Blocking an N-terminal acetylation-dependent protein interaction inhibits an E3 ligase

N-Terminal Acetylation by NatB Is Required for the Shutoff Activity of Influenza A Virus PA-X

N-terminal acetylation is a major posttranslational modification in eukaryotes catalyzed by N-terminal acetyltransferases (NATs), NatA through NatF. Although N-terminal acetylation modulates diverse protein functions, little is known about its roles in virus replication. We found that NatB, which comprises NAA20 and NAA25, is involved in the shutoff activity of influenza virus PA-X. The shutoff activity of PA-X was suppressed in NatB-deficient cells, and PA-X mutants that are not acetylated by NatB showed reduced shutoff activities. We also evaluated the importance of N-terminal acetylation of PA, because PA-X shares its N-terminal sequence with PA. Viral polymerase activity was reduced in NatB-deficient cells. Moreover, mutant PAs that are not acetylated by NatB lost their function in the viral polymerase complex. Taken together, our findings demonstrate that N-terminal acetylation is required for the shutoff activity of PA-X and for viral polymerase activity.

Targeting DCN1-UBC12 Protein-Protein Interaction for Regulation of Neddylation Pathway

Protein neddylation is one type of posttranslational modifications that regulates the activity of the substrate proteins. Neddylation modification is catalyzed by NEDD8-activating enzyme (NAE, E1), NEDD8-conjugating enzyme (E2), and NEDD8 ligase (E3) to attach NEDD8, an ubiquitin-like molecule, to a lysine residue of a substrate protein. The best known neddylation substrates are cullin family members, which are scaffold components of cullin-RING ligases (CRLs), and cullin neddylation is required for activation of CRLs. In mammalian cells, there are one E1, two E2s (UBC12/UBE2M and UBE2F), and over a dozen E3s. MLN4924, the first-in-class small-molecule inhibitor of NAE, blocks the entire neddylation modification to inactivate activity of all CRLs. MLN4924 is currently in the Phase I/II clinical trials for anticancer application.In the last few years, targeting protein-protein interactions of the neddylation complexes has been pursued as a potential strategy to selectively inhibit the activity of individual CRL. Analysis of the co-crystal structures of DCN1, a co-E3 for neddylation, and its binding partners UBC12 (a neddylation E2) suggested that it may be amenable for the design of potent, small-molecule inhibitors. In this chapter, we will review the discovery of small-molecule inhibitors that block the interactions of DCN1 with UBC12 (hereafter called DCN1 inhibitors) from a number of laboratories, including ours, leading to selective inactivation of CRL-1 and/or CRL-3. We will also discuss potential therapeutic applications of these small-molecule inhibitors.

Targeting Protein Neddylation for Cancer Therapy

Neddylation is a posttranslational modification that conjugates a ubiquitin-like protein NEDD8 to substrate proteins. The best-characterized substrates of neddylation are the cullin subunits of cullin-RING E3 ubiquitin ligase complexes (CRLs). CRLs as the largest family of E3 ubiquitin ligases control many important biological processes, including tumorigenesis, through promoting ubiquitylation and subsequent degradation of a variety of key regulatory proteins. The process of protein neddylation is overactivated in multiple types of human cancers, providing a sound rationale as an attractive anticancer therapeutic strategy, evidenced by the development of the NEDD8-activating enzyme (NAE) inhibitor MLN4924 (also known as pevonedistat). Recently, increasing evidence strongly indicates that neddylation inhibition by MLN4924 exerts anticancer effects mainly by triggering cell apoptosis, senescence, and autophagy and causing angiogenesis suppression, inflammatory responses, and chemo-/radiosensitization in a context-dependent manner. Here, we briefly summarize the latest progresses in this field, focusing on the preclinical studies to validate neddylation modification as a promising anticancer target.

Pharmaceutical Inhibition of Neddylation as Promising Treatments for Various Cancers

BACKGROUND

Neddylation is an important post-translational modification of proteins, in which a NEDD8 (neural-precursor-cell-expressed developmentally down-regulated 8) is covalently introduced onto the substrate proteins to regulate their functions and homeostasis. As neddylation is frequently up-regulated in various cancers, its interference was proposed as a promising therapy of related diseases.

OBJECTIVE

The recent advances in developing neddylation interfering agents were summarized to provide an overview of current achievements and perspectives for future development.

METHODS

Reports on neddylation interfering agents were acquired from Pubmed as well as the EPO and clinicaltrials.gov websites, which were subsequently analyzed and summarized according to targets, chemical structures and biological activities.

