Estrogen, SERDs and SERMs induce distinct intracellular behavior of ERα. A) SK19 cells were incubated for 1 h with E2 and different anti-estrogens (SERDs or SERMs), fixed, stained with DAPI and examined by fluorescence microscopy using an Olympus IX-81 inverted microscope. GFP-ERα forms intranuclear foci in the presence of 10 nM E2, 1 μM RU58 and 1 μM ICI, but remains uniformly distributed in the nucleus after addition of 1 μM OHT and 1 μM RU39. Linescans indicate relative fluorescence intensities in the cytoplasm and the nucleus in the cells imaged using identical parameters. Pictures are representative of at least three independent experiments. Bar, 5 μm. B) Representative electron micrograph of MCF-7 cells treated with 1 μM ICI for 1 h. Inset indicates formation of ERα clusters in the nucleus after ICI addition. Bar, 2 μm and 500 nm.