TY - JOUR
T1 - Regulation of Transforming Growth Factor β-Activated Kinase Activation by Epigallocatechin-3-Gallate in Rheumatoid Arthritis Synovial Fibroblasts
T2 - Suppression of K63-Linked Autoubiquitination of Tumor Necrosis Factor Receptor-Associated Factor 6
AU - Singh, Anil K.
AU - Umar, Sadiq
AU - Riegsecker, Sharayah
AU - Chourasia, Mukesh
AU - Ahmed, Salahuddin
N1 - Publisher Copyright:
© 2015, American College of Rheumatology.
PY - 2016/2/1
Y1 - 2016/2/1
N2 - Objective Transforming growth factor β-activated kinase 1 (TAK1) is a key MAPKKK family protein in interleukin-1β (IL-1β), 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-1β-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-1β-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.
AB - Objective Transforming growth factor β-activated kinase 1 (TAK1) is a key MAPKKK family protein in interleukin-1β (IL-1β), 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-1β-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-1β-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.
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U2 - 10.1002/art.39447
DO - 10.1002/art.39447
M3 - Article
C2 - 26473505
AN - SCOPUS:84956810331
SN - 2326-5191
VL - 68
SP - 347
EP - 358
JO - Arthritis and Rheumatology
JF - Arthritis and Rheumatology
IS - 2
ER -