Role of insulin-like growth factor-I in regulating estrogen receptor-α gene expression

✍ Scribed by Adriana Stoica; Miguel Saceda; Amina Fakhro; Michael Joyner; Mary Beth Martin

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 170 KB
• Volume: 76
• Category: Article
• ISSN: 0730-2312
• DOI: 10.1002/(sici)1097-4644(20000315)76:4<605::aid-jcb9>3.0.co;2-t

✦ Synopsis

The role of insulin-like growth factor-I (IGF-I) in regulating estrogen receptor-␣ (ER-␣) gene expression and activity was investigated in the human breast cancer cell line MCF-7. Treatment of cells with 40 ng/ml IGF-I resulted in a 60% decrease in ER-␣ protein concentration by 3 h, and the amount of ER-␣ remained suppressed for 24 h. A multiple-dose ligand-binding assay demonstrated that the decrease in ER-␣ protein corresponded to a similar decrease of 50% in estradiol-binding sites with no effect on the binding affinity of ER-␣. The dissociation constant of the estradiol-ER-␣ complex in the absence of IGF-I (K d ϭ 3 ϫ 10 Ϫ10 Ϯ 0.5 ϫ 10 Ϫ10 M) was similar to the dissociation constant in the presence of IGF-I (K d ϭ 6 ϫ 10 Ϫ10 Ϯ 0.3 ϫ 10 Ϫ10 M). The decrease in ER-␣ protein concentration was paralleled by an 80% decrease in the steady-state amount of ER-␣ mRNA by 3 h. The IGF-I induced decrease in ER-␣ mRNA was due to the inhibition of ER-␣ gene transcription. When an 128-base pair ER-␣-promoter-CAT construct was transfected into MCF-7 cells, treatment with IGF-I resulted in a 40% decrease in CAT activity. In contrast to the effects on ER-␣, treatment with IGF-I induced two endogenous estrogen-regulated genes, progesterone receptor and pS2, by 4-and twofold, respectively. The pure antiestrogen ICI-164,384 blocked this induction, suggesting that ER-␣ mediates the effects of IGF-I. Transient co-transfections of wild-type ER-␣ and an estrogen response element-CAT reporter into COS-1 cells demonstrated that IGF-I increased reporter gene activity. This effect was also blocked by ICI 164,384. Protein kinase A and phosphatidylinositol 3-kinase inhibitors blocked the IGF-I effects on ER-␣ expression and activity, suggesting that these kinases may be involved in the cross-talk between the IGF-I and ER-␣ pathways.