Molecular mapping of the oncogene MYB and rearrangements in malignant melanoma

Characterisation of the R2R3 Myb subgroup 9 family of transcription factors in tomato

Tomato (Solanum lycopersicum) has many epidermal cell outgrowths including conical petal cells and multiple types of trichomes. These include the anther-specific trichome mesh which holds the anthers connate. The R2R3 Myb Subgroup 9 family of transcription factors is involved in development of epidermal cell outgrowths throughout the angiosperms. No previous study has examined all members of this transcription factor family in a single species. All 7 R2R3 Myb Subgroup 9 genes were isolated from tomato. They were ectopically expressed in tobacco to assess their ability to induce epidermal cell outgrowth. Endogenous expression patterns were examined by semi-quantitative RT-PCR at different stages of floral development relative to the development of anther trichomes. We report variation in the degree of epidermal cell outgrowth produced in transgenic tobacco by each ectopically expressed gene. Based on expression profile and ectopic activity, SlMIXTA-2 is likely involved in the production of leaf trichomes. SlMIXTA-2 is expressed most strongly in the leaves, and not expressed in the floral tissue. SlMYB17-2 is the best candidate for the regulation of the anther trichome mesh. SlMYB17-2 is expressed strongly in the floral tissue and produces a clear phenotype of epidermal cell outgrowths when ectopically expressed in tobacco. Analysis of the phenotypes of transgenic plants ectopically expressing all 7 genes has revealed the different extent to which members of the same transcription factor subfamily can induce cellular outgrowth.

Gastric metastasis from nodular malignant melanoma of the auricle with multigene aberrations: A rare case report and literature review

Primary malignant melanoma (MM) of the external ear accounts for a low proportion of cases of cutaneous MM, and its incidence in non-white women is very low. The stomach is a rare metastatic site for MM. Gastric metastasis of MM of the external ear is extremely rare, and the associated gene alterations and mechanisms are poorly understood. The present report describes the case of a 58-year-old Asian woman who had a mass on the left auricle for 5 years and was diagnosed with nodular MM with the BRAF V600E mutation after surgical resection. Postoperative metastases to the stomach and descending duodenum appeared 1 year after resection. After 11 months of BRAF-targeted therapy and immunotherapy, the patient developed drug resistance and died from systemic metastases to the brain, lungs, liver, left adrenal gland and peritoneum. Genetic testing revealed additional aberrations in MYB, p16, MYC and PTEN. The clinical characteristics of MM of the external ear and gastric metastatic MM were also summarized through a retrospective literature review. Immunohistochemical staining is critical in the diagnosis of gastric metastasis from MM of the external ear. This disease often requires a multidisciplinary treatment approach, including surgery, targeted therapy and immunotherapy. The present study provides some genetic information about this rare disease and discusses appropriate treatment strategies. The findings of the present study suggests that the surgical margin size, tumor histological type and number of genetic aberrations may be closely associated with metastasis potential, therapeutic efficacy and patient outcome.

Tumor progression, early diagnosis and prognosis of melanoma

Primary melanomas evolve from melanocytes or from precursor lesions through two stages: the radial and vertical growth phases. The radial growth phase may be in situ or microinvasive, but is a non-tumorigenic neoplastic process, while the vertical growth phase is tumorigenic. The prognosis in radial growth phase is excellent irrespective of thickness or other variables. Curable radial growth phase melanomas can be recognized by surveillance of patients identified by screening for risk markers which include dysplastic nevi, common nevi, freckles, and other indicators of chronic or acute sun exposure or sun sensitivity. The prognosis in vertical growth phase depends on attributes of the tumor and of the host. The tumor mitotic rate, the presence of host tumor-infiltrating lymphocytes (TIL) within the vertical growth phase, and tumor thickness are the most powerful predictors of survival. New prognostic attributes are needed not only to provide for more accurate prognosis and diagnosis, but also to test the relevance of in vitro or animal studies in a human neoplastic system. Such attributes will be developed in the future based on markers that are associated with tumor progression. Candidate markers include growth factors and cytokines and their receptors, adhesion molecules and their ligands, chemotactic and motility factors, immune response-related molecules, and tumor-associated proteases. Some of these markers that are represented in the transition from radial to vertical growth phase will be reviewed. The tumor progression model presented here has been of value in the development of more accurate prognostic models, and in the elucidation of mechanisms of the malignant phenotype in melanoma.

