Dynamic changes in subcellular localization of mineralocorticoid receptor in living cells: In comparison with glucocorticoid receptor using dual-color labeling with green fluorescent protein spectral variants

Mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) are ligand -dependent transcription factors. Although it is generally accepted that GR is translocated into the nucleus from the cytoplasm only after ligand bind ing, the subcellular localization of MR is still quite controversial. We ex amined the intracellular trafficking of MR in living neurons and nonneural cells using a fusion protein of green fluorescent protein (GFP) and rat MR (GFP-MR). Corticosterone (CORT) induced a rapid nuclear accumulation of GFP -MR, whereas in the absence of ligand, GFP-MR was distributed in both cytop lasm and nucleus in the majority of transfected cells. Given the differenti al action of MR and GR in the central nervous system, it is important to el ucidate how the trafficking of these receptors between cytoplasm and nucleu s is regulated by ligand, To examine the simultaneous trafficking of MR and GR within single living cells, we use different spectral variants of GFP, yellow fluorescent protein (YFP) and cyan fluorescent protein (CFP), linked to MR and GR, respectively. In COS-1 cells, expressing no endogenous corti costeroid receptors, the YFP-MR chimera was accumulated in the nucleus fast er than the CFP-GR chimera in the presence of 10(-9) M CORT, while there wa s no significant difference in the nuclear accumulation rates in the presen ce of 10(-6) M CORT, On the other hand, in primary cultured hippocampal neu rons expressing endogenous receptors, the nuclear accumulation rates of the YFP-MR chimera and CFP-GR chimera were nearly the same in the presence of both concentrations of CORT. These results suggest that CORT-induced nuclea r translocation of MR and GR exhibits differential patterns depending on li gand concentrations or cell types.