Up-regulation of cyclin-dependent kinase 4/cyclin D2 expression but down-regulation of cyclin-dependent kinase 2/cyclin E in testicular germ cell tumors.

Testicular germ cell tumors (GCT) characteristically display two chromosome 12 abnormalities: the isochromosome i(12p) and concomitant deletions of the long arm. Some genes important in the control of the G(1)-S cell cycle checkpoint G(1)-S, i.e., cyclin-dependent kinases 2 and 4, cyclin D2 are located on this chromosomal region. Therefore, testicular GCTs were analyzed as to the expression of CDK2, CDK4, CDK6, and the expression of their catalytic partners cyclins D1, D2 and E by semiquantitative reverse transcription-PCR. Cyclin D2, located on 12p, was overexpressed in 69% (31 of 45) of the tumors by a mean factor of 8, including all histological subtypes. In addition, the cyclin D2 partner CDK4 was increased in 41% (21 of 51) of all tumors by a factor of 6, most strongly in embryonal carcinomas. Sixty-four percent of the seminomas and 23% of the non-seminomas had decreased expression of CDK6 by a mean factor of 5 (P = 0.009). Statistical analysis using configural frequency analysis and regression analysis revealed that cyclin D2 and CDK4 expression were strongly correlated (r(2) = 0.682; P = 0.000052), whereas expression of CDK6 did not correlate with either of them (r(2) = 0.382; P = 0.00085). CDK2 and its catalytic partner cyclin E were down-regulated in 40% (19 of 47) and 42% (19 of 45) of the tumors, respectively, by a factor of 7 each. Western blots and immunohistochemical experiments confirmed cyclin D2 and CDK4 overrepresentation and reduced expression of cyclin E and CDK2 tumors in the few tumors under protein study. Despite its localization on 12q13, a hot spot for loss of heterozygosity in testicular GCTs (>40%), Southern blotting revealed no gross DNA alteration of the CDK2 gene. Because up-regulation of the cyclin D2/CDK4 complex and down-regulation of cyclin E/CDK2 complex were found in seminomas as well as in non-seminomas and in all tumor stages, these findings seem to be early events during tumorigenesis of testicular GCTS: Together with previous findings that retinoblastoma mRNA and protein expression is strongly decreased in these tumors, these data suggest an unusual deregulated G(1)-S checkpoint as a decisive event for germ cell tumors.

Alterations of the metastasis suppressor gene nm23 and the proto-oncogene c-myc in human testicular germ cell tumors.

The putative metastasis suppressor genes nm23-H1, nm23-H2 and the c-myc proto-oncogene were investigated in testicular germ cell tumors (GCTs) using Southern and Northern blotting as well as semiquantitative reverse transcription polymerase chain reaction (RT-PCR) and single strand conformation polymorphism (SSCP) analysis. When studying Bgl II RFLPs, allelic losses of the nm23 gene were found in 3/12 (25%) informative tumors, and all 3 had lymph node and/or distant metastases. A 2 to 7 fold nm23 mRNA overexpression was found in 22/34 (64.7%) tumors examined. RT-PCR revealed that this phenomenon is mainly a consequence of nm23-H2 overexpression. Overexpression of both the H1 and the H2 gene was predominantly found in the seminoma subtype and was not associated with tumor stage. Only 1/25 tumors, a seminoma with distant metastases, had a point mutation in the coding region of the nm23-H2 gene as demonstrated by SSCP analysis. None of the 8 seminomas and only 1/13 non-seminomas had c-myc overexpression. No abnormalities of the c-myc gene could be detected on the DNA level. Despite the fact that in previous investigations nm23-H2 was demonstrated to be a putative transcription factor for c-myc, no coexpression of c-myc and nm23-H2 was found by quantitative RT-PCR in this study.

Quantification of additional short arms of chromosome 12 in germ cell tumours using the polymerase chain reaction.

Male germ cell tumours are characterised by the over-representation of 12p sequences, most often in the form of isochromosome i(12p). This study describes the development of a quantitative detection system for additional copies of 12p employing the polymerase chain reaction (PCR). The validity of this method was assessed on two i(12p) containing tumour cell lines in which the number of i(12p) was determined by fluorescence in situ hybridisation. Fourteen primary male germ cell tumours were analysed using the PCR-based method. While 3/8 seminomatous germ cell cancers did not contain any additional 12p, all 6 non-seminomatous tumours did and the severity of the disease correlated with the respective copy number. The ease of the PCR-based method makes it possible for the quantification of additional 12p to become a routine diagnostic and prognostic tool for testicular germ cell tumours, thereby helping to define the role of the i(12p) anomality in larger retrospective studies.

Analysis of the DCC tumor suppressor gene in testicular germ cell tumors: mutations and loss of expression.

