DNA methylation changes in human testicular cancer

Cryptorchidism and testicular cancer in the dog: unresolved questions and challenges in translating insights from human studies†

Cryptorchidism, the failure of one or both testes to descend into the scrotum, and testicular cancer show a strong correlation in both dogs and humans. Yet, long-standing medical debates persist about whether the location of undescended testes directly causes testicular cancer in humans or if both conditions stem from a common origin. Although testicular cancer is a prevalent disease in dogs, even less is known about its cause and correlation with testicular descent in this species. This review investigates the relation between these two disorders in dogs, drawing insights from human studies, and examines key biomarkers identified thus far. In addition, it explores potential causal links, including the impact of temperature on maturing testicular cells and a potential shared genetic origin. Notably, this literature review reveals significant differences between men and dogs in reproductive development, histological and molecular features of testicular tumors, and the prevalence of specific tumor types, such as Sertoli cell tumors in cryptorchid dogs and germ cell tumors in humans. These disparities caution against using dogs as models for human testicular cancer research and underscore the limitations when drawing comparisons between species. The paper concludes by suggesting specific research initiatives to enhance our understanding of the complex interplay between cryptorchidism and testicular cancer in dogs.

Epigenetic Regulation of Driver Genes in Testicular Tumorigenesis

In testicular germ cell tumor type II (TGCT), a seminoma subtype expresses an induced pluripotent stem cell (iPSC) panel with four upregulated genes, OCT4/POU5F1, SOX17, KLF4, and MYC, and embryonal carcinoma (EC) has four upregulated genes, OCT4/POU5F1, SOX2, LIN28, and NANOG. The EC panel can reprogram cells into iPSC, and both iPSC and EC can differentiate into teratoma. This review summarizes the literature on epigenetic regulation of the genes. Epigenetic mechanisms, such as methylations of cytosines on the DNA string and methylations and acetylations of histone 3 lysines, regulate expression of these driver genes between the TGCT subtypes. In TGCT, the driver genes contribute to well-known clinical characteristics and the driver genes are also important for aggressive subtypes of many other malignancies. In conclusion, epigenetic regulation of the driver genes are important for TGCT and for oncology in general.

Human Endogenous Retrovirus Reactivation: Implications for Cancer Immunotherapy

Human endogenous retroviruses (HERVs) derive from ancestral exogenous retroviruses whose genetic material has been integrated in our germline DNA. Several lines of evidence indicate that cancer immunotherapy may benefit from HERV reactivation, which can be induced either by drugs or by cellular changes occurring in tumor cells. Indeed, several studies indicate that HERV proviral DNA can be transcribed either to double-stranded RNA (dsRNA) that is sensed as a "danger signal" by pattern recognition receptors (PRRs), leading to a viral mimicry state, or to mRNA that is translated into proteins that may contribute to the landscape of tumor-specific antigens (TSAs). Alternatively, HERV reactivation is associated with the expression of long noncoding RNAs (lncRNAs). In this review, we will highlight recent findings on HERV reactivation in cancer and its implications for cancer immunotherapy.

Aberrant epigenetic inactivation of RASSF1A and MGMT gene and genetic mutations of KRAS, cKIT and BRAF in Indian testicular germ cell tumours

Testicular germ cell tumor (TGCT) development may involve a series of modification at epigenetic and genetic level which may act synergistically and transform the primordial gonocyte. This study evaluated the frequency and distribution pattern of RASSF1A/MGMT gene methylation and KRAS, BRAF and cKIT gene mutation in Indian TGCT patient, and their correlation with clinicopathological features. Forty-one TGCT tumors were used to investigate hypermethylation of RASSF1A and MGMT gene and mutations of KRAS codon 12/13, BRAF V600E and cKIT exon 17 mutations. RASSF1A and MGMT methylation was noted in 58.5% and 10% of the TGCTs. A higher frequency of RASSF1A methylation was noted in seminomas (71%, 17/24), while MGMT methylation was frequent in mixed tumors (23%, 3/13). Interestingly, 3 of 41 cases showed concurrent methylation of both the genes. The absence of tumor necrosis was significantly associated with increased frequency of MGMT hypermethylation (30% vs. 3%, p = 0.03). KRAS mutation was identified in 17% (7/41), while none showed BRAF and cKIT mutation. KRAS mutations were predominantly found in codon 12 with G12V as the most recurrent mutations. Mixed germ tumors tends to show increased frequency of KRAS mutation (31%, 4/13), followed by pure seminomas (4%, 1/24). Interestingly, KRAS mutation rate was significantly higher in metastatic tumors in comparison to primary tumors (100% vs. 13%, p = 0.02). No other association of RASSF1A/MGMT/KRAS alterations with other clinicopathological features was noted. In conclusion, these data support the notion that the cancer-associated alterations in the RASSF1, MGMT and KRAS gene may significantly contribute to TGCT pathogenesis.