RESULTS

Neddylation as a sophisticated procedure comprises proteolytic processing of NEDD8 precursor, deploying conjugating enzymes E1 (NAE), E2 (UBE2M and UBE2F) and various E3, as well as translocating NEDD8 along these conjugating enzymes sequentially and finally to substrate proteins. Among these nodes, NAE, UBE2M and the interaction between UBE2M-DCN1 have been targeted by small molecules, metal complexes, peptides and RNAi. A NAE inhibitor pevonedistat (MLN4924) is currently under evaluation in clinical trials for the treatment of various cancers.

CONCLUSION

With multiple inhibitory approaches of neddylation being introduced, the development of neddylation interference as a novel cancer therapy is significantly boosted recently, although its efficacy and the best way to achieve that are still to be demonstrated in clinical trials.

Discovery of candesartan cilexetic as a novel neddylation inhibitor for suppressing tumor growth

Protein neddylation is a posttranslational modification of conjugating the neuronal precursor cell-expressed developmentally down-regulated protein 8 (Nedd8) to substrates. Our previous work revealed that neddylation pathway is overactivated in various human lung cancers and correlates with the disease progression, whereas pharmacologically targeting this pathway has emerged as an attractive therapeutic strategy. As a follow-up research, 1331 approved drugs were investigated the inhibitory activities of cullin1 neddylation for screening the hit compounds via an improved enzyme-based assay. An antihypertensive agent, candesartan cilexetic (CDC), was identified as a novel neddylation inhibitor that ATP-competitively suppressing Nedd8-activating enzyme (NAE, E1) in mechanism, which inhibited the cullins neddylation superior than two representative non-covalent NAE inhibitors, M22 and mitoxantrone. Following with the findings such as apoptotic induction and tumor growth suppression in human lung cancer A549 in vitro and in vivo, CDC represents a potential anticancer lead compound with promising neddylation inhibitory activity.

Discovery of Novel Pyrazolo-pyridone DCN1 Inhibitors Controlling Cullin Neddylation

Chemical control of cullin neddylation is attracting increased attention based largely on the successes of the NEDD8-activating enzyme (E1) inhibitor pevonedistat. Recently reported chemical probes enable selective and time-dependent inhibition of downstream members of the neddylation trienzymatic cascade including the co-E3, DCN1. In this work, we report the optimization of a novel class of small molecule inhibitors of the DCN1-UBE2M interaction. Rational X-ray co-structure enabled optimization afforded a 25-fold improvement in potency relative to the initial screening hit. The potency gains are largely attributed to additional hydrophobic interactions mimicking the N-terminal acetyl group that drives binding of UBE2M to DCN1. The compounds inhibit the protein-protein interaction, block NEDD8 transfer in biochemical assays, engage DCN1 in cells, and selectively reduce the steady-state neddylation of Cul1 and Cul3 in two squamous carcinoma cell lines harboring DCN1 amplification.

Biochemical and structural analysis of N-terminal acetyltransferases

N-terminal acetylation is a co- and post-translational modification catalyzed by the conserved N-terminal acetyltransferase (NAT) family of enzymes. A majority of the human proteome is modified by the human NATs (NatA-F and H), which are minimally composed of a catalytic subunit and as many as two auxiliary subunits. Together, NATs specifically regulate many cellular functions by influencing protein activities such as their degradation, membrane targeting, and protein-protein interactions. This chapter will describe methods developed for their preparation, and their biochemical and structural characterization. This will include methodologies for expression and purification of recombinant NAT protein, kinetic assays, biochemical and biophysical assays, and strategies for structural studies.

Role of the COP9 Signalosome (CSN) in Cardiovascular Diseases

The constitutive photomorphogenesis 9 (COP9) signalosome (CSN) is an evolutionarily conserved multi-protein complex, consisting of eight subunits termed CSN1-CSN8. The main biochemical function of the CSN is the control of protein degradation via the ubiquitin-proteasome-system through regulation of cullin-RING E3-ligase (CRL) activity by deNEDDylation of cullins, but the CSN also serves as a docking platform for signaling proteins. The catalytic deNEDDylase (isopeptidase) activity of the complex is executed by CSN5, but only efficiently occurs in the three-dimensional architectural context of the complex. Due to its positioning in a central cellular pathway connected to cell responses such as cell-cycle, proliferation, and signaling, the CSN has been implicated in several human diseases, with most evidence available for a role in cancer. However, emerging evidence also suggests that the CSN is involved in inflammation and cardiovascular diseases. This is both due to its role in controlling CRLs, regulating components of key inflammatory pathways such as nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), and complex-independent interactions of subunits such as CSN5 with inflammatory proteins. In this case, we summarize and discuss studies suggesting that the CSN may have a key role in cardiovascular diseases such as atherosclerosis and heart failure. We discuss the implicated molecular mechanisms ranging from inflammatory NF-κB signaling to proteotoxicity and necrosis, covering disease-relevant cell types such as myeloid and endothelial cells or cardiomyocytes. While the CSN is considered to be disease-exacerbating in most cancer entities, the cardiovascular studies suggest potent protective activities in the vasculature and heart. The underlying mechanisms and potential therapeutic avenues will be critically discussed.

