Low doses of bisphenol A promote human seminoma cell proliferation by activating PKA and PKG via a membrane G-protein-coupled estrogen receptor.

Endocrine-disrupting chemicals (EDCs) are hormone-like agents present in the environment that may alter the endocrine system of wildlife and humans. In particular, xenoestrogens have been hypothesized to be involved in developmental, reproductive, and malignant diseases by mimicking the natural hormone 17β-estradiol (E2) and interfering with endogenous endocrine regulation at specific periods, such as during fetal growth. Several organochloride pesticides—polychlorinated biphenyls (PCBs), phthalates, and bisphenol A (BPA)—used in the chemical industry have been considered as estrogenic EDCs. However, all of these EDCs have a very weak affinity for binding through the classical nuclear estrogen receptors (ERs), 1,000–2,000 times lower than that of E2 (Bonefeld-Jorgensen et al. 2001; Crain et al. 1998; Massaad and Barouki 1999). Studies of the nuclear transcriptional regulatory activities of nonphysiologic estrogens have mostly been unable to explain the actions of these chemicals in mediating endocrine disruption in animals and humans at the low picomolar or nano molar concentrations widespread in the environment (Calafat et al. 2005; Vandenberg et al. 2007). In the last few years, EDCs have been reported to act through hormone-independent mechanisms (Welshons et al. 2006) or through a nongenomic activation of membrane-initiated signaling pathways via membrane forms of ERs (Alonso-Magdalena et al. 2005; Bulayeva and Watson 2004; Nadal et al. 2000; Noguchi et al. 2002). Indeed, there is now convincing evidence that estrogens, in addition to the classical regulation of estrogen-responsive genes via nuclear ERs, are able to trigger rapid membrane activation of a variety of second-messenger–mediated signal transduction pathways (Kelly and Levin 2001; Vasudevan and Pfaff 2007), with possible implications for cell proliferation, apoptosis, or survival (Levin 2002). However, the nature of these membrane ER(s), their relation to the classical ERs, and the precise signaling pathways that are activated remain to be elucidated (Manavathi and Kumar 2006; Vasudevan and Pfaff 2007). Moreover, fetal exposure to xenoestrogens is believed to be involved in male reproductive and developmental patho genesis. Diethylestylbestrol (DES), a potent synthetic estrogen used as an antiabortive drug in the 1970s, has a well-known deleterious effect in adults exposed in utero (Newbold et al. 2006). DES can produce different developmental or carcinogenic effects in rodents (Newbold 2004) when given during specific developmental windows, including fetal or perinatal periods, such as cryptorchidism or breast, prostate, or endometrial cancers. However, although indirect epidemiologic data show a constant increase of testicular cancer in young men (Huyghe et al. 2007) and an increased relative risk via professional exposure to persistent organic pollutants, no experimental model has validated the possible carcinogenic role of exposure to xenoestrogens in developing a testicular germ cell cancer (Rajpert-De Meyts 2006). BPA, initially produced like DES as a synthetic estrogen (Dodds and Lawson 1936), has been rapidly and widely used as a cross-linking chemical in the manufacture of polycarbonate plastic and epoxy resins. Because of incomplete polymerization and degradation of the polymers by exposure to higher than usual temperatures, BPA leaches out from food and beverage containers (Biles et al. 1997; Krishnan et al. 1993; Le et al. 2008), as well as from dental sealants. BPA is found in the serum, milk, saliva, and urine of humans at nanomolar concentrations (Calafat et al. 2005; Olea et al. 1996; Sun et al. 2004; Vandenberg et al. 2007). Remarkably, BPA has been measured in amniotic fluid at concentrations 5-fold higher than those measured in maternal plasma (Ikezuki et al. 2002). Fetal and perinatal exposures to BPA in rodents have been shown to affect the brain, mammary gland, and reproductive tract, including hormone-dependent cancer (Durando et al. 2007; Ho et al. 2006; Maffini et al. 2006; Markey et al. 2001; Munoz-de-Toro et al. 2005). Although BPA induces an estrogenic effect through classical nuclear ERs at high concentrations and with a reduced affinity relative to E2 (Gaido et al. 1997; Krishnan et al. 1993; Perez et al. 1998), it also is able to trigger a non genomic effect in pancreatic islet, endothelial, and hypophysial cells and in breast cancer cells by initiating rapid responses at low concentrations (Alonso-Magdalena et al. 2005; Bulayeva and Watson 2004; Nadal et al. 2000; Noguchi et al. 2002). We recently reported that E2 coupled to bovine serum albumin (E2-BSA) stimulated the proliferation of human seminoma cells (JKT-1) in vitro through a G-protein–coupled nonclassical membrane ER (GPCR) (Bouskine et al. 2008). In the present study, we investigated the hypothesis that BPA could stimulate seminoma cell proliferation through such a nongenomic action. We observed a promoting effect of BPA on seminoma cells through a rapid activation of cAMP-dependent protein kinase (PKA) and cGMP-dependent protein kinase (PKG) signaling pathways via a GPCR, illustrating that xenoestrogens, suspected to act as deleterious factors in breast and prostate cancers, could also act in this nongenomic pathway as possible promoting agents in testicular germ cell cancer.