WISP genes are members of the connective tissue growth factor family that are up-regulated in wnt-1-transformed cells and aberrantly expressed in human colon tumors

Wnt family members are critical to many developmental processes, and components of the Wnt signaling pathway have been linked to tumorigenesis in familial and sporadic colon carcinomas. Here we report the identification of two genes, WISP-1 and WISP-2, that are up-regulated in the mouse mammary epithelial cell line C57MG transformed by Wnt-1, but not by Wnt-4. Together with a third related gene, WISP-3, these proteins define a subfamily of the connective tissue growth factor family. Two distinct systems demonstrated WISP induction to be associated with the expression of Wnt-1. These included (i) C57MG cells infected with a Wnt-1 retroviral vector or expressing Wnt-1 under the control of a tetracyline repressible promoter, and (ii) Wnt-1 transgenic mice. The WISP-1 gene was localized to human chromosome 8q24.1-8q24.3. WISP-1 genomic DNA was amplified in colon cancer cell lines and in human colon tumors and its RNA overexpressed (2- to >30-fold) in 84% of the tumors examined compared with patient-matched normal mucosa. WISP-3 mapped to chromosome 6q22-6q23 and also was overexpressed (4- to >40-fold) in 63% of the colon tumors analyzed. In contrast, WISP-2 mapped to human chromosome 20q12-20q13 and its DNA was amplified, but RNA expression was reduced (2- to >30-fold) in 79% of the tumors. These results suggest that the WISP genes may be downstream of Wnt-1 signaling and that aberrant levels of WISP expression in colon cancer may play a role in colon tumorigenesis.

Neoplastic progression and prognosis in melanoma

Most melanomas evolve through an initial stage known as radial growth phase (RGP), encompassing in situ and microinvasive malignancies in which the probability of cure approaches 100%. At the present time, despite a shift toward earlier recognition of melanoma, by the time of diagnosis roughly 70% of melanomas have evolved to a point, known as vertical growth phase (VGP) or tumorigenic melanoma, at which cure is not certain, and prognosis depends upon certain attributes of the neoplasm and the host. Attempts have been made to assemble these attributes into prognostic models to permit estimation of the probability of cure for individuals and for groups of patients. Attributes that have been identified as independent prognostic variables include thickness of the primary neoplasm, the numbers of mitotic figures, and the presence of tumor-infiltrating lymphocytes (TIL). Other biologically important prognostic variables are on the horizon, and some will likely be based on molecules (markers) expressed on neoplastic cells that show functional significance in mechanisms of metastasis.

Assignment of Alu-repetitive sequences to large restriction fragments from human chromosomes 6 and 22

We have employed a pulsed field gel electrophoresis and Alu hybridization approach for identification of large restriction fragments on chromosome 6 and 22. This technique allows large portions of selected human chromosomes to be visualized as discrete hybridization signals. Somatic cell hybrid DNA which contains chromosome 6 or chromosome 22 was restricted with either Notl or Mlul. The restriction fragments were separated by pulsed field gel electrophoresis (PFGE) and hybridized against an Alu repetitive sequence (Blur 8). The hybridization signals result in a fingerprint-like pattern which is unique for each chromosome and each restriction enzyme. In addition, a continuous pattern of restriction fragments was demonstrated by gradually increasing puls times. This approach will also be suitable to analyze aberrant human chromosomes retained in somatic cell hybrids and can be used to analyze flow sorted human chromosomes. To this end, our method provides a valuable alternative to standard cytogenetic analysis.

