Ubiquitin-specific Protease-7 Inhibition Impairs Tip60-dependent Foxp3+ T-regulatory Cell Function and Promotes Antitumor Immunity

Comprehensive analysis of the relationship between ubiquitin-specific protease 21 (USP21) and prognosis, tumor microenvironment infiltration, and therapy response in colorectal cancer

BACKGROUND

Ubiquitin-specific proteases family is crucial to host immunity against pathogens. However, the correlations between USP21 and immunosurveillance and immunotherapy for colorectal cancer (CRC) have not been reported.

METHODS

The differential expression of USP21 between CRC tissues and normal tissues was analyzed using multiple public databases. Validation was carried out in clinical samples through qRT-PCR and IHC. The correlation between USP21 and the prognosis, as well as clinical pathological characteristics of CRC patients, was investigated. Moreover, cell models were established to assess the influence of USP21 on CRC growth and progression, employing CCK-8 assays, colony formation assays, and wound-healing assays. Subsequently, gene set variation analysis (GSVA) was used to explore the potential biological functions of USP21 in CRC. The study also examined the impact of USP21 on cytokine levels and immune cell infiltration in the tumor microenvironment (TME). Finally, the effect of USP21 on the response to immunotherapy and chemotherapy in CRC was analyzed.

RESULTS

The expression of USP21 was significantly upregulated in CRC. High USP21 is correlated with poor prognosis in CRC patients and facilitates the proliferation and migration capacities of CRC cells. GSVA indicated an association between low USP21 and immune activation. Moreover, low USP21 was linked to an immune-activated TME, characterized by high immune cell infiltration. Importantly, CRC with low USP21 exhibited higher tumor mutational burden, high PD-L1 expression, and better responsiveness to immunotherapy and chemotherapeutic drugs.

CONCLUSION

This study revealed the role of USP21 in TME, response to therapy, and clinical prognosis in CRC, which provided novel insights for the therapeutic application in CRC.

Deubiquitinating enzymes: potential regulators of the tumor microenvironment and implications for immune evasion

Ubiquitination and deubiquitination are important forms of posttranslational modification that govern protein homeostasis. Deubiquitinating enzymes (DUBs), a protein superfamily consisting of more than 100 members, deconjugate ubiquitin chains from client proteins to regulate cellular homeostasis. However, the dysregulation of DUBs is reportedly associated with several diseases, including cancer. The tumor microenvironment (TME) is a highly complex entity comprising diverse noncancerous cells (e.g., immune cells and stromal cells) and the extracellular matrix (ECM). Since TME heterogeneity is closely related to tumorigenesis and immune evasion, targeting TME components has recently been considered an attractive therapeutic strategy for restoring antitumor immunity. Emerging studies have revealed the involvement of DUBs in immune modulation within the TME, including the regulation of immune checkpoints and immunocyte infiltration and function, which renders DUBs promising for potent cancer immunotherapy. Nevertheless, the roles of DUBs in the crosstalk between tumors and their surrounding components have not been comprehensively reviewed. In this review, we discuss the involvement of DUBs in the dynamic interplay between tumors, immune cells, and stromal cells and illustrate how dysregulated DUBs facilitate immune evasion and promote tumor progression. We also summarize potential small molecules that target DUBs to alleviate immunosuppression and suppress tumorigenesis. Finally, we discuss the prospects and challenges regarding the targeting of DUBs in cancer immunotherapeutics and several urgent problems that warrant further investigation.

Investigating the T regulatory cells and Sirtuin-I serum level in immunotherapy treated house dust mite allergic asthma patients

OBJECTIVES

House dust mite aeroallergens are predominant triggers of frequent asthma attacks among adults and children. The intensity of asthma and immune reaction necessitates treatment alternatives based on adjusting chosen immunity biomarkers to control the exacerbation of symptoms and establish long-term immune tolerance. In this study, we selected CD4+CD25+Foxp3+ regulatory T cells (Tregs), FOXP3, and Sirtuin-1 as they are known to have a potential role in the immune reaction in different allergic diseases. We investigated their interplay during HDM allergic asthma and its respective immunotherapy.

METHODS

Eighty-four subjects were divided into 3 groups; healthy controls (CT), HDM asthma patients without immunotherapy (WOIT), and HDM asthma patients treated with subcutaneous immunotherapy for 6 months before recruitment (WIT). They were enrolled according to the pulmonary function, skin prick tests, and HDM-specific IgE. CD4+ CD25+ and CD4+ CD25+ FOXP3+hi T cells Cell percentages, FOXP3 gene expression, and Sirtuin-1 (Sirt1) serum level were analyzed.

RESULTS

We found that there is a significant difference between WOIT and WIT groups in the CD4+ CD25+ and CD4+ CD25+ FOXP3+hi T cell percentages. While there is no statistically significant difference between WOIT and WIT groups in FOXP3 level. On the controversy, the SIRT1 level in the CT group (4.53 ± 3.880) significantly decreased in the WOIT and WIT groups.

CONCLUSION

This study revealed that both CD4 CD25 and CD4 CD25 high FOXP3 cell percentages increased in the WIT group and declined in the WOIT group. While, FOXP3 gene expression increased in both groups. In addition, the Sirt1 serum level showed some improvement in WIT group after a serious drop in the WOIT group comparing with the CT group. The modulation of these biomarkers for the remission and control of allergic asthma can be a prognostic outcome of immunotherapy which needs to be confirmed by larger scale studies.

USP7 inhibitors suppress tumour neoangiogenesis and promote synergy with immune checkpoint inhibitors by downregulating fibroblast VEGF

BACKGROUND

Understanding how to modulate the microenvironment of tumors that are resistant to immune checkpoint inhibitors represents a major challenge in oncology.Here we investigate the ability of USP7 inhibitors to reprogram the tumor microenvironment (TME) by inhibiting secretion of vascular endothelial growth factor (VEGF) from fibroblasts.

METHODS

To understand the role played by USP7 in the TME, we systematically evaluated the effects of potent, selective USP7 inhibitors on co-cultures comprising components of the TME, using human primary cells. We also evaluated the effects of USP7 inhibition on tumor growth inhibition in syngeneic models when dosed in combination with immune checkpoint inhibitors (ICIs).

RESULTS

Abrogation of VEGF secretion from fibroblasts in response to USP7 inhibition resulted in inhibition of tumor neoangiogenesis and increased tumor recruitment of CD8-positive T-lymphocytes, leading to significantly improved sensitivity to immune checkpoint inhibitors. In syngeneic models, treatment with USP7 inhibitors led to striking tumor responses resulting in significantly improved survival.