Epigenetic treatment combinations to effectively target cisplatin-resistant germ cell tumors: past, present, and future considerations

BACKGROUND

Type II germ cell tumors represent the most common solid malignancy in men aged 15-45 years. Despite high cure rates of >90% over all stages, 10-15% of advanced patients develop treatment resistance and potentially succumb to their disease. Treatment of refractory germ cell tumors remains unsatisfactory, and new approaches are needed to further improve outcomes.

OBJECTIVES

With this narrative review, we highlight epigenetic mechanisms related to resistance to standard systemic treatment, which may act as promising targets for novel combined epigenetic treatment approaches.

MATERIALS AND METHODS

A comprehensive literature search of PubMed and MEDLINE was conducted to identify original and review articles on resistance mechanisms and/or epigenetic treatment of germ cell tumors in vitro and in vivo. Review articles were hand-searched to identify additional articles.

RESULTS

Distinct epigenetic phenomena have been linked to chemotherapy resistance in germ cell tumors, among which DNA hypermethylation, histone acetylation, and bromodomain proteins appear as promising targets for therapeutic exploitation. Inhibitors of key regulators, for example DNA methyltransferases (e.g. decitabine, guadecitabine), histone deacetylases (e.g. romidepsin), and bromodomain proteins (e.g. JQ1) decreased cell viability, triggered apoptosis, and growth arrest. Additionally, these epigenetic drugs induced differentiation and led to loss of pluripotency and re-sensitization towards cisplatin in cell lines and animal models.

DISCUSSION

Epigenetic treatments hold promise to (i) reduce the treatment burden of and (ii) overcome resistance to standard cisplatin-based chemotherapy. Combined approaches may enhance activity, while the ideal target and treatment combination of epigenetic drugs, either with another epigenetic agent or conventional cytotoxic agents need to be defined.

CONCLUSION

Epigenetic (combination) treatment for germ cell tumors should be further explored in pre-clinical and clinical research for its potential to further improve germ cell tumor treatment.

New insights into germ cell tumor genomics

BACKGROUND

Testicular germ cell tumors (GCTs) represent the most common malignancy in young men. While GCTs represent a model for curable solid tumors due to exquisite chemosensitivity, mortality for patients with GCT comprises the most life years lost for non-pediatric malignancies. Given limited options for patients with platinum-resistant disease, improved insight into GCT biology could identify novel therapeutic options for patients with platinum-resistant disease. Recent studies into molecular characteristics of both early stage and advanced germ cell tumors suggest a role for rationally targeted agents and potentially immunotherapy.

RECENT DEVELOPMENTS

Recent GWAS meta-analyses have uncovered additional susceptibility loci for GCT and provide further evidence that GCT risk is polygenic. Chromosome arm level amplifications and reciprocal loss of heterozygosity have been described as significantly enriched in GCT compared to other cancer types. Contemporary analyses confirm ubiquitous gain of isochromosome 12 and mutations in addition to previously described GCT-associated genes such as KIT and KRAS. Alterations within the TP53-MDM2 signal transduction pathway appear to be enriched among patients with platinum-resistant disease. Potentially actionable targets, including alterations in TP53-MDM2, Wnt/β-catenin, PI3K, and MAPK signaling, are present in significant proportions of patients with platinum-resistant disease and may be exploited as therapeutic options. Pre-clinical and early clinical data also suggest a potential role for immunotherapy among patients with GCTs.

CONCLUSION

Molecular characterization of GCT patients may provide biologic rationale for novel treatment options in patients with platinum-resistant disease.

