Ubiquitin specific protease 21 is dispensable for normal development, hematopoiesis and lymphocyte differentiation

Histone H2A deubiquitinases in the transcriptional programs of development and hematopoiesis: a consolidated analysis

Monoubiquitinated lysine 119 of histone H2A (H2AK119ub) is a highly abundant epigenetic mark, associated with gene repression and deposited on chromatin by the polycomb repressor complex 1 (PRC1), which is an essential regulator of diverse transcriptional programs in mammalian development and tissue homeostasis. While multiple deubiquitinases (DUBs) with catalytic activity for H2AK119ub (H2A-DUBs) have been identified, we lack systematic analyses of their roles and cross-talk in transcriptional regulation. Here, we address H2A-DUB functions in epigenetic regulation of mammalian development and tissue maintenance by conducting a meta-analysis of 248 genomics datasets from 32 independent studies, focusing on the mouse model and covering embryonic stem cells (ESCs), hematopoietic, and immune cell lineages. This covers all the publicly available datasets that map genomic H2A-DUB binding and H2AK119ub distributions (ChIP-Seq), and all datasets assessing dysregulation in gene expression in the relevant H2A-DUB knockout models (RNA-Seq). Many accessory datasets for PRC1-2 and DUB-interacting proteins are also analyzed and interpreted, as well as further data assessing chromatin accessibility (ATAC-Seq) and transcriptional activity (RNA-seq). We report co-localization in the binding of H2A-DUBs BAP1, USP16, and to a lesser extent others that is conserved across different cell-types, and also the enrichment of antagonistic PRC1-2 protein complexes at the same genomic locations. Such conserved sites enriched for the H2A-DUBs and PRC1-2 are proximal to transcriptionally active genes that engage in housekeeping cellular functions. Nevertheless, they exhibit H2AK119ub levels significantly above the genomic average that can undergo further increase with H2A-DUB knockout. This indicates a cooperation between H2A-DUBs and PRC1-2 in the modulation of housekeeping transcriptional programs, conserved across many cell types, likely operating through their antagonistic effects on H2AK119ub and the regulation of local H2AK119ub turnover. Our study further highlights existing knowledge gaps and discusses important directions for future work.

Exploiting E3 ubiquitin ligases to reeducate the tumor microenvironment for cancer therapy

Tumor development relies on a complex and aberrant tissue environment in which cancer cells receive the necessary nutrients for growth, survive through immune escape, and acquire mesenchymal properties that mediate invasion and metastasis. Stromal cells and soluble mediators in the tumor microenvironment (TME) exhibit characteristic anti-inflammatory and protumorigenic activities. Ubiquitination, which is an essential and reversible posttranscriptional modification, plays a vital role in modulating the stability, activity and localization of modified proteins through an enzymatic cascade. This review was motivated by accumulating evidence that a series of E3 ligases and deubiquitinases (DUBs) finely target multiple signaling pathways, transcription factors and key enzymes to govern the functions of almost all components of the TME. In this review, we systematically summarize the key substrate proteins involved in the formation of the TME and the E3 ligases and DUBs that recognize these proteins. In addition, several promising techniques for targeted protein degradation by hijacking the intracellular E3 ubiquitin-ligase machinery are introduced.

Targeting KRAS mutant cancers: from druggable therapy to drug resistance

Kirsten Rat Sarcoma Viral Oncogene Homolog (KRAS) is the most frequently mutated oncogene, occurring in a variety of tumor types. Targeting KRAS mutations with drugs is challenging because KRAS is considered undruggable due to the lack of classic drug binding sites. Over the past 40 years, great efforts have been made to explore routes for indirect targeting of KRAS mutant cancers, including KRAS expression, processing, upstream regulators, or downstream effectors. With the advent of KRAS (G12C) inhibitors, KRAS mutations are now druggable. Despite such inhibitors showing remarkable clinical responses, resistance to monotherapy of KRAS inhibitors is eventually developed. Significant progress has been made in understanding the mechanisms of drug resistance to KRAS-mutant inhibitors. Here we review the most recent advances in therapeutic approaches and resistance mechanisms targeting KRAS mutations and discuss opportunities for combination therapy.

