Growth Factors Change Nuclear Distribution of Estrogen Receptor-α via Mitogen-Activated Protein Kinase or Phosphatidylinositol 3-Kinase Cascade in a Human Breast Cancer Cell Line

Abstract

In the present study, to examine the dynamic changes in the localization of nuclear estrogen receptor (ER)α induced by growth factors, we used time-lapse confocal microscopy to directly visualized ERα fused with green fluorescent protein (GFP-ERα) in single living cells treated with epidermal growth factor (EGF) or IGF-I. We observed that 17β-estradiol (E2) changed the normally diffuse distribution of GFP-ERα throughout the nucleoplasm to a hyperspeckled distribution within 10 min. Both EGF and IGF-I also changed the nuclear distribution of GFP-ERα, similarly to E2 treatment. However, the time courses of the nuclear redistribution of GFP-ERα induced by EGF or IGF-I were different from that induced by E2 treatment. In the EGF-treated cells, the GFP-ERα nuclear redistribution was observed at 30 min and reached a maximum at 60 min, whereas in the IGF-I-treated cells, the GFP-ERα nuclear redistribution was observed at 60 min and reached a maximum at 90 min. The EGF-induced redistribution of GFP-ERα was blocked by pretreatment with a MAPK cascade inhibitor, PD98059, whereas the IGF-I-induced redistribution of GFP-ERα was blocked by pretreatment with a phosphatidylinositol 3-kinase inhibitor, LY294002. Analysis using an activation function-2 domain deletion mutant of GFP-ERα showed that the change in the distribution of GFP-ERα was not induced by E2, EGF, or IGF-I treatment. These data suggest that MAPK and phosphatidylinositol 3-kinase cascades are involved in the nuclear redistribution of ERα by EGF and IGF-I, respectively, and that the activation function-2 domain of ERα may be needed for the nuclear redistribution of ERα.