Adaptor Proteins and Ras Synergistically Regulate IL-1-Induced ADAMTS-4 Expression in Human Chondrocytes

Abstract

Aggrecanases (a dystrophin and metalloproteinase with thrombospondin motif, ADAMTSs) are principal proteases involved in cartilage extracellular matrix aggrecan degradation. The role and relative contribution of MyD88, IRAK1, and TRAF6 adaptor proteins in IL-1β regulation of aggrecanase-1 (ADAMTS-4) is unknown. By small interfering RNAs-mediated knockdown, we show that IL-1β-induced up-regulation of ADAMTS-4 in chondrocytes requires MyD88, IRAK1, and TRAF6 adaptor proteins. However, partial inhibition of ADAMTS-4 induction by their knockdown suggested the involvement of additional signaling proteins. Because IL-1β is also known to induce reactive oxygen species (ROS) through Ras-mediated activation of NADPH oxidase, we investigated the implication of Ras in ADAMTS-4 regulation. Ras knockdown, or inhibition of ROS by antioxidants along with the ablation of MyD88, IRAK1, or TRAF6 more potently down-regulated IL-1β-induced ADAMTS-4. In addition, IL-1β-induced phosphorylation of downstream effectors, IκB kinase αβ, IκBα, and activation of transcription factor NF-κB was significantly reduced in the MyD88-, IRAK1-, TRAF6-, or Ras-deficient cells. The combined knockdown of Ras and individual adaptor proteins strongly blocked the activation of IKKαβ, IκBα, and NF-κB. These findings suggest that Ras, ROS along with MyD88, IRAK1, or TRAF6 synergistically mediate ADAMTS-4 regulation by IL1-β. Thus, complete ablation of ADAMTS-4 induction could be achieved by combined inhibition of Ras and individual adaptor proteins, which may be of therapeutic value in arthritis.

Interleukin-32α production is regulated by MyD88-dependent and independent pathways in IL-1β-stimulated human alveolar epithelial cells

“…It was recently reported that IL-1␤-induced dystrophin and metalloproteinase with thrombospondin motif (ADAMTS)-4 upregulation was only partially inhibited by the knockdown of MyD88, IRAK1, and TNF receptor-associated factor (TRAF)6 (Ahmad et al 2009), suggesting the existence of a MyD88-independent pathway in IL-1R-mediated signaling. In the present study, PKC␦ was phosphorylated by IL-1␤ in human alveolar epithelial cells ( Fig.…”

Anabolic/Catabolic Balance in Pathogenesis of Osteoarthritis: Identifying Molecular Targets

“…A disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)‐4 and ADAMTS‐5, also referred to as aggrecanase‐1 and aggrecanase‐2, are principally responsible for aggrecan degradation in degenerative cartilage diseases. In human osteoarthritis, both ADAMTS‐4 and ADAMTS‐5 are expressed and ADAMTS‐4 is regulated by IL‐1 and TNF‐α [102,103]. In human synoviocytes, expression of ADAMTS‐4 but not ADAMTS‐5 is suppressed by inhibition of TNF‐α or IL‐1β signaling by the TNF‐α blocker Ethernacept or neutralizing IL‐1β antibodies, respectively [102].…”

The role of ADAMTSs in arthritis

“…Furthermore, treatment with oncostatin M and either IL-1β or TNF-α in human chondrocytes or cartilage explants, leads to a marked induction of ADAMTS-4 with a lesser upregulation of ADAMTS-5 (Song et al, 2007). This process seems to be mediated by Ras signaling (Ahmad et al, 2009). Additionally, some data demonstrate that only ADAMTS-4 levels are increased in OA cartilage (Malfait et al, 2002; Roach et al, 2005; Naito et al, 2007).…”