A20 undermines alternative NF-κB activity and expression of anti-apoptotic genes in Helicobacter pylori infection

ALPK1-Dependent cIAP1 Degradation Regulates Helicobacter pylori-Induced Apoptosis

Helicobacter pylori infection poses a significant risk for disrupting the gastric epithelium by inducing inflammation and apoptosis. Here, we identify alpha kinase 1 (ALPK1) as essential in H. pylori-induced apoptosis. The absence of ALPK1 leads to the accumulation of cellular inhibitor of apoptosis 1 (cIAP1) upon H. pylori infection, which raises the threshold for the induction of apoptosis. Ablation of cIAP1 with a SMAC-mimetic restores the level of apoptosis induced by H. pylori in these cells. Our findings highlight the impact of ALPK1 on the stability of cIAP1, influencing H. pylori-induced apoptosis.

CYLD-TRAF6 interaction promotes ADP-heptose-induced NF-κB signaling in H. pylori infection

The inflammatory response associated with Helicobacter pylori (H. pylori) infection causes a multitude of alterations in the gastric microenvironment, leading to the slow and steady disruption of the gastric epithelial barrier. Activation of NF-κB during H. pylori infection is crucial to this inflammatory response. Here, we show that CYLD, which interacts constitutively with TRAF6, enhances H. pylori's ADP-heptose-induced activation of the classical NF-κB pathway in gastric epithelial cells. This activating effect of CYLD contrasts with the inhibitory effect of CYLD on receptor-mediated NF-κB activity. Mechanistically, CYLD counteracts the hydrolysis of ubiquitin chains from TRAF6 by deubiquitinylase A20 in a catalytically independent manner, thus supporting the auto-ubiquitinylation of TRAF6 upon activation of NF-κB in early H. pylori infection. In addition, the subsequent classical NF-κB-dependent de novo synthesis of A20 provides a negative feedback loop leading to shutdown not only of the classical but also of the alternative NF-κB pathway. Our findings highlight the regulatory relationship between CYLD and A20 in controlling classical as well as alternative NF-κB signaling in H. pylori infection.

The Role of A20 in Cancer: Friend or Foe?

A20 is a ubiquitin-editing enzyme that has emerged as a key regulator of inflammatory signaling with paradoxical roles in cancer. Acting as both an oncogene and a tumor suppressor gene depending on the cellular context, A20 modulates important cell pathways, such as NF-κB signaling and autophagy. In this review, we summarize the dual roles of A20 in tumorigenesis, highlighting its ability to promote tumor progression in cancers, such as breast and melanoma, while functioning as a tumor suppressor in lymphomas and hepatocellular carcinoma. We discuss the interplay of A20 with autophagy, a process that is important for maintaining cellular homeostasis and influencing tumor dynamics. By integrating recent findings, we provide insight into how dysregulation of A20 and its associated pathways can either suppress or drive cancer development, which may lead to improved therapeutic intervention.

Dysregulation of deubiquitinylases: a linchpin of gastrointestinal diseases

Ubiquitinylation of proteins regulates manifold processes and is reversed by deubiquitinylating enzymes (DUBs), which are therefore implicated in a plethora of cellular processes. DUBs are frequently upregulated in many diseases, while in a few cases downregulation of DUBs is associated with disease progression. This review focuses on the involvement of DUBs in the development and progression of gastrointestinal diseases with a particular emphasis on hepatic steatosis and hepatocellular, cholangio-, esophageal, gastric, colorectal, and pancreatic ductal carcinomas. In addition, pathogens that trigger the activity of several DUBs and thus suppress the immune response and cell survival are discussed. Finally, we highlight recent approaches made towards the therapeutic treatment of gastrointestinal diseases using DUB inhibitors.

Differential expression of the ubiquitin-editing enzyme A20 in gastric biopsies indicates the severity of disease

A20, an ubiquitin-editing enzyme, plays a pivotal role in regulating cell signaling and immune responses. Dysregulated A20 expression has been associated with various pathological conditions, including inflammatory diseases and malignancies, where its expression levels often correlate with differing prognoses in solid tumors. This study aimed to explore the expression and cellular localization of A20 in both nonpathological and diseased human gastric tissues to gain deeper insights into its involvement in gastric pathologies. We analyzed paraffin-embedded gastric tissue samples from 326 patients. A20 expression was assessed using immunohistochemistry (IHC) with results categorized according to the Remmele and Stegner immunoreactive score (IRS). The study compared A20 expression across a spectrum of gastric pathologies, including Helicobacter pylori (HP) gastritis, autoimmune gastritis (A-gastritis), reactive gastropathy (C-gastritis), Ex-HP-gastritis, adenomas, and adenocarcinomas, with nonpathological gastric mucosa serving as a baseline. Our findings demonstrate a significant increase in A20 expression in HP-gastritis (p = 0.019), A-gastritis (p = 0.001), adenomas (p < 0.001), and adenocarcinomas (p < 0.001). Conversely, no significant differences in A20 expression were observed in C-gastritis or Ex-HP-gastritis cases.

