The human placenta is an endocrine tissue with a unique capacity for rapid, but tightly controlled, proliferation and invasion. Gestational trophoblastic diseases (GTDs) are placental pathologies with endocrine activity and partially malignant potential and include hydatidiform moles, placental site nodules, and tumors such as placental site trophoblastic tumor and choriocarcinomas. The activating protein-1 (AP-1) family of transcription factors is composed of the cellular homologs of the Jun and Fos oncoproteins, which are immediately involved in cellular proliferation, differentiation, and invasion processes and in the regulation of endocrine genes. The expression pattern of the AP-1 family in the normal human placenta has been recently described, where most of the factors were found in the extravillous (invasive) trophoblast. Their systematic expression in GTD has not been studied thus far. For this reason in this study, we investigated the expression pattern of the AP-1 family in GTDs and compared it with the expression in normal placenta using immunohistochemistry with specific polyclonal antibodies against all members of the AP-1 family (JunB, JunD, c-Jun, c-Fos, FosB, Fra-1, Fra-2). Immunohistochemistry was performed on normal human placentas (positive control) and on 28 cases of GTD including 7 choriocarcinomas and 21 hydatidiform moles. In the normal placenta and in hydatidiform molar samples, most AP-1 factors (especially c-Jun, JunD, and Fra2) were expressed in the intermediate (extravillous) trophoblast. In addition, in molar lesions, strong expression was found in trophoblasts proliferating from the surface of villi. There was only a weak expression of JunB and Fra2 in small fractions of villous cyto- and syncytiotrophoblast nuclei. In choriocarcinomas, there was a strong expression for c-Jun, JunD, Fra1, and Fra2. The specific localization to extravillous trophoblasts and their expression pattern in GTDs indicate that the AP-1 family of transcription factors might be implicated in regulating proliferation and invasion of trophoblasts and play a role in the pathogenesis of GTDs.
