Transcriptional Repression of Matrix Metalloproteinase Gene Expression by the Orphan Nuclear Receptor NURR1 in Cartilage

Abstract

The NR4A orphan receptors (Nur77, NURR1, and NOR-1) are emerging as key regulators of cytokine and growth factor action in chronic inflammatory diseases. In this study, we address the role of these receptors in cartilage homeostasis during inflammatory joint disease. We document for the first time expression of the NR4A receptors in osteoarthritic cartilage. Relative to Nur77 and NOR-1, NURR1 is expressed at the highest level and correlates with cyclooxygenase-2 levels in cartilage. Consistent with this observation, cyclooxygenase-2-derived prostaglandin E 2 (PGE 2 ) rapidly and potently induces NURR1 expression in chondrocytes, suggesting that this receptor may regulate PGE 2 -mediated processes in cartilage. We demonstrate that PGE 2 represses interleukin-1␤-induced matrix metalloproteinase (MMP)-1 and that transient overexpression of NURR1 is sufficient to antagonize expression of this gene. Furthermore, MMP-1 promoter activity is potently suppressed by NURR1, resulting in a significant reduction in endogenous MMP-1 mRNA and secreted pro-MMP-1 protein. In addition, NURR1 selectively antagonizes cytokine-induced MMP-3 and -9 expression with minimal effects on MMP-2 and -13 and tissue inhibitor of matrix metalloproteinases-1 and -2. To explore the molecular mechanisms of NURR1 transrepression, we reveal that this receptor targets a critical region of the MMP-1 promoter (؊1772 to ؊1546 bp) and that repression does not require consensus binding sites for NURR1. We confirm that NURR1 targets a 40-bp promoter sequence that is also positively regulated by ETS transcription factors. Finally, functional studies indicate that transcriptional antagonism exists between NURR1 and ETS1 on the MMP-1 promoter. We propose a protective function for NURR1 in cartilage homeostasis by selectively repressing MMP gene expression during inflammation.Nuclear hormone receptors comprise a large family of tightly regulated transcription factors that play critical roles in normal physiology and disease processes (1). Several of these receptors are activated by ligands such as vitamins and hormones, which cause allosteric changes in the receptors and alter the transcription of target genes. Modulation of these receptors with synthetic ligands has shown great promise in the treatment of cancer and inflammatory diseases (2). In contrast, orphan nuclear receptors control gene expression in the absence of ligands, and elucidating the functions and transcriptional targets of these receptors may also lead to therapeutic advances.The NR4A receptors are a subfamily of orphan nuclear receptors consisting of nerve growth factor-induced clone B (Nur77, NR4A1), NURR1 (nuclear receptor related-1; NR4A2), and NOR-1 (neuron-derived orphan receptor-1; NR4A3) (3). As ligand-independent receptors (4), the activity of these transcription factors is tightly controlled at the level of expression. Nur77, NURR1, and NOR-1 exhibit distinct and overlapping expression patterns in a number of cell and tissue types (3), indicating that these receptors have unique an...

Prostaglandin E2 Exerts Catabolic Effects in Osteoarthritis Cartilage: Evidence for Signaling via the EP4 Receptor

“…Increased MMP-13 expression was accompanied by increased cleavage of collagen and decreased proteoglycan synthesis in cartilage explant cultures. How the divergent synthesis of MMP-1 and -13 is regulated remains unknown, but we have previously reported that up-regulation of the nuclear orphan receptor NURR1 (NR4A2) in OA cartilage causes similar divergent effects, suggesting that the mechanism of PGE 2 on MMP-1 and MMP-13 may be a result of NURR1 activation (NR4A2) (20).…”

“…RNA content was estimated using a spectrophotometer, the 260:280 ratio for purified RNA was ϳ2.0. The integrity of RNA was confirmed using 1% formaldehyde agarose gel electrophoresis (19,20).…”

“…RNA was extracted in TRI Reagent (MRC Labs) for 4 h on a rocker, and total RNA was precipitated with equal volumes of isopropanol. The RNA pellet was further purified using a Qiagen RNeasy mini kit according to the manufacturer's RNA clean-up protocol (19,20).…”

Identification of NURR1 as a Mediator of MIF Signaling During Chronic Arthritis

“…40,42,46 We have previously demonstrated that NURR1 is the major cytokine-regulated member of the NR4A subfamily in inflamed human synovium and cartilage. 38,39,41,44,46 NURR1 characteristically regulates target gene expression through interaction with a specific consensus sequence in the promoters of target genes, known as the nerve growth factor-induced clone B response element (NBRE). 47 Phosphorylation or interaction with other transcription factors and co-regulatory proteins can also influence NURR1-mediated gene regulation.…”

Adenosine regulates thrombomodulin and endothelial protein C receptor expression in folliculostellate cells of the pituitary gland

“…Adenosine, acting in particular through the A2a receptor and NR4A2 has also been shown to mediate the antiinflammatory effects of methotrexate in rheumatoid arthritis [45]. NR4A2 also mediates the repression of matrix metalloproteinases during inflammation [46].…”