Inactivation of the DCC (Deleted in Colon Carcinoma) tumor suppressor gene by allelic loss and/or reduced expression is associated with the development of colon cancer, gliomas, gastric and prostatic malignancies. In a total cohort of 51 testicular germ cell tumors (GCT) of different histologies we analyzed restriction fragment length polymorphism (RFLP) for DCC at two specific DNA sites in 37 GCT and DCC mRNA expression compared to that of the adjacent normal testicular tissue in 41 GCT, one Leydig cell tumor and one testicular metastasis of a non-small cell lung cancer (NSCLC). Two of 17 tumors (11.7%) informative for the Msp I polymorphic site of the DCC gene and 6/25 tumors (24.0%) informative for variable number of tandem repeat (VNTR) showed loss of heterozygosity (LOH). DCC expression was analyzed by semi-quantitative polymerase chain reaction after initial reverse transcription (RT-PCR). Thirty of 41 GCT (73.1%) and both, the Leydig cell tumor and the testicular metastasis of NSCLC, had a nearly complete or total loss of DCC mRNA expression. Six of 11 (54.5%) seminomas and 24/30 (80.0%) nonseminomas had this loss of expression. Twelve of 17 (70.5%) localized tumors, 9/13 (69.2%) tumors with lymph node involvement and 9/11 (82.2%) tumors with distant metastases showed decreased or absent DCC expression. This data suggests that inactivation of the DCC gene, especially the loss of DCC expression, is associated with the development and progression of human GCT.

[Angiogenesis--principles and significance in urologic tumors]. / Angiogenese--Grundlagen und Bedeutung bei urologischen Tumoren.

Physiologically, angiogenesis in adults is a controlled process which plays a role, for example, in wound healing. Pathological angiogenesis is observed in tumor formation and represents a multifactorial process, in which specific angiogenic factors, as well as growth factors, extracellular matrix proteins and cell adhesion molecules are involved. Tumor growth is characterized by an imbalance in favor of angiogenic over angiogenesis-inhibiting factors. Some of the most frequently examined angiogenic factors are vascular endothelial growth factor, acidic/basic fibroblast growth factors and the platelet-derived endothelial cell growth factor. The most important angiogenesis inhibitors are angiostatin and thrombospondin. To date, the clinical relevance of tumor angiogenesis has been shown for several human tumors. For most urological tumors, the grade of tumor vessel formation, measured as microvessel density, has been associated with metastases, tumor growth and clinical course. The prognostic value of this feature of malignant growth seems to be higher than that of most of the classical and newer prognostic factors. Systematic investigations of tumor angiogenesis are becoming increasingly relevant for diagnostic and therapeutic strategies and offer opportunities for the development of new specific therapeutic approaches in clinical oncology.

Current and future strategies to block tumor angiogenesis, invasion, and metastasis.

Progression of malignancy involves a series of sequential steps that ultimately lead to cancer-cell dissemination. In addition to the loss of growth control, an imbalanced regulation of motility and proteolysis is a prerequisite for invasion and metastasis. These factors are also necessary for angiogenesis-an integral process occurring at both the primary and the metastatic sites. Investigators have elucidated in detail many of the molecular mechanisms involved in the sequential steps of the metastatic cascade and have thereby provided new targets for therapeutic intervention. For each step, different model systems have been developed and various strategies for antimetastatic therapy have been tested in vitro as well as in murine systems. Difficulties in translating results obtained in preclinical models into the clinical setting have become apparent and have not been unexpected in light of the sometimes highly artificial interaction in the experimental setting. Nevertheless, continued development of model systems and further research into the genetic control of malignancy should lead to the identification of common signal-transduction pathways. Interference at such sites promises to be particularly effective in inhibiting proliferation and metastasis.

Immunostaining of p53 protein in ovarian carcinoma: correlation with histopathological data and clinical outcome.

OBJECTIVE: The objective of this study was to analyze the incidence of immunohistochemically detectable p53 protein accumulation in epithelial ovarian carcinomas and to correlate these data with the clinical outcome so as to clarify further the role of p53 mutations in prognosis with these patients. METHODS: Tumor tissues from 179 patients with epithelial ovarian carcinoma were used for immuno-histochemical analysis with monoclonal antibody DO1 and BP 53-12-1 on formalin-fixed, paraffin-embedded tissue. RESULTS: A total of 78 cases (44%) showed positive nuclear p53 staining. The p53-positive cases were found in all histological types of epithelial ovarian tumors. p53 staining was found in tumors of all stages with a higher percentage of positive cases in stage IV ovarian carcinomas (not significant). Poorly differentiated carcinomas showed a significantly higher percentage of p53 protein expression than did highly differentiated tumors (P = 0.0002). Clinical follow-up of up to 14 years (median 25 months) showed a slightly but not significantly shortened disease-free and overall survival time for patients with p53-positive epithelial ovarian carcinomas. CONCLUSIONS: We conclude from our data that p53 expression in ovarian carcinoma is associated with poor differentiation but not with the disease being in an advanced stage. There was a tendency for shortened disease-free and overall survival for patients with p53-positive tumors.

