A novel functional interaction between the Sp1-like protein KLF13 and SREBP-Sp1 activation complex underlies regulation of low density lipoprotein receptor promoter function.
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 co-regulatory 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, and reporter assays, deletion, and site-directed mutagenesis, we demonstrated that KLF13 mediates repression in a DNA context-selective manner. KLF13 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. Chromatin immunoprecipitation assay confirmed that KLF13 binds proximal LDLR DNA sequences in vivo and that exogenous oxysterol up-regulates such binding. Together these studies identify a novel regulatory pathway in which gene repression by KLF13 must be overcome by the Sp1-SREBP complex to activate the LDLR promoter. Therefore, these data should replace a pre-existent and more simple paradigm that takes into consideration only the 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.
Natesampillai
Sekar
S
Endocrine Research Unit and Gastroenterology Research Unit, Department of Internal Medicine, Mayo School of Graduate Medical Education, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA.
Fernandez-Zapico
Martin E
ME
Urrutia
Raul
R
Veldhuis
Johannes D
JD
D000818:Animals; D015153:Blotting, Western; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D047369:Chromatin Immunoprecipitation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005640:Follicle Stimulating Hormone / Q000378:metabolism; D017353:Gene Deletion; D017930:Genes, Reporter; D005982:Glutathione Transferase / Q000378:metabolism; D006107:Granulosa Cells / Q000166:cytology; D056572:Histone Deacetylase Inhibitors; D006655:Histone Deacetylases / Q000378:metabolism; D051741:Kruppel-Like Transcription Factors / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010053:Ovary / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D011973:Receptors, LDL / Q000235:genetics*; D011987:Receptors, Steroid / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry; D012097:Repressor Proteins / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016329:Sp1 Transcription Factor / Q000378:metabolism*; D051780:Sterol Regulatory Element Binding Protein 1 / Q000378:metabolism; D051782:Sterol Regulatory Element Binding Protein 2 / Q000378:metabolism; D051779:Sterol Regulatory Element Binding Proteins / Q000378:metabolism*; D013552:Swine; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection; D015854:Up-Regulation; D000098825:Oxysterol Binding Proteins
D018797:Cell Cycle Proteins; D004791:Enzyme Inhibitors; D056572:Histone Deacetylase Inhibitors; C486423:KLF13 protein, human; D051741:Kruppel-Like Transcription Factors; D034741:RNA, Small Interfering; D011973:Receptors, LDL; D011987:Receptors, Steroid; D011994:Recombinant Proteins; D012097:Repressor Proteins; D016329:Sp1 Transcription Factor; D051780:Sterol Regulatory Element Binding Protein 1; D051782:Sterol Regulatory Element Binding Protein 2; D051779:Sterol Regulatory Element Binding Proteins; D000098825:Oxysterol Binding Proteins; D005640:Follicle Stimulating Hormone; D005982:Glutathione Transferase; D006655:Histone Deacetylases