The deubiquitinating enzyme OTUD7b protects dendritic cells from TNF-induced apoptosis by stabilizing the E3 ligase TRAF2

Inflammation and cancer cell survival: TRAF2 as a key player

TNF receptor-associated factor 2 (TRAF2) plays a crucial role in both physiological and pathological processes. It takes part in the regulation of cell survival and death, tissue regeneration, development, endoplasmic reticulum stress response, autophagy, homeostasis of the epithelial barrier and regulation of adaptive and innate immunity. Initially identified for its interaction with TNF receptor 2 (TNFR2), TRAF2 contains a TRAF domain that enables homo- and hetero-oligomerization, allowing it to interact with multiple receptors and signaling molecules. While best known for mediating TNFR1 and TNFR2 signaling, TRAF2 also modulates other receptor pathways, including MAPK, NF-κB, and Wnt/β-catenin cascades. By regulating NF-κB-inducing kinase (NIK), TRAF2 is a key activator of the alternative NF-κB pathway, linking it to inflammatory diseases, immune dysfunction, and tumorigenesis. In the innate immune system, TRAF2 influences macrophage differentiation, activation, and survival and stimulates natural killer cell cytotoxicity. In the adaptive immune system, it represses effector B- and T-cell activity while sustaining regulatory T-cell function, thus promoting immune suppression. The lack of fine-tuning of TRAF2 activity leads to excessive NF-kB activation, driving chronic inflammation and autoimmunity. Although TRAF2 can act as a tumor suppressor, it is predominantly described as a tumor promoter, as its expression has been correlated with increased metastatic potential and poorer prognosis in several types of cancer. Targeting TRAF2 or TRAF2-dependent signaling pathways might represent a promising anti-cancer therapeutic strategy.

Deubiquitinase OTUD7B stabilizes HNF4α to alleviate pressure overload-induced cardiac hypertrophy by regulating fatty acid oxidation and inhibiting ferroptosis

BACKGROUND

Cardiac hypertrophy, a leading cause of heart failure, threatens global public health. Deubiquitinating enzymes (DUBs) are critical in cardiac pathophysiology by regulating protein stability, function, and degradation. Here, we investigated the role and regulating mechanism of ovarian tumor domain-containing 7B (OTUD7B) in cardiac hypertrophy by modulating fatty acid metabolism.

METHODS

Mice subjected to transverse aortic constriction (TAC) and cardiomyocytes treated with phenylephrine (PE) were used to explore the role of OTUD7B in myocardial hypertrophy. The potential molecular mechanisms underlying OTUD7B's regulation of cardiac hypertrophy were explored through transcriptome analysis and further validated in cardiomyocytes.

RESULTS

Reduced OTUD7B expression was observed in hypertrophic hearts following TAC surgery. Cardiac-specific OTUD7B deficiency exacerbated, while OTUD7B overexpression mitigated, pressure overload-induced hypertrophy and cardiac dysfunction both in vivo and in vitro. OTUD7B knockdown resulted in ferroptosis, as evidenced by decreased mitochondrial cristae, increased Fe2+ ion content, lipid peroxide accumulation, while OTUD7B overexpression inhibited ferroptosis. Mechanistically, transcriptomic analysis identified OTUD7B plays a role in the regulation of fatty acid metabolism and pathological cardiac hypertrophy. OTUD7B was found to directly bind to HNF4α, a transcription factor regulating fatty acid oxidation-related genes. Further, OTUD7B exerted deubiquitination activity to stabilize the HNF4α protein by removing K48-linked ubiquitin chains, thereby preventing its degradation via the proteasomal pathway and linking the HNF4α degradation and ferroptosis. Finally, ferroptosis inhibitors, ferrostatin-1, alleviated OTUD7B inhibition-induced ferroptosis, fatty acid metabolism suppression, and myocardial hypertrophy.

CONCLUSIONS

We confirmed that OTUD7B is involved in the regulation of ferroptosis in pressure overload-induced cardiac hypertrophy and highlighted that OTUD7B alleviates cardiac hypertrophy by regulating ferroptosis and fatty acid oxidation through deubiquitination and stabilization of HNF4α.

Staphylococcal SplA and SplB serine proteases target ubiquitin(-like) specific proteases

Staphylococcus aureus is a Gram-positive opportunistic pathogen that has colonized nearly 30% of the human population and can cause life-threatening infections. S. aureus exports a variety of virulence factors, such as a novel set of extracellular serine protease-like proteins (Spls). Spls are expressed by most clinical isolates of S. aureus, but their pathophysiological substrates and role during the infection are largely unknown. Here we characterized the substrate and cleavage specificity of recombinantly expressed SplA and SplB proteins. We identified a group of ubiquitin or ubiquitin-like modifying enzymes including deubiquitinating enzymes from human as well as from bacterial sources to be so far unknown SplA and SplB substrates. Distinct cleavage sites within these substrates for SplA (YLY↓T, FMY↓N) and SplB (VCD↓S) were identified by mass spectrometry and confirmed by site-directed mutagenesis of the target proteins. Since many cellular immune signaling pathways are tightly regulated by ubiquitination, the specific cleavage of ubiquitin modifying enzymes strongly suggests a specific role of Spls in manipulating immune signaling and in competing with other bacteria.

