Cullin RING Ligase 5 (CRL-5): Neddylation Activation and Biological Functions

Ubiquitin Ligase RBX2/SAG Regulates Mitochondrial Ubiquitination and Mitophagy

BACKGROUND

Clearance of damaged mitochondria via mitophagy is crucial for cellular homeostasis. Apart from Parkin, little is known about additional Ub (ubiquitin) ligases that mediate mitochondrial ubiquitination and turnover, particularly in highly metabolically active organs such as the heart.

METHODS

In this study, we have combined in silico analysis and biochemical assay to identify CRL (cullin-RING ligase) 5 as a mitochondrial Ub ligase. We generated cardiomyocytes and mice lacking RBX2 (RING-box protein 2; also known as SAG [sensitive to apoptosis gene]), a catalytic subunit of CRL5, to understand the effects of RBX2 depletion on mitochondrial ubiquitination, mitophagy, and cardiac function. We also performed proteomics analysis and RNA-sequencing analysis to define the impact of loss of RBX2 on the proteome and transcriptome.

RESULTS

RBX2 and CUL (cullin) 5, 2 core components of CRL5, localize to mitochondria. Depletion of RBX2 inhibited mitochondrial ubiquitination and turnover, impaired mitochondrial membrane potential and respiration, increased cardiomyocyte cell death, and has a global impact on the mitochondrial proteome. In vivo, deletion of the Rbx2 gene in adult mouse hearts suppressed mitophagic activity, provoked accumulation of damaged mitochondria in the myocardium, and disrupted myocardial metabolism, leading to the rapid development of dilated cardiomyopathy and heart failure. Similarly, ablation of RBX2 in the developing heart resulted in dilated cardiomyopathy and heart failure. The action of RBX2 in mitochondria is not dependent on Parkin, and Parkin gene deletion had no impact on the onset and progression of cardiomyopathy in RBX2-deficient hearts. Furthermore, RBX2 controls the stability of PINK1 (PTEN-induced kinase 1) in mitochondria.

CONCLUSIONS

These findings identify RBX2-CRL5 as a mitochondrial Ub ligase that regulates mitophagy and cardiac homeostasis in a Parkin-independent, PINK1-dependent manner.

Discovery of novel small molecules targeting the USP21/JAK2/STAT3 axis for the treatment of triple-negative breast cancer

The deficiency in available targeted agents and frequency of chemoresistance are primary challenges in clinical management of triple-negative breast cancer (TNBC). The aberrant expression of USP21 and JAK2 represents a characterized mechanism of TNBC progression and resistance to paclitaxel (PTX). Despite its clear that high expression of USP21-mediated de-ubiquitination leads to increased levels of JAK2 protein, we lack regulator molecules to dissect the mechanisms that the interaction between USP21 and JAK2 contributes to the phenotype and resistance of TNBC. Here, we report a USP21/JAK2/STAT3 axis-targeting regulator 13c featuring a N-anthraniloyl tryptamine scaffold that showed excellent anti-TNBC potency and promising safety profile. Importantly, the therapeutic potential of using 13c in combination with PTX in PTX-resistant TNBC was demonstrated. This study showcases N-anthraniloyl tryptamine derivatives as a novel anti-TNBC chemotype with a pharmacological mode of action targeting the USP21/JAK2/STAT3 axis and provides a potential therapeutic target for the treatment of TNBC.

The Ubiquitin Ligase RBX2/SAG Regulates Mitochondrial Ubiquitination and Mitophagy