CONCLUSIONS

USP7-mediated reprograming of the TME is not linked to its previously characterized role in modulating MDM2 but does require p53 and UHRF1 in addition to the well-characterized VEGF transcription factor, HIF-1α. This represents a function of USP7 that is unique to fibroblasts, and which is not observed in cancer cells or other components of the TME. Given the potential for USP7 inhibitors to transform "immune desert" tumors into "immune responsive" tumors, this paves the way for a novel therapeutic strategy combining USP7 inhibitors with immune checkpoint inhibitors (ICIs).

Reprogramming of regulatory T cells in inflammatory tumor microenvironment: can it become immunotherapy turning point?

Overcoming the immunosuppressive tumor microenvironment and identifying widely used immunosuppressants with minimal side effects are two major challenges currently hampering cancer immunotherapy. Regulatory T cells (Tregs) are present in almost all cancer tissues and play an important role in preserving autoimmune tolerance and tissue homeostasis. The tumor inflammatory microenvironment causes the reprogramming of Tregs, resulting in the conversion of Tregs to immunosuppressive phenotypes. This process ultimately facilitates tumor immune escape or tumor progression. However, current systemic Treg depletion therapies may lead to severe autoimmune toxicity. Therefore, it is crucial to understand the mechanism of Treg reprogramming and develop immunotherapies that selectively target Tregs within tumors. This article provides a comprehensive review of the potential mechanisms involved in Treg cell reprogramming and explores the application of Treg cell immunotherapy. The interference with reprogramming pathways has shown promise in reducing the number of tumor-associated Tregs or impairing their function during immunotherapy, thereby improving anti-tumor immune responses. Furthermore, a deeper understanding of the mechanisms that drive Treg cell reprogramming could reveal new molecular targets for future treatments.

SP1-activated USP27X-AS1 promotes hepatocellular carcinoma progression via USP7-mediated AKT stabilisation

BACKGROUND

Hepatocellular carcinoma (HCC) continues to pose a significant threat to patient survival. Emerging evidence underscores the pivotal involvement of long non-coding RNAs (lncRNAs) in the cancer process. Nevertheless, our understanding of the roles and processes of lncRNAs in HCC remains limited.

METHODS

The expression level of USP27X-AS1 was assessed in an HCC patient cohort through a combination of bioinformatics analysis and qRT-PCR. Subsequent biological experiments were conducted to delve into the functional aspects of USP27X-AS1. Additional molecular biology techniques, including RNA pulldown and RNA immunoprecipitation (RIP), were employed to elucidate the potential mechanisms involving USP27X-AS1 in HCC. Finally, CUT-RUN assay and other investigations were carried out to determine the factors contributing to the heightened expression of USP27X-AS1 in HCC.

RESULTS

High expression of the novel oncogene USP27X-AS1 predicted poor prognosis in HCC patients. Further investigation confirmed that USP27X-AS1 promoted the proliferation and metastasis of HCC by enabling USP7 to interact with AKT, which reduced level of AKT poly-ubiquitylation and enhanced AKT protein stability, which improves protein stabilisation of AKT and promotes the progression of HCC. Moreover, we also revealed that SP1 binds to USP27X-AS1 promoter to activate its transcription.

CONCLUSIONS

Novel oncogenic lncRNA USP27X-AS1 promoted HCC progression via recruiting USP7 to deubiquitinate AKT. SP1 transcriptionally activated USP27X-AS1 expression. These findings shed light on HCC and pointed to USP27X-AS1 as a potential predictive biomarker and treatment target for the malignancy.

The functions of FOXP transcription factors and their regulation by post-translational modifications

The forkhead box subfamily P (FOXP) of transcription factors, consisting of FOXP1, FOXP2, FOXP3, and FOXP4, is involved in the regulation of multisystemic functioning. Disruption of the transcriptional activity of FOXP proteins leads to neurodevelopmental disorders and immunological diseases, as well as the suppression or promotion of carcinogenesis. The transcriptional activities of FOXP proteins are directly or indirectly regulated by diverse post-translational modifications, including phosphorylation, ubiquitination, SUMOylation, acetylation, O-GlcNAcylation, and methylation. Here, we discuss how post-translational modifications modulate the multiple functions of FOXP proteins and examine the implications for tumorigenesis and cancer therapy.

Treg plasticity and human diseases

INTRODUCTION

As a subset of CD4+ T cells, regulatory T cells (Tregs) with the characteristic expression of transcription factor FOXP3 play a key role in maintaining self-tolerance and regulating immune responses. However, in some inflammatory circumstances, Tregs can express cytokines of other T help (Th) cells by internal reprogramming, which is called Treg plasticity. These reprogrammed Tregs with impaired suppressive ability contribute to the progression of diseases by secreting pro-inflammatory cytokines. However, in the tumor microenvironment (TME), such changes in phenotype rarely occur in Tregs, on the contrary, Tregs usually display a stronger suppressive function and inhibit anti-tumor immunity. It is important to understand the mechanisms of Treg plasticity in inflammatory diseases and cancers.

OBJECTIVES

In this review, we summarize the characteristics of different Th-like Tregs and discuss the potential mechanisms of these changes in phenotype. Furthermore, we summarize the Treg plasticity in human diseases and discuss the effects of these changes in phenotype on disease progression, as well as the potential application of drugs or reagents that regulate Treg plasticity in human diseases.

CONCLUSIONS

Treg plasticity is associated with inflammatory diseases and cancers. Regulating Treg plasticity is a promising direction for the treatment of inflammatory diseases and cancers.

Targeting ubiquitin specific proteases (USPs) in cancer immunotherapy: from basic research to preclinical application

Tumors have evolved in various mechanisms to evade the immune system, hindering the antitumor immune response and facilitating tumor progression. Immunotherapy has become a potential treatment strategy specific to different cancer types by utilizing multifarious molecular mechanisms to enhance the immune response against tumors. Among these mechanisms, the ubiquitin-proteasome system (UPS) is a significant non-lysosomal pathway specific to protein degradation, regulated by deubiquitinating enzymes (DUBs) that counterbalance ubiquitin signaling. Ubiquitin-specific proteases (USPs), the largest DUB family with the strongest variety, play critical roles in modulating immune cell function, regulating immune response, and participating in antigen processing and presentation during tumor progression. According to recent studies, the expressions of some USP family members in tumor cells are involved in tumor immune escape and immune microenvironment. This review explores the potential of targeting USPs as a new approach for cancer immunotherapy, highlighting recent basic and preclinical studies investigating the applications of USP inhibitors. By providing insights into the structure and function of USPs in cancer immunity, this review aims at assisting in developing new therapeutic approaches for enhancing the immunotherapy efficacy.