Biologic and therapeutic significance of MYB expression in human melanoma

We investigated the therapeutic potential of employing antisense oligodeoxynucleotides to target the disruption of MYB, a gene which has been postulated to play a pathogenetic role in cutaneous melanoma. We found that MYB was expressed at low levels in several human melanoma cell lines. Also, growth of representative lines in vitro was inhibited in a dose- and sequence-dependent manner by targeting the MYB gene with unmodified or phosphorothioate-modified antisense oligodeoxynucleotides. Inhibition of cell growth correlated with specific decrease of MYB mRNA. In SCID mice bearing human melanoma tumors, infusion of MYB antisense transiently suppressed MYB gene expression but effected long-term growth suppression of transplanted tumor cells. Toxicity of the oligodeoxynucleotides was minimal in mice, even when targeted to the murine Myb gene. These results suggest that the MYB gene may play an important, though undefined, role in the growth of at least some human melanomas. Inhibition of MYB expression might be of use in the treatment of this disease.

Management of recurrent cutaneous melanoma

Recurrent melanoma occurs in approximately one third of patients treated for cutaneous melanoma. Although the majority of recurrence occurs within the first few years of primary therapy, a significant number remains at risk beyond 10 years. With rising incidence of recurrent melanoma in Western countries, physicians will undoubtedly face the challenge of managing these patients with the limited therapeutic options currently available. Once melanoma has recurred, the overall prognosis is poor. Localized disease is best treated with complete resection, if indicated. Our existing armamentarium for systemic treatment falls short of altering the course of natural history of melanoma, but regional chemotherapy is an effective modality for in-transit disease and satellitosis. Translational research in molecular genetics and immunology will fuel new ideas for the design of rational strategies toward tumor eradication. Ongoing trials that use gene-modified melanoma cells have begun a new chapter in cancer therapeutics and lend us a closer examination of bench-top science at the bedside.

Cytogenetic findings in primary uveal melanoma

We analyzed cytogenetic abnormalities in 10 cases of primary uveal melanoma. Clonal chromosomal abnormalities were present in nine cases. Chromosome 6 was most commonly affected (seven cases) and included gain of material from 6 and/or loss of material from 6q. Trisomy of chromosome 8 or gain in material from 8q, mostly in the form of an i(8q) resulting in three to five copies of the 8q segment was seen in six cases. Monosomy of chromosome 3 and rearrangements of chromosome 9 were less frequent and were altered in three cases each. Clinical, histopathologic, and cytogenetic abnormalities are correlated.

Growth factor independence and growth regulatory pathways in human melanoma development

This review concentrates on growth autonomy of tumor cells in relation to tumor progression. Human malignant melanoma serves as an example for progressive growth factor independence at subsequent stages of tumor progression. Mechanisms by which malignant cells acquire growth factor independence are discussed. In melanoma, deregulation of growth regulatory pathways has been described on four levels: 1) aberrant production of autocrine growth factors that substitute for exogenous growth factors (basic fibroblast growth factor [bFGF]); 2) alterations in the response to negative autocrine growth factors (interleukin [IL]-6 and transforming growth factor [TGF]-beta); 3) overexpression of epidermal growth factor receptors (EGF-R); and 4) alterations of cellular protooncogenes involved in signal transduction (RAS, MYB) and growth suppression (p53). In addition to bFGF and IL-6, multiple other growth factor genes are activated in malignant melanoma cells but not normal melanocytes. These include both chains of platelet-derived growth factor (PDGF), TGF-alpha, IL-1, IL-8, and tumor necrosis factor (TNF)-alpha. Of these, PDGF-B has been investigated in more detail. Melanoma-derived PDGF clearly does not act in a direct autocrine mode, but has important paracrine effects on normal tissue constituents, notably fibroblasts and endothelial cells, that are essential for tumor development in vivo. It is speculated that other melanoma-derived growth factors with as yet undefined functions similarly exert such paracrine or 'indirect' autocrine effects that cannot be sufficiently addressed in studies on cultured cells.