Potent 5-Cyano-6-phenyl-pyrimidin-Based Derivatives Targeting DCN1-UBE2M Interaction

Neddylation of the Cullin-RING E3 ligases (CRLs) regulates the homeostasis of approximately 20% of cellular proteins. Defective in cullin neddylation 1 (DCN1), as a co-E3 ligase, interacts with UBE2M to enhance the activation of CRLs, and this interaction is emerging as a therapeutic target for human diseases. Here, we present a series of pyrimidin-based small molecular inhibitors targeting DCN1-UBE2M interaction. After finding a novel inhibitor DC-1 with IC₅₀ = 1.2 μM, we performed a series of chemical optimizations, which finally led to the discovery of a potent thiazole containing 5-cyano-6-phenylpyrimidin-based inhibitor DC-2 (IC₅₀ = 15 nM). Next, using protein and cellular thermal shift assays, coimmunoprecipitation, molecular docking, and site-specific mutation experiments, we further proved that DC-2 specifically inhibited the interaction of UBE2M and DCN1 at molecule and cellular levels, resulting in the decrease of cullin3 neddylation and accumulation of its substrate, NRF2. Our findings indicate that DC-2 may serve as a novel lead compound for specific derivatives targeting DCN1-UBE2M interaction.

Patent highlights October-November 2018

A snapshot of noteworthy recent developments in the patent literature of relevance to pharmaceutical and medical research and development.

Co-translational, Post-translational, and Non-catalytic Roles of N-Terminal Acetyltransferases

Recent studies of N-terminal acetylation have identified new N-terminal acetyltransferases (NATs) and expanded the known functions of these enzymes beyond their roles as ribosome-associated co-translational modifiers. For instance, the identification of Golgi- and chloroplast-associated NATs shows that acetylation of N termini also happens post-translationally. In addition, we now appreciate that some NATs are highly specific; for example, a dedicated NAT responsible for post-translational N-terminal acetylation of actin was recently revealed. Other studies have extended NAT function beyond Nt acetylation, including functions as lysine acetyltransferases (KATs) and non-catalytic roles. Finally, emerging studies emphasize the physiological relevance of N-terminal acetylation, including roles in calorie-restriction-induced longevity and pathological α-synuclein aggregation in Parkinson's disease. Combined, the NATs rise as multifunctional proteins, and N-terminal acetylation is gaining recognition as a major cellular regulator.

Visualizing ubiquitination in mammalian cells

Covalent modification of proteins with ubiquitin is essential for the majority of biological processes in mammalian cells. Numerous proteins are conjugated with single or multiple ubiquitin molecules or chains in a dynamic fashion, often determining protein half-lives, localization or function. Experimental approaches to study ubiquitination have been dominated by genetic and biochemical analysis of enzyme structure-function relationships, reaction mechanisms and physiological relevance. Here, we provide an overview of recent developments in microscopy-based imaging of ubiquitination, available reagents and technologies. We discuss the progress in direct and indirect imaging of differentially linked ubiquitin chains in fixed and living cells using confocal fluorescence microscopy and super-resolution microscopy, illustrated by the role of ubiquitin in antibacterial autophagy and pro-inflammatory signalling. Finally, we speculate on future developments and forecast a transition from qualitative to quantitative super-resolution approaches to understand fundamental aspects of ubiquitination and the formation and distribution of functional E3 ligase protein complexes in their native environment.