Regulation of post-translational modification of PD-L1 and advances in tumor immunotherapy

The immune checkpoint molecules programmed cell death receptor 1 (PD-1) and programmed death ligand 1 (PD-L1) are one of the most promising targets for tumor immunotherapy. PD-L1 is overexpressed on the surface of tumor cells and inhibits T cell activation upon binding to PD⁃1 on the surface of T cells, resulting in tumor immune escape. The therapeutic strategy of targeting PD-1/PD-L1 involves blocking this binding and restoring the tumor-killing effect of immune cells. However, in clinical settings, a relatively low proportion of cancer patients have responded well to PD-1/PD-L1 blockade, and clinical outcomes have reached a bottleneck and no substantial progress has been made. In recent years, PD-L1 post-translation modifications (PTMs) have gradually become a hot topic in the field of PD-L1 research, which will provide new insights to improve the efficacy of current anti-PD-1/PD-L1 therapies. Here, we summarized and discussed multiple PTMs of PD-L1, including glycosylation, ubiquitination, phosphorylation, acetylation and palmitoylation, with a major emphasis on mechanism-based therapeutic strategies (including relevant enzymes and targets that are already in clinical use and that may become drugs in the future). We also summarized the latest research progress of PTMs of PD-L1/PD-1 in regulating immunotherapy. The review provided novel strategies and directions for tumor immunotherapy research based on the PTMs of PD-L1/PD-1.

Modulation of the ubiquitin-proteasome system by phytochemicals: Therapeutic implications in malignancies with an emphasis on brain tumors

Regarding the multimechanistic nature of cancers, current chemo- or radiotherapies often fail to eradicate disease pathology, and frequent relapses or resistance to therapies occur. Brain malignancies, particularly glioblastomas, are difficult-to-treat cancers due to their highly malignant and multidimensional biology. Unfortunately, patients suffering from malignant tumors often experience poor prognoses and short survival periods. Thus far, significant efforts have been conducted to discover novel and more effective modalities. To that end, modulation of the ubiquitin-proteasome system (UPS) has attracted tremendous interest since it affects the homeostasis of proteins critically engaged in various cell functions, for example, cell metabolism, survival, proliferation, and differentiation. With their safe and multimodal actions, phytochemicals are among the promising therapeutic tools capable of turning the operation of various UPS elements. The present review, along with an updated outline of the role of UPS dysregulation in multiple cancers, provided a detailed discussion on the impact of phytochemicals on the UPS function in malignancies, especially brain tumors.

Ubiquitin-specific protease 7 (USP7): an emerging drug target for cancer treatment

INTRODUCTION

Ubiquitin-specific protease 7 (USP7) also known as herpesvirus-associated ubiquitin-specific protease (HAUSP) is a well-characterized cysteine protease that belongs to the largest subfamily of deubiquitinating enzymes (DUBs). It is involved in multiple signaling pathways, some of them dysregulated in malignant tumors. USP7 inhibition can lead to cell growth arrest and apoptosis through inhibition of tumor promoters and stabilization of tumor suppressors, making it a promising druggable target for cancer therapy.

AREAS COVERED

This review covers the structure of USP7, its function in multiple signaling pathways and relevance in cancer, as well as recent advances and future perspectives in the development of USP7 inhibitors for cancer therapy.

EXPERT OPINION

Literature reports display the multiple antitumor activities of USP7 inhibitors, both in vitro and in vivo. Nonetheless, none have entered clinical trials so far, highlighting the need to delve into a deeper understanding of USP7 binding sites and the development of more accurate compound screening methods. Despite these challenges, further development of USP7 inhibitors is promising as a valuable new approach for cancer treatment, including the ability to address chemoresistance.

Emerging role of deubiquitination modifications of programmed death-ligand 1 in cancer immunotherapy

Immune evasion is essential for carcinogenesis and cancer progression. Programmed death-ligand 1 (PD-L1), a critical immune checkpoint molecule, interacts with programmed death receptor-1 (PD-1) on immune cells to suppress anti-tumor immune responses. In the past decade, antibodies targeting PD-1/PD-L1 have tremendously altered cancer treatment paradigms. Post-translational modifications have been reported as key regulators of PD-L1 expression. Among these modifications, ubiquitination and deubiquitination are reversible processes that dynamically control protein degradation and stabilization. Deubiquitinating enzymes (DUBs) are responsible for deubiquitination and have emerged as crucial players in tumor growth, progression, and immune evasion. Recently, studies have highlighted the participation of DUBs in deubiquitinating PD-L1 and modulating its expression. Here, we review the recent developments in deubiquitination modifications of PD-L1 and focus on the underlying mechanisms and effects on anti-tumor immunity.

USP7 - a crucial regulator of cancer hallmarks

Over the course of three decades of study, the deubiquitinase Herpesvirus associated Ubiquitin-Specific Protease/Ubiquitin-Specific Protease 7 (HAUSP/USP7) has gradually come to be recognized as a crucially important molecule in cellular physiology. The fact that USP7 is overexpressed in a number of cancers, including breast, prostate, colorectal, and lung cancers, supports the idea that USP7 is also an important regulator of tumorigenesis. In this review, we discuss USP7's function in relation to the cancer hallmarks described by Hanahan and Weinberg. This post-translational modifier can support increased proliferation, block unfavorable growth signals, stop cell death, and support an unstable cellular genome by manipulating key players in the pertinent signalling circuit. It is interesting to note that USP7 also aids in the stabilization of molecules that support angiogenesis and metastasis. Targeting USP7 has now emerged as a crucial component of USP7 research because pharmacological inhibition of USP7 supports p53-mediated cell cycle arrest and apoptosis. Efficacious USP7 inhibition is currently being investigated in both synthetic and natural compounds, but issues with selectivity and a lack of co-crystal structure have hindered USP7 inhibition from being tested in clinical settings. Moreover, the development of new, more effective USP7 inhibitors and their encouraging implications by numerous groups give us a glimmer of hope for USP7-targeting medications as effective substitutes for hazardous cancer chemotherapeutics.

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.

USP1-regulated reciprocal differentiation of Th17 cells and Treg cells by deubiquitinating and stabilizing TAZ

The balance between inflammatory T helper type 17 (Th17) and immunosuppressive regulatory T (Treg) cells is critical for maintaining immune homeostasis in the human body and is tightly regulated under healthy conditions. An increasing number of studies have reported that deubiquitinases (DUBs) play a vital role in regulating Th17- and Treg-cell differentiation. However, the biological functions of only a small fraction of DUBs in Th17- and Treg-cell differentiation are well defined. In this study, we identified ubiquitin-specific peptidase 1 (USP1) as a vital regulator of CD4+ T-cell differentiation. USP1 promoted Th17-cell differentiation but attenuated Treg-cell differentiation, thereby promoting the development of inflammatory diseases. Mechanistically, USP1 in CD4+ T cells enhanced the activity of RORγt but promoted the proteasomal degradation of Foxp3 through deubiquitination and stabilization of TAZ in vitro and in vivo. Notably, ML323, a specific inhibitor of the USP1/UAF1 deubiquitinase complex, inhibited Th17-cell differentiation and promoted Treg-cell differentiation in vitro and in vivo, indicating that ML323 might be a promising candidate for the treatment of diseases associated with an imbalance between Th17 and Treg cells. Our study highlights the critical role of USP1 in regulating adaptive immune responses and suggests that USP1 might be a drug target for the treatment of diseases associated with an imbalance between Th17 and Treg cells.