Clearance of damaged mitochondria via mitophagy is crucial for cellular homeostasis. While the role of ubiquitin (Ub) ligase PARKIN in mitophagy has been extensively studied, increasing evidence suggests the existence of PARKIN-independent mitophagy in highly metabolically active organs such as the heart. Here, we identify a crucial role for Cullin-RING Ub ligase 5 (CRL5) in basal mitochondrial turnover in cardiomyocytes. CRL5 is a multi-subunit Ub ligase comprised by the catalytic RING box protein RBX2 (also known as SAG), scaffold protein Cullin 5 (CUL5), and a substrate-recognizing receptor. Analysis of the mitochondrial outer membrane-interacting proteome uncovered a robust association of CRLs with mitochondria. Subcellular fractionation, immunostaining, and immunogold electron microscopy established that RBX2 and Cul5, two core components of CRL5, localizes to mitochondria. Depletion of RBX2 inhibited mitochondrial ubiquitination and turnover, impaired mitochondrial membrane potential and respiration, and increased cell death in cardiomyocytes. In vivo , deletion of the Rbx2 gene in adult mouse hearts suppressed mitophagic activity, provoked accumulation of damaged mitochondria in the myocardium, and disrupted myocardial metabolism, leading to rapid development of dilated cardiomyopathy and heart failure. Similarly, ablation of RBX2 in the developing heart resulted in dilated cardiomyopathy and heart failure. Notably, the action of RBX2 in mitochondria is not dependent on PARKIN, and PARKIN gene deletion had no impact on the onset and progression of cardiomyopathy in RBX2-deficient hearts. Furthermore, RBX2 controls the stability of PINK1 in mitochondria. Proteomics and biochemical analyses further revealed a global impact of RBX2 deficiency on the mitochondrial proteome and identified several mitochondrial proteins as its putative substrates. These findings identify RBX2-CRL5 as a mitochondrial Ub ligase that controls mitophagy under physiological conditions in a PARKIN-independent, PINK1-dependent manner, thereby regulating cardiac homeostasis.

Noncanonical assembly, neddylation and chimeric cullin-RING/RBR ubiquitylation by the 1.8 MDa CUL9 E3 ligase complex

Ubiquitin ligation is typically executed by hallmark E3 catalytic domains. Two such domains, 'cullin-RING' and 'RBR', are individually found in several hundred human E3 ligases, and collaborate with E2 enzymes to catalyze ubiquitylation. However, the vertebrate-specific CUL9 complex with RBX1 (also called ROC1), of interest due to its tumor suppressive interaction with TP53, uniquely encompasses both cullin-RING and RBR domains. Here, cryo-EM, biochemistry and cellular assays elucidate a 1.8-MDa hexameric human CUL9-RBX1 assembly. Within one dimeric subcomplex, an E2-bound RBR domain is activated by neddylation of its own cullin domain and positioning from the adjacent CUL9-RBX1 in trans. Our data show CUL9 as unique among RBX1-bound cullins in dependence on the metazoan-specific UBE2F neddylation enzyme, while the RBR domain protects it from deneddylation. Substrates are recruited to various upstream domains, while ubiquitylation relies on both CUL9's neddylated cullin and RBR domains achieving self-assembled and chimeric cullin-RING/RBR E3 ligase activity.

Co-inhibition of BET and NAE enhances BIM-dependent apoptosis with augmented cancer therapeutic efficacy

Agents that inhibit bromodomain and extra-terminal domain (BET) proteins have been actively tested in the clinic as potential anticancer drugs. NEDD8-activating enzyme (NAE) inhibitors, represented by MLN4924, target the only activation enzyme in the neddylation pathway that has been identified as an attractive target for cancer therapy. In this study, we focus on the combination of BET inhibitors (BETis) and NAE inhibitors (NAEis) as a cancer therapeutic strategy and investigate its underlying mechanisms to explore and expand the application scope of both types of drugs. The results showed that this combination synergistically inhibited the proliferative activity of tumor cells from different tissues. Compared to a single drug, combination therapy had a weak effect on cycle arrest but significantly enhanced cell apoptosis. Furthermore, the growth of NCI-H1975 xenografts in nude mice was significantly inhibited by the combination without obvious body weight loss. Research on the synergistic mechanism demonstrated that combination therapy significantly increased the mRNA and protein levels of the proapoptotic gene BIM. The inhibition and knockout of BIM significantly attenuated the apoptosis induced by the combination, whereas the re-expression of BIM restored the synergistic effects, indicating that BIM induction plays a critical role in mediating the enhanced apoptosis induced by the co-inhibition of BET and NAE. Together, the enhanced transcription mediated by miR-17-92 cluster inhibition and reduced degradation promoted the increase in BIM levels, resulting in a synergistic effect. Collectively, these findings highlight the need for further clinical investigation into the combination of BETi and NAEi as a promising strategy for cancer therapy.

Emerging Roles of Cullin-RING Ubiquitin Ligases in Cardiac Development

Heart development is a spatiotemporally regulated process that extends from the embryonic phase to postnatal stages. Disruption of this highly orchestrated process can lead to congenital heart disease or predispose the heart to cardiomyopathy or heart failure. Consequently, gaining an in-depth understanding of the molecular mechanisms governing cardiac development holds considerable promise for the development of innovative therapies for various cardiac ailments. While significant progress in uncovering novel transcriptional and epigenetic regulators of heart development has been made, the exploration of post-translational mechanisms that influence this process has lagged. Culling-RING E3 ubiquitin ligases (CRLs), the largest family of ubiquitin ligases, control the ubiquitination and degradation of ~20% of intracellular proteins. Emerging evidence has uncovered the critical roles of CRLs in the regulation of a wide range of cellular, physiological, and pathological processes. In this review, we summarize current findings on the versatile regulation of cardiac morphogenesis and maturation by CRLs and present future perspectives to advance our comprehensive understanding of how CRLs govern cardiac developmental processes.