Insights Into the Properties, Biological Functions, and Regulation of USP21

Deubiquitylating enzymes (DUBs) antagonize ubiquitination by removing ubiquitin from their substrates. The role of DUBs in controlling various physiological and pathological processes has been extensively studied, and some members of DUBs have been identified as potential therapeutic targets in diseases ranging from tumors to neurodegeneration. Ubiquitin-specific protease 21 (USP21) is a member of the ubiquitin-specific protease family, the largest subfamily of DUBs. Although USP21 was discovered late and early research progress was slow, numerous studies in the last decade have gradually revealed the importance of USP21 in a wide variety of biological processes. In particular, the pro-carcinogenic effect of USP21 has been well elucidated in the last 2 years. In the present review, we provide a comprehensive overview of the current knowledge on USP21, including its properties, biological functions, pathophysiological roles, and cellular regulation. Limited pharmacological interventions for USP21 have also been introduced, highlighting the importance of developing novel and specific inhibitors targeting USP21.

Deubiquitination and Stabilization of PD-L1 by USP21

Recent studies have shown that the expression level of PD-L1 in tumor cells positively correlates with tumor metastasis and recurrence rate. The effects of post-translational modifications (PTMs) of PD-L1 are related to immunosuppression. However, the degradation of PD-L1 in cancers has not yet been sufficiently defined. Here, we identified USP21 as a novel deubiquitinase of PD-L1. Overexpression of USP21 significantly increased PD-L1 abundance while its knockdown induced PD-L1 degradation. In vitro deubiquitination assay revealed that USP21-WT, but not USP21-C221A, reduced polyubiquitin chains of PD-L1. These results highlight the role of USP21 in the deubiquitination and stabilization of PD-L1. Furthermore, we show that USP21 is the frequently amplified deubiquitinase in lung cancer, especially in lung squamous cell carcinoma, and its amplification is accompanied by upregulation of PD-L1. This study reveals the mechanism of USP21-mediated PD-L1 degradation, and suggests that USP21 might be a potential target for the treatment of lung cancer.

Anticipating resistance to KRAS inhibition: a novel role for USP21 in macropinocytosis regulation

This Outlook discusses the finding by Hou et al. describing the mechanism by which the deubiquitinase USP21 up-regulates the nutrient-scavenging process of macropinocytosis, rescuing PDAC cells from Kras extinction.

Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest cancers. Virtually all PDAC harbors an oncogenic mutation in the KRAS gene, making it the prime target for therapy. Most previous attempts to inhibit KRAS directly have been disappointing, but recent success in targeting some KRAS mutants presages a new era in PDAC therapy. Models of PDAC have predicted that identifying KRAS inhibitor resistance mechanisms will be critical. In this issue of Genes & Development, Hou and colleagues (pp. 1327–1332) identify one such mechanism in which the deubiquitinase USP21 up-regulates the nutrient-scavenging process of macropinocytosis, rescuing PDAC cells from Kras extinction.

USP21 deubiquitinase elevates macropinocytosis to enable oncogenic KRAS bypass in pancreatic cancer

Activating mutations in KRAS (KRAS*) are present in nearly all pancreatic ductal adenocarcinoma (PDAC) cases and critical for tumor maintenance. By using an inducible KRAS* PDAC mouse model, we identified a deubiquitinase USP21-driven resistance mechanism to anti-KRAS* therapy. USP21 promotes KRAS*-independent tumor growth via its regulation of MARK3-induced macropinocytosis, which serves to maintain intracellular amino acid levels for anabolic growth. The USP21-mediated KRAS* bypass, coupled with the frequent amplification of USP21 in human PDAC tumors, encourages the assessment of USP21 as a novel drug target as well as a potential parameter that may affect responsiveness to emergent anti-KRAS* therapy.

The Route of Early T Cell Development: Crosstalk between Epigenetic and Transcription Factors

Hematopoietic multipotent progenitors seed the thymus and then follow consecutive developmental stages until the formation of mature T cells. During this process, phenotypic changes of T cells entail stage-specific transcriptional programs that underlie the dynamic progression towards mature lymphocytes. Lineage-specific transcription factors are key drivers of T cell specification and act in conjunction with epigenetic regulators that have also been elucidated as crucial players in the establishment of regulatory networks necessary for proper T cell development. In this review, we summarize the activity of transcription factors and epigenetic regulators that together orchestrate the intricacies of early T cell development with a focus on regulation of T cell lineage commitment.