Discovery of Orally Bioavailable N-Benzylpiperidinol Derivatives as Potent and Selective USP7 Inhibitors with In Vivo Antitumor Immunity Activity against Colon Cancer

USP7 emerges as a potential therapeutic target for cancers, as it plays an important role in the development of tumorigenesis by stabilizing multiple cancer-relevant proteins. Nevertheless, the discovery of drug-like USP7 inhibitors remains challenging. Herein, we report a series of N-benzylpiperidinol derivatives as potent and selective USP7 inhibitors (e.g., X20 and X26: IC₅₀ = 7.6 and 8.2 nM), whose binding modes were revealed by crystallographic studies to be distinct from the known N-acylpiperidinol USP7 inhibitors. Among them, X36 with good oral PK profiles (rat: F = 40.8% and T_1/2 = 3.5 h) exhibited significant antitumor efficacy in the MC38 colon cancer syngeneic mouse model, at least partly through upregulating the tumor infiltration of CD8⁺ T, NK, and NKT cells and downregulating that of Tregs and MDSCs. These findings may further pave the way for the development of USP7 inhibitors as novel cancer immunotherapy drugs.

A deubiquitination module essential for Treg fitness in the tumor microenvironment

The tumor microenvironment (TME) enhances regulatory T (T_reg) cell stability and immunosuppressive functions through up-regulation of lineage transcription factor Foxp3, a phenomenon known as T_reg fitness or adaptation. Here, we characterize previously unknown TME-specific cellular and molecular mechanisms underlying T_reg fitness. We demonstrate that TME-specific stressors including transforming growth factor-β (TGF-β), hypoxia, and nutrient deprivation selectively induce two Foxp3-specific deubiquitinases, ubiquitin-specific peptidase 22 (Usp22) and Usp21, by regulating TGF-β, HIF, and mTOR signaling, respectively, to maintain T_reg fitness. Simultaneous deletion of both USPs in T_reg cells largely diminishes TME-induced Foxp3 up-regulation, alters T_reg metabolic signatures, impairs T_reg-suppressive function, and alleviates T_reg suppression on cytotoxic CD8⁺ T cells. Furthermore, we developed the first Usp22-specific small-molecule inhibitor, which dramatically reduced intratumoral T_reg Foxp3 expression and consequently enhanced antitumor immunity. Our findings unveil previously unappreciated mechanisms underlying T_reg fitness and identify Usp22 as an antitumor therapeutic target that inhibits T_reg adaptability in the TME.

USP7 Inhibitors in Cancer Immunotherapy: Current Status and Perspective

Ubiquitin-specific protease 7 (USP7) regulates the stability of a plethora of intracellular proteins involved in the suppression of anti-tumor immune responses and its overexpression is associated with poor survival in many cancers. USP7 impairs the balance of the p53/MDM2 axis resulting in the proteasomal degradation of the p53 tumor suppressor, a process that can be reversed by small-molecule inhibitors of USP7. USP7 was shown to regulate the anti-tumor immune responses in several cases. Its inhibition impedes the function of regulatory T cells, promotes polarization of tumor-associated macrophages, and reduces programmed death-ligand 1 (PD-L1) expression in tumor cells. The efficacy of small-molecule USP7 inhibitors was demonstrated in vivo. The synergistic effect of combining USP7 inhibition with cancer immunotherapy is a promising therapeutic approach, though its clinical efficacy is yet to be proven. In this review, we focus on the recent developments in understanding the intrinsic role of USP7, its interplay with other molecular pathways, and the therapeutic potential of targeting USP7 functions.

Highlights in USP7 inhibitors for cancer treatment

Ubiquitin-specific protease 7 (USP7) is a member of one of the most largely studied families of deubiquitylating enzymes. It plays a key role modulating the levels of multiple proteins, including tumor suppressors, transcription factors, epigenetic modulators, DNA repair proteins, and regulators of the immune response. The abnormal expression of USP7 is found in various malignant tumors and a high expression signature generally indicates poor tumor prognosis. This suggests USP7 as a promising prognostic and druggable target for cancer therapy. Nonetheless, no approved drugs targeting USP7 have already entered clinical trials. Therefore, the development of potent and selective USP7 inhibitors still requires intensive research and development efforts before the pre-clinical benefits translate into the clinic. This mini review systematically summarizes the role of USP7 as a drug target for cancer therapeutics, as well as the scaffolds, activities, and binding modes of some of the most representative small molecule USP7 inhibitors reported in the scientific literature. To wind up, development challenges and potential combination therapies using USP7 inhibitors for less tractable tumors are also disclosed.

Gallic acid induces T-helper-1-like Treg cells and strengthens immune checkpoint blockade efficacy

Background

Foxp3⁺ regulatory T (T_reg) cells facilitate tumor immune evasion by forming a suppressive tumor microenvironment. Therefore, immune therapies promoting T_reg fragility may greatly enhance immune checkpoint blockade (ICB) efficacy in cancers.

Methods

We have screened 2640 compounds and identified the gut microbial metabolite gallic acid, which promotes Foxp3 degradation and T_reg instability by repressing Usp21 gene transcription. In vivo and in vitro experiments have been performed to explore the roles of Usp21 in T_reg cells. Importantly, we treated tumor-bearing mice with gallic acid and anti-PD-1 antibody to explore the potential therapeutic value of gallic acid in clinical cancer immunotherapy.

Results

Mechanistically, gallic acid prevents STAT3 phosphorylation and the binding of phosphorylated STAT3 to Usp21 gene promoter. The deubiquitinated Usp21 and stabilized PD-L1 proteins boost the function of T_reg cells. Combination of gallic acid and anti-PD-1 antibody, in colorectal cancer (CRC) treatment, not only significantly dampen T_reg cell function by impairing PD-L1/PD-1 signaling and downregulating Foxp3 stability, but also promote CD8⁺ T cells’ production of IFN-γ and limited tumor growth.

Conclusion

Our findings have implications for improving the efficacy of ICB therapy in CRC by inducing T-helper-1-like Foxp3^lo T_reg cells.

