Abstract
Estrogen-like effects of the heavy metal cadmium have been reported in both in vitro and in vivo studies. Yet, the molecular mechanisms involved in the hormonal activity of cadmium ions have not been fully elucidated. There are extensive data on cross-talk between aryl hydrocarbon receptor (AhR) and estrogen receptor (ER). Recently, 17β-estradiol (E(2)) was found to modulate the expression of AhR and AhR-regulated genes in rat uterus (Kretzschmar et al. in Mol Cell Endocrinol 321:253-257, 2010). Thus, we hypothesized that cadmium may also affect AhR signaling and examined whether cadmium or E(2) modulate AhR-associated genes via the ER in rat uterus. Ovariectomized Wistar rats received E(2) (0.5 mg/kg bw) or cadmium chloride (0.05 and 2 mg/kg bw i.p.) alone and in combination with the pure anti-estrogen ZK191703. We also co-treated a group with E(2) and cadmium 2 mg/kg bw to assess how they act in concert. Uterus wet weight, uterus epithelial height, complement C3 mRNA, and progesterone receptor (PR) protein expression served as estrogen response parameters, and expression of Mt1a mRNA was analyzed as a cadmium responsive gene. The expression of AhR protein and AhR-associated gene expression, i.e., Ahr, Arnt1, Arnt2, Cyp1a1, and Gsta2, were analyzed to examine effects on AhR-mediated signaling pathways in the uterus of all groups. Both, E(2) and cadmium induced C3 and PR expression, and this was antagonized by ZK191703. Mt1a expression was clearly induced by cadmium but slightly reduced by E(2) compared to controls. Uterine Ahr, Arnt1, Arnt2, and Cyp1a1 expression was modulated by E(2) via the ER since down-regulation by E(2) was reversed by anti-estrogen. Cadmium apparently also modulated Cyp1a1 expression via the ER. Furthermore, cadmium-induced AhR was antagonized by E(2,) and anti-estrogen-induced Gsta2 expression was antagonized by cadmium. Together our findings provide evidence for cross-talk of ER and AhR in the rat uterus.