SREBP-1c and Sp1 interact to regulate transcription of the gene for phosphoenolpyruvate carboxykinase (GTP) in the liver.
The sterol regulatory element-binding protein-1c (SREBP-1c), as well as SREBP-1a and SREBP-2, inhibit transcription of the gene encoding the cytosolic form of phosphoenolpyruvate carboxykinase (GTP) (PEPCK-C). There are two SREBP regulatory elements (SREs) in the PEPCK-C gene promoter (-322 to -313 and -590 to -581). The SRE at -590 overlaps an Sp1 site on the opposite strand of the DNA. These SREs bound SREBP-1a and SREBP-1c with low affinity but the addition of purified upstream stimulatory activity enhanced the binding of SREBP-1 to both of these sites. Mutating these SREs increased both unstimulated (5-fold) and protein kinase A-stimulated transcription (8-27-fold) from the PEPCK-C gene promoter; this was lost when both SREs were mutated. The SRE at -590 differs by a single base pair from the SRE in the low density lipoprotein (LDL) receptor gene (T in the PEPCK-C gene promoter at -582, compared with an A in the SRE of the gene for the LDL receptor promoter). Introduction of the LDL receptor SRE into the PEPCK-C gene promoter increased SREBP-1c binding and caused a 10-fold enhancement of basal transcription from the promoter, rather than an inhibition as observed with the SRE in the PEPCK-C gene promoter. The T/A change does not alter the binding of Sp1 to its site on the opposite strand of the DNA. Sp1 bound to the promoter independently of SREBP-1c but competed with SREBP-1c for binding. Sp1 does not bind to the SRE at -322. Chromatin immunoprecipitation analysis, using rat hepatocytes, demonstrated that SREBP-1 and Sp1 were associated in vivo with putative regulatory regions corresponding to the SREs in the PEPCK-C gene promoter. We propose that insulin represses transcription of the gene for PEPCK-C by inducing SREBP-1c production in the liver, which interferes with the stimulatory effect of Sp1 at -590 of the PEPCK-C gene promoter.
Chakravarty
Kaushik
K
Department of Biochemistry, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106-4935, USA. kxc23@cwru.edu
Wu
Shwu-Yuan
SY
Chiang
Cheng-Ming
CM
Samols
David
D
Hanson
Richard W
RW
D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D022762:CCAAT-Enhancer-Binding Proteins / Q000502:physiology*; D002460:Cell Line; D002843:Chromatin / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D005799:Genes, Dominant; D017930:Genes, Reporter; D005822:Genetic Vectors; D005979:Glutathione Peroxidase; D006801:Humans; D008077:Lipoproteins, LDL / Q000378:metabolism; D008099:Liver / Q000201:enzymology* / Q000378:metabolism; D008156:Luciferases / Q000378:metabolism; D008957:Models, Genetic; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010729:Phosphoenolpyruvate Carboxykinase (GTP) / Q000235:genetics* / Q000378:metabolism*; D011233:Precipitin Tests; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D020033:Protein Isoforms; D011506:Proteins / Q000235:genetics / Q000502:physiology*; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry; D016329:Sp1 Transcription Factor / Q000378:metabolism / Q000502:physiology*; D051780:Sterol Regulatory Element Binding Protein 1; D051782:Sterol Regulatory Element Binding Protein 2; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D014162:Transfection
D022762:CCAAT-Enhancer-Binding Proteins; D002843:Chromatin; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D008077:Lipoproteins, LDL; D020033:Protein Isoforms; D011506:Proteins; D011994:Recombinant Proteins; C497387:SREBF1 protein, human; C497390:SREBF2 protein, human; D016329:Sp1 Transcription Factor; C497389:Srebf1 protein, rat; D051780:Sterol Regulatory Element Binding Protein 1; D051782:Sterol Regulatory Element Binding Protein 2; D014157:Transcription Factors; C014149:phosphoenolpyruvate carboxykinase ferroactivator protein, rat; D005979:Glutathione Peroxidase; D008156:Luciferases; D017868:Cyclic AMP-Dependent Protein Kinases; D010729:Phosphoenolpyruvate Carboxykinase (GTP)