317

Testicular germ cell tumors (TGCTs) are the most common carcinomas of males between the ages of 15 and 35. Embryonal carcinoma (EC) are the malignant stem cells of TGCTs and are pluripotent. EC additionally possess remarkable similarities to embryonic stem cells (ES). Evidence has suggested that certain tumors share characteristics of undifferentiated embryonic cells, implicating pluripotency genes in the pathogenesis of cancer. The expression of known pluripotent genes FGF4, Utf1 and Nanog is regulated by consensus Oct4 and Sox2 elements in their respective promoter and enhancer regions. The etiology of TGCTs has remained unclear, though amplification of chromosome 12p sequences has been identified as a consistent early event in TGCT pathogenesis. We have discovered a cluster of candidate pluripotency genes on chromosome 12p that are repressed by retinoic acid (RA) precisely as EC lose tumorigenicity. Several of these genes, including EDR1, Nanog, Glut3, GDF3 and CD9 are important pluripotency factors, or stem cell markers. EDR1 is a member of the well conserved Polycomb gene family (PcG), in drosophila. More recently, PcG genes have been implicated in homeobox (HOX) gene repression in mammals via chromatin modification, including tri-methylation of lysine 27. We have now identified near consensus Oct4 and Sox2 enhancer sequences within the EDR1 gene. Knockdown of the Oct4 gene by RNA interference (siRNA) results in down-regulation of EDR1 expression. Further, chromatin immunoprecipitation (ChIP) analysis indicates that Oct4 binds to enhancer/promoter regions of the EDR1 gene in vivo. Cloning and characterization of the EDR1 promoter will further elucidate the potential role of EDR1 as a new and critical downstream target of Oct4 and Sox2. Further studies will determine whether EDR1 and other 12p genes, with potential stem cell characteristics, drive the progression and proliferation of TGCTs and whether EDR1 is an important new downstream target of Oct4 and Sox2.

[Proc Amer Assoc Cancer Res, Volume 47, 2006]