Estrogen signaling in trout liver: estrogen receptor and non-estrogen receptor mediated cellular response

Studies were conducted to determine intracellular hepatic signaling pathways associated with estrogen exposure in rainbow trout. These studies were initiated as a first step in elucidating potential signal transduction pathways associated with exposure to environmental estrogens in fish. Studies include analysis of intracellular pathways that are dependent upon estrogen receptor signaling including vitellogenin and choriogenin biosynthesis, and key pathways thought to act through specific kinase cascades. Exposure of 5 mg/kg estradiol to juvenile rainbow trout resulted in a strong and specific ‘estrogenic’ response as measured by the de novo synthesis of vitellogenin and choriogenin in plasma of both male and female trout. Estrogen receptor levels were quantified by both E2 binding and mobility shift assays and demonstrated a significant increase in treated fish. Protein kinase A activity was consistently decreased in estrogen treated males and females, whereas juvenile female trout demonstrated a consistent increase in MAP kinase activity with a concatenate rise in the DNA binding activity of AP-1. Further studies are underway in our laboratories to address whether these cellular responses are estrogen receptor dependent and/or independent signaling events.