Effect of deubiquitinase USP8 on hypoxia/reoxygenation‑induced inflammation by deubiquitination of TAK1 in renal tubular epithelial cells

Overexpression of USP8 inhibits inflammation and ferroptosis in chronic obstructive pulmonary disease by regulating the OTUB1/SLC7A11 signaling pathway

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is a familiar disease, and owns high morbidity and mortality, which critically damages the health of patients. Ubiquitin-specific peptidase 8 (USP8) is a pivotal protein to join in the regulation of some diseases. In a previous report, it was determined that USP8 expression is down-regulated in LPS-treated BEAS-2B cells, and USP8 restrains inflammatory response and accelerates cell viability. However, the regulatory roles of USP8 on ferroptosis in COPD are rarely reported, and the associated molecular mechanisms keep vague.

OBJECTIVE

To investigate the regulatory functions of USP8 in COPD progression.

MATERIAL AND METHODS

The lung functions were measured through the Buxco Fine Pointe Series Whole Body Plethysmography (WBP). The Fe level was tested through the Fe assay kit. The protein expressions were assessed through western blot. The levels of tumor necrosis -factor-α, interleukin 6, and interleukin 8 were evaluated through enzyme-linked immunosorbent serologic assay. Cell viability was tested through CCK-8 assay.

RESULTS

In this work, it was discovered that overexpression of USP8 improved lung function in COPD mice. In addition, overexpression of USP8 repressed ferroptosis by regulating glutathione peroxidase 4 and acyl-CoA synthetase long-chain family 4 expressions in COPD mice. Overexpression of USP8 suppressed inflammation in COPD mice. Furthermore, overexpression of USP8 suppressed ferroptosis in COPD cell model. At last, it was verified that overexpression of USP8 accelerated ubiquitin aldehyde-binding protein 1 (OTUB1)/solute carrier family 7 member 11 (SLC7A11) pathway.

CONCLUSION

This study manifested that overexpression of USP8 restrained inflammation and ferroptosis in COPD by regulating the OTUB1/SLC7A11 signaling pathway. This discovery hinted that USP8 could be a potential target for COPD treatment.

Ubiquitin ligase enzymes and de-ubiquitinating enzymes regulate innate immunity in the TLR, NLR, RLR, and cGAS-STING pathways

Ubiquitination (or ubiquitylation) and de-ubiquitination, which are both post-translational modifications (PTMs) of proteins, have become a research hotspot in recent years. Some ubiquitinated or de-ubiquitinated signaling proteins have been found to promote or suppress innate immunity through Toll-like receptor (TLR), RIG-like receptor (RIG-I-like receptor, RLR), NOD-like receptor (NLR), and the cyclic guanosine monophosphate (GMP)-adenosine monophosphate (AMP) synthase (cGAS)-STING pathway. This article aimed to provide a review on the role of ubiquitination and de-ubiquitination, especially ubiquitin ligase enzymes and de-ubiquitinating enzymes, in the above four pathways. We hope that our work can contribute to the research and development of treatment strategies for innate immunity-related diseases such as inflammatory bowel disease.

The METTL3/MALAT1/PTBP1/USP8/TAK1 axis promotes pyroptosis and M1 polarization of macrophages and contributes to liver fibrosis

Pro-inflammatory M1 macrophages, via activating hepatic stellate cells, contribute to liver fibrosis. In this study, we examined the mechanism and the significance of a signaling axis, METTL3/MALAT1/PTBP1/USP8/TAK1, in regulating pyroptosis and M1 polarization of hepatic macrophages. Liver fibrosis model was established in vivo by CCl₄ treatment; M1 polarization was induced in vitro by treating macrophages with lipopolysaccharide or interferon γ. Expressions of METTL3, MALAT1, PTBP1, USP8, and TAK1 were measured by RT-PCR and/or Western blot in Kupffer cells (KCs) isolated from in vivo model or in vitro activated macrophages. Macrophage phenotypes including inflammation (RT-qPCR analysis of a panel of proinflammatory cytokines and ELISA on productions of interleukin (IL)−1β and IL-18) and pyroptosis (Western blot of NLRP3, Caspase-1, and GSDMD) were investigated. The impact of METTL3 on m⁶A methylation of MALAT1 was examined by methylated RNA immunoprecipitation (RIP), the interaction between PTBP1 and MALAT1 or USP8 mRNA by combining RNA pull-down, RIP, and RNA stability assays, and the crosstalk between USP8 and TAK1 by co-immunoprecipitation and protein degradation assays. Functional significance of individual component of METTL3/MALAT1/PTBP1/USP8/TAK1 axis was assessed by combining gain-of-function and loss-of-function approaches. In KCs isolated from in vivo liver fibrosis model or in vitro M1-polarized macrophages, METTL3 was up-regulated, and sequentially, it increased MALAT1 level via m⁶A methylation, which promoted USP8 mRNA degradation through the interaction with PTBP1. Reduced USP8 expression regulated the ubiquitination and protein stability of TAK1, which promoted pyroptosis and inflammation of macrophages. The signaling cascade METTL3/MALAT1/PTBP1/USP8/TAK1, by essentially stimulating pyroptosis and inflammation of macrophages, aggravates liver fibrosis. Therefore, targeting individual components of this axis may benefit the treatment of liver fibrosis.