Neddylation Regulation of Immune Responses

Neddylation plays a vital role in post-translational modification, intricately shaping the regulation of diverse biological processes, including those related to cellular immune responses. In fact, neddylation exerts control over both innate and adaptive immune systems via various mechanisms. Specifically, neddylation influences the function and survival of innate immune cells, activation of pattern recognition receptors and GMP-AMP synthase-stimulator of interferon genes pathways, as well as the release of various cytokines in innate immune reactions. Moreover, neddylation also governs the function and survival of antigen-presenting cells, which are crucial for initiating adaptive immune reactions. In addition, neddylation regulates T cell activation, proliferation, differentiation, survival, and their effector functions, thereby ensuring an appropriate adaptive immune response. In this review, we summarize the most recent findings in these aspects and delve into the connection between dysregulated neddylation events and immunological disorders, especially inflammatory diseases. Lastly, we propose future directions and potential treatments for these diseases by targeting neddylation.

Cullin 5 aggravates hypoxic pulmonary hypertension by activating TRAF6/NF-κB/HIF-1α/VEGF

Hypoxic pulmonary hypertension (HPH) lacks effective pharmacologic treatments. Microarray-based gene expression indicates the crucial role of Cullin 5 (Cul 5) in HPH. This study showed that Cul 5 was upregulated in HPH patients and a murine model of HPH. In vitro, Cul 5 promoted the angiogenesis and adhesion capacity of human pulmonary artery endothelial cells (PAECs), which could be mitigated by Cul 5 inactivation mediated by pevonedistat or NEDD8 silence. In vivo, silencing of Cul 5 in the endothelium and Cul 5 inactivation by pevonedistat could also alleviate hypoxic vascular remodeling. Mechanistic research showed that Cul 5 participated in HPH pathogenesis via the TRAF6/NF-κB/HIF-1α/VEGF pathway. Inhibition of the TRAF6/NF-κB/HIF-1α/VEGF pathway could reverse Cul 5-induced human PAEC dysfunction. These findings demonstrate that Cul 5 is an important mediator of HPH via the TRAF6/NF-κB/HIF-1α/VEGF pathway firstly, and could be considered as a potential therapeutic target in the clinical treatment of HPH.

Discovery of neddylation E2s inhibitors with therapeutic activity

Neddylation is the writing of monomers or polymers of neural precursor cells expressed developmentally down-regulated 8 (NEDD8) to substrate. For neddylation to occur, three enzymes are required: activators (E1), conjugators (E2), and ligators (E3). However, the central role is played by the ubiquitin-conjugating enzymes E2M (UBE2M) and E2F (UBE2F), which are part of the E2 enzyme family. Recent understanding of the structure and mechanism of these two proteins provides insight into their physiological effects on apoptosis, cell cycle arrest and genome stability. To treat cancer, it is therefore appealing to develop novel inhibitors against UBE2M or UBE2F interactions with either E1 or E3. In this evaluation, we summarized the existing understanding of E2 interaction with E1 and E3 and reviewed the prospective of using neddylation E2 as a pharmacological target for evolving new anti-cancer remedies.

Cul5 mediates taurine-stimulated mTOR mRNA expression and proliferation of mouse mammary epithelial cells

Cullin5 (Cul5) protein can regulate multiple signaling pathways; however, it is still largely unknown the role and molecule mechanism of Cul5 in regulation of the mTOR signaling. In this study, we determined the effect of Cul5 on the proliferation of HC11 cells, a mouse mammary epithelial cell line, and explored the corresponding molecular mechanism. We found that Cul5 was highly expressed in mammary gland tissues in the lactation stage compared with that in puberty and involution. Using gene knockdown and activation methods, we showed that Cul5 promoted proliferation of HC11 cells, mRNA expression and protein phosphorylation of mTOR. Taurine (Tau) affected Cul5 mRNA and protein levels in a dose-dependent manner. Cul5 localized to the nucleus and knockdown of Cul5 almost totally blocked the stimulation of Tau on mTOR mRNA expression and protein phosphorylation. PI3K inhibition almost totally abolished the stimulation of Tau on Cul5 expression. In summary, our data uncover that Cul5 is a positive regulator of proliferation of HC11 cells, and mediates the stimulation of Tau on mRNA expression and subsequent protein phosphorylation of mTOR. Our data lay a new theoretical foundation for regulating mammary cell proliferation and promoting milk yield.

