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The intracellular localization of transcriptionally active green fluorescent protein (GFP) chimeras linked to PPARs for human PPAR[alpha] (GFP-PPARh[alpha]) and mouse PPAR[alpha], [beta], and [gamma]1 (GFP-PPARm[alpha], GFP-PPARm[beta], and GFP-PPARm[gamma], respectively) was examined in the mouse hepatoma cell line, Hepa-1, using fluorescence microscopy. A predominantly nuclear and diffuse distribution of each isoform was found in both the presence and absence of specific ligands for each receptor. GFP-PPARm[alpha]-G (containing a Glu282Gly substitution of PPARm[alpha]) and a phosphorylation mutant, GFP-PPARm[gamma]-A (containing a Ser82Ala substitution of PPARm[gamma]), exhibited altered transcriptional activities, but displayed similar intracellular localization patterns compared with their respective wild-type receptors. Coexpression of nuclear receptor corepressor suppressed, whereas steroid receptor coactivator-1 enhanced the transcriptional activity of each of the GFP-PPAR isoforms, but did not discernibly alter their intracellular distributions, both in the presence and absence of PPAR ligands. Interestingly, coexpression of the obligate heterodimeric partner of PPARs, RXR[alpha], resulted in an intranuclear redistribution of the GFP-PPARm[gamma] isoform characterized by a reticulated pattern of the green fluorescent label for PPAR[gamma] within the nucleus, but not in nucleoli, and a heightened concentration of the fluorescent label surrounding nucleolar structures and at the nuclear membrane. Conversely, coexpression of yellow fluorescent protein-RXR[alpha] and native PPARm[gamma] resulted in a similar distribution of the yellow fluorescent tag. This localization pattern was not discernibly altered by PPAR[gamma] or RXR[alpha]-specific ligands. These results implicate RXR[alpha] in the nuclear reorganization of PPAR[gamma] and suggest that PPAR[gamma] colocalizes with RXR[alpha] at specific locations within the nucleus independent of added ligand.

Copyright (C) 2002 by The Endocrine Society