-14) in primary and 7.8 (range 1-16) in metastatic lesions. Frequent losses involved 9p and 10q, whereas gains most often occurred at 1q, 6p, 7q, and 8q. Distinct, high-level amplifications were mapped to 1p12-p21 and 1p22-p31 in both tumor types. Amplification of 4q12-q13.1, 7q21.3-qter and 8q23-qter were detected only in primary tumors. The 20q13-qter amplicon was present in a metastatic tumor. The number of genetic alterations were significantly higher in primary tumors which developed metastases within one year after the surgery compared to tumors without metastasis during this time period. Fluorescence in situ hybridization with centromeric and locus-specific probes was applied to validate CGH results on a subset of tumors. Comparison of FISH and CGH data gave good correlation. The aggressive behavior of melanoma is associated with accumulation of multiple genetic alterations. Chromosome regions, which differ in the primary and metastatic lesions, may represent potential targets to identify metastases-related chromosomal alterations.

Immunotherapy: on the edge between experimental and clinical oncology

Cancer immunotherapy is still largely confined to the laboratory bench and experimental animal models. Yet the field is rapidly moving forward and some immunological tools are now entering into clinical use. The first and perhaps best example of such progress is given by bioengineered humanized monoclonal antibodies of which some have been already approved for therapy in B-cell lymphoma and breast cancer. Unexpectedly, another remarkable form of immunotherapy has turned out to derive from T-cell adoptive therapy associated with allogeneic bone marrow transplantation. Its benefits render such an approach the first choice therapy for a large number of hematological malignancies and it is now being adapted also for treatment of advanced solid tumors. Finally, harnessing the immune system against the autologous tumor remains the most ambitious but still distant design for immunotherapy. Recent technical advances and a better understanding of the immune system in cancer patients should concur in defining the best strategy for active immunotherapy in clinical oncology.

Oral mucosal melanoma: epidemiology and pathobiology

The vast majority of healthy individuals have some form of melanocytic lesions with most having several cutaneous melanocytic nevocellular nevi. The incidence of cutaneous melanoma, despite improved prevention and early diagnosis of precursor melanocytic lesions, is on the increase with a projection that one in 75 persons born in the year 2000 will develop cutaneous melanoma in his/her lifetime. With cutaneous melanoma, the number, location and type of nevi, sun exposure and inability to tan, and presence or absence of dysplastic nevi affect transformation to a malignant process. Certain familial factors, syndromes, cytogenetic abnormalities, and mutations in tumor suppressor genes also influence tumor formation. In contrast, mucosal melanoma involving the oral cavity and head and neck regions is not as well understood or characterized. No doubt, this is due to the fact that this subtype of melanoma accounts for less than 1% of all cases. Mucosal melanomas tend to present at a higher stage, are more aggressive, and in a vertical growth phase of disease. A definitive precursor lesion for mucosal melanoma has not been identified; however, atypical melanocytic hyperplasia may represent a proliferative phase before overt tumorigenesis occurs. Melanoma-related antigens, growth factors, and proliferation markers have been identified in cutaneous melanoma, and allow for development of immunotherapy directed against melanoma-associated entities. It is currently possible to evaluate the cytogenetic make-up of precursor melanocytic lesions and frank melanoma, and the constitutional genetic background of individuals at risk for melanoma. No doubt, as concerted investigations of mucosal melanomas of the oral cavity and head and neck evolve, similar factors will be identified which will direct therapy and predict recurrence and survival. In the not too distant future, innovative retroviral transfection, antibodies against specific melanoma-associated factors, vaccination against melanoma, and gene therapy to repair cytogenetic abnormalities and tumor suppressor gene mutations may provide effective therapy and protection against melanomas.

Mutation testing in melanoma families: INK4A, CDK4 and INK4D

The INK4A gene which codes for the cyclin-dependent kinase (CDK) inhibitor INK4A or p16 underlies susceptibility to melanoma in some families. Germline mutations in the gene that codes for the target protein of p16, CDK4, underlie susceptibility in very rare families. We report mutation screening of the INK4A and CDK4 genes in 42 UK families. A total of nine families were identified with INK4A mutations and none with CDK4 exon 2 mutations. These mutations were in 8/22 (35%) families with three or more cases of melanoma and 1/20 (5%) families with only two cases. In one of these nine families a novel single base pair substitution was identified, Gly67Arg. In an attempt to identify another melanoma susceptibility gene, a member of the INK4 family, the p19 INK4D gene has been studied. The p19 gene was sequenced in DNA from the 42 UK families and six additional US families. No mutations were identified.

MSG1 (melanocyte-specific gene 1): mapping to chromosome Xq13.1, genomic organization, and promoter analysis

MSG1 (melanocyte-specific gene 1) is a recently isolated gene predominantly expressed in cultured normal melanocytes and pigmented melanoma cells. MSG1 encodes a 27-kDa nuclear protein that has strong intrinsic transcriptional transactivating activity. In this report, the human MSG1 gene was mapped to chromosome Xq13.1 using X chromosome-specific somatic cell hybrids, and the mouse Msg1 gene was mapped 1.9 +/- 1.3 cM proximal to Xist using an interspecific backcross panel. Both the human and the mouse MSG1 genes consist of three exons and two introns within 5 kb of genomic DNA, and their genomic structures are highly conserved. Southern blot analysis suggests the existence of MSG1 homologues in chicken, zebrafish, and Drosophila. A 2.0-kb fragment of the 5'-flanking region of the mouse Msg1 gene contains a TATA box and potential binding sites for several transcription factors including USF, Brn-3, Brn-2, TFE3, Oct-1, AP-2, and Spl. This promoter fragment activates transcription of a reporter gene in pigmented melanoma cells, but not in amelanotic melanoma cells or nonmelanocytic cells, indicating that Msg1 expression is at least partially regulated at the transcriptional level.