Selective intranuclear redistribution of PPAR isoforms by RXR alpha.
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.
Akiyama
Taro E
TE
Laboratory of Metabolism, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
Baumann
Christopher T
CT
Sakai
Shuichi
S
Hager
Gordon L
GL
Gonzalez
Frank J
FJ
D021581:Active Transport, Cell Nucleus; D000409:Alanine / Q000378:metabolism; D019943:Amino Acid Substitution; D000818:Animals; D015153:Blotting, Western; D002467:Cell Nucleus / Q000378:metabolism; D019281:Dimerization; D049452:Green Fluorescent Proteins; D051548:Histone Acetyltransferases; D006801:Humans; D008024:Ligands; D008164:Luminescent Proteins / Q000235:genetics; D051379:Mice; D008856:Microscopy, Fluorescence; D009687:Nuclear Proteins / Q000378:metabolism; D056971:Nuclear Receptor Co-Repressor 1; D056920:Nuclear Receptor Coactivator 1; D010766:Phosphorylation; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D018168:Receptors, Retinoic Acid / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism; D047488:Retinoid X Receptors; D012694:Serine / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D008024:Ligands; D008164:Luminescent Proteins; C539127:NCOR1 protein, human; C539128:Ncor1 protein, mouse; D009687:Nuclear Proteins; D056971:Nuclear Receptor Co-Repressor 1; D018160:Receptors, Cytoplasmic and Nuclear; D018168:Receptors, Retinoic Acid; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D047488:Retinoid X Receptors; D014157:Transcription Factors; D049452:Green Fluorescent Proteins; D012694:Serine; D051548:Histone Acetyltransferases; C538859:NCOA1 protein, human; C538861:Ncoa1 protein, mouse; D056920:Nuclear Receptor Coactivator 1; D000409:Alanine