Chromosome and growth factor abnormalities in melanoma

Morphogenesis and molecular considerations on congenital cardiac septal defects

The primary unseptated heart tube undergoes extensive remodeling including septation at the atrial, atrioventricular, ventricular, and ventriculo-arterial level. Alignment and fusion of the septal components is required to ensure full septation of the heart. Deficiencies lead to septal defects at various levels. Addition of myocardium and mesenchymal tissues from the second heart field (SHF) to the primary heart tube, as well as a population of neural crest cells, provides the necessary cellular players. Surprisingly, the study of the molecular background of these defects does not show a great diversity of responsible transcription factors and downstream gene pathways. Epigenetic modulation and mutations high up in several transcription factor pathways (e.g. NODAL and GATA4) may lead to defects at all levels. Disturbance of modulating pathways, involving primarily the SHF-derived cell populations and the genes expressed therein, results at the arterial pole (e.g. TBX1) in a spectrum of ventricular septal defects located at the level of the outflow tract. At the venous pole (e.g. TBX5), it can explain a variety of atrial septal defects. The various defects can occur as isolated anomalies or within families. In this review developmental, morphological, genetic, as well as epigenetic aspects of septal defects are discussed.

Heterogeneity of bromodeoxyuridine sensitivity of cultured cells from melanoma metastases

Continuously growing cell cultures, testing positive for tyrosine activity, were derived from two brain and three lymph-node metastases of five patients with malignant melanoma. These cell cultures were analyzed regarding their proliferation rate with continuous bromodeoxyuridine (BrdUrd) labeling followed by bivariate Hoechst 33258/ethidium bromide flow cytometry. Melanoma cell cultures are more sensitive toward BrdUrd in comparison to human diploid fibroblast cultures: 50% growth inhibition at 360 +/- 130 microM BrdUrd (range: 130-520; n = 11) vs. 650 +/- 50 microM BrdUrd (n = 3) for fibroblasts. Moreover, BrdUrd sensitivity in melanoma cells is oxygen dependent: 50% growth inhibition at 200 +/- 55 microM (range: 65-400 microM) for 20% oxygen vs. 360 +/- 130 microM BrdUrd for 5% oxygen. The cell cycle kinetic mechanisms of BrdUrd-induced growth inhibition is accumulation of cells in the G2 phase. Cultures from a single metastasis showed up to a 3-fold variation in BrdUrd sensitivity. In one of the brain metastases two populations of different ploidy level (pseudotriploid vs. pseudotetraploid) and BrdUrd sensitivity could be resolved. Thus, continuous BrdUrd labeling followed by bivariate Hoechst 33258/ethidium bromide flow cytometry is a powerful tool to detect heterogeneity in proliferative capacity and drug sensitivity of cell populations within one tumor biopsy.

Human malignant melanoma. A genetic disease?

BACKGROUND

Human hereditary malignant melanoma, comprising 5% of all cases of malignant melanoma, occurs in association with other malignancies, predominantly in families with dysplastic nevus syndrome. Additionally, higher incidences of malignant melanoma have been reported in individuals with genetic disorders such as ataxia telangiectasia and xeroderma pigmentosum. The results and observations as reported in the literature on the involvement of oncogenes and chromosomal aberrations in the development of malignant melanoma are reviewed and compared with the authors' own experimental and clinical experience.

RESULTS

Numerous chromosomal regions, as on chromosomes 1 and 9, were altered. The long arm of chromosome 6 was affected in 60% of melanomas. Introduction of a normal copy of chromosome 6 resulted in loss of tumorigenicity in vitro. True melanoma genes were evident in two animal models: the Sinclair swine and the teleost fish Xiphophorus. In the Xiphophorus system, the crossing-conditioned elimination of a tumor suppressor gene led to the uncontrolled activity of a dominantly acting oncogene in certain hybrids. The causative oncogene, Xmrk, encodes a receptor tyrosine kinase closely related to human epidermal growth factor receptor (EGFR). Among the numerous studied human oncogenes, mutations in the extensively investigated ras family are the result rather than the cause of malignant transformation. High expression of nuclear oncogenes simply may be a common feature of rapidly dividing cells. The receptor tyrosine kinase EGFR may be involved in late stage melanoma; the human exon with homology to Xmrk shows elevated transcription levels in 80% of human melanoma metastases. Deletions of the tumor suppressor gene MTS 1 may be important for melanoma formation, whereas deletions of p53 appear to be of minor relevance.

CONCLUSION

Scientific progress in treating and diagnosing malignant melanoma will largely depend on experimental approaches to define relevant genetic changes by functional analysis rather than descriptive phenomenology and correlative observations.

Chromosomal findings in cultured melanocytes from a giant congenital nevus

A giant congenital pigmented nevus was observed in a newborn male. A melanocyte culture was established from nevus fragments removed at age 6 days. Analysis of 136 metaphases harvested from the primary culture showed 74% normal mitoses, 22% polyploids, and 4% mitoses with chromosome rearrangements involving in particular 1p, 12q, and 19p. In addition, the culture showed a high level of HLA-DR expression. Although histology showed no sign of malignancy, these findings may illustrate one of the first events which might eventually progress toward malignancy.

