Identification of NR4A2 as a transcriptional activator of IL-8 expression in human inflammatory arthritis.
Expression of the orphan nuclear receptor NR4A2 is controlled by pro-inflammatory mediators, suggesting that NR4A2 may contribute to pathological processes in the inflammatory lesion. This study identifies the chemoattractant protein, interleukin 8 (IL-8/CXCL8), as a molecular target of NR4A2 in human inflammatory arthritis and examines the mechanism through which NR4A2 modulates IL-8 expression. In TNF-alpha-activated human synoviocyte cells, enhanced expression of IL-8 mRNA and protein correspond to temporal changes in NR4A2 transcription and nuclear distribution. Ectopic expression of NR4A2 leads to robust changes in endogenous IL-8 mRNA levels and co-treatment with TNF-alpha results in significant (p<0.001) secretion of IL-8 protein. Transcriptional effects of NR4A2 on the human IL-8 promoter are enhanced in the presence of TNF-alpha, suggesting molecular crosstalk between TNF-alpha signalling and NR4A2. A dominant negative IkappaB kinase antagonizes the combined effects of NR4A2 and TNF-alpha on IL-8 promoter activity. Co-expression of NR4A2 and the p65 subunit of NF-kappaB enhances IL-8 transcription and functional studies indicate that transactivation occurs independently of NR4A2 binding to DNA or heterodimerization with additional nuclear receptors. The IL-8 minimal promoter region is sufficient to support NR4A2 and NF-kappaB/p65 co-operative activity and NR4A2 can interact with NF-kappaB/p65 on a 39bp sequence within this region. In patients treated with methotrexate for active inflammatory arthritis, a reduction in NR4A2 synovial tissue levels correlate significantly (n=10, r=0.73, p=0.002) with changes in IL-8 expression. Collectively, these data delineate an important role for NR4A2 in modulating IL-8 expression and reveal novel transcriptional responses to TNF-alpha in human inflammatory joint disease.
Aherne
Carol M
CM
College of Life Sciences, UCD Veterinary Sciences Centre, University College Dublin, Belfield, Dublin 4, Ireland.
McMorrow
Jason
J
Kane
David
D
FitzGerald
Oliver
O
Mix
Kimberlee S
KS
Murphy
Evelyn P
EP
D021581:Active Transport, Cell Nucleus / Q000235:genetics / Q000276:immunology; D001168:Arthritis / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D002467:Cell Nucleus / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D016209:Interleukin-8 / Q000096:biosynthesis* / Q000235:genetics / Q000276:immunology; D008297:Male; D057126:Nuclear Receptor Subfamily 4, Group A, Member 2; D011401:Promoter Regions, Genetic / Q000235:genetics / Q000276:immunology; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology; D013583:Synovial Membrane / Q000276:immunology / Q000378:metabolism*; D051996:Transcription Factor RelA / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000276:immunology / Q000378:metabolism
C508606:CXCL8 protein, human; D004268:DNA-Binding Proteins; D016209:Interleukin-8; C539882:NR4A2 protein, human; D057126:Nuclear Receptor Subfamily 4, Group A, Member 2; C498143:RELA protein, human; D012333:RNA, Messenger; D051996:Transcription Factor RelA; D014157:Transcription Factors; D014409:Tumor Necrosis Factor-alpha