Volume 5 Supplement 3

3rd World Congress of the Global Arthritis Research Network (GARN): International Arthritis Summit

Open Access

CCAAT/enhancer-binding proteins mediate the repression of transcription of cartilage-derived retinoic acid-sensitive protein induced by IL-1β

  • K Okazaki1,
  • Y Iwamoto1 and
  • L Sandell2
Arthritis Res Ther20035(Suppl 3):60

https://doi.org/10.1186/ar861

Published: 12 September 2003

Introduction

IL-1β is one of the major proinflammatory cytokines involved in arthritis joints. IL-1β promotes the arachidonic acid cascade, resulting in production of prostaglandin. In addition, IL-1β represses the expression of matrix proteins in cartilage, such as type II, type IX and type XI collagen and cartilage-derived retinoic acid-sensitive protein (CD-RAP), leading to degradation of the cartilage structures.

Objective

To investigate the transcriptional mechanism by which CD-RAP expression is repressed by IL-1β.

Methods and results

Deletion constructs of the CD-RAP promoter were transfected into rat chondrocytes and incubated in the absence or presence of IL-1β. The results revealed an IL-1β-responsive element located between -2138 and -2068 bp. As this element contains the CCAAT/enhancer-binding protein (C/EBP) motif, the function of C/EBP-β was examined. IL-1β stimulated the expression of C/EBP-β. The direct binding of C/EBP-β to the C/EBP motif was confirmed by electrophoretic mobility shift assay. Expression of the -2251 bp CD-RAP promoter construct was downregulated by cotransfection with C/EBP-β expression vectors in a dose-dependent manner. Mutation of the C/EBP motif within the -2251 bp construct abolished the inhibitory response to IL-1β. These results suggest that C/EBP-β is a critical factor mediating IL-1β-induced repression of CD-RAP transcription. C/EBP-β expression vectors were also found to downregulate the reporter construct containing the promoter and enhancer of the type II collagen gene. The IL-1β-induced repression of CD-RAP and type II collagen genes via stimulation of C/EBP-β were confirmed in chondrocytes from normal human articular cartilage. Finally, the enhancer factor, Sox9, known to be downregulated by IL-1, was shown to bind adjacent to the C/EBP site competing with C/EBP binding.

Discussion

C/EBP-β is known to mediate the arachidonic acid cascade induced by IL-1β. These results suggest that C/EBP-β play an important role in the distinct effects of IL-1β : the promotion of inflammatory reaction and the repression of cartilage-specific proteins in joint disease. Expression of matrix proteins are influenced by availability of both positive and negative transacting factors.

Authors’ Affiliations

(1)
Department of Orthopaedic Surgery, Graduate School of Medical Sciences, Kyushu University
(2)
Department of Orthopaedic Surgery, Washington University School of Medicine

Copyright

© The Author(s) 2003

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