The USP7 protein interaction network and its roles in tumorigenesis

Ubiquitin-specific protease (USP7), also known as Herpesvirus-associated ubiquitin-specific protease (HAUSP), is a deubiquitinase. There has been significant recent attention on USP7 following the discovery that USP7 is a key regulator of the p53-MDM2 pathway. The USP7 protein is 130 kDa in size and has multiple domains which bind to a diverse set of proteins. These interactions mediate key developmental and homeostatic processes including the cell cycle, immune response, and modulation of transcription factor and epigenetic regulator activity and localization. USP7 also promotes carcinogenesis through aberrant activation of the Wnt signalling pathway and stabilization of HIF-1α. These findings have shown that USP7 may induce tumour progression and be a therapeutic target. Together with interest in developing USP7 as a target, several studies have defined new protein interactions and the regulatory networks within which USP7 functions. In this review, we focus on the protein interactions of USP7 that are most important for its cancer-associated roles.

Acetylation in Tumor Immune Evasion Regulation

Acetylation is considered as one of the most common types of epigenetic modifications, and aberrant histone acetylation modifications are associated with the pathological process of cancer through the regulation of oncogenes and tumor suppressors. Recent studies have shown that immune system function and tumor immunity can also be affected by acetylation modifications. A comprehensive understanding of the role of acetylation function in cancer is essential, which may help to develop new therapies to improve the prognosis of cancer patients. In this review, we mainly discussed the functions of acetylase and deacetylase in tumor, immune system and tumor immunity, and listed the information of drugs targeting these enzymes in tumor immunotherapy.

Ubiquitin-Specific Peptidase 7: A Novel Deubiquitinase That Regulates Protein Homeostasis and Cancers

Ubiquitin-Specific Peptidase 7 (USP7), or herpes virus-associated protease (HAUSP), is the largest family of the deubiquitinating enzymes (DUBs). Recent studies have shown that USP7 plays a vital role in regulating various physiological and pathological processes. Dysregulation of these processes mediated by USP7 may contribute to many diseases, such as cancers. Moreover, USP7 with aberrant expression levels and abnormal activity are found in cancers. Therefore, given the association between USP7 and cancers, targeting USP7 could be considered as an attractive and potential therapeutic approach in cancer treatment. This review describes the functions of USP7 and the regulatory mechanisms of its expression and activity, aiming to emphasize the necessity of research on USP7, and provide a better understanding of USP7-related biological processes and cancer.

Cancer cell-derived exosomal circUSP7 induces CD8+ T cell dysfunction and anti-PD1 resistance by regulating the miR-934/SHP2 axis in NSCLC

Background

CD8⁺ T cells play a critical role in the innate antitumour immune response. Recently, CD8⁺ T cell dysfunction has been verified in various malignant cancers, including non-small cell lung cancer (NSCLC). However, the molecular biological mechanisms of CD8⁺ T cell dysfunction in human NSCLC are still unclear.

Methods

The expression of circular ubiquitin-specific protease-7 (circUSP7) in NSCLC tissues, exosomes, and cell lines was detected by quantitative real-time polymerase chain reaction (qRT-PCR). Exosomes were isolated from the culture medium of NSCLC cells and the plasma of NSCLC patients using an ultracentrifugation method and the ExoQuick Exosome Precipitation Solution kit. The exosomes were then characterized by transmission electronic microscopy (TEM), NanoSight and western blotting. The role of circUSP7 in CD8⁺ T cell dysfunction was assessed by enzyme-linked immunosorbent assay (ELISA). In vivo circular RNA (circRNA) precipitation (circRIP), RNA immunoprecipitation (RIP), and luciferase reporter assays were performed to explore the molecular mechanisms of circUSP7 in CD8⁺ T cells. In a retrospective study, the clinical characteristics and prognostic significance of circUSP7 in NSCLC tissues were determined.

Results

The expression levels of circUSP7 were higher in human NSCLC tissues than in matched adjacent nontumour tissues. Increased levels of circUSP7 indicate poor clinical prognosis and CD8⁺ T cell dysfunction in patients with NSCLC. The circUSP7 found in NSCLC patient plasma is predominantly secreted by NSCLC cells in an exosomal manner, and circUSP7 inhibits IFN-γ, TNF-α, Granzyme-B and Perforin secretion by CD8⁺ T cells. Furthermore, circUSP7 inhibits CD8⁺ T cell function by upregulating the expression of Src homology region 2 (SH2)-containing protein tyrosine phosphatase 2 (SHP2) via sponging miR-934. Finally, we show that circUSP7 may promote resistance to anti-PD1 immunotherapy in NSCLC patients.

Conclusions

Exosomal circUSP7 is predominantly secreted by NSCLC cells and contributes to immunosuppression by promoting CD8⁺ T cell dysfunction in NSCLC. CircUSP7 induces resistance to anti-PD1 immunotherapy, providing a potential therapeutic strategy for NSCLC patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12943-021-01448-x.

Regulatory T Cells in Autoimmunity and Cancer: A Duplicitous Lifestyle

Regulatory T (Treg) cells, possess a strategic role in the maintenance of immune homeostasis, and their function has been closely linked to development of diverse pathologies including autoimmunity and cancer. Comprehensive studies in various disease contexts revealed an increased plasticity as a characteristic of Treg cells. Although Treg cell plasticity comes in various flavors, the major categories enclose the loss of Foxp3 expression, which is the master regulator of Treg cell lineage, giving rise to “ex-Treg” cells and the “fragile” Treg cells in which FOXP3 expression is retained but accompanied by the engagement of an inflammatory program and attenuation of the suppressive activity. Treg cell plasticity possess a tremendous therapeutic potential either by inducing Treg cell de-stabilization to promote anti-tumor immunity, or re-enforcing Treg cell stability to attenuate chronic inflammation. Herein, we review the literature on the Treg cell plasticity with lessons learned in autoimmunity and cancer and discuss challenges and open questions with potential therapeutic implications.

Recent advances on the intervention sites targeting USP7-MDM2-p53 in cancer therapy

The ubiquitin-specific protease 7 (USP7)-murine double minute 2 (MDM2)-p53 network plays an important role in the regulation of p53, a tumor suppressor which plays critical roles in regulating cell growth, proliferation, cell cycle progression, apoptosis and immune response. The overexpression of USP7 and MDM2 in human cancers contributes to cancer initiation and progression, and their inhibition reactivates p53 signalings and causes cell cycle arrest and apoptosis. Herein, the current state of pharmacological characterization, potential applications in cancer treatment and mechanism of action of small molecules used to target and inhibit MDM2 and USP7 proteins are highlighted, along with the outcomes in clinical and preclinical settings. Moreover, challenges and advantages of these strategies, as well as perspectives in USP7-MDM2-p53 field are analyzed in detail. The investigation and application of MDM2 and USP7 inhibitors will deepen our understanding of the function of USP7-MDM2-p53 network, and feed in the development of effective and safe cancer therapies where USP7-MDM2-p53 network is implicated.