Testicular cancer from diagnosis to epigenetic factors

Testicular cancer (TC) is one of the most common neoplasms that occurs in male and includes germ cell tumors (GCT), sex cord-gonadal stromal tumors and secondary testicular tumors. Diagnosis of TC involves the evaluation of serum tumor markers alpha-fetoprotein, human chorionic gonadotropin and lactate dehydrogenase, but clinically several types of immunohistochemical markers are more useful and more sensitive in GCT, but not in teratoma. These new biomarkers are genes expressed in primordial germ cells/gonocytes and embryonic pluripotency-related cells but not in normal adult germ cells and they include PLAP, OCT3/4 (POU5F1), NANOG, SOX2, REX1, AP-2γ (TFAP2C) and LIN28. Gene expression in GCT is regulated, at least in part, by DNA and histone modifications, and the epigenetic profile of these tumours is characterised by genome-wide demethylation. There are different epigenetic modifications in TG-subtypes that reflect the normal developmental switch in primordial germ cells from an under- to normally methylated genome. The main purpose of this review is to illustrate the findings of recent investigations in the classification of male genital organs, the discoveries in the use of prognostic and diagnostic markers and the epigenetic aberrations mainly affecting the patterns of DNA methylation/histone modifications of genes (especially tumor suppressors) and microRNAs (miRNAs).

Current Concepts of Epigenetics in Testicular Cancer

Testicular germ cell tumors (GCTs) are characterized into seminomas (SGCTs) and non-seminomatous testicular germ cell tumors (NSGCTs). Serum tumor markers (STMs) play an important role in testicular cancer as they provide useful information for diagnosis, staging, and detection of recurrence. Nonetheless, additional tumor markers for early diagnosis and therapeutic options are required to enhance specificity of serological diagnosis of testes cancers. Epigenetics is defined as inherited changes in gene expression that are not encoded in the DNA structure. Epigenetic changes include DNA methylation, histone modifications, and microRNA (miRNA) regulation. It is through the study of epigenetics that diagnostic methods for early detection and novel therapeutic strategies may be established for testicular cancer. We performed a comprehensive review of the English medical literature in PubMed by combining search terms including DNA methylation, histone modifications, microRNA (miRNA) regulation, epigenetics, and testicular cancer. DNA methylation is the most extensively studied epigenetic modification. It consists of the addition of a methyl group to nucleotide bases. It has been reported that SGCT contain reduced levels of DNA methylation compared to NSGCT. MiRNAs are small non-coding RNAs that regulate posttranscriptional gene expression. It has been suggested that miRNAs may play a role in the pathogenesis of GCT. Specific expression patterns have been displayed by various miRNAs in patients with GCT. Histones are proteins intertwined with coiled, double-stranded genomic DNA that form a structure known as a nucleosome. The most widely studied histone modifications include acetylation, methylation, and phosphorylation. Methylation of histone proteins has been found in all types of NSGCT. Epigenetics may offer an additional and effective tool in establishing a diagnosis of GCT of the testes, including prognostic information and perhaps enabling targeted treatment in patients with testicular GCT.

DNA hypomethylation and aberrant expression of the human endogenous retrovirus ERVWE1/syncytin-1 in seminomas

BACKGROUND

Syncytin-1 and 2, human fusogenic glycoproteins encoded by the env genes of the endogenous retroviral loci ERVWE1 and ERVFRDE1, respectively, contribute to the differentiation of multinucleated syncytiotrophoblast in chorionic villi. In non-trophoblastic cells, however, the expression of syncytins has to be suppressed to avoid potential pathogenic effects. Previously, we have shown that the transcriptional suppression of ERVWE1 promoter is controlled epigenetically by DNA methylation and chromatin modifications. In this study, we describe the aberrant expression of syncytin-1 in biopsies of testicular germ cell tumors.

RESULTS

We found efficient expression and splicing of syncytin-1 in seminomas and mixed germ cell tumors with seminoma component. Although another fusogenic gene, syncytin-2 was also derepressed in seminomas, its expression was significantly lower than that of syncytin-1. Neither the transcription factor GCM1 nor the increased copy number of ERVWE1 were sufficient for this aberrant expression of syncytin-1 in seminomas. In accordance with our recent finding of the highly increased expression of TET1 dioxygenase in most seminomas, the ERVWE1 promoter was significantly hypomethylated in comparison with the matched controls. In contrast, 5-hydroxymethylcytosine levels were not detectable at the ERVWE1 promoter. We further describe that another endogenous retroviral element adjacent to ERVWE1 remains transcriptionally suppressed and two additional HERV-W family members are only slightly upregulated in seminomas.