Coupled monoubiquitylation of the co-E3 ligase DCNL1 by Ariadne-RBR E3 ubiquitin ligases promotes cullin-RING ligase complex remodeling

Cullin-RING E3 ubiquitin ligases (CRLs) are large and diverse multisubunit protein complexes that contribute to about one-fifth of ubiquitin-dependent protein turnover in cells. CRLs are activated by the attachment of the ubiquitin-like protein neural precursor cell expressed, developmentally down-regulated 8 (NEDD8) to the cullin subunits. This cullin neddylation is essential for a plethora of CRL-regulated cellular processes and is vital for life. In mammals, neddylation is promoted by the five co-E3 ligases, defective in cullin neddylation 1 domain-containing 1–5 (DCNL1–5); however, their functional regulation within the CRL complex remains elusive. We found here that the ubiquitin-associated (UBA) domain–containing DCNL1 is monoubiquitylated when bound to CRLs and that this monoubiquitylation depends on the CRL-associated Ariadne RBR ligases TRIAD1 (ARIH2) and HHARI (ARIH1) and strictly requires the DCNL1's UBA domain. Reconstitution of DCNL1 monoubiquitylation in vitro revealed that autoubiquitylated TRIAD1 mediates binding to the UBA domain and subsequently promotes a single ubiquitin attachment to DCNL1 in a mechanism previously dubbed coupled monoubiquitylation. Moreover, we provide evidence that DCNL1 monoubiquitylation is required for efficient CRL activity, most likely by remodeling CRLs and their substrate receptors. Collectively, this work identifies DCNL1 as a critical target of Ariadne RBR ligases and coupled monoubiquitylation of DCNL1 as an integrated mechanism that affects CRL activity and client–substrate ubiquitylation at multiple levels.

Control of protein degradation by N-terminal acetylation and the N-end rule pathway

Nα-terminal acetylation (Nt-acetylation) occurs very frequently and is found in most proteins in eukaryotes. Despite the pervasiveness and universality of Nt-acetylation, its general functions in terms of physiological outcomes remain largely elusive. However, several recent studies have revealed that Nt-acetylation has a significant impact on protein stability, activity, folding patterns, cellular localization, etc. In addition, Nt-acetylation marks specific proteins for degradation by a branch of the N-end rule pathway, a subset of the ubiquitin-mediated proteolytic system. The N-end rule associates a protein's in vivo half-life with its N-terminal residue or modifications on its N-terminus. This review provides a current understanding of intracellular proteolysis control by Nt-acetylation and the N-end rule pathway.

Targeting TRAF6 E3 ligase activity with a small-molecule inhibitor combats autoimmunity

Constitutive NF-κB signaling represents a hallmark of chronic inflammation and autoimmune diseases. The E3 ligase TNF receptor-associated factor 6 (TRAF6) acts as a key regulator bridging innate immunity, pro-inflammatory cytokines, and antigen receptors to the canonical NF-κB pathway. Structural analysis and point mutations have unraveled the essential role of TRAF6 binding to the E2-conjugating enzyme ubiquitin-conjugating enzyme E2 N (Ubc13 or UBE2N) to generate Lys⁶³-linked ubiquitin chains for inflammatory and immune signal propagation. Genetic mutations disrupting TRAF6-Ubc13 binding have been shown to reduce TRAF6 activity and, consequently, NF-κB activation. However, to date, no small-molecule modulator is available to inhibit the TRAF6-Ubc13 interaction and thereby counteract NF-κB signaling and associated diseases. Here, using a high-throughput small-molecule screening approach, we discovered an inhibitor of the TRAF6-Ubc13 interaction that reduces TRAF6-Ubc13 activity both in vitro and in cells. We found that this compound, C25-140, impedes NF-κB activation in various immune and inflammatory signaling pathways also in primary human and murine cells. Importantly, C25-140 ameliorated inflammation and improved disease outcomes of autoimmune psoriasis and rheumatoid arthritis in preclinical in vivo mouse models. Hence, the first-in-class TRAF6-Ubc13 inhibitor C25-140 expands the toolbox for studying the impact of the ubiquitin system on immune signaling and underscores the importance of TRAF6 E3 ligase activity in psoriasis and rheumatoid arthritis. We propose that inhibition of TRAF6 activity by small molecules represents a promising novel strategy for targeting autoimmune and chronic inflammatory diseases.