Molecular genetics of human malignant melanoma

Due to a variety of known and unknown control mechanisms, the human genome is remarkably stable when compared to most other species. The long latency periods of most solid tumors, during which the cell undergoes malignant transformation, are presumably due to this stability. The molecular basis responsible for the induction of genetic instability and the resultant biological characteristics manifest in tumor populations is not well understood. The discovery of both oncogenes and tumor suppressor genes, however, has placed the phenomenon of human genome stability on a more solid conceptual footing. These types of genes clearly place multiple barriers to oncogenic transformation, and traversing these barriers apparently requires both time and the accumulation of genetic defects that cannot be corrected. The evolution of neoplasias can, therefore, be predicted to be due to: (1) consistent and progressive loss of tumor suppressor genes; (2) gene amplification, resulting in the over-expression of proteins that aid in tumor progression; (3) gene mutation, which alters the orderly biochemistry of the normal cell; (4) genes that allow a cell like the melanocyte to escape the confining nature of the epidermis and to invade through the dermis into the circulatory and lymphatic systems in order to disseminate itself to other organs (e.g., proteolytic enzymes, enzyme inhibitors, integrins, metastases genes, chemotactic factors etc.); (5) factors, perhaps such as TGF beta 2, that may impact negatively on MHC antigens and confuse host defense mechanisms; and (6) S.O.S.-type genes, which may be expressed as a direct response to the accumulating damage in an attempt to correct the damage, but that may then become part of the problem instead of the solution. The extraordinary plasticity and instability of the genome of a melanoma cell suggests an inordinate amount of genetic flux. In addition to activating and inactivating various genes, this constant shuffling and rearranging of the genome in neoplasms such as MM may be constantly altering gene dose. Cytogenetic and molecular biological studies have been the Rosetta stone for understanding the etiological relevant genetic events in human cancers. Genetic alterations fundamental to the pathology of MM have begun to be defined. Studies designed to understand these perturbations at the biochemical and organismic level are underway.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of GRO alpha, beta and gamma expression in human colonic tumours: potential significance of cytokine involvement

The GRO genes, isolated from transformed fibroblasts, belong to a superfamily of genes such as platelet factor 4 and neutrophil activating peptide/IL-8. Three related GRO genes are described which are closely linked on chromosome 4: GRO alpha, GRO beta, and GRO gamma: GRO beta and GRO gamma share 90 and 86% sequence homology with GRO alpha. The GRO alpha gene product shares homology with, and is melanocyte growth stimulatory activity (MGSA). The MGSA/GRO alpha has potent chemotactic, growth regulatory and transformative functions. The function of GRO beta and gamma is unknown. Expression of GRO alpha is well characterized in vitro; studies in actual human tissues are not reported. We chose to determine the specific expression of GRO alpha, beta and gamma in both normal and transformed human colonic tissues and to assess the role of exogenous cytokines on their induction. Tissues from ten patients with colonic neoplasia were obtained at the time of colectomy. All specimens underwent Northern analysis for GRO gene expression, comparing normal colonic mucosa with neoplastic mucosa. Differential GRO alpha, beta and gamma expressions were determined by polymerase chain reaction (PCR). GRO alpha expression was evaluated in the tumour specimens compared with normal, while there was constitutive expression of GRO gamma in both normal and neoplastic colonic mucosa. Expression of GRO beta was minimal in all tissue specimens. In addition, HT29 colon carcinoma cells stimulated with IL-1 beta and TNF alpha demonstrated induction of GRO alpha and IL-8. Thus, GRO alpha is differently elevated in in vivo colon carcinoma specimens. GRO gamma was constitutively expressed in colonic tissues; GRO beta was not similarly expressed.

Absence of structural rearrangements of chromosome 11 in human primary malignant melanoma

Cytogenetic analysis of 10 primary and 18 metastatic malignant melanomas revealed that structural abnormalities of chromosome 11 were present in 50% of metastatic lesions and were not found in primary tumors. Our findings suggest that chromosome 11 aberrations represent secondary changes in malignant melanoma tumorigenesis.

Mutational analysis of the human p53 gene in malignant melanoma

Nine metastatic melanoma cell lines and two melanocyte cell lines were analyzed for point mutations in highly conserved regions of the p53 gene. No mutations were detected in the two melanocytic cell lines and in eight melanoma cell lines. However, a C----T transition at codon 248, resulting in a substitution of tryptophan for arginine, was found in one melanoma cell line. On immunohistochemical staining, only this cell line showed reactivity for mouse monoclonal antibody 1801, which is immunoreactive with human p53 protein. The original paraffin-embedded specimen from which this mutant cell line was established was obtained, and sequence analysis detected the identical mutation in the p53 gene as that seen in the derived cell line. This is the first report indicating point mutations in the p53 gene in malignant melanocytic tissues.