Leptin increases tissue inhibitor of metalloproteinase I (TIMP-1) gene expression by a specificity protein 1/signal transducer and activator of transcription 3 mechanism.
Leptin has properties of a profibrogenic cytokine. In liver, the activated hepatic stellate cell (HSC) is responsible for a net production of extracellular matrix. A key molecule synthesized is the tissue inhibitor of metalloproteinase I (TIMP-1), which acts to inhibit the activity of matrix metalloproteinases. The purpose of the present ... study was to determine how leptin, a gp130 cytokine, orchestrates the regulation of TIMP-1 gene activation and expression. Transient transfection of primary HSCs revealed that leptin significantly increased luciferase activity of a 229-bp TIMP-1 promoter construct (TIMP-1-229). An EMSA revealed that leptin enhanced specificity protein 1 (Sp1) binding. Site-directed mutagenesis for Sp1 reduced the enhancing effect of leptin on TIMP-1 transcriptional activation, and this effect was dose dependent on the number of Sp1 sites mutated. Chromatin immunoprecipitation revealed that leptin enhanced binding of Sp1; however, inhibition of signal transducer and activator of transcription (STAT) 3 phosphorylation by AG490 also blocked Sp1 phosphorylation and significantly reduced leptin-associated TIMP-1-229 promoter activity, indicating that one mechanism for leptin-increased transcriptional activity is via phosphorylation of Sp1 and subsequent promoter binding. Finally, we demonstrate that leptin also results in intranuclear pSTAT3 binding to Sp1. We propose a novel mechanism whereby leptin-mediated TIMP-1 transcription employs a Sp1/pSTAT3-dependent mechanism, one of which is a noncanonical association between Sp1 and pSTAT3. These data provide a new molecular mechanism whereby the adipocytokine leptin plays a role in complications of the metabolic syndrome.
Mesh Terms:
Animals, Base Sequence, Chromatin Immunoprecipitation, Gene Expression, Gene Expression Regulation, Leptin, Liver, Molecular Sequence Data, Oligonucleotides, Phosphorylation, Promoter Regions, Genetic, RNA, Messenger, Rats, STAT3 Transcription Factor, Sequence Deletion, Sp1 Transcription Factor, Sp3 Transcription Factor, Tissue Inhibitor of Metalloproteinase-1, Transcriptional Activation
Animals, Base Sequence, Chromatin Immunoprecipitation, Gene Expression, Gene Expression Regulation, Leptin, Liver, Molecular Sequence Data, Oligonucleotides, Phosphorylation, Promoter Regions, Genetic, RNA, Messenger, Rats, STAT3 Transcription Factor, Sequence Deletion, Sp1 Transcription Factor, Sp3 Transcription Factor, Tissue Inhibitor of Metalloproteinase-1, Transcriptional Activation
Mol. Endocrinol.
Date: Dec. 01, 2006
PubMed ID: 16931573
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