Post-Translational Regulations of Foxp3 in Treg Cells and Their Therapeutic Applications

Regulatory T (Treg) cells are indispensable for immune homeostasis due to their roles in peripheral tolerance. As the master transcription factor of Treg cells, Forkhead box P3 (Foxp3) strongly regulates Treg function and plasticity. Because of this, considerable research efforts have been directed at elucidating the mechanisms controlling Foxp3 and its co-regulators. Such work is not only advancing our understanding on Treg cell biology, but also uncovering novel targets for clinical manipulation in autoimmune diseases, organ transplantation, and tumor therapies. Recently, many studies have explored the post-translational regulation of Foxp3, which have shown that acetylation, phosphorylation, glycosylation, methylation, and ubiquitination are important for determining Foxp3 function and plasticity. Additionally, some of these targets have been implicated to have great therapeutic values. In this review, we will discuss emerging evidence of post-translational regulations on Foxp3 in Treg cells and their exciting therapeutic applications.

Regulation of B Lymphocyte Development by Histone H2A Deubiquitinase BAP1

BAP1 is a deubiquitinase (DUB) of the Ubiquitin C-terminal Hydrolase (UCH) family that regulates gene expression and other cellular processes, via deubiquitination of histone H2AK119ub and other substrates. BAP1 is an important tumor suppressor in human, expressed and functional across many cell-types and tissues, including those of the immune system. B lymphocytes are the mediators of humoral immune response, however the role of BAP1 in B cell development and physiology remains poorly understood. Here we characterize a mouse line with a selective deletion of BAP1 within the B cell lineage (Bap1fl/fl mb1-Cre) and establish a cell intrinsic role of BAP1 in the regulation of B cell development. We demonstrate a depletion of large pre-B cells, transitional B cells, and mature B cells in Bap1fl/fl mb1-Cre mice. We characterize broad transcriptional changes in BAP1-deficient pre-B cells, map BAP1 binding across the genome, and analyze the effects of BAP1-loss on histone H2AK119ub levels and distribution. Overall, our work establishes a cell intrinsic role of BAP1 in B lymphocyte development, and suggests its contribution to the regulation of the transcriptional programs of cell cycle progression, via the deubiquitination of histone H2AK119ub.

Ubiquitin-Dependent Regulation of Treg Function and Plasticity

As an indispensable part of peripheral tolerance, regulatory T (Treg) cells play an important role in immune homeostasis by suppressing other immune cells. Behind this function is a complex network of transcription factors and signaling cascades that regulates the function and plasticity of regulatory T cells. Among these, Forkhead box P3 (Foxp3) is considered as the master transcription factor, and its stability will influence the function and viability of Treg cells. Because of this, understanding the mechanisms that regulate Foxp3 and its co-regulators will provide more understanding to Treg cells and uncover more targets to manipulate Treg cells in treating autoimmune diseases, organ transplantation, and tumor. Interestingly, several recent studies show that ubiquitin-dependent pathways are important regulators of Foxp3, which suggest both great scientific and therapeutic values. In this chapter, we cover emerging evidence of ubiquitin-dependent, posttranslational regulation of Treg function and plasticity.

Schistosoma japonicum Infection in Treg-Specific USP21 Knockout Mice

The E3 deubiquitinating enzyme ubiquitin-specific proteolytic enzyme 21 (USP21) plays vital roles in physiological activities and is required for Treg-cell-mediated immune tolerance. Using a murine model infected with Schistosoma japonicum, we observed that there were more cercariae developed into adults and more eggs deposited in the livers of the USP21^fl/flFOXP3^Cre (KO) mice. However, immunohistochemistry showed that the degree of egg granuloma formation and liver fibrosis was reduced. In USP21^fl/flFOXP3^Cre mice, levels of IFN-gamma, IL-4, anti-soluble egg antigen (SEA) IgG and anti-soluble worm antigen preparation (SWAP) IgG increased in blood, as determined using ELISAs and multiplex fluorescent microsphere immunoassays, while the levels of IL-10, lL-17A, IL-23, IL-9, and anti-SEA IgM decreased. In addition, the levels of the USP21 protein and mRNA in the liver and spleen of KO mice decreased. We further observed increased Th1 responses amplified by Tregs (regulatory T cells) and compromised Th17 responses, which alleviated the liver immunopathology. We speculated that these changes were related to polarization of Th1-like Tregs. Our results revealed the roles of USP21 in Treg-cell-mediated regulation of immune interactions between Schistosoma and its host. USP21 may have potential for regulating hepatic fibrosis in patients with schistosomiasis.