VPO1 Promotes Programmed Necrosis of Cardiomyocytes in Rats with Chronic Heart Failure by Upregulating CYLD

BACKGROUND

Chronic heart failure (CHF) is a serious cardiovascular condition. Vascular peroxidase 1 (VPO1) is associated with various cardiovascular diseases, yet its role in CHF remains unclear. This research aims to explore the involvement of VPO1 in CHF.

METHODS

CHF was induced in rats using adriamycin, and the expression levels of VPO1 and cylindromatosis (CYLD) were assessed. In parallel, the effects of VPO1 on programmed necrosis in H9c2 cells were evaluated through cell viability assays, lactate dehydrogenase (LDH) level measurements, and analysis of receptor-interacting protein kinase 1/receptor-interacting protein kinase 3/mixed lineage kinase domain-like protein (RIPK1/RIPK3/MLKL) pathway-related proteins. The impact of CYLD on RIPK1 protein stability and ubiquitination was also investigated, along with the interaction between VPO1 and CYLD. Additionally, cardiac structure and function were assessed using echocardiography, Hematoxylin-eosin (HE) staining, Masson staining, and measurements of myocardial injury-related factors, including N-terminal prohormone of brain natriuretic peptide (NT-proBNP), Aspartate aminotransferase (AST), LDH, and creatine kinase-myocardial band (CK-MB).

RESULTS

VPO1 expression was upregulated in CHF rats and in H9c2 cells treated with adriamycin. In cellular experiments, VPO1 knockdown improved cell viability, inhibited necrosis and the expression of proteins associated with the RIPK1/RIPK3/MLKL pathway. Mechanistically, VPO1 promoted cardiomyocyte programmed necrosis by interacting with the deubiquitinating enzyme CYLD, which enhanced RIPK1 ubiquitination and degradation, leading to activation of the RIPK1/RIPK3/MLKL signaling pathway. At animal level, overexpression of CYLD counteracted the cardiac failure, cardiac hypertrophy, myocardial injury, myocardial fibrosis, and tissue necrosis caused by VPO1 knockdown.

CONCLUSIONS

VPO1 exacerbates cardiomyocyte programmed necrosis in CHF rats by upregulating CYLD, which activates the RIPK1/RIPK3/MLKL signaling pathway. Thus, VPO1 may represent a potential therapeutic target for CHF.

OTUD7B promotes cell migration and invasion, predicting poor prognosis of gastric cancer

BACKGROUND

OTUD7B, a member of the ovarian tumor (OTU) protein superfamily, functions as a deubiquitinating enzyme and is associated with various biological processes and disease conditions, including tumors. In this study, we aimed to explore the expression patterns, prognostic significance, and the functional roles and underlying mechanisms of OTUD7B in gastric cancer (GC).

MATERIALS AND METHODS

Using a blend of bioinformatics, clinical case reviews, and molecular experiments, we evaluated the expression of OTUD7B in GC at both mRNA and protein levels. We examined the relationship between OTUD7B expression and clinicopathological characteristics of GC patients. Additionally, in vitro assays were utilized to assess the effects of OTUD7B on the migratory and invasive capabilities of GC cells. RNA sequencing analysis was conducted to identify critical genes and pathways linked to OTUD7B in GC.

RESULTS

OTUD7B was found to be significantly overexpressed in GC, both at mRNA and protein levels. Higher levels of OTUD7B were positively associated with advanced tumor TNM stage, higher histological grade, and presence of lymph/vein invasion. These correlations were indicative of poorer overall survival (OS) and disease-free survival (DFS) in GC patients. In vitro assays revealed that genetic knockout of OTUD7B markedly reduced the migration and invasion of GC cells, while overexpression of OTUD7B led to enhanced cellular migration and invasion. Furthermore, RNA sequencing and bioinformatic analyses indicated that the absence of OTUD7B suppressed signaling pathways related to cancer progression, metastasis, and metabolism. Mechanistically, OTUD7B likely promotes GC metastasis through the WNT signaling pathway, specifically targeting β-catenin.

CONCLUSIONS

OTUD7B serves as a novel marker for poor prognosis in GC and actively promotes tumor metastasis. Our results shed light on the signaling pathways regulated by OTUD7B and highlight potential targets for therapeutic intervention.

