Abstract
Proteins are the keystone for the execution of various life activities, and the maintenance of protein normalization is crucial for organisms. Ubiquitination, as a post-transcriptional modification, is widely present in organisms, and it relies on the sophisticated ubiquitin-proteasome (UPS) system that controls protein quality and modulates protein lifespan. Deubiquitinases (DUBs) counteract ubiquitination and are essential for the maintenance of homeostasis. Ubiquitin specific peptidase 3 (USP3) is a member of the DUBs that has received increasing attention in recent years. USP3 is a novel chromatin modifier that tightly regulates the DNA damage response (DDR) and maintains genome integrity. Meanwhile, USP3 acts as a key regulator of inflammatory vesicles and sustains the normal operation of the innate immune system. In addition, USP3 is aberrantly expressed in a wide range of cancers, such as gastric cancer, glioblastoma and neuroblastoma, implicating that USP3 could be an effective target for targeted therapies. In this review, we retrace all the current researches of USP3, describe the structure of USP3, elucidate its functions in DNA damage, immune and inflammatory responses and the cell cycle, and summarize the important role of USP3 in multiple cancers and diseases.
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Facts
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USP3 regulates the DNA damage response, and USP3 deficiency results in impaired cytogenetic stability.
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USP3 is involved in cell cycle regulation and affects cell division and proliferation.
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USP3 plays different roles in different cancers and functions as an oncogene in most cancers.
Open Questions
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There are no targeted therapeutic agents or inhibitors for USP3, an area where current research is lacking.
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Research on USP3 in cancer is still limited to cellular and animal models, and further clinical trials are necessary.
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The regulatory mechanisms regarding USP3 are not sufficiently detailed and complete, and further in-depth investigation may be required in the future.
Introduction
Ubiquitination, a widespread post-translational modification, plays a crucial role in regulating cellular functions, with the majority of cellular proteins undergoing ubiquitination [1]. The ubiquitin molecule consists of 76 amino acids that exhibit a high degree of conservation throughout evolutionary processes [2]. Ubiquitin attaches covalently to lysine residues on the substrate through a series of enzymatic reactions involving ubiquitin-activating (E1s), ubiquitin-conjugating (E2s), and ubiquitin ligase (E3s) enzymes [3,4,5], resulting in mono-ubiquitination (single ubiquitin) and poly-ubiquitination (ubiquitin chains) [6]. The ubiquitin-proteasome system (UPS) governs the degradation of over 80% of intracellular proteins, oversees protein quality control, and upholds protein homeostasis [7].
Ubiquitination is a reversible process that is accomplished by deubiquitinases (DUBs). The approximately 100 DUBs in the human body are categorized into nine families [8]: ubiquitin‐specific proteases (USPs), ovarian tumor proteases (OTUs), ubiquitin C‐terminal hydrolases (UCHs), Machado‐Joseph domain‐containing proteases (MJDs, also known as Josephins), JAMM/MPN domain‐associated Zn‐depend metalloproteases (JAMMs, also known as MPN+), the motif interacting with ubiquitin (MIU)‐containing novel DUB family (MINDYs), monocyte chemotactic protein‐induced proteins (MCPIPs), permuted papain fold peptidases of dsRNA viruses and eukaryotes (PPPDEs), and zinc finger (ZnF) containing ubiquitin peptidase 1 (ZUP1) [9]. A burgeoning volume of researches has demonstrated that dysregulation of the balance between ubiquitination and deubiquitination can lead to a wide variety of adverse consequences [10]. USP3 is a member of the USPs, the largest family in DUBs. As the study of USP3 continues, researchers have found that USP3 is involved in a variety of physiological and pathological processes in cell. In the realm of innate immunity, USP3 plays a role in dampening antiviral responses by impeding the activation of the type I interferon (IFN) pathway through the elimination of Lysine 63 (K63)-linked polyubiquitin chains on RIG-I [11]. Within the context of renal cell carcinoma (RCC), the tumor suppressor E74-like transcription factor 5 has the ability to hinder the progression of RCC by promoting USP3-mediated deubiquitination and stabilization of WD40 and tetratricopeptide repeats 1 [12]. The multifaceted role of USP3 in various physiological processes underscores the importance of comprehensively investigating its structure, functions, and regulatory mechanisms, as such insights may offer novel therapeutic opportunities in the future. This review provides a comprehensive overview of the structure, functions, regulation and current research on USP3 in tumors and other diseases, and discusses the gaps and prospects for USP3 research. Particularly, the timeline of USP3 is listed in Fig. 1.