DUBbing Down Translation: The Functional Interaction of Deubiquitinases with the Translational Machinery

Cancer cells revamp the regulatory processes that control translation to induce tumor-specific translational programs that can adapt to a hostile microenvironment as well as withstand anticancer therapeutics. Translational initiation has been established as a common downstream effector of numerous deregulated signaling pathways that together culminate in prooncogenic expression. Other mechanisms, including ribosomal stalling and stress granule assembly, also appear to be rewired in the malignant phenotype. Therefore, better understanding of the underlying perturbations driving oncogenic translation in the transformed state will provide innovative therapeutic opportunities. This review highlights deubiquitinating enzymes that are activated/dysregulated in hematologic malignancies, thereby altering the translational output and contributing to tumorigenesis.

HAUSP promoted the growth of glioma cells in vitro and in vivo via stabilizing NANOG

OBJECTIVE

To investigate the role and mechanisms of HAUSP (Herpesvirus Associated Ubiquitin Specific Protease) and NANOG in pathogenesis of malignant human gliomas progression.

METHODS

Lentivirus-mediated HAUSP over-expression and RNAiHAUSP mediated HAUSP down-regulation were established in the glioma cells (U87 and U251 cell lines). Firstly, Real-time qPCR, western-blot (WB) and immunofluorescence staining were performed to detect mRNA levels, protein expressions and deposition of HAUSP and NANOG in the glioma cells, respectively. Then cell proliferation, invasion, apoptosis and xenograft tumor growth in nude mice were assessed by using cell counting kit-8 (CCK-8) assay, transwell assay, flow cytometry (FCM) and Hematoxylin-Eosin (HE) staining.

RESULTS

We first demonstrated HAUSP was significantly increased in lentivirus- mediated HAUSP over-expression cells compared to the Control group. HAUSP over-expression could upregulate genes involved in proliferation and invasion such as NANOG. However, the mRNA of NANOG had no significant changes. Similarly, in RNAiHAUSP mediated HAUSP down-regulation group, HAUSP were significantly decreased compared to the Control group. Simultaneously, NANOG protein were decreased significantly, which decreased the proliferation and invasion, increased the apoptosis rate of glioma cells. Finally, low expression of HAUSP could suppress xenograft tumors growth in nude mice in different periods.

CONCLUSION

This study revealed that HAUSP-NANOG pathway is a key target to inhibit glioma cells proliferation, and NANOG play important role in the formation and evolution of glioma cells. The regulation of HAUSP could change the biological activity of glioma cells through regulate NANOG expression.

Ubiquitin Dynamics in Stem Cell Biology: Current Challenges and Perspectives

Ubiquitination plays a central role in the regulation of stem cell self-renewal, propagation, and differentiation. In this review, the functions of ubiquitin dynamics in a myriad of cellular processes, acting along side the pluripotency network, to regulate embryonic stem cell identity are highlighted. The implication of deubiquitinases (DUBs) and E3 Ubiquitin (Ub) ligases in cellular functions beyond protein degradation is reported, including key functions in the regulation of mRNA stability, protein translation, and intra-cellular trafficking; and how it affects cell metabolism, the micro-environment, and chromatin organization is discussed. Finally, unsolved issues in the field are emphasized and will need to be tackled in order to fully understand the contribution of ubiquitin dynamics to stem cell self-renewal and differentiation.