Rab40c regulates focal adhesions and PP6 activity by controlling ANKRD28 ubiquitylation

Rab40c is a SOCS box-containing protein which binds Cullin5 to form a ubiquitin E3 ligase complex (Rab40c/CRL5) to regulate protein ubiquitylation. However, the exact functions of Rab40c remain to be determined, and what proteins are the targets of Rab40c-Cullin5-mediated ubiquitylation in mammalian cells are unknown. Here we showed that in migrating MDA-MB-231 cells Rab40c regulates focal adhesion's number, size, and distribution. Mechanistically, we found that Rab40c binds the protein phosphatase 6 (PP6) complex and ubiquitylates one of its subunits, ankyrin repeat domain 28 (ANKRD28), thus leading to its lysosomal degradation. Furthermore, we identified that phosphorylation of FAK and MOB1 is decreased in Rab40c knock-out cells, which may contribute to focal adhesion site regulation by Rab40c. Thus, we propose a model where Rab40c/CRL5 regulates ANKRD28 ubiquitylation and degradation, leading to a decrease in PP6 activity, which ultimately affects FAK and Hippo pathway signaling to alter focal adhesion dynamics.

The Many Potential Fates of Non-Canonical Protein Substrates Subject to NEDDylation

Neuronal precursor cell-expressed developmentally down-regulated protein 8 (NEDD8) is a ubiquitin-like protein (UBL) whose canonical function involves binding to, and thus, activating Cullin-Ring finger Ligases (CRLs), one of the largest family of ubiquitin ligases in the eukaryotic cell. However, in recent years, several non-canonical protein substrates of NEDD8 have been identified. Here we attempt to review the recent literature regarding non-canonical NEDDylation of substrates with a particular focus on how the covalent modification of NEDD8 alters the protein substrate. Like much in the study of ubiquitin and UBLs, there are no clear and all-encompassing explanations to satisfy the textbooks. In some instances, NEDD8 modification appears to alter the substrates localization, particularly during times of stress. NEDDylation may also have conflicting impacts upon a protein's stability: some reports indicate NEDDylation may protect against degradation whereas others show NEDDylation can promote degradation. We also examine how many of the in vitro studies measuring non-canonical NEDDylation were conducted and compare those conditions to those which may occur in vivo, such as cancer progression. It is likely that the conditions used to study non-canonical NEDDylation are similar to some types of cancers, such as glioblastoma, colon and rectal cancers, and lung adenocarcinomas. Although the full outcomes of non-canonical NEDDylation remain unknown, our review of the literature suggests that researchers keep an open mind to the situations where this modification occurs and determine the functional impacts of NEDD8-modification to the specific substrates which they study.

Cullin-5 (CUL5) as a potential prognostic marker in a pan-cancer analysis of human tumors

There is some evidence supporting an association between Cullin-5 (CUL5) and cancer, but no research using pan-cancer analysis has been conducted previously. We therefore investigated the oncogenic role of CUL5 in 33 tumors from the Gene Expression Omnibus and The Cancer Genome Atlas databases. Many cancers reduce CUL5 levels, and the prognosis of certain cancers is vitally linked with CUL5 expression. CUL5 expression is associated with CD8 + T-cell infiltration levels in uveal melanomas and head and neck squamous cell carcinomas, and we observed a positive relationship between CUL5 and Tcm (T central memory) cells, and a negative relationship between T helper (Th) cells and pDC (plasmacytoid DC). CUL5 had negative associations with NK cells, NK CD56^bright cells, NK CD56^dim cells, Tregs, cytotoxic cells, and Th17 cells. Functions relating to protein processing and ubiquitin were included in the CUL5 functional mechanisms. The top 100 genes that are most strongly related to CUL5 were identified, and enrichment analysis indicated that the biological process with the closest relationship was neddylation, related pathways included the TGF-beta signaling pathway and intracellular receptor signaling pathway. CUL5 is related to biological cell behaviors such as chromosome segregation and positive regulation of chromosome organization. As the first study to perform a pan-cancer analysis of CUL5, the present findings will improve the understanding of the oncogenic role of CUL5 in different tumors.

