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Vol. 18, Issue 3, 930-942, March 2007

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Adipocyte Enhancer-binding Protein-1 Promotes Macrophage Inflammatory Responsiveness by Up-Regulating NF-B via IB Negative Regulation

Department of Biochemistry and Molecular Biology, Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia, Canada B3H 1X5

Submitted March 21, 2006; Revised December 18, 2006; Accepted December 22, 2006
Monitoring Editor: William Tansey

Nuclear factor B (NF-B) subunits comprise a family of eukaryotic transcription factors that are critically involved in cell proliferation, inflammation, and apoptosis. Under basal conditions, NF-B subunits are kept under inhibitory regulation by physical interaction with NF-B inhibitors (IB subunits) in the cytosol. Upon stimulation, IB subunits become phosphorylated, ubiquitinated, and subsequently degraded, allowing NF-B subunits to translocate to the nucleus and bind as dimers to B responsive elements of target genes. Previously, we have shown that AEBP1 enhances macrophage inflammatory responsiveness by inducing the expression of various proinflammatory mediators. Herein, we provide evidence suggesting that AEBP1 manifests its proinflammatory function by up-regulating NF-B activity via hampering IB, but not IB, inhibitory function through protein–protein interaction mediated by the discoidin-like domain (DLD) of AEBP1. Such interaction renders IB susceptible to enhanced phosphorylation and degradation, subsequently leading to augmented NF-B activity. Collectively, we propose a novel molecular mechanism whereby NF-B activity is modulated by means of protein–protein interaction involving AEBP1 and IB. Moreover, our study provides a plausible mechanism explaining the differential regulatory functions exhibited by IB and IB in various cell types. We speculate that AEBP1 may serve as a potential therapeutic target for the treatment of various chronic inflammatory diseases and cancer.

Address correspondence to: Hyo-Sung Ro (hsro{at}dal.ca)

Abbreviations used: AEBP1, adipocyte enhancer-binding protein 1; CHX, cycloheximide; DLD, discoidin-like domain; EMSA, electromobility gel shift assay; IB, inhibitor of NF-B; IKK, IB kinase; LPS, lipopolysaccharide; NF-B, nuclear factor kappa B; TLR4, toll-like receptor 4; t_1/2, half-life.