GFP-GR and GFP-MR plasmid was transfected into COS cells and brain cells from the hippocampus and time-lapse images were aquired by a cooled CCD camera. Colchicine treatment caused the disruption of microtubule but this did not affect the subsequent nuclear accumulation of GFP-GR. After blocking by geldanamycin you can see the inhibition of translocation of GR as well as MR from the cytoplasm to the nucleus
indicating that HSP 90 is necessary for the transport of adrenal corticosteroid receptors to the nucleus. CFP-GR was translocated to the nucleus and in accordance with this
YFP-importin a also changed from the cytoplasm to the nucleus
suggesting that importin a/b system is involved in GR nuclear transport. In order to examine whether GR and MR are colocalized in the nucleus
we analyzed the subnuclear localization of these two receptors by confocal microscope. Two receptors showed a partial colocalization at 30 min and nearly complete colocalization at 60 min. after addition of carticosterone. The occurrence of FRET between GR and MR was observed. FRAP analysis showed that cytoplasmic GR was very dynamic and nuclear GR was also mobile
but its mobility is different. Before estradiol treatment
both YFP-ER alfa and CFP-ER beta showed a diffuse distribution throughout the nucleus but was excluded from nucleolus. Upon the ligand treatment YFP-ER alfa and CFP-ER bata in the same cell was relocalized to show discrete pattern. These discrete cluster formation was appeared within 10 min. and reached in maximum within 30 min. and they were localized at the same discrete cluster
suggesing that both subtypes of ERs were bound to the same nucleuar sites. In the absence of the ligand
any significant relationship between the diffuse distribution of GFP-ERs and the discrete distribution of BRg-1. In the presence of the estradiol
however
the discrete staining pattern of GFP-ER alfa nad bata were mostly overlapped with BRG-1
indicating that most of the ERs clusters are involved in the chromatin remodeling machinery. Treatment by MAP kinase inhibitor
PD98059 did not block AR transport from the cytoplasm to the nucleus
suggesting that MAPkinase is not directly involved in the AR translocation. Nuclear receptors and their ligands are interplaying each other at the stage of the cells and visualization of nuclear receptors and the trandcriptional regulators in libing cells by using GFPs provided a number of findings that can not be detected by biochemial methods.
