HSP27 regulates IL-1 stimulated IKK activation through interacting with TRAF6 and affecting its ubiquitination

Heat shock protein 27 (HSP27) is an ubiquitiously expressed protein, which has been mediated in various biological functions. Here, we present a novel mechanism utilized by HSP27 in regulating IL-1beta induced NF-small ka, CyrillicB activation. Both over-expression and RNAi experiments indicate that HSP27 physically interacts with tumor necrosis factor receptor-associated factor 6 (TRAF6) and promotes TRAF6 ubiquitination. Over-expressed HSP27 augments IL-1beta induced TRAF6 ubiquitination and Ismall ka, CyrillicB kinase (IKK) activation. On the other hand, IL-1beta stimulation reduces endogenous HSP27/TRAF6 association, but inhibiting HSP27 phosphorylation by using SB202190, an inhibitor of p38, and MAPKAPK2 RNAi increases HSP27/TRAF6 association and thereby enhances TRAF6 ubiquitination, IKK phosphorylation as well as NF-small ka, CyrillicB activation. Furthermore, co-transfection study shows that HSP27 S78/82A, two phosphorylated serine site deficient mutants, but not wild-type HSP27 (HSP27 WT) and HSP27 S15A mutant increases TRAF6 ubiquitination and thereby mediates IL-1beta triggered IKK phosphorylation. Taken together, our data indicate that HSP27 regulates IL-1beta triggered NF-small ka, CyrillicB activation via a feedback loop which includes the interaction between HSP27 phosphorylation and ability of HSP27 to bind with TRAF6. The findings of this study reveal a novel mechanism by which HSP27 controls cytokine stimulation.