Cullin 2-RBX1 E3 ligase and USP2 regulate antithrombin ubiquitination and stability

Hemophilia A and B are congenital bleeding disorders caused by a deficiency in pro-coagulant factor VIII or IX that is treated by downregulation of antithrombin. However, the molecular mechanisms that regulate antithrombin expression remain poorly understood. Here, we identified Cullin 2 and USP2 (ubiquitin-specific peptidase-2) as novel regulators of antithrombin expression that act by modulating antithrombin ubiquitination. Inhibition of the proteasome caused accumulation of antithrombin and its ubiquitinated forms in HepG2 and SMMC7721 cells. Notably, inhibition of neddylation with MLN4924 suppressed both ubiquitination and degradation of antithrombin, which is recapitulated by silencing of the neddylation enzymes, NAE1, UBA3, and UBE2M, with small interfering RNA (siRNA). We identified Cullin 2 as the interaction partner of antithrombin, and siRNA-mediated Cullin 2 knockdown reduced antithrombin ubiquitination and increased antithrombin protein. We further found that USP2 interacted with antithrombin and regulated antithrombin expression, showing that overexpression of USP2 inhibits the ubiquitination and proteasomal clearance of antithrombin, whereas pharmacological inhibition or siRNA-mediated knockdown of USP2 downregulates antithrombin. Collectively, these results suggest that Cullin 2 E3 ubiquitin ligase and USP2 coordinately regulate antithrombin ubiquitination and degradation. Thus, targeting Cullin 2 and USP2 could be a potential strategy for treatment of hemophilia.

The Negative Cross-Talk between SAG/RBX2/ROC2 and APC/C E3 Ligases in Regulation of Cell Cycle Progression and Drug Resistance

Anaphase-promoting complex/cyclosome (APC/C) is a well-characterized E3 ligase that couples with UBE2C and UBE2S E2s for substrate ubiquitylation by the K11 linkage. Our recent data show that SAG/RBX2/ROC2, a RING component of Cullin-RING E3 ligase, also complexes with these E2s for K11-linked substrate polyubiquitylation. Whether these two E3s cross-talk with each other was previously unknown. Here, we report that SAG competes with APC2 for UBE2C/UBE2S binding to act as a potential endogenous inhibitor of APC/C, thereby regulating the G2-to-M progression. As such, SAG knockdown triggers premature activation of APC/C, leading to mitotic slippage and resistance to anti-microtubule drugs. On the other hand, SAG itself is a substrate of APC/C^CDH1 for targeted degradation at the G1 phase. The degradation-resistant mutant of SAG-R98A/L101A accelerates the G1-to-S progression. Our study reveals that the negative cross-talk between SAG and APC/C is likely a mechanism to ensure the fidelity of cell cycle progression.

Zhang et al. provide a mechanistic insight of how negative cross-talk between E3 ligases SAG and APC/C ensures proper cell cycle progression. SAG knockdown prematurely activates APC/C to promote mitotic progression and trigger anti-microtubule drugs resistance, whereas SAG degradation by APC/C^CDH1 mainly occurs in G1 phase for proper G1-to-S transition.

Targeting neddylation E2s: a novel therapeutic strategy in cancer

Ubiquitin-conjugating enzyme E2 M (UBE2M) and ubiquitin-conjugating enzyme E2 F (UBE2F) are the two NEDD8-conjugating enzymes of the neddylation pathway that take part in posttranslational modification and change the activity of target proteins. The activity of E2 enzymes requires both a 26-residue N-terminal docking peptide and a conserved E2 catalytic core domain, which is the basis for the transfer of neural precursor cell-expressed developmentally downregulated 8 (NEDD8). By recruiting E3 ligases and targeting cullin and non-cullin substrates, UBE2M and UBE2F play diverse biological roles. Currently, there are several inhibitors that target the UBE2M-defective in cullin neddylation protein 1 (DCN1) interaction to treat cancer. As described above, this review provides insights into the mechanism of UBE2M and UBE2F and emphasizes these two E2 enzymes as appealing therapeutic targets for the treatment of cancers.

