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A more recent version of this article appeared on February 10, 2006
Papers In Press, published online ahead of print November 22, 2005
J. Biol. Chem, 10.1074/jbc.M509417200
Submitted on August 25, 2005
Revised on November 9, 2005
Accepted on November 22, 2005
A novel functional interaction between the Sp1-like protein KLF13 and SREBP/Sp1 activation complex underlies regulation of low density lipoprotein-receptor promoter function
Sekar Natesampillai, Martin E. Fernandez-Zapico, Raul Urrutia, and Johannes D. Veldhuis
Endocrine Research Unit, Department of Internal Medicine, Mayo Clinic College of Medicine, Rochester, MN 55905
Corresponding Author: veldhuis.johannes{at}mayo.edu
Cholesterol homeostasis is regulated by a family of transcription factors designated sterol regulatory-element binding proteins (SREBPs). Precise control of SREBP-targeted genes requires additional interactions with coregulatory transcription factors. In the case of the low-density lipoprotein receptor (LDLR), SREBP cooperates with the specificity protein, Sp1, to activate the promoter. In this report, we describe a novel pathway in LDLR transcriptional regulation distinct from the SREBP/Sp1 activation complex involving the Sp1-like protein, Krueppel-like factor 13 (KLF13). Using a combination of RNA interference, electrophoretic mobility-shift, chromatin-immunoprecipitation (ChIP) and reporter assays, deletion and site-directed mutagenesis, we demonstrate that KLF13 mediates repression in a DNA context-selective manner. KLF13s repression of LDLR promoter activity appears to be needed to keep the receptor silent, a state that can be antagonized by Sp1, SREBP and inhibitors of histone deacetylase activity. ChIP assay confirmed that KLF13 binds proximal LDLR DNA sequences in vivo, and that exogenous oxysterol upregulates such binding. Together these studies identify a novel regulatory pathway, in which gene repression by KLF13 must be overcome by the Sp1/SREBP complex in order to activate the LDLR promoter. Therefore, these data should replace a preexistent and more simple paradigm that takes into consideration only induction of the activator proteins Sp1/SREBP as necessary for LDLR promoter drive without including default repression, such as that by KLF13, of the LDLR gene.

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Copyright © 2005 by the American Society for Biochemistry and Molecular Biology.
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