Gene expression profiling identifies new biological markers to neoplastic germ cells.

A2

To elucidate transcriptional programs in intratubular germ cell neoplasia undetermined (IGCNU) and testicular germ cell tumors (TGCT), we investigated the global gene expression in 10 TGCT, 7 IGCNU and 3 normal testes. We identified a set of genes that are upregulated in neoplastic germ cells of IGCNU which included RAS related genes (KRAS2, RALA, RAB39B) and various core markers of embryonic stem cells. The expression of several functionally important genes was studied by immunohistochemistry or in-situ hybridization in tissue microarrays containing 126 TGCT, IGCNU and normal testes. Products of genes related to the 12p13 locus including NANOG, GDF3, STELLAR as well as proteins of novel genes CD9, PODXL and centromere-specific histone-H3-like protein CENPA were detected in IGCNU, seminomas and embryonal carcinomas. In contrast, gene expression profiling and immunohistochemical analyses revealed that the core embryonic stem cell regulator SOX2 and downstream targets of the Nodal pathway were differentially upregulated in embryonal carcinoma subtype only, but not in IGCNU or seminomas indicating their role in the establishment of a embryonal carcinoma phenotype. Next, the analysis of gene expression in seminomas and adjacent IGCNU vs. embryonal carcinomas and adjacent IGCNU reveals different gene expression patterns in IGCNU lesions depending on histological types of TGCT. In conclusion, our study determines genes which are involved in early pathogenetic events of neoplastic germ cell formation, provides new insights into genetic pathways driving the transition of embryonal carcinoma and seminoma from its precursor lesion and identifies new biomarkers of neoplastic germ cells such as CD9 and PODXL.