CONCLUSIONS

We conclude that DNA demethylation of the ERVWE1 promoter in seminomas is a prerequisite for syncytin-1 derepression. We propose the spliced syncytin-1 expression as a marker of seminoma and suggest that aberrant expression of endogenous retroviruses might be a correlate of the hypomethylated genome of seminomas.

Testicular germ cell tumor genomics

PURPOSE OF REVIEW

Testicular germ cell tumors (TGCTs) are a model for curable cancer because of exquisite chemosensitivity and incorporation of multimodal therapy. Nevertheless, our ability to predict metastases in early-stage disease and responders to chemotherapy in advanced disease is limited. Treatment options for cisplatin-resistant disease are sparse. A further understanding of TGCT biology may allow for more precise patient counseling and identify novel therapies in patients with cisplatin-resistant disease.

RECENT FINDINGS

Adult TGCTs are characterized by frequent chromosomal anomalies and low rates of somatic mutations. Large-scale integrated molecular analysis of early-stage TGCT patients is actively underway. In addition to ubiquitous gain of isochromosome 12p, current molecular studies have confirmed mutations of previously described genes (i.e., KIT and KRAS) and described novel mutations. Analysis of cisplatin-resistant cases has identified high rates of alterations within the TP53-MDM2 axis and a high proportion of patients with potentially actionable targets, including TP53-MDM2, PI3 kinase, and MAPK signaling pathway alterations. The role of epigenetics in TGCT development and prognosis is also being further characterized.

SUMMARY

Further molecular characterization of TGCT may allow for avoidance of unnecessary treatment in patients with early-stage disease and also provide new treatment options in patients with cisplatin-resistant disease.

MGMT and CALCA promoter methylation are associated with poor prognosis in testicular germ cell tumor patients

Testicular germ cell tumors (TGCT) represent the second main cause of cancer-related death in young men. Despite high cure rates, refractory disease results in poor prognosis. Epigenetic reprogramming occurs during the development of seminomas and non-seminomas. Understanding the molecular and genetic basis of these tumors would represent an important advance in the search for new TGCT molecular markers. Hence the frequency of methylation of a gene panel (VGF, MGMT, ADAMTS1, CALCA, HOXA9, CDKN2B, CDO1 and NANOG) was evaluated in 72 primary TGCT by quantitative methylation specific PCR. A high frequency of MGMT (90.9%, 20/22; p=0.019) and CALCA (90.5%, 19/21; p<0.026) methylation was associated with non-seminomatous tumors while CALCA methylation was also associated with refractory disease (47.4%, 09/19; p=0.005). Moreover, promoter methylation of both genes predicts poor clinical outcome for TGCT patients (5-year EFS: 50.5% vs 77.1%; p=0.032 for MGMT and 51.3% vs 77.0%; p=0.029 for CALCA). The findings of this study indicate that methylation of MGMT and CALCA are frequent and could be used as new molecular markers of prognosis in TGCT.

DNA methylation in spermatogenesis and male infertility

Infertility is a significant problem for human reproduction, with males and females equally affected. However, the molecular mechanisms underlying male infertility remain unclear. Spermatogenesis is a highly complex process involving mitotic cell division, meiosis cell division and spermiogenesis; during this period, unique and extensive chromatin and epigenetic modifications occur to bring about specific epigenetic profiles in spermatozoa. It has recently been suggested that the dysregulation of epigenetic modifications, in particular the methylation of sperm genomic DNA, may serve an important role in the development of numerous diseases. The present study is a comprehensive review on the topic of male infertility, aiming to elucidate the association between sperm genomic DNA methylation and poor semen quality in male infertility. In addition, the current status of the genetic and epigenetic determinants of spermatogenesis in humans is discussed.

Epigenetic biomarkers in urological tumors: A systematic review

Prostate, bladder, kidney and testis cancers, the most common genitourinary (GU) neoplasms, are generally clinically silent at their earliest stages when curative treatment is most likely successful. However, there are no consensual guidelines for GU cancer screening and available methods are characterized by suboptimal sensitivity and specificity. Moreover, standard clinical and pathological parameters meet with important limitations in the assessment of prognosis in an individual basis. Herein, we focus on the development of epigenetic-based GU cancer biomarkers, which have emerged from exploratory studies in recent years and that hold the promise to revolutionize the clinical management of GU cancer patients.

