A20

Xiaojun Zhao, Jian-Gang Xie, Chujun Duan, Lin-Xiao Wang, Yi Si, Shan-Shou Liu, Qian-Mei Wang, Dan Wu, Yifan Wang, Wen Yin, R. Zhuang, Jun-Jie Li

Acute lung injury is a serious complication of sepsis with high morbidity and mortality. Pyroptosis is a proinflammatory form of programmed cell death that leads to immune dysregulation and organ dysfunction during sepsis. We previously found that adenosine deaminase acting on double-stranded RNA 1 (ADAR1) plays regulatory roles in the pathology of sepsis, but the mechanism of ADAR1 in sepsis-induced pyroptosis and lung injury remains unclear. Here, we mainly investigated the regulatory effects and underlying mechanism of ADAR1 in sepsis-induced lung injury and pyroptosis of pulmonary macrophages through RNA sequencing of clinical samples, caecal ligation and puncture (CLP)-induced septic mouse models, and in vitro cellular experiments using RAW264.7 cells with lipopolysaccharide (LPS) stimulation. The results showed that pyroptosis was activated in peripheral blood mononuclear cells (PBMCs) from patients with sepsis. In the CLP-induced septic mouse model, pyroptosis was mainly activated in pulmonary macrophages. LPS-stimulated RAW264.7 cells showed significantly increased activation of the NLRP3 inflammasome. ADAR1 was downregulated in PMBCs of patients with sepsis, and overexpression of ADAR1 alleviated CLP-induced lung injury and NLRP3 inflammasome activation. Mechanistically, the regulatory effects of ADAR1 on macrophage pyroptosis were mediated by the miR-21/A20/NLRP3 signalling cascade. ADAR1 attenuated sepsis-induced lung injury and hindered the activation of pyroptosis in pulmonary macrophages in sepsis through the miR-21/A20/NLRP3 axis. Our study highlights the role of ADAR1 in protecting pulmonary macrophages against pyroptosis and suggests targeting ADAR1/miR-21 signalling as a therapeutic opportunity in sepsis-related lung injury.

Urekha Karri, Magdalena Harasimowicz, Manuel Carpio Tumba, Daniella M. Schwartz

Jiayun Yu, Hanwen Li, Yongyao Wu, Min Luo, Si-Yuan Chen, Guo-Bo Shen, Xia-Wei Wei, Bin Shao

Significance Previous study suggested that A20 plays a crucial role in regulating NLRP3 inflammasome activation, yet the specific mechanism remains to be investigated. Here, we revealed that A20 notably diminishes the expression of NEK7, leveraging its role in moderating the NF-κB signaling pathway. A20 directly binds with NEK7, facilitating its proteasomal degradation by enhancing ubiquitination. Crucially, K189 and K293 residues on NEK7 are pivotal for supporting A20-mediated ubiquitination. A20 affects the binding of NEK7 to NLRP3 complex potentially through its OTU domain and/or synergistic effect of its ZnF4 and ZnF7 motifs. Utilizing A20-derived peptides and genetic approaches, we showed that interfering NEK7 function in macrophages can significantly dampen pyroptosis and alleviate the process of sepsis.

Ashley E Culver-Cochran, Aishlin Hassan, Kathleen M Hueneman, Kwangmin Choi, Averil Ma, Brett VanCauwenbergh, E. O'Brien, M. Wunderlich, J. Perentesis, D. Starczynowski

Acute myeloid leukemia (AML) is a deadly hematopoietic malignancy. Although many patients achieve complete remission with standard induction therapy, a combination of cytarabine and anthracycline, ~40% of patients have induction failure. These refractory patients pose a treatment challenge, as they do not respond to salvage therapy or allogeneic stem cell transplant. Herein, we show that AML patients who experience induction failure have elevated expression of the NF-κB target gene tumor necrosis factor alpha-induced protein-3 (TNFAIP3/A20) and impaired necroptotic cell death. A20High AML are resistant to anthracyclines, while A20Low AML are sensitive. Loss of A20 in AML restores sensitivity to anthracycline treatment by inducing necroptosis. Moreover, A20 prevents necroptosis in AML by targeting the necroptosis effector RIPK1, and anthracycline-induced necroptosis is abrogated in A20High AML. These findings suggest that NF-κB-driven A20 overexpression plays a role in failed chemotherapy induction and highlights the potential of targeting an alternative cell death pathway in AML. Patients with Acute myeloid leukemia (AML) who do not respond to standard chemotherapy have limited treatment options. Here, the authors show that high expression of the gene TNFAIP3/A20 in AML cells contributes to chemotherapy resistance by blocking a type of cell death called necroptosis.

Eva Bagyinszky, Seong Soo A. An

TNF-α-induced protein 3 (TNFAIP3), commonly referred to as A20, is an integral part of the ubiquitin-editing complex that significantly influences immune regulation, apoptosis, and the initiation of diverse immune responses. The A20 protein is characterized by an N-terminal ovarian tumor (OTU) domain and a series of seven zinc finger (ZNF) domains. Mutations in the TNFAIP3 gene are implicated in various immune-related diseases, such as Behçet’s disease, polyarticular juvenile idiopathic arthritis, autoimmune thyroiditis, autoimmune hepatitis, and rheumatoid arthritis. These mutations can lead to a spectrum of symptoms, including, but not limited to, recurrent fever, ulcers, rashes, musculoskeletal and gastrointestinal dysfunctions, cardiovascular issues, and respiratory infections. The majority of these mutations are either nonsense (STOP codon) or frameshift mutations, which are typically associated with immune dysfunctions. Nonetheless, missense mutations have also been identified as contributors to these conditions. These genetic alterations may interfere with several biological pathways, notably abnormal NF-κB signaling and dysregulated ubiquitination. Currently, there is no definitive treatment for A20 haploinsufficiency; however, therapeutic strategies can alleviate the symptoms in patients. This review delves into the mutations reported in the TNFAIP3 gene, the clinical progression in affected individuals, potential disease mechanisms, and a brief overview of the available pharmacological interventions for A20 haploinsufficiency. Mandatory genetic testing of the TNFAIP3 gene should be performed in patients diagnosed with autoinflammatory disorders to better understand the genetic underpinnings and guide treatment decisions.