Frequent promoter hypermethylation of the O6-Methylguanine-DNA Methyltransferase (MGMT) gene in testicular cancer

Abstract

Testicular germ cell tumours are classified into two major histological subgroups, seminomas and nonseminomas. All tumours display several recurrent chromosomal aberrations, but few target genes have been identified. Previous studies have shown that genome-wide hypermethylation of CpG islands is significantly more prevalent in nonseminomas than in seminomas. We have studied two potential target genes in testicular cancer. A series of 70 tumours were analysed for methylation of CpG sites in the O 6 -methylguanine-DNA methyltransferase (MGMT) gene promoter, and in exon 1a of the cyclin-dependent kinase inhibitor 2A gene (CDKN2A). In addition, eight microsatellite markers within and flanking these genes at chromosome arms 10q and 9p, respectively, were analysed for allelic imbalances. Allele alterations were frequently seen at 9p loci (47 out of 70, 67%), but none of the tumours (none out of 55) showed methylation of CDKN2A. On the other hand, a high frequency of MGMT promoter methylation (32 out of 69, 46%) was found, as well as allelic imbalances at 10q markers (50 out of 70, 71%). A significantly higher methylation frequency was found in nonseminomas (24 out of 35, 69%) compared to seminomas (eight out of 33, 24%) (P=0.0003, Fisher's exact test). Immunohistochemical analysis of the MGMT protein in a subgroup (n=20) of the testicular tumours supported the hypothesis of gene silencing being the functional consequence of the promoter methylation. In summary, our data suggest that inactivation of MGMT contributes to development of nonseminomatous testicular cancer.

NKX3.1 Expression Is Lost in Testicular Germ Cell Tumors

“…13 This was evident both across the whole sample series and within specific histological subtypes. Because MGMT was recently reported to be frequently hypermethylated in promoter sequences in TGCT, 21 this correlation suggests an epigenetic silencing mechanism also for NKX3.1. In fact, DNA methylation seems to be a major mechanism for regulating gene expression in TGCT.…”

Generating mutations but providing chemosensitivity: the role of O6-methylguanine DNA methyltransferase in human cancer

“…This profile, thanks to the popularization of bisulfite-PCR techniques (Fraga and Esteller, 2002), has been expanded in additional reports of MGMT inactivation in other tumor types (Toyooka et al, 2001;Virmani et al, 2001;Choy et al, 2002;Lee et al, 2002;Maruyama et al, 2002;Smith-Sorensen et al, 2002), summarized in Figure 3. This aberrant MGMT methylation has been correlated with the loss of MGMT protein (Esteller et al, 1999a(Esteller et al, , 2002cHerfarth et al, 1999.…”

DNA methylation in germ cell tumour aetiology: current understanding and outstanding questions

“…Although the malignant non-seminomas exhibit increased hypermethylation (Netto et al 2008, Wermann et al 2010, they also exhibit hypomethylation of LINE1 repetitive elements (Jeyapalan et al 2011, Ushida et al 2012, which is reminiscent of other cancer cells and normal PGCs. The observation that different components of mixed tumours display distinct methylation profiles further supports the conclusion that aberrant methylation is a key factor in the development of GCT subtypes (Smith-Sorensen et al 2002, Honorio et al 2003, Netto et al 2008. Further analysis of the aberrant hypermethylation seen in non-seminomas will be necessary to determine whether …”

“…The differing methylation profiles of the various GCT subtypes appear to be independent of location, gender (Furukawa et al 2009, Wermann et al 2010, Jeyapalan et al 2011 or genetic aberrations (Smiraglia et al 2002, Smith-Sorensen et al 2002, Lind et al 2007. With respect to age, differences between paediatric and adult GCTs have been suggested (Kato et al 2003, Furukawa et al 2009, Jeyapalan et al 2011; Table 2), but this does not stand up to close scrutiny.…”

“…This conclusion is based on studies using both candidate gene approaches (Koul et al 2002, Smith-Sorensen et al 2002, Honorio et al 2003, Kempkensteffen et al 2006, Lind et al 2006, Brait et al 2012) and genome-wide approaches (Smiraglia et al 2002, Netto et al 2008, Wermann et al 2010, which have mainly focused on adult testicular GCTs (Table 2). Although some of these studies focused on a limited number of genes, microarray and genome-wide studies confirm that the methylation profile distinction between seminomas and non-seminomas is not restricted to just a few specific gene promoters (Lind et al 2007).…”