The structure of USP3
USP3, located on human chromosome 15q22.31, contains 520 amino acid residues. USP3 contains two conserved protein domains: the ZnF domain and the catalytic domain (UCH) [13]. Amino acids 1–121 constitute the UBP ZnF, whereas amino acids 159–511 constitute the UCH. The structure of the UBP ZnF domain is unique and does not resemble any other known structure. It has a compact globular fold with a deep cleft and a pocket accommodating the C terminus of ubiquitin (Fig. 2) [14]. The core catalytic structure of USPs is generally composed of three subdomains, which have been likened to the palm, thumb, and finger. The “fingers” are responsible for grabbing ubiquitin and the catalytic center is between the “palm” and the “thumb” [15]. The catalytic core domain of USPs contains a conserved cysteine catalytic triad, and the extended finger domain, together with the palm and thumb domains, forms the binding pocket of ubiquitin that recognizes the extended tail of ubiquitin and presents its c terminus to the active site cysteine [16]. ZnF and UCH jointly function, both are indispensable. Experiments confirmed that mutation of UBP ZnF significantly reduced the interaction of USP3 with ubiquitinated histone uH2A both in vivo and in vitro, suggesting that this is the major domain mediating the interaction between USP3 and ubiquitin [17]. In addition, USP3 was found to inhibit type I IFN signaling by deubiquitinating RIG-I-like receptors. However, the ZnF domain of USP3 alone cannot inhibit RIG-I-induced type I IFN activation, and the UCH domain may require ZnF for maximal catalytic activity, suggesting that both intact ZnF and the catalytic domain are required for USP3 to exert its deubiquitination function [11]. USP3 has the capability to interact with Claspin via the UCH domain for the purpose of deubiquitinating it, resulting in the activation of Claspin-dependent ATR-Chk1 signaling that ultimately contributes to the augmentation of glioblastoma radiation resistance [18]. In summary, the biological activity of USP3 is contingent upon the structural integrity of its UBP ZnF and UCH domains, which work in tandem to fulfill the physiological role of USP3.
The functions of USP3
USP3 is a cysteine protease involved in a variety of physiological activities and perturbations in its function can result in adverse consequences. USP3 is implicated in DNA repair, cell cycle regulation, and apoptosis, with a particular focus on describing its role in maintaining genome stability and modulating inflammation.
In genome stability
Genomic instability is deemed to be a hallmark of cancer [19]. DNA is vulnerable to alterations caused by external and internal factors, leading organisms to safeguard the genome via the DNA damage response (DDR) and cell-cycle checkpoints [20]. The DDR comprises two main signaling pathways: ATR-CHK1 and ATM-CHK2, with checkpoint kinase 1 (CHK1) being activated by phosphorylation from the upstream kinase ATR [21]. The interaction between USP3 and CHK1 results in the direct removal of the inhibitory ubiquitin chain at K63, leading to the release of CHK1 from chromatin and subsequent down-regulation of USP3, which enhances gene stability [22]. Histone ubiquitination is essential for the activation of DDR, and USP3 acts as a chromatin modifier by deubiquitinating monoubiquitinated H2A (uH2A) and H2B (uH2B) in vivo. The ZnF domain and uH2A are identified as the major structural domains and substrates, respectively, for USP3-mediated deubiquitination [17]. Further studies revealed that in addition to uH2A, USP3 also deubiquitinates conjugate Ub-γH2AX (variant H2A) at K13-15. In addition, USP3 regulates the aggregation of DDR factors (BRCA1 and 53BP1) at DNA damage sites, and overexpression of USP3 impairs the recruitment of these factors [23]. USP3 regulates mitotic progression, and USP3 deficiency induces DNA damage leading to replication defects and S-phase delays as well as activation of the corresponding checkpoints [17]. USP3 deubiquitinates and stabilizes the cell division cycle 25A (Cdc25A), a bispecific phosphatase that regulates the cell cycle, and degradation of Cdc25A in the presence of DNA damage causes cells to arrest in G1 phase [24]. Stem cell homeostasis is also critical for maintaining genomic stability. USP3-deficient mouse models exhibit severe haematopoietic impairment and hematopoietic stem cell (HSC) defects, with a decline in lymphocytes as they age, particularly in B-cell lines and T-cell lines. USP3 shields HSC from ionizing radiation (IR) and defends against spontaneous DNA damage in vivo via ubiquitin-dependent DDR. Deficiency of USP3 makes HSC more sensitive to genotoxicity and contributes to severe genomic rearrangements due to spontaneously generated DSB-triggered repair pathways [25].