Metabolic Controls on Epigenetic Reprogramming in Regulatory T Cells

Forkhead box protein 3 (Foxp3⁺)-expressing regulatory T (Treg) cells are a unique CD4⁺T cell subset that suppresses excessive immune responses. The epigenetic plasticity and metabolic traits of Treg cells are crucial for the acquisition of their phenotypic and functional characteristics. Therefore, alterations to the epigenetics and metabolism affect Treg cell development and function. Recent evidence reveals that altering the metabolic pathways and generation of metabolites can regulate the epigenetics of Treg cells. Specifically, some intermediates of cell metabolism can directly act as substrates or cofactors of epigenetic-modifying enzymes. Here, we describe the metabolic and epigenetic features during Treg cell development, and discuss how metabolites can contribute to epigenetic alterations of Treg cells, which affects Treg cell activation, differentiation, and function.

Transcriptional and posttranslational regulation of Th17/Treg balance in health and disease

Regulatory T (Treg) cells and T helper type 17 (Th17) cells play important roles in adaptive immune responses, antagonizing each other in immune disorders. Th17/Treg balance is critical to maintaining the immune homeostasis of human bodies and is tightly regulated under healthy conditions. The transcription factors that are required for driving Th17 and Treg cell lineages differentiation respectively, RORγt and FOXP3 are tightly regulated under different tissue microenvironment, especially the transcriptional induction, posttranslational modifications, and dynamic enzymatic cofactors binding. The imbalance caused by alteration of the quantity or properties of RORγt⁺ Th17 or FOXP3⁺ Treg can contribute to inflammatory disorders in humans. Restoring Th17/Treg balance by modifying the enzymatic activities of RORγt and FOXP3 binding partners may be therapeutically applied to treat severe immune disorders. In this review, we focus on the transcriptional and posttranslational regulations of Th17/Treg balance, immune disorders caused by Th17/Treg imbalance, and new therapeutic strategies for restoring immune homeostasis.

Emerging role of PD-L1 modification in cancer immunotherapy

Accumulating evidence demonstrates that the expression levels of programmed cell death protein 1 (PD-1) and programmed death ligand 1 (PD-L1) are regulated at the various levels, including transcription, post-transcriptional modification and post-translational modifications (PTMs). The PTMs of PD-1/PD-L1 contain phosphorylation, ubiquitination, methylation, glycosylation and palmitoylation. Recently, PD-L1 was reported to be acetylated at Lys263 site by p300 and was deacetylated by histone deacetylase 2 (HDAC2). Acetylation of PD-L1 prevented its translocation to the nucleus and led to a reduction of the nuclear portion of PD-L1, resulting in evading immune surveillance of tumor cells. In this review article, we briefly describe the PTMs of PD-1/PD-L1 and mainly summarize the novel findings of PD-L1 acetylation in tumor cells. Moreover, we discuss the associations of PD-L1 acetylation and ubiquitination, phosphorylation and methylation. Furthermore, we highlight that targeting acetylation of PD-L1 by HDAC inhibitors might be useful for enhancing tumor immunotherapy.

Obesity-related IL-18 Impairs Treg Function and Promotes Lung Ischemia-reperfusion Injury

RATIONALE

Primary graft dysfunction (PGD) is a severe form of acute lung injury, leading to increased early morbidity and mortality after lung transplantation. Obesity is a major health problem, and recipient obesity is one of the most significant risk factors for developing PGD.

OBJECTIVES

We hypothesized that T-regulatory (Treg) cells are able to dampen early ischemia/reperfusion events and thereby decrease risk of PGD, whereas that action is impaired in obese recipients.

METHODS

We evaluated Treg, T cells and inflammatory markers, plus clinical data, in 79 lung and 41 liver or kidney transplant recipients and studied two groups of mice on high fat diet (HFD), who developed ("inflammatory" HFD) or not ("healthy" HFD) low-grade inflammation with decreased Treg function.

RESULTS

We identified increased levels of IL-18 as a previously unrecognized mechanism that impairs Treg suppressive function in obese individuals. IL-18 decreases levels of FOXP3, the key Treg transcription factor, decreases FOXP3 di- and oligomerization and increases the ubiquitination and proteasomal degradation of FOXP3. IL-18-treated Tregs or Treg from obese mice fail to control PGD, while IL-18 inhibition ameliorates lung inflammation. The IL-18 driven impairment in Treg suppressive function pre-transplant was associated with increased risk and severity of PGD in clinical lung transplant recipients.

CONCLUSION

Obesity-related IL-18 induces Treg dysfunction that may contribute to the pathogenesis of PGD. Evaluation of Treg suppressive function along with IL-18 levels may serve as screening tools to identify pre-transplant obese recipients with increased risk of PGD.

Deubiquitinating Enzymes Orchestrate the Cancer Stem Cell-Immunosuppressive Niche Dialogue: New Perspectives and Therapeutic Potential

Cancer stem cells (CSCs) are sparks for igniting tumor recurrence and the instigators of low response to immunotherapy and drug resistance. As one of the important components of tumor microenvironment, the tumor associated immune microenvironment (TAIM) is driving force for the heterogeneity, plasticity and evolution of CSCs. CSCs create the inhibitory TAIM (ITAIM) mainly through four stemness-related signals (SRSs), including Notch-nuclear factor-κB axis, Hedgehog, Wnt and signal transducer and activator of transcription. Ubiquitination and deubiquitination in proteins related to the specific stemness of the CSCs have a profound impact on the regulation of ITAIM. In regulating the balance between ubiquitination and deubiquitination, it is crucial for deubiquitinating enzymes (DUBs) to cleave ubiquitin chains from substrates. Ubiquitin-specific peptidases (USPs) comprise the largest family of DUBs. Growing evidence suggests that they play novel functions in contribution of ITAIM, including regulating tumor immunogenicity, activating stem cell factors, upregulating the SRSs, stabilizing anti-inflammatory receptors, and regulating anti-inflammatory cytokines. These overactive or abnormal signaling may dampen antitumor immune responses. The inhibition of USPs could play a regulatory role in SRSs and reversing ITAIM, and also have great potential in improving immune killing ability against tumor cells, including CSCs. In this review, we focus on the USPs involved in CSCs signaling pathways and regulating ITAIM, which are promising therapeutic targets in antitumor therapy.