The USP21/YY1/SNHG16 axis contributes to tumor proliferation, migration, and invasion of non-small-cell lung cancer

Deubiquitinases (DUBs) and noncoding RNAs have been the subjects of recent extensive studies regarding their roles in lung cancer, but the mechanisms involved are largely unknown. In our study, we used The Cancer Genome Atlas data set and bioinformatics analyses and identified USP21, a DUB, as a potential contributor to oncogenesis in non-small-cell lung cancer (NSCLC). We further demonstrated that USP21 was highly expressed in NSCLCs. We then conducted a series of in vitro and in vivo assays to explore the effect of USP21 on NSCLC progression and the underlying mechanism involved. USP21 promoted NSCLC cell proliferation, migration, and invasion and in vivo tumor growth by stabilizing a well-known oncogene, Yin Yang-1 (YY1), via mediating its deubiquitination. Furthermore, YY1 transcriptionally regulates the expression of SNHG16. Moreover, StarBase bioinformatics analyses predicted that miR-4500 targets SNHG16 and USP21. A series of in vitro experiments indicated that SNHG16 increased the expression of USP21 through miR-4500. In summary, the USP21/YY1/SNHG16 axis plays a role in promoting the progression of NSCLC. Therefore, the USP21/YY1/SNHG16/miR-4500 axis may be a potential therapeutic target in NSCLC treatment.

Therapies targeting a molecular feedback loop involved in tumor growth may prove valuable for treating non-small-cell lung cancer. Fangbao Ding, Jianbing Huang, and co-workers at Shanghai Jiao Tong University in Shanghai, China, have shown how an enzyme called USP21 promotes cancer cell proliferation and tumor growth in non-small-cell lung cancer. The team took cancerous and non-cancerous lung tissue samples from 42 patients, and analyzed the expression and behavior of USP21. The enzyme was highly expressed in cancerous tissues, where it stabilized a known gene with the potential to cause cancer called YY1. This gene also regulated the expression of a particular RNA molecule, which in turn worked to increase levels of USP21. This cyclical process encouraged the proliferation, migration and invasion of non-small-cell lung cancer cells, and may provide a future therapeutic target.

Ubiquitin-Specific Protease 21 Promotes Colorectal Cancer Metastasis by Acting as a Fra-1 Deubiquitinase

Fos-related-antigen-1 (Fra-1), a member of the activator protein-1 (AP-1) transcription factor superfamily, has an essential role in cancer progress and metastasis and Fra-1 is considered a therapeutic target in metastatic cancer including metastatic colorectal cancer (mCRC). However, its regulation at protein level has not yet been clearly elucidated. We found that ubiquitin-specific protease 21 (USP21) increases Fra-1 stability by deubiquitinating Fra-1 and enhances the expression of Fra-1 target genes in colon cancer cells. We also showed that USP21 controlled Fra-1-dependent migration and invasion activities. The oncogenic property of USP21 was confirmed by a significant reduction in liver metastasis when USP21-knockdown cancer cells were injected intrasplenically into mice. Consistently, clinicopathological analysis of colorectal cancer patients revealed a correlation of USP21 expression with high-grade carcinoma and life span. These results demonstrate that USP21 enhances Fra-1 stability and AP-1 target gene expression by deubiquitinating Fra-1. Therefore, USP21 is considered an attractive therapeutic target in mCRC with high Fra-1 expression.

USP21 modulates Goosecoid function through deubiquitination

The homeobox gene Goosecoid (GSC), which is known to regulate craniofacial development, is activated by mono-ubiquitination; however, the deubiquitylase responsible for GSC deubiquitination and inhibition has yet to be identified. In the present study, we constructed the recombinant plasmid pFlag-CMV-2-GSC and the SRY (sex-determining region Y)-box 6 (Sox6) reporter gene system to identify deubiquitylases that regulate GSC expression. We demonstrate that the ubiquitin carboxyl-terminal hydrolase 21 (USP21) regulates the deubiquitination of GSC negatively, as demonstrated by its inhibition of Sox6 reporter gene transcription. USP21 interacted with GSC to promote GSC deubiquitination while having no effect on GSC protein stability. Cell viability, migration, and function in ATDC5 cells were probably influenced by USP21 through GSC. These findings suggest that USP21 modulates GSC function through deubiquitination.