Chronic and Cycling Hypoxia: Drivers of Cancer Chronic Inflammation through HIF-1 and NF-κB Activation: A Review of the Molecular Mechanisms

Chronic (continuous, non-interrupted) hypoxia and cycling (intermittent, transient) hypoxia are two types of hypoxia occurring in malignant tumors. They are both associated with the activation of hypoxia-inducible factor-1 (HIF-1) and nuclear factor κB (NF-κB), which induce changes in gene expression. This paper discusses in detail the mechanisms of activation of these two transcription factors in chronic and cycling hypoxia and the crosstalk between both signaling pathways. In particular, it focuses on the importance of reactive oxygen species (ROS), reactive nitrogen species (RNS) together with nitric oxide synthase, acetylation of HIF-1, and the action of MAPK cascades. The paper also discusses the importance of hypoxia in the formation of chronic low-grade inflammation in cancerous tumors. Finally, we discuss the effects of cycling hypoxia on the tumor microenvironment, in particular on the expression of VEGF-A, CCL2/MCP-1, CXCL1/GRO-α, CXCL8/IL-8, and COX-2 together with PGE₂. These factors induce angiogenesis and recruit various cells into the tumor niche, including neutrophils and monocytes which, in the tumor, are transformed into tumor-associated neutrophils (TAN) and tumor-associated macrophages (TAM) that participate in tumorigenesis.

TAK1-TABs Complex: A Central Signalosome in Inflammatory Responses

Transforming growth factor-β (TGF-β)-activated kinase 1 (TAK1) is a member of the MAPK kinase kinase (MAPKKK) family and has been implicated in the regulation of a wide range of physiological and pathological processes. TAK1 functions through assembling with its binding partners TAK1-binding proteins (TAB1, TAB2, and TAB3) and can be activated by a variety of stimuli such as tumor necrosis factor α (TNFα), interleukin-1β (IL-1β), and toll-like receptor ligands, and they play essential roles in the activation of NF-κB and MAPKs. Numerous studies have demonstrated that post-translational modifications play important roles in properly controlling the activity, stability, and assembly of TAK1-TABs complex according to the indicated cellular environment. This review focuses on the recent advances in TAK1-TABs-mediated signaling and the regulations of TAK1-TABs complex by post-translational modifications.

Deubiquitinating Enzyme: A Potential Secondary Checkpoint of Cancer Immunity

The efficacy of cancer immunotherapy depends on the fine interplay between tumoral immune checkpoints and host immune system. However, the up-to-date clinical performance of checkpoint blockers in cancer therapy revealed that higher-level regulation should be further investigated for better therapeutic outcomes. It is becoming increasingly evident that the expression of immune checkpoints is largely associated to the immunotherapeutic response and consequent prognosis. Deubiquitinating enzymes (DUBs) with their role of cleaving ubiquitin from proteins and other molecules, thus reversing ubiquitination-mediated protein degradation, modulate multiple cellular processes, including, but not limited to, transcriptional regulation, cell cycle progression, tissue development, and antiviral response. Accumulating evidence indicates that DUBs also have the critical influence on anticancer immunity, simply by stabilizing pivotal checkpoints or key regulators of T-cell functions. Therefore, this review summarizes the current knowledge about DUBs, highlights the secondary checkpoint-like role of DUBs in cancer immunity, in particular their direct effects on the stability control of pivotal checkpoints and key regulators of T-cell functions, and suggests the therapeutic potential of DUBs-based strategy in targeted immunotherapy for cancer.

Involvement of E3 Ligases and Deubiquitinases in the Control of HIF-α Subunit Abundance

The ubiquitin and hypoxia-inducible factor (HIF) pathways are cellular processes involved in the regulation of a variety of cellular functions. Enzymes called ubiquitin E3 ligases perform protein ubiquitylation. The action of these enzymes can be counteracted by another group of enzymes called deubiquitinases (DUBs), which remove ubiquitin from target proteins. The balanced action of these enzymes allows cells to adapt their protein content to a variety of cellular and environmental stress factors, including hypoxia. While hypoxia appears to be a powerful regulator of the ubiquitylation process, much less is known about the impact of DUBs on the HIF system and hypoxia-regulated DUBs. Moreover, hypoxia and DUBs play crucial roles in many diseases, such as cancer. Hence, DUBs are considered to be promising targets for cancer cell-specific treatment. Here, we review the current knowledge about the role DUBs play in the control of HIFs, the regulation of DUBs by hypoxia, and their implication in cancer progression.