A20 Alleviates the Inflammatory Response in Bovine Endometrial Epithelial Cells by Promoting Autophagy

Endometritis represents a prevalent condition in perinatal dairy cows. Bovine endometrial epithelial cells (BEECs), as the primary interface between cavity and the external environment, are particularly vulnerable to infection by pathogenic bacteria following parturition. A20 is essential for regulating inflammation and modulating immune responses. Nevertheless, the exact role of A20 in the BEECs in response to inflammatory response is not fully understood. An endometritis model infected by Escherichia coli (E. coli) in vivo and a BEECs inflammation model induced with lipopolysaccharide (LPS) in vitro were built to investigate the function and governing mechanisms of A20 in endometritis. The results showed that infection with E. coli resulted in endometrial damage, inflammatory cell infiltration, and upregulation of inflammatory factors in dairy cows. Furthermore, A20 expression was upregulated in the endometrium of cows with endometritis and in BEECs following LPS stimulation. A20 overexpression attenuated the level of proinflammatory cytokines in LPS-stimulated BEECs; conversely, A20 knockdown lead to an exacerbated response to LPS stimulation. The overexpression of A20 was shown to activate autophagy and suppress the NF-κB signaling pathway in LPS-stimulated BEECs. However, blocking autophagy with chloroquine notably attenuated the anti-inflammatory effect of A20, leading to the activation of the NF-κB signaling pathway. In summary, the study demonstrated that A20's suppression of inflammation in LPS-stimulated BEECs is associated with the activation of autophagy. Therefore, the A20 protein showed potential as a novel treatment focus for managing endometritis in dairy cows.

Increased ONECUT2 induced by Helicobacter pylori promotes gastric cancer cell stemness via an AKT-related pathway

Helicobacter pylori (HP) infection initiates and promotes gastric carcinogenesis. ONECUT2 shows promise for tumor diagnosis, prognosis, and treatment. This study explored ONECUT2's role and the specific mechanism underlying HP infection-associated gastric carcinogenesis to suggest a basis for targeting ONECUT2 as a therapeutic strategy for gastric cancer (GC). Multidimensional data supported an association between ONECUT2, HP infection, and GC pathogenesis. HP infection upregulated ONECUT2 transcriptional activity via NFκB. In vitro and in vivo experiments demonstrated that ONECUT2 increased the stemness of GC cells. ONECUT2 was also shown to inhibit PPP2R4 transcription, resulting in reduced PP2A activity, which in turn increased AKT/β-catenin phosphorylation. AKT/β-catenin phosphorylation facilitates β-catenin translocation to the nucleus, initiating transcription of downstream stemness-associated genes in GC cells. HP infection upregulated the reduction of AKT and β-catenin phosphorylation triggered by ONECUT2 downregulation via ONECUT2 induction. Clinical survival analysis indicated that high ONECUT2 expression may indicate poor prognosis in GC. This study highlights a critical role played by ONECUT2 in promoting HP infection-associated GC by enhancing cell stemness through the PPP2R4/AKT/β-catenin signaling pathway. These findings suggest promising therapeutic strategies and potential targets for GC treatment.

OTUD7B deubiquitinates and stabilizes YAP1 to upregulate NUAK2 expression, thus accelerating gastric cancer procession

BACKGROUND

Gastric cancer (GC) is one of the most common malignancies worldwide. Ovarian tumor protein superfamily serves a crucial role in tumor growth progression, among them, ovarian tumor domain-containing 7B (OTUD7B) as a deubiquitinase (DUB) is frequently found in various cancers, but the role of OTUD7B in GC is poorly understood.

AIMS

To clarify the effect of OTUD7B on GC progression.

METHODS

Functional experiments were performed to detect the proliferation, migration and invasion of GC cells. Xenografts were used to measure the effects in vivo. Co-immunoprecipitation (Co-IP) and ubiquitination assays showed the interaction of OTUD7B and YAP1.

