Estrogen-induced growth inhibition of human seminoma cells expressing estrogen receptor β and aromatase

It is now well established that estrogens participate in the control of normal spermatogenesis and endogenous or environmental estrogens are involved in pathological germ cell proliferation including testicular germ cell tumors. Studying a human testicular seminoma cell line, JKT-1, we show here that 17β-estradiol (10−12 to 10−6 M) induced in vitro a significant dose-dependent decrease of cell growth. This antiproliferative effect was maximum after 4 days of exposure at a physiologically intratesticular concentration of 10−9 M, close to the Kd of ER, and reversed by ICI 182780, an ER antagonist, suggesting an ER-mediated pathway. By RT-PCR and Western blot we were able to confirm that JKT-1, like tumoral seminoma cells and normal human testicular basal germ cells, expresses estrogen receptor β (ERβ), including ERβ1 and ERβ2, a dominant negative variant, but not ERα. Using immunofluorescence and confocal microscopy, ERβ was observed as perinuclear intracytoplasmic spots in JKT-1 and tumoral seminoma cells without significant translocation of ERβ into the nucleus, under 17β-estradiol exposure. Double staining observed by confocal microscopy revealed that ERβ colocalized in JKT-1 cells with cytochrome C, a mitochondrial marker. We report for the first time the expression of a functional aromatase complex in seminoma cells as assessed by RT-PCR, Western blot and enzymatic assay. Seminoma cells are able to respond to estrogens through a possible autocrine or paracrine loop. These preliminary results support estrogen-dependency of human testicular seminoma, the most frequent tumor of young men, and suggest potential pharmacological use. Whether this estrogen control, however, involves an ERβ-mediated stimulation of cell apoptosis and/or an ERβ-mediated inhibition of cell proliferation, remains to be further determined.