The role of ubiquitin-specific peptidases in cancer progression

Protein ubiquitination is an important mechanism for regulating the activity and levels of proteins under physiological conditions. Loss of regulation by protein ubiquitination leads to various diseases, such as cancer. Two types of enzymes, namely, E1/E2/E3 ligases and deubiquitinases, are responsible for controlling protein ubiquitination. The ubiquitin-specific peptidases (USPs) are the main members of the deubiquitinase family. Many studies have addressed the roles of USPs in various diseases. An increasing number of studies have indicated that USPs are critical for cancer progression, and some USPs have been used as targets to develop inhibitors for cancer prevention. Herein we collect and organize most of the recent studies on the roles of USPs in cancer progression and discuss the development of USP inhibitors for cancer therapy in the future.

Regulation of T cell differentiation and function by ubiquitin-specific proteases

T cells play critical roles in immune responses to pathogens, autoimmunity, and antitumor immunity. During the past few decades, increasing numbers of studies have demonstrated the significance of protein ubiquitination in T cell-mediated immunity. Several E3 ubiquitin ligases and deubiquitinases (DUBs) have been identified as either positive or negative regulators of T cell development and function. In this review, we mainly focus on the roles of DUBs (especially ubiquitin-specific proteases (USPs)) in modulating T cell differentiation and function, as well as the molecular mechanisms. Understanding how T cell development and function is regulated by ubiquitination and deubiquitination will provide novel strategies for treating infection, autoimmune diseases, and cancer.

Epigenetic modifications in chronic myeloid leukemia cells through ruxolitinib treatment

Chronic myeloid leukemia is a clonal malignancy of hematopoietic stem cell that is characterized by the occurrence of t(9;22)(q34;q11.2) translocation, named Philadelphia chromosome. Ruxolitinib is a powerful Janus tyrosine kinase 1 and 2 inhibitor that is used for myelofibrosis treatment. DNA-histone connection mediates a wide range of genes that code methylation, demethylation, acetylation, deacetylation, ubiquitination, and phosphorylation enzymes. Epigenetic modifications regulate chromatin compactness, which plays pivotal roles in critical biological processes including the transcriptional activity and cell proliferation as well as various pathological mechanisms, including CML. This study is aimed to determine the alterations of the expression levels of epigenetic modification-related genes after ruxolitinib treatment. Total RNA was isolated from K-562 cells treated with the IC₅₀ value of ruxolitinib and untreated K-562 control cells. A reverse transcription procedure was performed for complementary DNA synthesis, and gene expressions were detected by real-time polymerase chain reaction compared with the untreated cells. Ruxolitinib treatment caused a significant alteration in the expression levels of epigenetic regulation-related genes in K-562 cells. Our novel results suggested that ruxolitinib has inhibitor effects on epigenetic modification-regulator genes.

Ubiquitin-specific protease 21 stabilizes BRCA2 to control DNA repair and tumor growth

Tumor growth relies on efficient DNA repair to mitigate the detrimental impact of DNA damage associated with excessive cell division. Modulating repair factor function, thus, provides a promising strategy to manipulate malignant growth. Here, we identify the ubiquitin-specific protease USP21 as a positive regulator of BRCA2, a key mediator of DNA repair by homologous recombination. USP21 interacts with, deubiquitinates and stabilizes BRCA2 to promote efficient RAD51 loading at DNA double-strand breaks. As a result, depletion of USP21 decreases homologous recombination efficiency, causes an increase in DNA damage load and impairs tumor cell survival. Importantly, BRCA2 overexpression partially restores the USP21-associated survival defect. Moreover, we show that USP21 is overexpressed in hepatocellular carcinoma, where it promotes BRCA2 stability and inversely correlates with patient survival. Together, our findings identify deubiquitination as a means to regulate BRCA2 function and point to USP21 as a potential therapeutic target in BRCA2-proficient tumors.BRCA2 is essential for the repair of DNA damage; therefore, defects in BRCA2 are associated with tumorigenesis but also with increased susceptibility to genotoxic stress. Here the authors show that USP21 regulates the ability of tumor cells to repair damaged DNA by regulating BRCA2 stability.