Alterations of the p16 (MTS1) gene in testicular, ovarian, and endometrial malignancies.

PURPOSE: The p16 (MTS1) gene codes for a cyclin-dependent kinase inhibitor and may be a new tumor suppressor gene. It is frequently mutated in a variety of cell lines established from tumors. This is the first report of screening for alteration of the p16 gene in testicular, ovarian and endometrial malignancies. MATERIALS AND METHODS: We examined alterations of p16 in 78 primary genital tumors (42 testicular, 21 ovarian and 15 endometrial cancers) and mononuclear cells from 2 patients with Lynch syndrome II as well as 5 testicular tumor cell lines by single-strand conformation polymorphism (SSCP) and Southern blot hybridization. RESULTS: The DNA from the p16 gene of 2 testicular tumors (5%), an ovarian cancer (4%) and a testicular tumor cell line (20%) had altered migration in gel electrophoresis as shown by SSCP. Analysis of DNA sequence of these samples revealed a polymorphism at codon 140. Southern blot hybridization detected neither deletions nor rearrangements of the p16 gene in any of the samples. CONCLUSIONS: Taken together, these results suggest that p16 alterations probably are not important for tumorigenesis of testicular, ovarian and endometrial tumors.

Expression of the c-kit proto-oncogene and its ligand stem cell factor (SCF) in normal and malignant human testicular tissue.

Recent findings suggest an important role of the proto-oncogene c-kit, a surface membrane receptor of the tyrosine kinase family, and its ligand stem cell factor (SCF) in normal spermatogenesis and possibly in the pathogenesis of certain testicular germ cell tumors. To further investigate this potential role, the expression of c-kit and SCF was studied in normal and malignant human testicular tissue specimens at the mRNA and protein level by Northern blot analysis and immunohistochemistry, respectively. The detection of the c-kit receptor in normal human germ cells and its natural ligand SCF in Sertoli cells suggests the presence of a local trophic regulatory system that may be active in human spermatogenesis. Additionally, c-kit expression was detected in the seminoma but not in the nonseminoma subtype of human testicular germ cell tumors (GCT). Stem cell factor was not expressed at the mRNA level in tissue from either subtype of GCT as determined by Northern blot analysis; however, the protein was detected immunohistochemically in the cytoplasm of rare tumor cells.

Theories on the metastatic process and possible therapeutic options.

A sequence of steps are prerequisite for cancer cells before metastases are established. Metastasis has been shown to be an inefficient process limited by both random and selective events. By differentiating invasion from metastasis, sequential steps in the metastatic cascade have been defined and studied separately. This approach has yielded a variety of new potential therapeutic strategies. However, increasing knowledge of the mechanisms relating to metastasis has also revealed the complexity of each step. In spite of difficulties in translating results obtained in preclinical models into the clinical setting, continued development of such model systems and further research into the genetic control of metastatic dissemination will lead to improved strategies for prevention of metastasis formation and for treatment of metastatic tumor cells.

[Overexpression of p53 protein in ovarian carcinomas: correlation with histopathologic data and clinical course]. / p53 Proteinüberexpression in Ovarialkarzinomen: Korrelation mit histopathologischen Daten und klinischem Verlauf.

OBJECTIVES: The accumulation of p53 protein was analysed immunohistochemically in ovarian cancer and correlated with clinical data to further clarify the role of p53 mutations for prognosis in these patients. METHODS: Tumor tissues from 126 epithelial ovarian carcinomas were analysed immunohistochemically on paraffin embedded tissue and in 21 cases on frozen tissue with monoclonal antibodies PAb 1801, PAb 421 and PAb 240. RESULTS: Nuclear p53 staining was found in 31 ovarian carcinomas (25%) and correlated with advanced stage of the disease (p = 0,038) and poor differentiation (P = 0,032) of the tumor. Disease-free and overall-survival time were slightly, but not significantly shortened for patients with p53 positive tumors. CONCLUSION: Immunohistochemically detectable p53 protein expression in ovarian carcinoma is associated with poor differentiation, advanced stage of the disease and a tendency for shortened disease-free and overall survival.

p53 mutations and MDM-2 amplification in renal cell cancers.