RESULTS

OTUD7B was highly expressed in tumor tissues from GC patients, and high mRNA expression was strongly associated with poor prognosis, suggesting that OTUD7B was an independent prognostic factor. Moreover, OTUD7B overexpression promoted GC cell proliferation and metastasis both in vitro and in vivo, whereas OTUD7B knockdown exhibited opposing biological effects. Mechanically, OTUD7B promoted downstream target genes of YAP1 including NUAK2, Snail, Slug, CDK6, CTGF, and BIRC5. Importantly, OTUD7B enhanced the activation of YAP1 via deubiquitinating and stabilizing to upregulate NUAK2 expression.

CONCLUSIONS

OTUD7B is a novel DUB of the YAP1 pathway and accelerates GC progression. Therefore, OTUD7B may be a promising therapeutic target against GC.

A20 ameliorates Aspergillus fumigatus keratitis by promoting autophagy and inhibiting NF-κB signaling

Fungal keratitis (FK) is a serious, potentially sight-threatening corneal infection, which is associated with poor prognosis. A20, also called TNFAIP3, plays significant roles in the negative regulation of inflammation and immunity. However, the function of A20 in Aspergillus fumigatus (A. fumigatus) keratitis remains obscure. Herein, we found that the level of A20 is increased in human corneal epithelial cells (HCECs) and in mouse corneas with A. fumigatus infection, and that nuclear factor-κB (NF-κB) signaling is required for A20 upregulation. A20 overexpression inhibits A. fumigatus-mediated inflammatory responses, while A20 knockdown results in opposite effect. Mechanically, we showed that A20 inhibits NF-κB signaling and activates autophagy in infected HCECs. We also showed that inhibition of NF-κB signaling reverses the increased inflammatory responses in infected HCECs with A20 knockdown. Furthermore, autophagy blockage impedes the anti-inflammatory effect of A20 in A. fumigatus infected HCECs. Moreover, A20 ameliorates the corneal damage and inflammation in A. fumigatus infected mouse corneas. In conclusion, this study reveals that A20 alleviates A. fumigatus keratitis by activating autophagy and inhibiting NF-κB signaling. This suggests that exogenous use of A20 protein may be a potentially promising therapeutic strategy for FK treatment.

Innate activation of human neutrophils and neutrophil-like cells by the pro-inflammatory bacterial metabolite ADP-heptose and Helicobacter pylori

Lipopolysaccharide inner core heptose metabolites, including ADP-heptose, play a substantial role in the activation of cell-autonomous innate immune responses in eukaryotic cells, via the ALPK1-TIFA signaling pathway, as demonstrated for various pathogenic bacteria. The important role of LPS heptose metabolites during Helicobacter pylori infection of the human gastric niche has been demonstrated for gastric epithelial cells and macrophages, while the role of heptose metabolites on human neutrophils has not been investigated. In this study, we aimed to gain a better understanding of the activation potential of bacterial heptose metabolites for human neutrophil cells. To do so, we used pure ADP-heptose and, as a bacterial model, H. pylori, which can transport heptose metabolites into the human host cell via the Cag Type 4 Secretion System (CagT4SS). Main questions were how bacterial heptose metabolites impact on the pro-inflammatory activation, alone and in the bacterial context, and how they influence maturation of human neutrophils. Results of the present study demonstrated that neutrophils respond with high sensitivity to pure heptose metabolites, and that global regulation networks and neutrophil maturation are influenced by heptose exposure. Furthermore, activation of human neutrophils by live H. pylori is strongly impacted by the presence of LPS heptose metabolites and the functionality of its CagT4SS. Similar activities were determined in cell culture neutrophils of different maturation states and in human primary neutrophils. In conclusion, we demonstrated that specific heptose metabolites or bacteria producing heptoses exhibit a strong activity on cell-autonomous innate responses of human neutrophils.

The conundrum of Helicobacter pylori-associated apoptosis in gastric cancer

Helicobacter pylori is a human microbial pathogen that colonizes the gastric epithelium and causes type B gastritis with varying degrees of active inflammatory infiltrates. The underlying chronic inflammation induced by H. pylori and other environmental factors may promote the development of neoplasms and adenocarcinoma of the stomach. Dysregulation of various cellular processes in the gastric epithelium and in different cells of the microenvironment is a hallmark of H. pylori infection. We address the conundrum of H. pylori-associated apoptosis and review distinct mechanisms induced in host cells that either promote or suppress apoptosis in gastric epithelial cells, often simultaneously. We highlight key processes in the microenvironment that contribute to apoptosis and gastric carcinogenesis.

