TGF-beta 1, EGF and FGF4 synergistically induce differentiation of the seminoma cell line TCam-2 into a cell type resembling mixed non-seminoma

Malignant germ-cell tumours arise from a neoplastic precursor, the carcinoma in situ, and develop into seminomas and/or non-seminomas (embryonal carcinomas, teratomas, yolk-sac tumours and choriocarcinomas). Based on histological and clinical findings, it has been postulated that seminomas can eventually transform into non-seminomas. Here, we used the cell line TCam-2 as model for seminomas and interrogated their differentiation potential. We demonstrate that TCam-2 cells are able to differentiate into mixed non-seminomatous lineages after supplementing the media with TGF-beta 1, EGF and FGF4. On a molecular level, the differentiation is initiated by repression of BMP/SMAD signalling. As a consequence, BLIMP1, a molecule known to inhibit the differentiation of murine primordial germ cells, is down-regulated and differentiation-inhibiting histone modifications are lost. The appearance of multinucleated giant cells and the expression of marker genes indicate that cells differentiate predominantly into extra-embryonic choriocarcinoma-like cells. This is most likely due to the presence of components of the Hippo pathway, TEAD4 and YAP1. These molecules have been described to trigger extraembryonic fate determination in the murine system. This study supports the model that seminomas indeed have an intrinsic ability to transform into a non-seminoma. In addition, the data suggest that the transformation does not require an additional mutation, but can be triggered by changes in the tumour microenvironment.