Genomic ERα activity in breast cancer cells is not directly enhanced by obesity-associated circulating factors. Genomic ERα activity in response to 2% obese (Ob) or control (Con) patient sera exposure was measured in MCF-7 and T47D cells with an ERE luciferase reporter (A) and qPCR analysis of pS2 expression (B). Expression of cyclin D1, which is regulated by both ERα and the PI3K/Akt and MAPK pathways, was assessed by qPCR analysis in both cell lines following growth in 2% Ob or Con patient sera (C). The effect of 2% Ob(-AI) and Con(-AI) patient sera on genomic ERα activity in MCF-7 cells was also measured by ERE luciferase reporter (D). This pooled sera excluded breast cancer patients receiving aromatase inhibitors at the time of collection. Data shown represent the average of at least three independent experiments. *, P < 0.05 in comparison to Con. ERα, estrogen receptor alpha; ERE, estrogen response element.