DNA methylation profiles delineate epigenetic heterogeneity in seminoma and non-seminoma

BACKGROUND

It remains important to understand the biology and identify biomarkers for less studied cancers like testicular cancer. The purpose of this study was to determine the methylation frequency of several cancer-related genes in different histological types of testicular cancer and normal testis tissues (NT).

METHODS

DNA was isolated from 43 seminomas (SEs), 14 non-SEs (NSEs) and 23 NT, and was assayed for promoter methylation status of 15 genes by quantitative methylation-specific PCR. The methylation status was evaluated for an association with cancer, and between SEs and NSEs.

RESULTS

We found differential methylation pattern in SEs and NSEs. MGMT, VGF, ER-β and FKBP4 were predominately methylated in NSEs compared with SEs. APC and hMLH1 are shown to be significantly more methylated in both subtypes in comparison with NT. When combining APC, hMLH1, ER-β and FKBP4, it is possible to identify 86% of the NSEs, whereas only 7% of the SEs.

CONCLUSIONS

Our results indicate that the methylation profile of cancer-associated genes in testicular cancer correlates with histological types and show cancer-specific pattern for certain genes. Further methylation analysis, in a larger cohort is needed to elucidate their role in testicular cancer development and potential for therapy, early detection and disease monitoring.

Dissecting the molecular pathways of (testicular) germ cell tumour pathogenesis; from initiation to treatment-resistance

Human type II germ cell tumours (GCTs) originate from an embryonic germ cell, either as a primordial germ cell or gonocyte. This start determines the biological as well as clinical characteristics of this type of cancer, amongst others their totipotency as well as their overall (exceptional) sensitivity to DNA damaging agents. The histology of the precursor lesion, either carcinoma in situ or gonadoblastoma, depends on the level of testicularization (i.e. testis formation) of the gonad. The impact of either intrinsic (genetic) - and environmental factors involved in the pathogenesis is demonstrated by disorders of sex development as well as testicular dysgenesis syndrome as risk factors, including cryptorchidism, hypospadias and disturbed fertility as parameters. This knowledge allows identification of individuals at risk for development of this type of cancer, being a population of interest for screening. Factors known to regulate pluripotency during embryogenesis are proven to be of diagnostic value for type II GCTs, including OCT3/4, even applicable for non-invasive screening. In addition, presence of stem cell factor, also known as KITLG, allows distinction between delayed matured germ cells and the earliest stages of malignant transformation. This is of special interest because of the identified association between development of type II GCTs of the testis and a limited number of single nucleotide polymorphisms, including some likely related to KITL. Transition from the precursor lesion to an invasive cancer is associated with gain of the short arm of chromosome 12, in which multiple genes might be involved, including KRAS2 and possibly NANOG (pseudogenes). While most precursor lesions will progress to an invasive cancer, only a limited number of cancers will develop treatment resistance. Putative explanatory mechanisms are identified, including presence of microsatellite instability, BRAF mutations, apoptosis suppression and p21 sub-cellular localization. It remains to be investigated how these different pathways integrate to each other and how informative they are at the patient-individual level. Further understanding will allow development of more targeted treatment, which will benefit quality of life of these young cancer patients.

Global DNA hypomethylation in intratubular germ cell neoplasia and seminoma, but not in nonseminomatous male germ cell tumors

Alterations in methylation of CpG dinucleotides at the 5 position of deoxycytidine residues (5(m)C) are a hallmark of cancer cells, including testicular germ cell tumors. Virtually all testicular germ cell tumors are believed to be derived from intratubular germ cell neoplasia unclassified (IGCNU), which is thought to arise from primordial germ cells. Prior studies revealed that seminomas contain reduced levels of global DNA methylation as compared with nonseminomatous germ cell tumors. Smiraglia et al have proposed a model whereby seminomas arise from IGCNU cells derived from primordial germ cells that have undergone 5(m)C erasure, and nonseminomas arise from IGCNU cells derived from primordial germ cells that have already undergone de novo methylation after the original erasure of methylation and contain normal 5(m)C levels. Yet the methylation status of IGCNU has not been determined previously. We used immunohistochemical staining against 5(m)C to evaluate global methylation in IGCNU and associated invasive testicular germ cell tumors. Strikingly, staining for 5(m)C was undetectable (or markedly reduced) in the majority of IGCNU and seminomas, yet there was robust staining in nonseminomatous germ cell tumors. The lack of staining for 5(m)C in IGCNU and seminomas was also found in mixed germ cell tumors containing both seminomatous and nonseminomatous components. Lack of 5(m)C staining was not related to a lack of the maintenance methyltransferase (DNA methyltransferase 1) protein. We conclude that testicular germ cell tumors are derived in most cases from IGCNU cells that have undergone developmentally programmed 5(m)C erasure and that the degree of subsequent de novo methylation is most closely related to the differentiation state of the neoplastic cells. That is, IGCNU cells and seminoma cells remain unmethylated, whereas all other histological types appear to arise after de novo methylation.

