Figure 3. IGF-1 and E₂ affect ERα expression in vivo and in vitro.

(A) Western blot analysis showing that the expression of ERα is reduced in mammary glands from postpubertal compared with prepubertal mice. ERα levels are further and significantly reduced in glandular extracts from postpubertal Tg mice compared with age-matched WT mice. Graphs present mean ± SD of densitometric analyses of 4 independent experiments, with representative Western blots shown. *P < 0.05 versus prepubertal WT; ^#P < 0.05 versus prepubertal Tg; ^†P < 0.05 versus postpubertal WT as determined by Student’s t test. (B) In MCF-7 cells, ERα expression is reduced following 6 hours of treatment with either 10 nmol/l E₂ alone or with a combination of 40 ng/ml IGF-1 and 10 nmol/l E₂ in SFM. (C) Also in MCF-7 cells, ERα levels are reduced following 24 hours of treatment with E₂ and further and significantly reduced by treatment with a combination of E₂ and IGF-1. *P < 0.05 versus untreated cells; ^#P < 0.05 versus IGF-1–treated cells; ^†P < 0.05 versus E₂-treated cells, as determined by Student’s t test.