A role for the histone H2A deubiquitinase MYSM1 in maintenance of CD8+ T cells

Several previous studies outlined the importance of the histone H2A deubiquitinase MYSM1 in the regulation of stem cell quiescence and haematopoiesis. In this study we investigated the role of MYSM1 in T-cell development. Using mouse models that allow conditional Mysm1 ablation at late stages of thymic development, we found that MYSM1 is intricately involved in the maintenance, activation and survival of CD8⁺ T cells. Mysm1 ablation resulted in a twofold reduction in CD8⁺ T-cell numbers, and also led to a hyperactivated CD8⁺ T-cell state accompanied by impaired proliferation and increased pro-inflammatory cytokine production after ex vivo stimulation. These phenotypes coincided with an increased apoptosis and preferential up-regulation of p53 tumour suppressor protein in CD8⁺ T cells. Lastly, we examined a model of experimental cerebral malaria, in which pathology is critically dependent on CD8⁺ T cells. In the mice conditionally deleted for Mysm1 in the T-cell compartment, CD8⁺ T-cell numbers remained reduced following infection, both in the periphery and in the brain, and the mice displayed improved survival after parasite challenge. Collectively, our data identify MYSM1 as a novel factor for CD8⁺ T cells in the immune system, increasing our understanding of the role of histone H2A deubiquitinases in cytotoxic T-cell biology.

USP21 promotes cell proliferation and metastasis through suppressing EZH2 ubiquitination in bladder carcinoma

Bladder cancer (BC) is the second most common malignant tumor of the urinary tract in the world. In this study, we found that ubiquitin-specific protease (USP21) was upregulated in BC and the ectopic expression of USP21 was closely associated with tumor size and metastasis. Moreover, patients with higher levels of USP21 had poorer survival rate. Multiple function analysis such as CCK-8, colony formation, wound healing, and transwell analysis indicated that USP21 regulated cell proliferation and metastasis in bladder carcinoma cell lines. We also found that USP21 could facilitate epithelial–mesenchymal transition. As EZH2 has been reported to promote cell metastasis in BC, our work identified that USP21 deubiquitinated EZH2 and stabilized it. Our data demonstrated that USP21 might play a crucial role in regulating BC progression and could provide a potential therapeutic strategy for BC.

The deubiquitinase USP21 maintains the stemness of mouse embryonic stem cells via stabilization of Nanog

Nanog is a master pluripotency factor of embryonic stem cells (ESCs). Stable expression of Nanog is essential to maintain the stemness of ESCs. However, Nanog is a short-lived protein and quickly degraded by the ubiquitin-dependent proteasome system. Here we report that the deubiquitinase USP21 interacts with, deubiquitinates and stabilizes Nanog, and therefore maintains the protein level of Nanog in mouse ESCs (mESCs). Loss of USP21 results in Nanog degradation, mESCs differentiation and reduces somatic cell reprogramming efficiency. USP21 is a transcriptional target of the LIF/STAT3 pathway and is downregulated upon differentiation. Moreover, differentiation cues promote ERK-mediated phosphorylation and dissociation of USP21 from Nanog, thus leading to Nanog degradation. In addition, USP21 is recruited to gene promoters by Nanog to deubiquitinate histone H2A at K119 and thus facilitates Nanog-mediated gene expression. Together, our findings provide a regulatory mechanism by which extrinsic signals regulate mESC fate via deubiquitinating Nanog.

Nanog regulates embryonic stem cell (ESC) pluripotency but what controls Nanog protein stability is unclear. Here, the authors show that in mouse ESCs, Nanog protein is ubiquitinated and stabilized by the deubiquitinase USP21, which in turn is regulated by extrinsic signals, STAT3 and ERK.

USP21 prevents the generation of T-helper-1-like Treg cells

FOXP3⁺ Regulatory T (Treg) cells play a key role in the maintenance of immune homeostasis and tolerance. Disruption of Foxp3 expression results in the generation of instable Treg cells and acquisition of effector T-cell-like function. Here we report that the E3 deubiquitinase USP21 prevents the depletion of FOXP3 at the protein level and restricts the generation of T-helper-1-like Treg cells. Mice depleted of Usp21 specifically in Treg cells display immune disorders characterized by spontaneous T-cell activation and excessive T-helper type 1 (Th1) skewing of Treg cells into Th1-like Treg cells. USP21 stabilizes FOXP3 protein by mediating its deubiquitination and maintains the expression of Treg signature genes. Our results demonstrate how USP21 prevents FOXP3 protein depletion and controls Treg lineage stability in vivo.