Neddylation regulation of mitochondrial structure and functions

Mitochondria are the powerhouse of a cell. The structure and function of mitochondria are precisely regulated by multiple signaling pathways. Neddylation, a post-translational modification, plays a crucial role in various cellular processes including cellular metabolism via modulating the activity, function and subcellular localization of its substrates. Recently, accumulated data demonstrated that neddylation is involved in regulation of morphology, trafficking and function of mitochondria. Mechanistic elucidation of how mitochondria is modulated by neddylation would further our understanding of mitochondrial regulation to a new level. In this review, we first briefly introduce mitochondria, then neddylation cascade, and known protein substrates subjected to neddylation modification. Next, we summarize current available data of how neddylation enzymes, its substrates (including cullins/Cullin-RING E3 ligases and non-cullins) and its inhibitor MLN4924 regulate the structure and function of mitochondria. Finally, we propose the future perspectives on this emerging and exciting field of mitochondrial research.

The application of ubiquitin ligases in the PROTAC drug design

Protein ubiquitylation plays important roles in many biological activities. Protein ubiquitylation is a unique process that is mainly controlled by ubiquitin ligases. The ubiquitin-proteasome system (UPS) is the main process to degrade short-lived and unwanted proteins in eukaryotes. Many components in the UPS are attractive drug targets. Recent studies indicated that ubiquitin ligases can be employed as tools in proteolysis-targeting chimeras (PROTACs) for drug discovery. In this review article, we will discuss the recent progress of the application of ubiquitin ligases in the PROTAC drug design. We will also discuss advantages and existing problems of PROTACs. Moreover, we will propose a few principles for selecting ubiquitin ligases in PROTAC applications.

Transgenic expression of Sag/Rbx2 E3 causes early stage tumor promotion, late stage cytogenesis and acinar loss in the Kras-PDAC model

SAG (Sensitive to Apoptosis Gene), also known as RBX2 or ROC2, is a RING component of CRL (Cullin-RING ligase), required for its activity. Our previous studies showed that Sag/Rbx2 co-operated with Kras or Pten loss to promote tumorigenesis in the lung and prostate, respectively, but antagonized Kras to inhibit skin tumorigenesis, suggesting a tissue/context dependent function of Sag. The role of SAG in KRAS-induced pancreatic tumorigenesis is unknown. In this study, we mined a cancer database and found that SAG is overexpressed in pancreatic cancer tissues and correlates with decreased patient survival. Whether Sag overexpression plays a causal role in pancreatic tumorigenesis is unknown. Here, we reported the generation of Sag transgenic mouse model alone (CS), or in combination with KrasG12D, driven by p48-Cre (KCS mice) for pancreatic specific Sag expression. Sag transgenic expression alone has no phenotypical abnormality, but in combination with KrasG12D promotes ADM (acinar-to-ductal metaplasia) conversion in vitro and mPanIN1 formation in vivo at the early stage, and impairs pancreatic functions at the late stage, as evidenced by poor glucose tolerance and significantly reduced α-Amylase activity, and induction of cytogenesis and acinar cell loss, eventually leading to atrophic pancreata and shortened mouse life-span. Mechanistically, Sag transgenic expression altered several key signaling pathways, particularly inactivation of mTORC1 signaling due to Deptor accumulation, and activation of the antioxidant Nrf2-Nqo1 axis. Thus, Sag plays a stage dependent promotion (early) and fate-changing (late) role during Kras-pancreatic tumorigenesis, likely via regulating its key substrates, which control growth-related signal transduction pathways.

Cullin-RING Ligase 5: Functional characterization and its role in human cancers

Cullin-RING ligase 5 (CRL5) is a multi-protein complex and consists of a scaffold protien cullin 5, a RING protein RBX2 (also known as ROC2 or SAG), adaptor proteins Elongin B/C, and a substrate receptor protein SOCS. Through targeting a variety of substrates for proteasomal degradation or modulating various protein-protein interactions, CRL5 is involved in regulation of many biological processes, such as cytokine signal transduction, inflammation, viral infection, and oncogenesis. As many substrates of CRL5 are well-known oncoproteins or tumor suppressors, abnormal regulation of CRL5 is commonly found in human cancers. In this review, we first briefly introduce each of CRL5 components, and then discuss the biological processes regulated by four members of SOCS-box-containing substrate receptor family through substrate degradation. We next describe how CRL5 is hijacked by a variety of viral proteins to degrade host anti-viral proteins, which facilitates virus infection. We further discuss the regulation of CUL5 and its various roles in human cancers, acting as either a tumor suppressor or an oncoprotein in a context-dependent manner. Finally, we propose novel insights for future perspectives on the validation of cullin5 and other CRL5 components as potential targets, and possible targeting strategies to discover CRL5 inhibitors for anti-cancer and anti-virus therapies.