NF-κB-regulated ubiquitin-editing enzyme A20 paves the way for infection persistency

USP48 and A20 synergistically promote cell survival in Helicobacter pylori infection

The human pathogen Helicobacter pylori represents a risk factor for the development of gastric diseases including cancer. The H. pylori-induced transcription factor nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) is involved in the pro-inflammatory response and cell survival in the gastric mucosa, and represents a trailblazer of gastric pathophysiology. Termination of nuclear NF-κB heterodimer RelA/p50 activity is regulated by the ubiquitin-RING-ligase complex elongin-cullin-suppressor of cytokine signalling 1 (ECS^SOCS1), which leads to K48-ubiquitinylation and degradation of RelA. We found that deubiquitinylase (DUB) ubiquitin specific protease 48 (USP48), which interacts with the COP9 signalosome (CSN) subunit CSN1, stabilises RelA by deubiquitinylation and thereby promotes the transcriptional activity of RelA to prolong de novo synthesis of DUB A20 in H. pylori infection. An important role of A20 is the suppression of caspase-8 activity and apoptotic cell death. USP48 thus enhances the activity of A20 to reduce apoptotic cell death in cells infected with H. pylori. Our results, therefore, define a synergistic mechanism by which USP48 and A20 regulate RelA and apoptotic cell death in H. pylori infection.

Helicobacter pylori-induced NF-κB: trailblazer for gastric pathophysiology

NF-κB signaling pathways, induced by a variety of triggers, play a key role in regulating the expression of genes involved in the immune response and cellular responses to stress. The human pathogen Helicobacter pylori induces classical and alternative NF-κB signaling pathways via its effector ADP-L-glycero-β-D-manno-heptose (ADP-heptose). We review H. pylori- and NF-κB-dependent alterations in cellular processes and associated maladaptation leading to deleterious gastric pathophysiology that have implications for the diagnosis and treatment of gastric diseases. Therapeutic options for gastric cancer (GC) include clinically relevant small molecule inhibitors of NF-κB and epigenetic therapy approaches. In this context, gastric organoid biobanks originated from patient material, represent a valuable platform for translational applications to predict patient responses to chemotherapy, with a view to personalized medicine.

Downregulation of A20 Expression Increases the Immune Response and Apoptosis and Reduces Virus Production in Cells Infected by the Human Respiratory Syncytial Virus

Human respiratory syncytial virus (HRSV) causes severe lower respiratory tract infections in infants, the elderly, and immunocompromised adults. Regulation of the immune response against HRSV is crucial to limiting virus replication and immunopathology. The A20/TNFAIP3 protein is a negative regulator of nuclear factor kappa B (NF-κB) and interferon regulatory factors 3/7 (IRF3/7), which are key transcription factors involved in the inflammatory/antiviral response of epithelial cells to virus infection. Here, we investigated the impact of A20 downregulation or knockout on HRSV growth and the induction of the immune response in those cells. Cellular infections in which the expression of A20 was silenced by siRNAs or eliminated by gene knockout showed increased inflammatory/antiviral response and reduced virus production. Similar results were obtained when the expression of A20-interacting proteins, such as TAX1BP1 and ABIN1, was silenced. Additionally, downregulation of A20, TAX1BP1, and ABIN1 increased cell apoptosis in HRSV-infected cells. These results show that the downregulation of A20 expression might contribute in the control of HRSV infections by potentiating the early innate immune response and increasing apoptosis in infected cells.