Innate immune activation and modulatory factors of Helicobacter pylori towards phagocytic and nonphagocytic cells

Helicobacter pylori is an intriguing obligate host-associated human pathogen with a specific host interaction biology, which has been shaped by thousands of years of host-pathogen coevolution. Molecular mechanisms of interaction of H. pylori with the local immune cells in the human system are less well defined than epithelial cell interactions, although various myeloid cells, including neutrophils and other phagocytes, are locally present or attracted to the sites of infection and interact with H. pylori. We have recently addressed the question of novel bacterial innate immune stimuli, including bacterial cell envelope metabolites, that can activate and modulate cell responses via the H. pylori Cag type IV secretion system. This review article gives an overview of what is currently known about the interaction modes and mechanisms of H. pylori with diverse human cell types, with a focus on bacterial metabolites and cells of the myeloid lineage including phagocytic and antigen-presenting cells.

Dual RNA-Sequencing and Liquid Chromatography-Mass Spectrometry Unveil Specific Insights on the Pathogenicity of Trichophyton mentagrophytes Complex

Trichophyton mentagrophytes is increasingly considered to be a public health hazard because it causes the most severe manifestations of dermatophytosis. In this study, we performed a series of studies to determine the pathogenicity of the T. mentagrophytes complex. We show that the T. mentagrophytes complex interacts with keratinocytes through pattern-recognition receptors‒MAPK/noncanonical NF-κB pathways and that the hyphal form of T. mentagrophytes is responsible for the increased inflammatory responses in keratinocytes. Moreover, SN-38 is likely a toxin of T. mentagrophytes that induces apoptosis in keratinocytes both in vivo and in vitro. Our results explain the severe pathogenicity and destructiveness of T. mentagrophytes observed in the clinic and pave the way for designing novel toxin-directed therapies to improve patient outcomes.

Gastric Epithelial Barrier Disruption, Inflammation and Oncogenic Signal Transduction by Helicobacter pylori

Helicobacter pylori exemplifies one of the most favourable bacterial pathogens worldwide. The bacterium colonizes the gastric mucosa in about half of the human population and constitutes a major risk factor for triggering gastric diseases such as stomach cancer. H. pylori infection represents a prime example of chronic inflammation and cancer-inducing bacterial pathogens. The microbe utilizes a remarkable set of virulence factors and strategies to control cellular checkpoints of inflammation and oncogenic signal transduction. This chapter emphasizes on the pathogenicity determinants of H. pylori such as the cytotoxin-associated genes pathogenicity island (cagPAI)-encoded type-IV secretion system (T4SS), effector protein CagA, lipopolysaccharide (LPS) metabolite ADP-glycero-β-D-manno-heptose (ADP-heptose), cytotoxin VacA, serine protease HtrA, and urease, and how they manipulate various key host cell signaling networks in the gastric epithelium. In particular, we highlight the H. pylori-induced disruption of cell-to-cell junctions, pro-inflammatory activities, as well as proliferative, pro-apoptotic and anti-apoptotic responses. Here we review these hijacked signal transduction events and their impact on gastric disease development.

Human gastric fibroblasts ameliorate A20-dependent cell survival in co-cultured gastric epithelial cells infected by Helicobacter pylori

Crosstalk within the gastric epithelium, which is closely in contact with stromal fibroblasts in the gastric mucosa, has a pivotal impact in proliferation, differentiation and transformation of the gastric epithelium. The human pathogen Helicobacter pylori colonises the gastric epithelium and represents a risk factor for gastric pathophysiology. Infection of H. pylori induces the activation of the transcription factor nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), which is involved in the pro-inflammatory response but also in cell survival. In co-cultures with human gastric fibroblasts (HGF), we found that apoptotic cell death is reduced in the polarised human gastric cancer cell line NCI-N87 or in gastric mucosoids during H. pylori infection. Interestingly, suppression of apoptotic cell death in NCI-N87 cells involved an enhanced A20 expression regulated by NF-κB activity in response to H. pylori infection. Moreover, A20 acts as an important negative regulator of caspase-8 activity, which was suppressed in NCI-N87 cells during co-culture with gastric fibroblasts. Our results provide evidence for NF-κB-dependent regulation of apoptotic cell death in cellular crosstalk and highlight the protective role of gastric fibroblasts in gastric epithelial cell death during H. pylori infection.

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.