In inflammatory vesicles
Inflammatory vesicles are integral to the innate immune system, aiding in immune homeostasis, with NLRP3 inflammasomes being the subject of extensive research [26]. Apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) functions as a central bridging protein for multiple inflammatory vesicles, with USP3 playing a role in enhancing ASC stability through the removal of K48-linked ubiquitin chains. The formation of ASC speckles is indicative of NLRP3 inflammatory vesicle activation, with USP3 knockdown resulting in a significant reduction in the number of ASC speckles. Furthermore, in addition to NLRP3, USP3 overexpression in vivo also facilitates the activation of AIM2 and NLRC4 [27]. USP3, serving as a regulator of inflammatory vesicle activation, plays a crucial role in the precise control of inflammation and the maintenance of immune homeostasis.
Signaling pathways in USP3
USP3 is engaged in regulating multiple signaling pathways, such as type I IFN, NF-κB, and PI3K/AKT signaling pathways. This review specifically focuses on elucidating the mechanisms involved in the type I IFN and NF-κB pathways, which are crucial components of the innate immune system and are activated upon detection of pathogenic molecules by pattern recognition receptors (PRRs), such as Toll-like receptors (TLRs), Nod-like receptors (NLRs), and RIG-I-like receptors (RLRs) [28].
Type I IFN signaling
Type I IFN, a cytokine produced in response to viral infection, is generated through PRR-mediated mechanisms. RLRs serve as intracellular PRRs for pathogen detection, with humans possessing three RLRs: RIG-I, melanoma differentiation-associated gene 5 (MDA5), and LGP2 [29, 30]. The N-terminal caspase activation recruitment domain (CARD) of RIG-I and MDA5 interacts with the mitochondrial protein MASV (mitochondrial antiviral signaling) in a ligand-dependent manner. USP3 modulates the type I IFN response by specifically binding to the CARD domains of RIG-I and MDA5, thereby inhibiting their activation. USP3 selectively cleaves the K63-linked ubiquitin chains on RIG-I, which are crucial for initiating the type I IFN response, without affecting ubiquitin chains on other signaling proteins [11]. Influenza A virus (IAV), which has caused several world pandemics, is highly pathogenic to humans, and the IFN pathway is one of the effective ways to combat it. USP3 is a negative regulator of the type I IFN pathway, and miR-26a can attack USP3 to activate the IFN pathway and thus inhibit IAV infection [31].
NF-κB signaling
Acknowledgements
We would like to acknowledge the reviewers for their helpful comments on this paper.
Funding
This study was supported by the Major Program of the National Natural Science Foundation of China (62227803), the National Natural Science Foundation of China (62141109), the Foreword Leading Technology Fundamental Research Project of Jiangsu (BK20212012), and Jiangsu Province Social Development Project (BE2022812).
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YS proposed and conceived the outline; RY searched the literatures; YW wrote the original manuscript; KN contributed to the figures; QL provided the tables; KF polished the manuscript; WZ revised and edited the manuscript. All authors read and approved the final manuscript.
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Wang, Y., Shi, Y., Niu, K. et al. Ubiquitin specific peptidase 3: an emerging deubiquitinase that regulates physiology and diseases. Cell Death Discov. 10, 243 (2024). https://doi.org/10.1038/s41420-024-02010-6
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DOI: https://doi.org/10.1038/s41420-024-02010-6
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