Details

Autor(en) / Beteiligte

• Singh, Anil K
• Umar, Sadiq
• Riegsecker, Sharayah
• Chourasia, Mukesh
• Ahmed, Salahuddin

Titel

Regulation of Transforming Growth Factor [beta]-Activated Kinase Activation by Epigallocatechin-3-Gallate in Rheumatoid Arthritis Synovial Fibroblasts: Suppression of K63-Linked Autoubiquitination of Tumor Necrosis Factor Receptor-Associated Factor 6

Ist Teil von

• Arthritis & rheumatology (Hoboken, N.J.), 2016-02, Vol.68 (2), p.347

Ort / Verlag

Atlanta: Wiley Subscription Services, Inc

Erscheinungsjahr

2016

Quelle

Wiley Online Library Journals【Remote access available】

Beschreibungen/Notizen

• Objective Transforming growth factor [beta]-activated kinase 1 (TAK1) is a key MAPKKK family protein in interleukin-1[beta] (IL-1[beta]), tumor necrosis factor (TNF), and Toll-like receptor signaling. This study was undertaken to examine the posttranslational modification of TAK1 and its therapeutic regulation in rheumatoid arthritis (RA). Methods The effect of TAK1, IL-1 receptor-associated kinase 1 (IRAK-1), and TNF receptor-associated factor 6 (TRAF6) inhibition was evaluated in IL-1[beta]-stimulated human RA synovial fibroblasts (RASFs). Western blotting, immunoprecipitation, and 20S proteasome assay were used to study the ubiquitination process in RASFs. The efficacy of epigallocatechin-3-gallate (EGCG), a potent antiinflammatory molecule, in regulating these processes in RASFs was evaluated. Molecular docking was performed to examine the interaction of EGCG with human TAK1, IRAK-1, and TRAF6. These findings were confirmed using a rat model of adjuvant-induced arthritis (AIA). Results Inhibition of TAK1, but not IRAK-1 or TRAF6, completely abrogated IL-1[beta]-induced IL-6 and IL-8 synthesis in RASFs. EGCG inhibited TAK1 phosphorylation at Thr184/187 and occupied the C174 position, an ATP-binding site, to inhibit its kinase activity. EGCG pretreatment also inhibited K63-linked autoubiquitination of TRAF6, a posttranslational modification essential for TAK1 autophosphorylation, by forming a stable H bond at the K124 position on TRAF6. Furthermore, EGCG enhanced proteasome-associated deubiquitinase expression to rescue proteins from proteasomal degradation. Western blot analyses of joint homogenates from rats with AIA showed a significant increase in K48-linked polyubiquitination, TAK1 phosphorylation, and TRAF6 expression when compared to naive rats. Administration of EGCG (50 mg/kg/day) for 10 days ameliorated AIA in rats by reducing TAK1 phosphorylation and K48-linked polyubiquitination. Conclusion Our findings provide a rationale for targeting TAK1 for the treatment of RA with EGCG.