Heat Shock Protein 90 (Hsp90) Regulates The Stability Of TAK1 In IL-1β-induced Cell Signaling

Heat shock protein 90(Hsp90),the member of HSP90 family,is composed of three structure domain:a N-terminal conserved ATPase domain,a middle domain and a C-terminal domain that mediates Hsp90 dimerization.Hsp90 is an abundant and ubiquitously expressed chaperone,majority of whose client proteins are steroid hormone receptors,protein kinases,and transcription factors and play a key role in signal transduction pathways.GA or RAD,which is a specific inhibitor of Hsp90,could bind to the N-terminal ATP/ADP-binding pocket of HSP90 with high affinity and inactivate Hsp90,resulting in its client proteins degradation through proteasome-dependent pathway.Therefore,we could expand the list of Hsp90 client proteins with its inhibitors. Interleukin-1(IL-1)is a pro-inflammatory cytokine,which is produced from LPS-activated monocytes/macrophage cells and has a crucial role in the inflammatory response and in autoimmune diseases such as rheumatoid arthritis.TAK1 is an essential mitogen-activated protein kinase kinase kinase(MAPKKK)in IL-1β-induced MAPKs (JNK,p38)and NF-κB signaling pathways.It has been shown that Hsp90 could interact with TAK1 by proteomics analysis.We report a novel function of Hsp90 in IL-1β-induced cell signal transduction.We found that geldanamycin(GA)dramatically destabilized TAK1 and inhibited IL-1β-induced,TAK1-mediated activation of both MAPKs and nuclear factor-κB (NF-κB),resulting in the decrease of cyclooxygenase-2(COX-2)protein expression. Alternatively,we also obtained the same results when silencing of Hsp90 expression level through RNA interference(RNAi).In previous studies,T6RZC stable cell lines could simulate the IL-1β-stimulated cell signaling by Coumermycin A-induced T6RZC dimerization.So,we used T6RZC stable cells to avoid the effect of Hsp90 on IRAK1,a kinase on the upstream of TAK1 in IL-1β-induced signalling,when we studied the effect of Hsp90 on TAK1 in the activation of MAPKs and NF-κB.As described above,our findings showed the inhibitory effect of GA on the phosphorylation of JNK and p38 as well as the degradation of IκBαin T6RZC stable cell lines.The results of Co-immunoprecipitation showed that Hsp90 formed a complex with TAK1 in vivo via its N-terminal residues 1-401.Hsp90 specific inhibitors destabilized TAK1 at post-transcriptional level but with no effect on mRNA level,and in present study showed that GA-induced degradation of TAK1 protein was mediated by proteasome.These results demonstrated that Hsp90 was essential in IL-1β-induced signaling by interacting with TAK1.In conclusion,our study reveals a novel role of lisp90 in IL-1β-induced signaling by regulates the stability of TAK1 and elucidates a new funcation of Hsp90 in regulating the activation of MAPKs and NF-κB pathways,which provides a new insight for analyzing the function of Hsp90 in inflammatory cell signal transduction.