The BH3-only protein BAD mediates TNF\u03b1 cytotoxicity despite concurrent activation of IKK and NF-\u03baB in septic shock

Jie Yan,Beicheng Sun,Xiang Yuan,Yu Zhao,Hao Zhang,Anning Lin,Jialing Xiang

doi:10.1038/s41422-018-0041-7

Abstract

The inflammatory cytokine TNFα plays a crucial role in the pathology of many inflammatory and infectious diseases. However, the mechanism underlying TNFα cytotoxicity in these diseases is incompletely understood. Here we report that the pro-apoptotic BCL-2 family member BAD mediates TNFα cytotoxicity despite concurrent activation of IKK and NF-κB in vitro by inducing apoptosis in cultured cells and in vivo by eliciting tissue damage of multiple organs and contributing to mortality in septic shock. At high doses, TNFα significantly inactivates RhoA through activation of the Src-p190GAP pathway, resulting in massive actin stress fiber destabilization, followed by substantial BAD release from the cytoskeleton to the cytosol. Under this condition, activated IKK fails to phosphorylate all cytosolic BAD, allowing translocation of non-phosphorylated BAD to mitochondria to trigger apoptosis. Polymicrobial infection utilizes the same mechanism as high-dose TNFα to elicit apoptosis-associated tissue damage of multiple organs. Consequently, loss of Bad or elimination of BAD pro-apoptotic activity protects mice from tissue damage of multiple organs and reduces mortality rates. Our results support a model in which BAD mediates TNFα cytotoxicity despite concurrent activation of the IKK-NF-κB pathway in cultured mammalian cells and in septic shock.

Highlights

The inflammatory cytokine TNFα plays a crucial role in inflammatory and infectious diseases, from rheumatoid arthritis to septic shock.[1]
The difference between BAD(S26D) and BAD(S26A) mutant in terms of protection of the mice from polymicrobial infection was not the result of variations in Bad construct expressions, as the protein levels of WT and mutant BAD were similar to each other in liver or colon (Supplementary information, Figure S8). These results demonstrate that cytotoxic dose TNFα-induced proapoptotic activity of BAD has a crucial role in mortality and tissue damage of multiple organs in septic shock and suggest that blocking BAD-mediated TNFα cytotoxicity may have the potential in preserving the organ integrity and reduction of mortality rate in septic shock (Fig. 8)
It has long been recognized that TNFα typically does not induce apoptosis unless IKK-mediated activation of NF-κB and inactivation of BAD are impaired in various cultured cells and genetic animal models.[14, 70]

Summary

Introduction

The inflammatory cytokine TNFα plays a crucial role in inflammatory and infectious diseases, from rheumatoid arthritis to septic shock.[1]. Overwhelming evidence shows that TNFα does not typically induce apoptosis unless the IκB kinase (IKK) signaling pathway is impaired in cultured cells and various genetic animal models. TNFα-induced apoptosis in most cell types is suppressed by IKK, which has two catalytic subunits, IKKα and IKKβ, and two regulatory subunits NEMO/IKKγ and ELKS.[5] IKK inhibits TNFαinduced apoptosis through activation of the transcription factor NF-κB, whose target gene protein products include inhibitors of caspases (IAPs),[6,7,8] and prevents prolonged activation of JNK1.9–13 In addition to activation of NF-κB, IKK-mediated phosphorylation and inactivation of the BH3-only protein BAD is required for suppressing TNFα-induced apoptosis.[14]

Methods

Results

Conclusion