Cytogenetic analysis of uveal melanoma. Consistent occurrence of monosomy 3 and trisomy 8q

BACKGROUND

The genetic alterations associated with the pathogenesis of uveal melanoma have not been determined. To address this issue, the authors performed a prospective cytogenetic study of 35 uveal melanomas, including 23 primary untreated tumors and 12 tumors that were removed after local radiation therapy.

METHODS

Representative tumor tissue was processed by established methods for histopathologic and cytogenetic studies. Tumor cells were disaggregated and established in short-term culture; metaphases were prepared by standard methods for karyotypic analysis.

RESULTS

Successful analyses were achieved in 27 of the tumor specimens, including 20 of 23 tumors not exposed to radiation and 7 of 12 tumors exposed to radiation. All of the tumors had an abnormal karyotype. Recurrent chromosomal abnormalities detected in the tumors not exposed to radiation included monosomy 3 (13 of 20), trisomy 8 or 8q (11 of 20), loss of a sex chromosome (10 of 20), and loss of 6q (8 of 20). The tumors previously exposed to radiation were characterized by more complex changes, with monosomy 3 and trisomy 8q detected in three cases each.

CONCLUSIONS

Uveal melanoma is characterized by monosomy 3 and trisomy 8q in most cases. These findings, which are supported by data from other investigators, provide compelling evidence that loss of gene sequences on chromosome 3 and duplication of gene sequences on chromosome 8 are implicated in the genetic alterations associated with uveal melanoma and offer a basis for additional molecular genetic investigations.

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)

Rapid generation of region-specific genomic clones by chromosome microdissection: isolation of DNA from a region frequently deleted in malignant melanoma

Malignant melanoma is frequently characterized by the deletion of the long arm of chromosome 6 (usually encompassing 6q16-q21). In an effort to saturate this region with DNA markers, microdissection and molecular cloning of DNA from banded human metaphases recent development of a novel chromosome microdissection scheme that omits microchemical manipulation of DNA. Microdissection was targeted on band 6q21. Direct PCR amplification of dissected DNA was first used as a probe in chromosomal in situ hybridization of normal metaphases to confirm the specificity of material excised for cloning. A genomic library of 20,000 clones, which is highly enriched for sequences encompassing 6q21, was then constructed. Clones from this library have been mapped against a human-rodent somatic cell hybrid mapping panel that divides chromosome 6 into seven regions, confirming the localization of probes within the target region. Direct PCR amplification of DNA excised by microdissection greatly simplifies and facilitates this chromosome band-specific cloning strategy. The isolation of microclones from this region of chromosome 6 should assist in establishing a physical map of the melanoma deletion region.

Cellular and molecular biology of melanoma

Melanoma cells have surface markers that are expressed differently than in normal melanocytes and nevus cells. Monoclonal antibodies may define a phenotypic map of the various melanocytic lesions and can be used in immunohistopathology and immunoscintigraphy. Monoclonal antibodies directed against melanoma-associated glycoproteins and glycolipids are being tested for therapy. Rearrangements or deletions on chromosome 1, 6, and 7 are the most frequently observed cytogenetic abnormalities. Molecular studies have not given a clear picture. A subset of HRAS alleles has been reported to be associated with melanoma. NRAS activation by point mutation has been found in one fourth of the cases. Allele losses at different loci have been reported. Genetic linkage studies have given conflicting results on the presence of a gene for the melanoma-dysplastic nevus syndrome on the short arm of chromosome 1.

Characterization of four melanoma cell lines with electron microscopy, immunocytochemistry, cytogenetics, flow cytometry, and southern analysis

Four cell lines established from human metastatic malignant melanoma, derived from four patients, were analyzed. Ultrastructurally and immunocytochemically, the cultured tumor cells had retained characteristic features of melanocytes and of the primary malignant melanomas. The genetic stability was investigated by repeated flow-cytometric and cytogenetic analyses over 24 months of continuous cultivation. The DNA indices ranged from 1.7 to 2.1 and were stable during the entire period. The same was true for the karyotypes, which had modal numbers ranging from 50 to 84. The most common types of abnormalities were: isochromosomes i(1q), i(9q), translocations (1;17) and (3;6), and other aberrations (1p+,4p+,5p+,11p+,11q-,11q+). Abnormalities involving chromosome 1 were present in all cell lines, but loss of genetic material from chromosome 1p was demonstrated in only one of four cell lines when tested by the Southern blotting technique using a lambda MS1 probe.

