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Author Notes:

Address all correspondence and requests for reprints to: Frank A. Anania, Division of Digestive Diseases, Department, of Medicine, Emory University School of Medicine, Room, 248, Whitehead Biomedical Research Building, 615 Michael, Street, Atlanta, Georgia 30322. Email: fanania@emory.edu.

The authors have nothing to disclose.

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Research Funding:

This work was supported by National Institutes of Health Grants DK062092 and DK064399.

Leptin Increases Tissue Inhibitor of Metalloproteinase I (TIMP-1) Gene Expression by a Specificity Protein 1/Signal Transducer and Activator of Transcription 3 Mechanism

Tools:

Journal Title:

Molecular Endocrinology -Baltimore-

Volume:

Volume 20, Number 12

Publisher:

, Pages 3376-3388

Type of Work:

Article | Post-print: After Peer Review

Abstract:

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.

Copyright information:

© 2006 by The Endocrine Society

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