Abstract
PIWI pathway proteins are expressed during spermatogenesis where they play a key role in germ cell development. Epigenetic loss of PIWI proteins expression was previously demonstrated in testicular germ cell tumors (TGCTs), implying their involvement in TGCT development. In this work, apart from studying only normal testis and TGCT samples, we also analyzed an intermediate stage, i.e. preneoplastic testis tissues adjacent to TGCTs. Importantly, in this study, we minimized the contribution of patient-to-patient heterogeneity by using matched preneoplastic/TGCT samples. Surprisingly, expression of germ cell marker DDX4 suggests that spermatogenesis is retained in premalignant testis tissues adjacent to nonseminoma, but not those adjacent to seminoma. Moreover, this pattern is followed by expression of PIWI pathway genes, which impacts one of their functions: DNA methylation level over LINE-1 promoters is higher in preneoplastic testis tissues adjacent to nonseminomas than those adjacent to seminomas. This finding might imply distinct routes for development of the two types of TGCTs and could be used as a novel diagnostic marker, possibly, noninvasively. Finally, we studied the role of CpG island methylation in expression of PIWI genes in patient samples and using in vitro experiments in cell line models: a more complex interrelation between DNA methylation and expression of the corresponding genes was revealed.
Highlights
Testicular germ cell tumors (TGCTs) are heterogeneous cancers classified into less invasive seminomas and more aggressive nonseminomas and are believed to be caused by both genetic and environmental factors [1]
Since each CIS sample was matched to the corresponding TGCT, we were able to take into account patient-to-patient heterogeneity, which is an emerging feature of tumorigenesis [13,14,15]
We looked into expression of germ cell marker DDX4 to assess for the extent of spermatogenesis and carcinoma in situ markers POU5F1 (OCT3/4) and NANOG to evaluate the degree of testicular dysgenesis in the samples [16, 17]
Summary
Testicular germ cell tumors (TGCTs) are heterogeneous cancers classified into less invasive seminomas and more aggressive nonseminomas and are believed to be caused by both genetic and environmental factors [1]. Apart from distinct histological features, seminomas and nonseminomas differ in their prognosis and choice of treatment strategy [2]. These two types of TGCTs were shown to have numerous epigenetic differences and distinguishing expression of various biomarkers [3, 4]. One of the key players in spermatogenesis is PIWI pathway responsible for epigenetic silencing of retrotransposons [8, 9]. PIWI proteins have been implicated in development of various types of cancers [10, 11]. Ferreira et al [12] demonstrated CpG island (CGI) hypermethylation and a concomitant decrease in expression level of PIWI pathway genes in TGCTs compared to the testes of healthy individuals, suggesting a role of PIWI in TGCT tumorigenesis
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
