title: Orphan nuclear receptor NR4A2 induces synoviocyte proliferation, invasion, and matrix metalloproteinase 13 transcription.
abstract: OBJECTIVE
  To address the role of the nuclear receptor 4A (NR4A) family of orphan nuclear receptors in synoviocyte transformation, hyperplasia, and regulation of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) in models of inflammatory arthritis.
  
  
  METHODS
  NR4A messenger RNA levels in synovial tissue and primary synoviocytes were measured by quantitative reverse transcription-polymerase chain reaction (RT-PCR). NR4A2 was stably overexpressed in normal synoviocytes, and cell proliferation, survival, anchorage-independent growth, migration, and invasion were monitored in vitro. MMP and TIMP expression levels were analyzed by quantitative RT-PCR, and MMP-13 promoter activity was measured using reporter assays. Stable depletion of endogenous NR4A levels was achieved by lentiviral transduction of NR4A short hairpin RNA (shRNA), and the effects on proliferation, migration, and MMP-13 expression were analyzed.
  
  
  RESULTS
  NR4A2 was expressed at elevated levels in normal, OA, and RA synovial tissue and in primary RA synoviocytes. Tumor necrosis factor α (TNFα) rapidly and selectively induced expression of NR4A2 in synoviocytes. Ectopic expression of NR4A2 in normal synoviocytes significantly increased proliferation and survival, promoted anchorage-independent growth, and induced migration and invasion. MMP-13 gene expression was synergistically induced by NR4A2 and TNFα, while expression of TIMP-2 was antagonized. NR4A2 directly transactivated the proximal MMP-13 promoter, and a point mutation in the DNA binding domain of NR4A2 abolished transcriptional activation. Depletion of endogenous NR4A receptors with shRNA reduced synoviocyte proliferation, migration, and MMP-13 expression.
  
  
  CONCLUSIONS
  The orphan nuclear receptor NR4A2 is a downstream mediator of TNFα signaling in synovial tissue. NR4A2 transcriptional activity contributes to the hyperplastic and invasive phenotype of synoviocytes that leads to cartilage destruction, suggesting that this receptor may show promise as a therapeutic target in inflammatory arthritis.
authors.affiliation: Loyola University New Orleans, Department of Biological Sciences, New Orleans, Louisiana 70118, USA. kix@loyno.edu
authors.forename: Kimberlee S
authors.initials: KS
authors.lastname: Mix
authors.forename: Kevin
authors.initials: K
authors.lastname: McMahon
authors.forename: Jason P
authors.initials: JP
authors.lastname: McMorrow
authors.forename: Dana E
authors.initials: DE
authors.lastname: Walkenhorst
authors.forename: Aisling M
authors.initials: AM
authors.lastname: Smyth
authors.forename: Brenda L
authors.initials: BL
authors.lastname: Petrella
authors.forename: Martina
authors.initials: M
authors.lastname: Gogarty
authors.forename: Ursula
authors.initials: U
authors.lastname: Fearon
authors.forename: Douglas
authors.initials: D
authors.lastname: Veale
authors.forename: Mukundan G
authors.initials: MG
authors.lastname: Attur
authors.forename: Steven B
authors.initials: SB
authors.lastname: Abramson
authors.forename: Evelyn P
authors.initials: EP
authors.lastname: Murphy
mesh_terms: D001172:Arthritis, Rheumatoid / Q000235:genetics* / Q000378:metabolism; D002465:Cell Movement / Q000235:genetics*; D049109:Cell Proliferation; D006801:Humans; D053509:Matrix Metalloproteinase 13 / Q000235:genetics* / Q000378:metabolism; D057126:Nuclear Receptor Subfamily 4, Group A, Member 2 / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics; D013583:Synovial Membrane / Q000166:cytology / Q000378:metabolism*; D019714:Tissue Inhibitor of Metalloproteinases / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: C539882:NR4A2 protein, human; D057126:Nuclear Receptor Subfamily 4, Group A, Member 2; D019714:Tissue Inhibitor of Metalloproteinases; D053509:Matrix Metalloproteinase 13