Alu-PCR: characterization of a chromosome 6-specific hybrid mapping panel and cloning of chromosome-specific markers

The Alu-polymerase chain reaction (Alu-PCR) was applied to selectively amplify DNA sequences from human chromosome 6 using a single primer (A1) directed to the human Alu consensus sequence. A specific amplification pattern was demonstrated for a panel of eight somatic cell hybrids containing different portions of chromosome 6. This PCR pattern permits the identification of submicroscopic DNA alterations and can be utilized as a reference for additional chromosome 6-specific hybrids. To obtain new chromosome 6-specific markers we established two libraries from PCR-amplified sequences using two somatic cell hybrids (MCH381.2D and 640-5A). Out of a total of 109 clones that were found to be chromosome 6 specific, 13 clones were regionally assigned. We also included a procedure that allows the isolation of chromosome 6-specific markers from hybrids that contain human chromosomes other than 6. Our results will contribute to the molecular characterization of chromosome 6 by fostering characterization of somatic cell hybrids and by the generation of new regionally assigned DNA markers.

Evidence for linear extrachromosomal elements mediating gene amplification in the multidrug-resistant J774.2 murine cell line

Previous studies from our laboratory have demonstrated specific cytogenetic alterations accompanying development of colchicine resistance in the J774.2 murine cell line and in two sublines (J7.Cl-30 and J7.Cl-100). Although gene amplification is not observed in the parental J774.2 cell line, a approximately 35-fold amplification of the gene for p-glycoprotein (mdr) was noted in the J7.Cl-30 subline (770-fold CLCR) and a approximately 70-fold amplification in the J7.Cl-100 subline (2500-fold CLCR). In this study, we analyzed the localization and organization of the mdr gene. In the colchicine-resistant (CLCR) J7.Cl-30 subline, the p-glycoprotein domain was observed to reside on differently sized extrachromosomal elements. Our results indicate not only circular extrachromosomal elements but also linear extrachromosomal elements. By means of pulsed-field gel electrophoresis (PFGE), the sizes of the extrachromosomal elements were shown to be greater than 2,500 kilobase-pairs (kb), 800 kb, and 400 kb. In contrast, the J7.Cl-100 subline was characterized by the presence of homogeneously staining regions (HSRs). We have noted that with increasing colchicine resistance the extrachromosomal elements are replaced by HSRs. Our findings of linear elements that appear to be precursors of HSRs may offer a new way to interpret different theories of extrachromosomal gene amplification. The J7.Cl-30 cell line presents a unique system to analyze further the formation and structure of extrachromosomal elements.

Development and utilization of a somatic cell hybrid mapping panel to assign NotI linking probes to the long arm of human chromosome 6

A somatic cell hybrid mapping panel that defines seven regions of the long arm and one region of the short arm of human chromosome 6 has been developed. Utilizing this panel, 17 NotI boundary clones from a NotI linking library were regionally assigned to the long arm of chromosome 6. The majority of these clones (11) were found to localize within band regions 6q24-q27. The nonuniform distribution of NotI sites may indicate a cluster of HTF islands and likely represents a coincidence of coding sequences in this region of chromosome 6. Cross-hybridization of these linking clones to DNA from other species (zoo blots) provides further evidence for transcribed sequences in 7 of the NotI clones. These NotI clones were also used to identify corresponding NotI fragments using pulsed-field gel electrophoresis, facilitating further physical mapping of this region. Finally, regional assignment of five polymorphic probes to the long arm of chromosome 6 is also presented. These hybrids and probes should facilitate the construction of a physical and genetic linkage map to assist in the identification of disease loci along chromosome 6.