TRAF2 associates with cullin neddylation complex assembly

Cullin-based RING ligases (CRLs) comprise the largest family of ubiquitin E3 ligases. CRL activity is tightly regulated by cullin neddylation, which has been associated with various diseases. Although inhibitors of CRLs neddylation have been reported, there is a lack of small molecules that can selectively target individual cullins. Here, we identified a natural product, liquidambaric acid (LDA), with relatively selective inhibition properties against cullin (Cul) 2 neddylation, and found that its target, Tumor Necrosis Factor receptor-associated factor 2 (TRAF2) was required for the activity. TRAF2 associates with the Cul2 neddylation complex and regulates the machinery assembly, especially that of E2 (UBC12) and E3 (RBX1) enzymes. In addition, we demonstrated that by intervention of the associations between TRAF2 and the neddylation machinery, LDA disturbed NEDD8 transfer from E1 to E2, therefore blocking Cul2 neddylation. Taken together, we show that TRAF2 plays a positive role in neddylation cascades, and we have identified a small molecule capable of selective modulation of cullin neddylation.

Deubiquitinase USP5 regulates RIPK1 driven pyroptosis in response to myocardial ischemic reperfusion injury

BACKGROUND

Gasdermin D (GSDMD) mediated pyroptosis plays a significant role in the pathophysiology of myocardial ischemia/reperfusion (I/R) injury. However, the precise mechanisms regulating pyroptosis remain unclear. In the study, we aimed to investigate the underlying mechanism of pyroptosis in myocardial I/R injury.

METHODS

In the present study, we analyzed the effects of USP5 on the RIPK1 kinase activity mediated pyroptosis in vitro after H/R (hypoxia/reoxygenation) and in vivo in a MI/R mouse model. TTC and Evan's blue dye, Thioflavin S and immunohistochemistry staining were performed in wild-type, RIPK1flox/flox Cdh5-Cre and USP5 deficiency mice. CMEC cells were transfected with si-USP5. HEK293T cells were transfected with USP5 and RIPK1 overexpression plasmid or its mutants. The levels of USP5, RIPK1, Caspase-8, FADD and GSDMD were determined by Western blot. Protein interactions were evaluated by immunoprecipitation. The protein colocalization in cells was monitored using a confocal microscope.

RESULTS

In this study, our data demonstrate that RIPK1 is essential for limiting cardiac endothelial cell (CMEC) pyroptosis mediated by caspase-8 in response to myocardial I/R. Additionally, we investigate the role of ubiquitin-specific protease 5 (USP5) as a deubiquitinase for RIPK1. Mechanistically, USP5 interacts with RIPK1, leading to its deubiquitination and stabilization.

CONCLUSIONS

These findings offer new insights into the role of USP5 in regulating RIPK1-induced pyroptosis.

OTU deubiquitinase 7B facilitates the hyperthermia-induced inhibition of lung cancer progression through enhancing Smac-mediated mitochondrial dysfunction

Hyperthermia, as an adjuvant therapy, has shown promising anti-tumor effects. Ovarian tumor domain-containing 7B (OTUD7B) is a deubiquitinating enzyme that is frequently found in a variety of cancers. The aim of this study is to investigate the role of OTUD7B in lung cancer hyperthermia and the underlying mechanism. A549 and CALU-3 cells were respectively exposed to 42 or 44°C for the indicated times (0, 1, 3, or 6 h) followed by incubation at 37°C for 24 h. We found a temperature- and time-dependent decrease in cell viability and an increase in apoptosis levels. Compared with 0 h, heat treatment for 3 h inhibited the proliferation and invasion of A549 cells, reduced the expression levels of mitochondrial membrane potential, IAP family members (cIAP-1 and XIAP) proteins and ubiquitination of Smac, and increased Smac protein expression. Treatment with 10 μM Smac mimic BV6 further enhanced the anti-tumor effect of hyperthermia. Next, co-IP validation showed that OTUD7B interacted with Smac and stabilized Smac through deubiquitination. OTUD7B overexpression induced damage in A549 and CALU-3 cells, while silencing OTUD7B caused opposite effects. Overexpressing OTUD7B enhanced the anti-cancer effect of hyperthermia, while si-OTUD7B reversed the anti-cancer effect of hyperthermia, which was verified in the xenograft tumor model in nude mice. Taken together, OTUD7B may serve as a potential anticancer factor with potential clinical efficacy in the thermotherapeutic treatment of lung cancer.

Friend or foe? Reciprocal regulation between E3 ubiquitin ligases and deubiquitinases

Protein ubiquitination is a post-translational modification that entails the covalent attachment of the small protein ubiquitin (Ub), which acts as a signal to direct protein stability, localization, or interactions. The Ub code is written by a family of enzymes called E3 Ub ligases (∼600 members in humans), which can catalyze the transfer of either a single ubiquitin or the formation of a diverse array of polyubiquitin chains. This code can be edited or erased by a different set of enzymes termed deubiquitinases (DUBs; ∼100 members in humans). While enzymes from these distinct families have seemingly opposing activities, certain E3-DUB pairings can also synergize to regulate vital cellular processes like gene expression, autophagy, innate immunity, and cell proliferation. In this review, we highlight recent studies describing Ub ligase-DUB interactions and focus on their relationships.