Role of insulin-like growth factor-I in regulating estrogen receptor-alpha gene expression.
The role of insulin-like growth factor-I (IGF-I) in regulating estrogen receptor-alpha (ER-alpha) 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-alpha protein concentration by 3 h, and the amount of ER-alpha remained suppressed for 24 h. A multiple-dose ligand-binding assay demonstrated that the decrease in ER-alpha protein corresponded to a similar decrease of 50% in estradiol-binding sites with no effect on the binding affinity of ER-alpha. The dissociation constant of the estradiol-ER-alpha complex in the absence of IGF-I (K(d) = 3 x 10(-10) +/- 0.5 x 10(-10) M) was similar to the dissociation constant in the presence of IGF-I (K(d) = 6 x 10(-10) +/- 0.3 x 10(-10) M). The decrease in ER-alpha protein concentration was paralleled by an 80% decrease in the steady-state amount of ER-alpha mRNA by 3 h. The IGF-I induced decrease in ER-alpha mRNA was due to the inhibition of ER-alpha gene transcription. When an 128-base pair ER-alpha-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-alpha, 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-alpha mediates the effects of IGF-I. Transient co-transfections of wild-type ER-alpha 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-alpha expression and activity, suggesting that these kinases may be involved in the cross-talk between the IGF-I and ER-alpha pathways.
Stoica
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Lombardi Cancer Center, Department of Biochemistry and Molecular Biology, Georgetown University, Washington DC 20007-2197, USA.
Saceda
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Fakhro
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A
Joyner
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Martin
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MB
D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D019556:COS Cells; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004958:Estradiol / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D004965:Estrogen Antagonists / Q000494:pharmacology; D047628:Estrogen Receptor alpha; D005786:Gene Expression Regulation / Q000187:drug effects*; D017930:Genes, Reporter; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D053284:Polyunsaturated Alkamides; D011401:Promoter Regions, Genetic; D011485:Protein Binding / Q000187:drug effects; D047428:Protein Kinase Inhibitors; D011506:Proteins / Q000235:genetics; D012333:RNA, Messenger / Q000187:drug effects; D011960:Receptors, Estrogen / Q000235:genetics*; D011980:Receptors, Progesterone / Q000235:genetics; D014162:Transfection; D000071163:Trefoil Factor-1; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins
D004791:Enzyme Inhibitors; D004965:Estrogen Antagonists; D047628:Estrogen Receptor alpha; D053284:Polyunsaturated Alkamides; D047428:Protein Kinase Inhibitors; D011506:Proteins; D012333:RNA, Messenger; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; C051838:TFF1 protein, human; D000071163:Trefoil Factor-1; D025521:Tumor Suppressor Proteins; D004958:Estradiol; D007334:Insulin-Like Growth Factor I; C051781:ICI 164384