Transcription Factor AP-2γ Is a Developmentally Regulated Marker of Testicular CarcinomaIn situand Germ Cell Tumors

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Abstract
Purpose: Transcription factor activator protein-2γ (TFAP2C, AP-2γ) was reported previously in extraembryonic ectoderm and breast carcinomas but not in the testis. In our recent gene expression study we detected AP-2γ in carcinoma in situ testis (CIS, or intratubular germ cell neoplasia), precursor of testicular germ cell tumors. In this study we aimed to investigate the expression pattern of AP-2γ and to shed light on this factor in germ cell differentiation and the pathogenesis of germ cell neoplasia.Experimental Design: We analyzed expression pattern of AP-2γ at the RNA and protein level in normal human tissues and a panel of tumors and tumor-derived cell lines. In the gonads, we established the ontogeny of expression of AP-2γ in normal and dysgenetic samples. We also investigated the regulation of AP-2γ by steroids and retinoic acid.Results: We detected abundant AP-2γ in testicular CIS and in testicular germ cell tumors of young adults and confirmed differential expression of AP-2γ in somatic tumors. We found that AP-2γ expression was regulated by retinoic acid in an embryonal carcinoma cell line (NT2). The investigation of ontogeny of AP-2γ protein expression in fetal gonads revealed that it was confined to oogonia/gonocytes and was down-regulated with germ cell differentiation. In some prepubertal intersex cases, AP-2γ was detected outside of the normal window of expression, probably marking neoplastic transformation of germ cells.Conclusions: AP-2γ is developmentally regulated and associated with the undifferentiated phenotype in germ cells. This transcription factor may be involved in self-renewal and survival of immature germ cells and tissue-specific stem cells. AP-2γ is a novel marker of testicular CIS and CIS-derived tumors.