UC Davis

The enzyme aromatase (CYP19; cytochrome P450 19) in humans undergoes highly tissue- and promoter-specific regulation.In hormone-dependent breast cancer, aromatase is over-expressed via several normally inactive promoters (PII, I.3, I.7).Aromatase biosynthesizes estrogens, which stimulate breast cancer cell proliferation. The placenta produces estrogensrequired for healthy pregnancy and the major placental CYP19 promoter is I.1. Exposure to certain pesticides, such asatrazine, is associated with increased CYP19 expression, but little is known about the effects of neonicotinoid insecticideson CYP19. We developed sensitive and robust RT-qPCR methods to detect the promoter-specific expression of CYP19 inhuman adrenocortical carcinoma (H295R) and primary umbilical vein endothelial (HUVEC) cells, and determined thepotential promoter-specific disruption of CYP19 expression by atrazine and the commonly used neonicotinoidsimidacloprid, thiacloprid, and thiamethoxam. In H295R cells, atrazine concentration-dependently increased PII- and I.3-mediated CYP19 expression and aromatase catalytic activity. Thiacloprid and thiamethoxam induced PII- and I.3-mediatedCYP19 expression and aromatase activity at relatively low concentrations (0.1–1.0 mM), exhibiting non-monotonic concentration–response curves with a decline in gene induction and catalytic activity at higher concentrations. In HUVEC cells, atrazine slightly induced overall (promoter-indistinct) CYP19 expression (30 mM) and aromatase activity (≥ 3 mM), without increasing I.1 promoter activity. None of the neonicotinoids increased CYP19 expression or aromatase activity in HUVEC cells. Considering the importance of promoter-specific (over)expression of CYP19 in disease (breast cancer) or during sensitive developmental periods (pregnancy), our newly developed RT-qPCR methods will be helpful tools in assessing the risk that neonicotinoids and other chemicals may pose to exposed women.