Chromosomes, genes, and development of testicular germ cell tumors

A literature review found 265 articles on testicular germ cell tumors (TGCTs) detailing the copy number of chromosomal regions and expression of 245 genes. An initial precursor stage, intratubular germ cell neoplasia (IGCN), is characterized by triploidization and an upregulation of KIT, ALPP, CCDN2, and ZNF354A, and a downregulation of CDKN2D. TGCT regularly have a series of chromosomal aberrations: a decrease in copy number at 4q21 approximately qter and 5q14 approximately qter; an increase at 7p21 approximately pter, 7q21 approximately q33, and 8q12 approximately q23 (especially high increase in seminoma); a decrease at 11p11 approximately p15 and 11q14 approximately q24; an increase at 12p11 approximately pter; a decrease at 13q14 approximately q31; an increase of 17q11 approximately q21 (only for nonseminoma); a decrease of 18q12 approximately qter; and an increase at 21q21 approximately qter, 22q11 approximately qter (only for seminoma), and Xq. Macroscopically overt TGCT is associated with a characteristic series of abnormalities in the retinoblastoma pathway including upregulation of cyclin D2 and p27 and downregulation of RB1 and the cyclin-dependent kinase inhibitors p16, p18, p19, and p21. TGCT thus has a synergistic pattern in gene expressions of the retinoblastoma pathway that is rare in other malignancies.

Frequent epigenetic inactivation of the RASSF1A tumour suppressor gene in testicular tumours and distinct methylation profiles of seminoma and nonseminoma testicular germ cell tumours

Testicular germ cell tumours (TGCTs) are histologically heterogeneous neoplasms with variable malignant potential. Previously, we demonstrated frequent 3p allele loss in TGCTs, and recently we and others have shown that the 3p21.3 RASSF1A tumour suppressor gene (TSG) is frequently inactivated by promoter hypermethylation in a wide range of cancers including lung, breast, kidney and neuroblastoma. In order to investigate the role of epigenetic events in the pathogenesis of TGCTs, we analysed the promoter methylation status of RASSF1A and nine other genes that may be epigenetically inactivated in cancer (p16(INK4A), APC, MGMT, GSTP1, DAPK, CDH1, CDH13, RARbeta and FHIT) in 24 primary TGCTs (28 histologically distinct components). RASSF1A methylation was detected in four of 10 (40%) seminomas and 15 of 18 (83%) nonseminoma TGCT (NSTGCT) components (P=0.0346). None of the other nine candidate genes were methylated in seminomas, but MGMT (44%), APC (29%) and FHIT (29%) were frequently methylated in NSTGCTs. Furthermore, in two mixed germ cell tumours, the NSTGCT component for one demonstrated RASSF1A, APC and CDH13 promoter methylation, but the seminoma component was unmethylated for all genes analysed. In the second mixed germ cell tumour, the NSTGCT component was methylated for RASSF1A and MGMT, while the seminoma component was methylated only for RASSF1A. In all, 61% NSTGCT components but no seminoma samples demonstrated promoter methylation at two or more genes (P=0.0016). These findings are consistent with a multistep model for TGCT pathogenesis in which RASSF1A methylation occurs early in tumorigenesis and additional epigenetic events characterize progression from seminoma to NSTGCTs.

