Abstract
Sterol regulatory element-binding proteins (SREBPs) are a subfamily of basic helix-loop-helix-leucine zipper proteins that regulate lipid metabolism. We show novel evidence of the in vivo occurrence and subnuclear spatial localization of both exogenously expressed SREBP-1a and -2 homodimers and heterodimers obtained by two-photon imaging and spectroscopy fluorescence resonance energy transfer. SREBP-1a homodimers localize diffusely in the nucleus, whereas SREBP-2 homodimers and the SREBP-1a/SREBP-2 heterodimer localize predominantly to nuclear speckles or foci, with some cells showing a diffuse pattern. We also used tethered SREBP dimers to demonstrate that both homo- and heterodimeric SREBPs activate transcription in vivo. Ultrastructural analysis revealed that the punctate foci containing SREBP-2 are electron-dense nuclear bodies, similar or identical to structures containing the promyelocyte (PML) protein. Immunofluorescence studies suggest that a dynamic interplay exists between PML, as well as another component of the PML-containing nuclear body, SUMO-1, and SREBP-2 within these nuclear structures. These findings provide new insight into the overall process of transcriptional activation mediated by the SREBP family.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, Non-P.H.S.
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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CCAAT-Enhancer-Binding Proteins / analysis*
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CCAAT-Enhancer-Binding Proteins / genetics
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CCAAT-Enhancer-Binding Proteins / physiology*
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Cell Line
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Cell Nucleus / chemistry*
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Cell Nucleus / metabolism
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Cell Nucleus / ultrastructure
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DNA-Binding Proteins / analysis*
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DNA-Binding Proteins / genetics
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DNA-Binding Proteins / physiology*
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Dimerization
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Fluorescence Resonance Energy Transfer
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Genes, Reporter / genetics
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Humans
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Lipid Metabolism
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Luciferases / analysis
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Luciferases / genetics
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Neoplasm Proteins / analysis
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Neoplasm Proteins / metabolism
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Nuclear Proteins / analysis
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Nuclear Proteins / metabolism
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Photons
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Promoter Regions, Genetic / genetics
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Promyelocytic Leukemia Protein
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Protein Structure, Tertiary
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Receptors, LDL / genetics
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SUMO-1 Protein / analysis
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SUMO-1 Protein / metabolism
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Sequence Deletion
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Sterol Regulatory Element Binding Protein 1
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Sterol Regulatory Element Binding Protein 2
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Transcription Factors / analysis*
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Transcription Factors / genetics
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Transcription Factors / metabolism
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Transcription Factors / physiology*
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Transcription, Genetic
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Transcriptional Activation*
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Tumor Suppressor Proteins
Substances
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CCAAT-Enhancer-Binding Proteins
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DNA-Binding Proteins
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Neoplasm Proteins
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Nuclear Proteins
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Promyelocytic Leukemia Protein
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Receptors, LDL
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SREBF1 protein, human
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SREBF2 protein, human
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SUMO-1 Protein
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Sterol Regulatory Element Binding Protein 1
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Sterol Regulatory Element Binding Protein 2
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Transcription Factors
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Tumor Suppressor Proteins
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PML protein, human
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Luciferases