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(Circulation Research. 2006;99:e88.)
© 2006 American Heart Association, Inc.

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A Nuclear Receptor Corepressor–Dependent Pathway Mediates Suppression of Cytokine-Induced C-Reactive Protein Gene Expression by Liver X Receptor

Florian Blaschke, Yasunori Takata, Evren Caglayan, Alan Collins, Peter Tontonoz, Willa A. Hsueh, Rajendra K. Tangirala

From the Division of Endocrinology, Diabetes and Hypertension (F.B., Y.T., E.C., A.C., W.A.H., R.K.T.), David Geffen School of Medicine, University of California, Los Angeles; Department of Molecular and Genetic Medicine (Y.T.), Ehime University Graduate School of Medicine, Japan; Howard Hughes Medical Institute, Molecular Biology Institute, and Department of Pathology and Laboratory Medicine (P.T.), University of California, Los Angeles; and Max-Delbrueck Center for Molecular Medicine, Department of Molecular and Clinical Cardiology (F.B.), Franz-Volhard Clinic, HELIOS Clinics GmbH, Charité, Humboldt University, Berlin, Germany.

Correspondence to Rajendra K. Tangirala, PhD, Assistant Professor of Medicine, Division of Endocrinology, Diabetes and Hypertension, David Geffen School of Medicine, University of California, Los Angeles, CA 90095. E-mail rtangirala{at}mednet.ucla.edu

C-reactive protein (CRP), the prototypical human acute phase protein, is an independent risk predictor of future cardiovascular events, both in healthy individuals and in patients with known cardiovascular disease. In addition, previous studies indicate that CRP might have direct proatherogenic properties. Ligand activation of the liver X receptor (LXR), a member of the nuclear hormone receptor superfamily, inhibits inflammatory gene expression in macrophages and attenuates the development of atherosclerosis in various animal models. We demonstrate herein that 2 synthetic LXR ligands, T0901317 and GW3965, inhibit interleukin-1ß/interleukin-6–induced CRP mRNA and protein expression in human hepatocytes. Knockdown of LXR/ß by short interfering RNAs completely abolished the inhibitory effect of the LXR agonist T0901317 on cytokine-induced CRP gene transcription. Transient transfection experiments with 5'-deletion CRP promoter constructs identified a region from –125 to –256 relative to the initiation site that mediated the inhibitory effect of LXR ligands on CRP gene transcription. Depletion of the nuclear receptor corepressor by specific short interfering RNA increased cytokine-inducible CRP mRNA expression and promoter activity and reversed LXR ligand–mediated repression of CRP gene transcription. Chromatin immunoprecipitation assays indicated that nuclear receptor corepressor is present on the endogenous CRP promoter under basal conditions. Cytokine-induced clearance of nuclear receptor corepressor complexes was inhibited by LXR ligand treatment, maintaining the CRP gene in a repressed state. Finally, treatment of C57Bl6/J mice with LXR ligands attenuated lipopolysaccharide-induced mouse CRP and serum amyloid P component gene expression in the liver, whereas no effect was observed in LXRß knockout mice. Our observations identify a novel mechanism of inflammatory gene regulation by LXR ligands. Thus, inhibition of CRP expression by LXR agonists may provide a promising approach to impact initiation and progression of atherosclerosis.

Key Words: C-reactive protein • liver X receptor • nuclear receptor corepressor

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