Genomic DNA from 53 primary human renal cell tumors was screened for the presence of mutations in the tumor suppressor gene p53, using the polymerase chain reaction and single-strand conformation polymorphism analysis, followed by direct sequencing of DNA. Five cases showed mobility shifts. Sequencing of these samples revealed two cases of nonsense mutations (codons 182, 192), one case of a missense mutation (codon 285), and two cases of silent mutations at codon 213. The frequency of mutations altering the p53 (3/53 = 6%) was low when compared with the reported frequencies (15% to 65%) of allelic loss of 17p (location of p53) in renal cell cancers, suggesting the possible existence of another tumor suppressor gene in the region of the p53 gene, which when mutated is associated with these cancers. All three tumors with p53 mutations were cases with poor prognosis, i.e., highest pathological grade and/or advanced Robson stage. The human equivalent of the murine double-minute-2 was not amplified in the renal cell tumors. In summary, alterations of p53 may be associated with the development of renal cell carcinoma of higher grade and/or stage.

Mutations of the p53 gene are not detectable in human testicular tumors.

The tumor suppressor gene p53 is the most frequently mutated gene in human cancer. We have used polymerase chain reaction-single-strand conformation polymorphism analysis and sequencing to examine the status of the p53 gene in human testicular cancers of various histologies. We were unable to find in 40 samples and four cell lines any mutations in the regions of this gene (exons 5 through 8) that are usually mutated in other cancers. Northern blot analysis showed expression of this gene in most of the samples analyzed, as well as in four human testicular tumor cell lines. The MDM-2 gene is amplified and overexpressed in sarcomas; it binds and functionally inactivates p53. The 44 testicular tumor samples and cell lines were examined for amplification of MDM-2 by dot-blot analysis; none was found. The proto-oncogene c-kit probably plays an important role in normal testicular development. Mutation of the tyrosine phosphorylation site of a closely related member of this family of tyrosine kinase receptors (c-fms) is associated with cellular transformation and cancer. Codon 936 is the analogous tyrosine of c-kit; using polymerase chain reaction-single-strand conformation polymorphism analyses, we were unable to detect mutations at this site in our 44 testicular cancer samples. We conclude from our studies that mutations in the most conserved region of the p53 gene, as well as at codon 936 of the c-kit gene and amplification of MDM-2, are extremely rare in human testicular cancers.

Basic research in prostate cancer: molecular biology.

While a general appreciation for the importance of chromosomes in the development of cancer has existed for decades, molecular genetic analyses have gained considerable attention in recent years through identification of proto-oncogenes and tumor suppressor genes. Several different chromosomal aberrations, alterations of proto-oncogenes and suppressor genes have been described in prostate cancer. Loss of genetic material has been found to occur most frequently on chromosomes 7, 8, 10 and 16. The existence of tumor suppressor genes relevant to prostate carcinogenesis is suspected in these chromosomal locations. Several investigators are currently trying to identify these genes. Altered expression of several different oncogenes has been reported in prostate cancer. Among these, the ras- and myc-families of oncogenes have been studied most intensively. Structural oncogene alterations have been detected infrequently, most of the changes appear to occur transcriptionally. Despite an abundance of clinical material, knowledge about genetic lesions in prostate cancer is still very limited and sometimes conflicting results have been reported. With recent methodologic improvements and a growing interest in correlating genetic alterations with clinical disease progression, definition of prostate carcinogenesis at the molecular level will advance rapidly in the near future.

[Urothelial cancers. Cytogenetic and molecular biology principles]. / Urotheliale Karzinome. Zytogenetische und molekularbiologische Grundlagen.

Cytogenetic studies and analysis of restriction fragment polymorphism (RFLP) have revealed that chromosomes 9, 11 and 17 are frequently altered in urothelial tumors. There are several tumor suppressor genes that might be involved in the oncogenesis of these tumors. The retinoblastoma suppressor gene and p53 have been the subjects of several recent investigations and have been seen to be altered or inactivated in a significant number of tumors. Proto-oncogenes of the ras family have been studied extensively, and c-Ha-ras alterations have been demonstrated in approximately 10% of urothelial tumors. Other proto-oncogenes seem to be involved less frequently. Although correlations between these molecular genetic findings and clinical parameters have been shown by some investigators, further studies are needed to establish whether molecular data are clinically relevant for prognosis, diagnosis and therapy. The sensitivity of molecular genetic techniques combined with the relatively easy access to primary tumor cells (by biopsy or cytology) make this tumor type an ideal system for further investigation of the molecular genetic basis in the development of human neoplasms.

Molecular biologic investigations of proto-oncogenes and growth factors in human testicular tumors.

Molecular genetic alterations of known protoncogenes and growth factors, e.g. c-kit and its ligand SCF as well as hst1 and c-myc, are likely to play a role in the development of testicular cancer. In addition, identification and analysis of genes located on the frequently altered chromosome 12 represent an important focus of research. Genetic alterations may occur in a stepwise fashion, as described in other human tumors, leading to the development of the various histologic subtypes of testicular germ cell tumors. The characterization of these alterations are most likely to extend the traditional histopathologic tumor classifications.