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Molecular and Cellular Biology, April 2005, p. 2946-2956, Vol. 25, No. 8
0270-7306/05/$08.00+0     doi:10.1128/MCB.25.8.2946-2956.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Spatial Distribution and Function of Sterol Regulatory Element-Binding Protein 1a and 2 Homo- and Heterodimers by In Vivo Two-Photon Imaging and Spectroscopy Fluorescence Resonance Energy Transfer

Aikaterini Zoumi,1,{dagger} Shrimati Datta,2,{dagger} Lih-Huei L. Liaw,1 Cristen J. Wu,1 Gopi Manthripragada,1,{ddagger} Timothy F. Osborne,2 and Vickie J. LaMorte1*

Laser Microbeam and Medical Program, Beckman Laser Institute, Department of Surgery,1 Department of Molecular Biology and Biochemistry, University of California, Irvine, California2

Received 10 September 2004/ Returned for modification 15 October 2004/ Accepted 4 January 2005

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.

* Corresponding author. Mailing address: University of California, Irvine, Beckman Laser Institute, 1002 Health Sciences Rd., East Irvine, CA 92612. Phone: (949) 824-3513. Fax: (949) 824-8413. E-mail: lamorte{at}uci.edu.

{dagger} A.Z. and S.D. contributed equally to this work.

{ddagger} Present address: Department of Medicine, Georgetown University, Washington, D.C.

Molecular and Cellular Biology, April 2005, p. 2946-2956, Vol. 25, No. 8
0022-538X/05/$08.00+0     doi:10.1128/MCB.25.8.2946-2956.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.





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