| Research Abstract |
Nuclear receptors which include glucocorticoid receptor (GR), mineralocorticoid receptor (MR), estrogen receptor (ER) α and β, and androgen receptor (AR) are ligand-dependent transcriptional factor. With the advent of green fluorescent protein (GFP) and its color variants, the subcellular distribution of many nuclear receptors has been found to be much more dynamic than previously thought. GFP studies showed that microtubules are not involved in the translocation of GR and MR from cytoplasm to nucleus, but that HSP90 and importin system, at least in part, are strongly relevant to this translocation. Hormonal stimulation induced intranuclear receptor distribution from a homogeneous pattern to a heterogeneous dot-like image. GR and MR showed a partial colocalization at 30 min and nearly complete colocalization at 60 min after addition of corticosterone. The occurrence of FRET between GR and MR was observed in the nucleus. FRAP analysis showed that cytoplasmic GR was dynamic and nuclear GR was also mobile, but its mobility was different. Upon estradiol treatment ER α and β in the same cell were relocalized to show discrete pattern, and they were localized at the same discrete cluster, suggesting that both subtypes of Ers were bound to the same nuclear sites. In the absence of the ligand, any significant relationship between the diffuse distribution of Ers and the discrete distribution of Brg-1 was not observed. In the presence of the estradiol, however, the discrete staining pattern of ER α and β were mostly overlapped with Brg-1, indicating that most of the Ers clusters are involved in the chromatin remodeling machinery.
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