The immunosuppressive role of regulatory T (Treg) cells largely depends on their virtue of expressing the transcription factor FOXP3. Here the authors show that the E3 deubiquitinase USP21 stabilizes FOXP3 by mediating its deubiquitination and helps to maintain the expression of Treg signature genes and Treg lineage stability in mice.

USP21 deubiquitylates Nanog to regulate protein stability and stem cell pluripotency

The homeobox transcription factor Nanog has a vital role in maintaining pluripotency and self-renewal of embryonic stem cells (ESCs). Stabilization of Nanog proteins is essential for ESCs. The ubiquitin-proteasome pathway mediated by E3 ubiquitin ligases and deubiquitylases is one of the key ways to regulate protein levels and functions. Although ubiquitylation of Nanog catalyzed by the ligase FBXW8 has been demonstrated, the deubiquitylase that maintains the protein levels of Nanog in ESCs yet to be defined. In this study, we identify the ubiquitin-specific peptidase 21 (USP21) as a deubiquitylase for Nanog, but not for Oct4 or Sox2. USP21 interacts with Nanog protein in ESCs in vivo and in vitro. The C-terminal USP domain of USP21 and the C-domain of Nanog are responsible for this interaction. USP21 deubiquitylates the K48-type linkage of the ubiquitin chain of Nanog, stabilizing Nanog. USP21-mediated Nanog stabilization is enhanced in mouse ESCs and this stabilization is required to maintain the pluripotential state of the ESCs. Depletion of USP21 in mouse ESCs leads to Nanog degradation and ESC differentiation. Overall, our results demonstrate that USP21 maintains the stemness of mouse ESCs through deubiquitylating and stabilizing Nanog.

Regulation of Met1-linked polyubiquitin signalling by the deubiquitinase OTULIN

Modification of proteins with Met1‐linked ‘linear’ ubiquitin chains has emerged as a key regulatory signal to control inflammatory signalling via the master regulator, the transcription factor nuclear factor κB (NF‐κB). While the assembly machinery, the linear ubiquitin chain assembly complex (LUBAC), and receptors for this ubiquitin chain type have been known for years, it was less clear which deubiquitinating enzymes (DUBs) hydrolyse Met1 linkages specifically. In 2013, two labs reported the previously unannotated protein FAM105B/OTULIN to be this missing Met1 linkage‐specific DUB. Structural studies have revealed how OTULIN achieves its remarkable specificity, employing a mechanism of ubiquitin‐assisted catalysis in which a glutamate residue on the substrate complements the active site of the enzyme. The specificity of OTULIN enables it to regulate global levels of Met1‐linked polyubiquitin in cells. This ability led to investigations of NF‐κB activation from new angles, and also revealed involvement of Met1‐polyubiquitin in Wnt signalling. Interestingly, OTULIN directly interacts with LUBAC, and this interaction is dynamic and can be regulated by OTULIN phosphorylation. This provides a new paradigm for how individual linkage types can be regulated by dedicated enzyme complexes mediating assembly and removal. Here we review what has been learned about OTULIN's mechanism, regulation and function, discuss the open questions in the field, and discuss how DUBs regulate the NF‐κB response.

FOXP3(+) Treg Cells and Gender Bias in Autoimmune Diseases

CD4⁺CD25⁺ regulatory T (Treg) cells play a pivotal role in the maintenance of immune homeostasis, where the X-linked master transcription factor forkhead box P3 (FOXP3) determines Treg cell development and function. Genetic deficiency of foxp3 induces dysfunction of Treg cells and immuno-dysregulation, polyendocrinopathy, enteropathy, and X-linked syndrome in humans. Functionally deficient Treg cells or the development of exTreg cells positively correlate with autoimmune diseases, such as systemic lupus erythematosus (SLE), multiple sclerosis (MS), and ankylosing spondylitis (AS). In general, females are more susceptible to SLE and MS but less susceptible to AS, where the expression of FOXP3 and its protein complex are perturbed by multiple factors, including hormonal fluctuations, inflammatory cytokines, and danger signals. Therefore, it is critical to explore the potential molecular mechanisms involved and these differences linked to gender. Here, we review recent findings on the regulation of FOXP3 activity in Treg cells and also discuss gender difference in the determination of Treg cell function in autoimmune diseases.