Distinct epigenetic phenotypes in seminomatous and nonseminomatous testicular germ cell tumors

The genetic nature of testicular germ cell tumors and the molecular mechanisms underlying the morphological and clinical differences between the two subtypes, seminomas and nonseminomas, remains unclear. Genetic studies show that both subtypes exhibit many of the same regional genomic disruptions, although the frequencies vary and few clear differences are found. We demonstrate significant epigenetic differences between seminomas and nonseminomas by restriction landmark genomic scanning. Seminomas show almost no CpG island methylation, in contrast to nonseminomas that show CpG island methylation at a level similar to other solid tumors. We find an average of 1.11% of CpG islands methylation in nonseminomas, but only 0.08% methylated in seminomas. Furthermore, we demonstrate that seminomas are more highly hypomethylated than nonseminomas throughout their genome. Since both subtypes are thought to arise from primordial germ cells, the epigenetic differences seen between these subtypes may reflect the normal developmental switch in primordial germ cells from an undermethylated genome to a normally methylated genome. We discuss these findings in relation to different developmental models for seminomatous and nonseminomatous testicular germ cell tumors.

Amelogenin dosage compensation in carcinoma of colon, lung, liver and kidney, is not a marker of clonality in males

The analysis of patterns of X-chromosome inactivation is becoming increasingly utilized as a marker of clonal composition of tissues from women. To date, however, no analogous system has been found for the study of clonality in tissue from men. In the current study, the methylation patterns for portions of the amelogenin genes are tested, which are encoded on both the X- and Y-chromosome (AMGX and AMGY). The polymerase chain reaction (PCR) was used to amplify portions of AMGX and AMGY from genomic DNA of carcinomas of the colon, lung, liver and kidney, as well as from matched normal somatic tissues. The amplification target included Alu I methylation sensitive restriction endonuclease sites as well as a 189 bp sequence which is present in AMGX but is absent in AMGY. Polymerase chain reaction amplification of AMGX and AMGY was successful using genomic DNA from both tumour and normal control tissue in 24 of the 26 cases. Pretreatment of genomic DNA with Alu I blocked amplification of AMGX in all cases from both normal tissue and tumour. This indicates that AMGX and AMGY undergo a non-random pattern of methylation in both normal tissues and in tumours, precluding their use as a marker of clonality. Methylation of Alu I sites in AMGY suggests that the amelogenin genes undergo dosage compensation, which raises the possibility that the expression of amelogenin is not restricted to the development of the tooth bud but may also play some other role in various tissues of the body.

Genomic imprinting in testicular germ cell tumours

Genomic imprinting refers to the parental origin-specific functional difference between the paternally and maternally-derived mammalian haploid genome. Normal embryogenesis depends on the presence of both a paternal and a maternal copy of particular chromosomal regions, containing the so-called imprinted genes. Genomic imprinting is established somewhere in the maturation from a primordial germ cell to a mature gamete, either spermatid or oocyte. We discuss the value of testicular cancers, especially those derived from the germ cell lineage, as a model to study erasement of the biparental pattern of genomic imprinting as present in the zygote and establishment of the paternal pattern during spermatogenesis. In addition, we will present data on the presence of X-inactivation in these cancers.

Methylation similarities of two CpG sites within exon 5 of human H19 between normal tissues and testicular germ cell tumours of adolescents and adults, without correlation with allelic and total level of expression

Testicular germ cell tumours (TGCTs) of adolescents and adults morphologically mimic different stages of embryogenesis. Established cell lines of these cancers are used as informative models to study early development. We found that, in contrast to normal development, TGCTs show a consistent biallelic expression of imprinted genes, including H19, irrespective of histology. Methylation of particular cytosine residues of H19 correlates with inhibition of expression, which has not been studied in TGCTs thus far. We investigated the methylation status of two CpG sites within the 3' region of H19 (exon 5: positions 3321 and 3324) both in normal tissues as well as in TGCTs. To obtain quantitative data of these specific sites, the ligation-mediated polymerase chain reaction technique, instead of Southern blot analysis, was applied. The results were compared with the allelic status and the total level of expression of this gene. Additionally, the undifferentiated cells and differentiated derivatives of the TGCT-derived cell line NT2-D1 were analysed. While peripheral blood showed no H19 expression and complete methylation, a heterogeneous but consistent pattern of methylation and level of expression was found in the other normal tissues, without a correlation between the two. The separate histological entities of TGCTs resembled the pattern of their nonmalignant tissues. While the CpG sites remained completely methylated in NT2-D1, H19 expression was induced upon differentiation. These data indicate that methylation of the CpG sites within exon 5 of H19 is tissue dependent, without regulating allelic status and/or total level of expression. Of special note is the finding that, also regarding methylation of these particular sites of H19, TGCTs mimic their non-malignant counterparts, in spite of their consistent biallelic expression.