Covalent Small Molecule Immunomodulators Targeting the Protease Active Site

Cells of the immune system utilize multiple proteases to regulate cell functions and orchestrate innate and adaptive immune responses. Dysregulated protease activities are implicated in many immune-related disorders; thus, protease inhibitors have been actively investigated for pharmaceutical development. Although historically considered challenging with concerns about toxicity, compounds that covalently modify the protease active site represent an important class of agents, emerging not only as chemical probes but also as approved drugs. Here, we provide an overview of technologies useful for the study of proteases with the focus on recent advances in chemoproteomic methods and screening platforms. By highlighting covalent inhibitors that have been designed to target immunomodulatory proteases, we identify opportunities for the development of small molecule immunomodulators.

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.

MEF2D sustains activation of effector Foxp3+ Tregs during transplant survival and anticancer immunity

The transcription factor MEF2D is important in the regulation of differentiation and adaptive responses in many cell types. We found that among T cells, MEF2D gained new functions in Foxp3+ T regulatory (Treg) cells due to its interactions with the transcription factor Foxp3 and its release from canonical partners, like histone/protein deacetylases. Though not necessary for the generation and maintenance of Tregs, MEF2D was required for the expression of IL-10, CTLA4, and Icos, and for the acquisition of an effector Treg phenotype. At these loci, MEF2D acted both synergistically and additively to Foxp3, and downstream of Blimp1. Mice with the conditional deletion in Tregs of the gene encoding MEF2D were unable to maintain long-term allograft survival despite costimulation blockade, had enhanced antitumor immunity in syngeneic models, but displayed only minor evidence of autoimmunity when maintained under normal conditions. The role played by MEF2D in sustaining effector Foxp3+ Treg functions without abrogating their basal actions suggests its suitability for drug discovery efforts in cancer therapy.

Targeting ubiquitin signaling for cancer immunotherapy

Cancer immunotherapy has become an attractive approach of cancer treatment with tremendous success in treating various advanced malignancies. The development and clinical application of immune checkpoint inhibitors represent one of the most extraordinary accomplishments in cancer immunotherapy. In addition, considerable progress is being made in understanding the mechanism of antitumor immunity and characterizing novel targets for developing additional therapeutic approaches. One active area of investigation is protein ubiquitination, a post-translational mechanism of protein modification that regulates the function of diverse immune cells in antitumor immunity. Accumulating studies suggest that E3 ubiquitin ligases and deubiquitinases form a family of potential targets to be exploited for enhancing antitumor immunity in cancer immunotherapy.

Regulation of Treg Functions by the Ubiquitin Pathway

Regulatory T (Tregs) cells, required to maintain immune homeostasis, have significant power in disease outcomes. Treg dysfunction, predominantly characterized by the loss of the master transcription factor FoxP3 and the acquisition of T_eff-like phenotypes, can promote autoimmunity as well as enhance anti-tumor immunity. As FoxP3 expression and stability are pinnacle for Treg suppressive functions, understanding the pathways that regulate FoxP3 is crucial to ascertain Treg-mediated therapies for autoimmune diseases and cancer. Mechanisms controlling FoxP3 expression and stability range from transcriptional to posttranslational, revealing multiple therapeutic opportunities. While many of the transcriptional pathways have been explored in detail, a recent surge in interest on the posttranslational mechanisms regulating FoxP3 has arisen. Particularly, the role of ubiquitination on Tregs both directly and indirectly involving FoxP3 has gained interest. Here, we summarize the current knowledge on ubiquitin-dependent, FoxP3-mediated control of Treg function as it pertains to human diseases.

Inhibiting the coregulator CoREST impairs Foxp3+ Treg function and promotes antitumor immunity

Foxp3+ Tregs are key to immune homeostasis, but the contributions of various large, multiprotein complexes that regulate gene expression remain unexplored. We analyzed the role in Tregs of the evolutionarily conserved CoREST complex, consisting of a scaffolding protein, Rcor1 or Rcor2, plus Hdac1 or Hdac2 and Lsd1 enzymes. Rcor1, Rcor2, and Lsd1 were physically associated with Foxp3, and mice with conditional deletion of Rcor1 in Foxp3+ Tregs had decreased proportions of Tregs in peripheral lymphoid tissues and increased Treg expression of IL-2 and IFN-γ compared with what was found in WT cells. Mice with conditional deletion of the gene encoding Rcor1 in their Tregs had reduced suppression of homeostatic proliferation, inability to maintain long-term allograft survival despite costimulation blockade, and enhanced antitumor immunity in syngeneic models. Comparable findings were seen in WT mice treated with CoREST complex bivalent inhibitors, which also altered the phenotype of human Tregs and impaired their suppressive function. Our data point to the potential for therapeutic modulation of Treg functions by pharmacologic targeting of enzymatic components of the CoREST complex and contribute to an understanding of the biochemical and molecular mechanisms by which Foxp3 represses large gene sets and maintains the unique properties of this key immune cell.

Role of Epigenetics in the Regulation of Immune Functions of the Skin

This review is intended to illuminate the emerging understanding of epigenetic modifications that regulate both adaptive and innate immunity in the skin. Host defense of the epidermis and dermis involves the interplay of many cell types to enable homeostasis; tolerance to the external environment; and appropriate response to transient microbial, chemical, and physical insults. To understand this process, the study of cutaneous immunology has focused on immune responses that reflect both adaptive learned and genetically programmed innate defense systems. However, recent advances have begun to reveal that epigenetic modifications of chromatin structure also have a major influence on the skin immune system. This deeper understanding of how enzymatic changes in chromatin structure can modify the skin immune system and may explain how environmental exposures during life, and the microbiome, lead to both short-term and long-term changes in cutaneous allergic and other inflammatory processes. Understanding the mechanisms responsible for alterations in gene and chromatin structure within skin immunocytes could provide key insights into the pathogenesis of inflammatory skin diseases that have thus far evaded understanding by dermatologists.

Ubiquitin-Specific-Processing Protease 7 Regulates Female Germline Stem Cell Self-Renewal Through DNA Methylation

Ubiquitin-specific-processing protease 7 (Usp7) is a key deubiquitinase controlling epigenetic modification and regulating the self-renewal, proliferation, and differentiation of stem cells. However, the functions and mechanisms of action of Usp7 on female germline stem cells (FGSCs) are unknown. Here, we demonstrated that Usp7 regulated FGSC self-renewal via DNA methylation. The results of Cell Counting Kit-8 and 5-ethynyl-20-deoxyuridine assays showed that the viability and proliferation of FGSCs were negatively regulated by Usp7. Moreover, Usp7 downregulated the expression of self-renewal genes, such as Oct4, Etv5, Foxo1, and Akt, but upregulated the expression of differentiation-related genes including Stra8 and Sycp3. Mechanistically, RNA-seq results showed that Usp7 negatively regulated FGSC self-renewal but positively modulated differentiation in FGSCs. Meanwhile, both overexpression and knockdown of Usp7 resulted in significant changes in DNA methylation and histone modification in FGSCs. Additionally, RNA-seq and MeDIP-seq analyses showed that Usp7 regulates the self-renewal and differentiation of FGSCs mainly through DNA methylation rather than histone modification, which was also confirmed by a rescue assay. Our study not only offers a novel method to research FGSC self-renewal and differentiation in view of epigenetic modifications, but also provides a deep understanding of FGSC development.

