Inhibition of estrogen signaling with fulvestrant upregulates CycG2 expression in ER positive breast cancer cell lines. (A, B) MCF7 and T47D cells cultured in the presence or absence of fulvestrant (ICI, 100 nM) for 24 (A) or 48h (A, B) or absence of E2 (DM, 6 days) were assessed for changes in CycG2 expression by immunoblot analysis. (C) Confocal immunofluorescence microscopy images showing CycG2 expression (green) in fulvestrant-treated (ICI, bottom panel) and non-treated control (NT, top) MCF7 cells. Cells were stained with antibodies against CycG2 (green), and α-tubulin (α-Tub, red). (D) Immunoblot of CycG2 in MCF7 cells cultured for 48h in the absence (NT) or presence of the E2-signaling antagonists fulvestrant (ICI, 100 nM) or tamoxifen (TAM, 100 nM). (E) Immunoblot of CycG2 in E2-depleted (DM, 5 days) MCF7 cultures compared to E2-depleted cultures re-stimulated for an additional 48h with E2 alone or E2 plus ICI or TAM as indicated.