Dedifferentiation of human adult Sertoli cells in cross talk with seminoma cells in vitro

Germ cell neoplasia in situ (GCNIS) is the noninvasive precursor of testicular germ cell tumors type II (TGCT), the most common cancer in young men. GCNIS originates from embryonic germ cells blocked in their maturation. The causes are unknown. GCNIS is associated with impaired Sertoli cells that express fetal marker keratin 18 (KRT18) and pluripotency factor SOX2. According to the spread theory of the origin of GCNIS, these impaired Sertoli cells are prepubertal cells arrested in their maturation due to genetic anomalies and/ or environmental anti-androgens. Thus, they are unable to support the development of germ cells, leading to their maturational block with further progression into GCNIS. The alternative theory states that the impaired Sertoli cells are adult cells dedifferentiating secondarily due to the influence of GCNIS. To address this issue, we established a co-culture model of adult human Sertoli cells (FS1) and a seminoma cell line similar to GCNIS (TCam-2). After 2 weeks of co-culture, FS1 cells showed progressive expression of KRT18 and SOX2. Interestingly, TCam-2 cells in co-culture showed SOX2 expression and upregulation of further pluripotency- and reprogramming-associated genes (LEFTY1/2, GAL, DPPA5, NODAL, ZIC3, DND1, DPPA3, GDF3, BCAT1, JARID2, and DNMT3B), suggesting a seminoma to embryonal carcinoma transition. Thus, our FS1/ TCam-2 co-culture model is a valuable tool to investigate interactions between Sertoli cells and tumor cells. Our studies of human testicular biopsies with GCNIS further suggest that the impaired Sertoli cells associated to GCNIS represent adult cells undergoing progressive dedifferentiation. 4 independent samples each from 2 different cell types (FS1 and TCam2) kept either in monoculture or in co-culture (= total of 16 samples) hybridized on 16 microarrays.