The emerging nature of Ubiquitin-specific protease 7 (USP7): a new target in cancer therapy

Human ubiquitin-specific protease 7 (USP7) is a deubiquitinating enzyme that removes the ubiquitin (Ub) protein and spares substrates from degradation. Given its regulation of proteins involved in several cellular processes, abnormal expression and activity of USP7 are associated with several types of disease, including cancer. In this review, we summarize the developments in our understanding of USP7 over the past 5 years, focusing on its role in related cancers. Furthermore, we discuss clinical studies of USP7, including in vivo and pharmacological studies, as well as the development of USP7 inhibitors. A comprehensive understanding of USP7 will expand our knowledge of the structure and function of USP7-mediated signaling and shed light on drug discovery for different diseases in which USP7 is implicated.

Regulatory T Cell Plasticity and Stability and Autoimmune Diseases

CD4⁺CD25⁺ regulatory T cells (Tregs) are a class of CD4⁺ T cells with immunosuppressive functions that play a critical role in maintaining immune homeostasis. However, in certain disease settings, Tregs demonstrate plastic differentiation, and the stability of these Tregs, which is characterized by the stable expression or protective epigenetic modifications of the transcription factor Foxp3, becomes abnormal. Plastic Tregs have some features of helper T (Th) cells, such as the secretion of Th-related cytokines and the expression of specific transcription factors in Th cells, but also still retain the expression of Foxp3, a feature of Tregs. Although such Th-like Tregs can secrete pro-inflammatory cytokines, they still possess a strong ability to inhibit specific Th cell responses. Therefore, the plastic differentiation of Tregs not only increases the complexity of the immune circumstances under pathological conditions, especially autoimmune diseases, but also shows an association with changes in the stability of Tregs. The plastic differentiation and stability change of Tregs play vital roles in the progression of diseases. This review focuses on the phenotypic characteristics, functions, and formation conditions of several plastic Tregs and also summarizes the changes of Treg stability and their effects on inhibitory function. Additionally, the effects of Treg plasticity and stability on disease prognosis for several autoimmune diseases were also investigated in order to better understand the relationship between Tregs and autoimmune diseases.

Targeting the epigenetic regulation of antitumour immunity

Dysregulation of the epigenome drives aberrant transcriptional programmes that promote cancer onset and progression. Although defective gene regulation often affects oncogenic and tumour-suppressor networks, tumour immunogenicity and immune cells involved in antitumour responses may also be affected by epigenomic alterations. This could have important implications for the development and application of both epigenetic therapies and cancer immunotherapies, and combinations thereof. Here, we review the role of key aberrant epigenetic processes - DNA methylation and post-translational modification of histones - in tumour immunogenicity, as well as the effects of epigenetic modulation on antitumour immune cell function. We emphasize opportunities for small-molecule inhibitors of epigenetic regulators to enhance antitumour immune responses, and discuss the challenges of exploiting the complex interplay between cancer epigenetics and cancer immunology to develop treatment regimens combining epigenetic therapies with immunotherapies.

The deubiquitinase USP44 promotes Treg function during inflammation by preventing FOXP3 degradation

The transcription factor forkhead box P3 (FOXP3) is essential for the development of regulatory T cells (Tregs) and their function in immune homeostasis. Previous studies have shown that in natural Tregs (nTregs), FOXP3 can be regulated by polyubiquitination and deubiquitination. However, the molecular players active in this pathway, especially those modulating FOXP3 by deubiquitination in the distinct induced Treg (iTreg) lineage, remain unclear. Here, we identify the ubiquitin-specific peptidase 44 (USP44) as a novel deubiquitinase for FOXP3. USP44 interacts with and stabilizes FOXP3 by removing K48-linked ubiquitin modifications. Notably, TGF-β induces USP44 expression during iTreg differentiation. USP44 co-operates with USP7 to stabilize and deubiquitinate FOXP3. Tregs genetically lacking USP44 are less effective than their wild-type counterparts, both in vitro and in multiple in vivo models of inflammatory disease and cancer. These findings suggest that USP44 plays an important role in the post-translational regulation of Treg function and is thus a potential therapeutic target for tolerance-breaking anti-cancer immunotherapy.

N-benzylpiperidinol derivatives as novel USP7 inhibitors: Structure-activity relationships and X-ray crystallographic studies

USP7 as a deubiquitinase plays important roles in regulating the stability of some oncoproteins including MDM2 and DNMT1, and thus represents a potential anticancer target. Through comparative analysis of USP7 co-crystal structures in complex with the reported piperidinol inhibitors, we noticed that the USP7 Phe409 sub-site might have good adaptability to the ligands. Based on this observation, 55 N-aromatic and N-benzyl piperidinol derivatives were designed, synthesized and biologically evaluated, among which compound L55 was identified as a highly selective and potent USP7 inhibitor (IC₅₀ = 40.8 nM, K_D = 78.3 nM). X-ray crystallographic studies revealed that L55 bound to USP7 with a new pose that was very different from the previously reported inhibitors. The results of cellular assays showed that L55 had strong antitumor activity against LNCaP (IC₅₀ = 29.6 nM) and RS4; 11 (IC₅₀ = 41.6 nM) cells, probably through inducing cell death and restricting G0/G1 and S phases. Moreover, L55 dose-dependently reduced the protein levels of MDM2 and DNMT1 and increased the protein levels of p53 and p21. These findings could have valuable implications for designing novel structural classes of USP7 inhibitors.

Post-Translational Modifications of Transcription Factors Harnessing the Etiology and Pathophysiology in Colonic Diseases

Defects in mucosal immune balance can lead to colonic diseases such as inflammatory bowel diseases and colorectal cancer. With the advancement of understanding for the immunological and molecular basis of colonic disease, therapies targeting transcription factors have become a potential approach for the treatment of colonic disease. To date, the biomedical significance of unique post-translational modifications on transcription factors has been identified, including phosphorylation, methylation, acetylation, ubiquitination, SUMOylation, and O-GlcNAcylation. This review focuses on our current understanding and the emerging evidence of how post-translational regulations modify transcription factors involved in the etiology and pathophysiology of colonic disease as well as the implications of these findings for new therapeutic approaches in these disorders.