T4 lysozyme-facilitated crystallization of the human molybdenum cofactor-dependent enzyme mARC

The human mitochondrial amidoxime reducing component (hmARC) is a molybdenum cofactor-dependent enzyme that is involved in the reduction of a diverse range of N-hydroxylated compounds of either physiological or xenobiotic origin. In this study, the use of a fusion-protein approach with T4 lysozyme (T4L) to determine the structure of this hitherto noncrystallizable enzyme by X-ray crystallography is described. A set of four different hmARC-T4L fusion proteins were designed. Two of them contained either an N-terminal or a C-terminal T4L moiety fused to hmARC, while the other two contained T4L as an internal fusion partner tethered to the hmARC enzyme between two predicted secondary-structure elements. One of these internal fusion constructs could be expressed and crystallized successfully. The hmARC-T4L crystals diffracted to 1.7 Å resolution using synchrotron radiation and belonged to space group P212121 with one molecule in the asymmetric unit. Initial attempts to solve the structure by molecular replacement using T4L did not result in electron-density distributions that were sufficient for model building and interpretation of the hmARC moiety. However, this study emphasizes the utility of the T4L fusion-protein approach, which can be used for the crystallization and structure determination of membrane-bound proteins as well as soluble proteins.

New Insights into the Role of E2s in the Pathogenesis of Diseases: Lessons Learned from UBE2O

Intracellular communication via ubiquitin (Ub) signaling impacts all aspects of cell biology and regulates pathways critical to human development and viability; therefore aberrations or defects in Ub signaling can contribute to the pathogenesis of human diseases. Ubiquitination consists of the addition of Ub to a substrate protein via coordinated action of E1-activating, E2-conjugating and E3-ligating enzymes. Approximately 40 E2s have been identified in humans, and most are thought to be involved in Ub transfer; although little information is available regarding the majority of them, emerging evidence has highlighted their importance to human health and disease. In this review, we focus on recent insights into the pathogenetic roles of E2s (particularly the ubiquitin-conjugating enzyme E2O [UBE2O]) in debilitating diseases and cancer, and discuss the tantalizing prospect that E2s may someday serve as potential therapeutic targets for human diseases.

Probing ubiquitin and SUMO conjugation and deconjugation

Ubiquitin (Ub) and ubiquitin-like (Ubl) proteins including small Ubl modifier (SUMO) are small proteins which are covalently linked to target proteins to regulate their functions. In this review, we discuss the current state of the art and point out what we feel this field urgently needs in order to delineate the wiring of the system. We discuss what is needed to unravel the connections between different components of the conjugation machineries for ubiquitylation and SUMOylation, and to unravel the connections between the conjugation machineries and their substrates. Chemical probes are key tools to probe signal transduction by these small proteins that may help understand their action. This rapidly moving field has resulted in various small molecules that will help us to further understand Ub and SUMO function and that may lead to the development of new drugs.

Piperidinyl Ureas Chemically Control Defective in Cullin Neddylation 1 (DCN1)-Mediated Cullin Neddylation

We previously discovered and validated a class of piperidinyl ureas that regulate defective in cullin neddylation 1 (DCN1)-dependent neddylation of cullins. Here, we report preliminary structure-activity relationship studies aimed at advancing our high-throughput screen hit into a tractable tool compound for dissecting the effects of acute DCN1-UBE2M inhibition on the NEDD8/cullin pathway. Structure-enabled optimization led to a 100-fold increase in biochemical potency and modestly increased solubility and permeability as compared to our initial hit. The optimized compounds inhibit the DCN1-UBE2M protein-protein interaction in our TR-FRET binding assay and inhibit cullin neddylation in our pulse-chase NEDD8 transfer assay. The optimized compounds bind to DCN1 and selectively reduce steady-state levels of neddylated CUL1 and CUL3 in a squamous cell carcinoma cell line. Ultimately, we anticipate that these studies will identify early lead compounds for clinical development for the treatment of lung squamous cell carcinomas and other cancers.

Discovery of an Orally Bioavailable Inhibitor of Defective in Cullin Neddylation 1 (DCN1)-Mediated Cullin Neddylation

We previously reported the discovery, validation, and structure-activity relationships of a series of piperidinyl ureas that potently inhibit the DCN1-UBE2M interaction. We demonstrated that compound 7 inhibits both the DCN1-UBE2M protein-protein interaction and DCN1-mediated cullin neddylation in biochemical assays and reduces levels of steady-state cullin neddylation in a squamous carcinoma cell line harboring DCN1 amplification. Although compound 7 exhibits good solubility and permeability, it is rapidly metabolized in microsomal models (CL_int = 170 mL/min/kg). This work lays out the discovery of an orally bioavailable analogue, NAcM-OPT (67). Compound 67 retains the favorable biochemical and cellular activity of compound 7 but is significantly more stable both in vitro and in vivo. Compound 67 is orally bioavailable, well tolerated in mice, and currently used to study the effects of acute pharmacologic inhibition of the DCN1-UBE2M interaction on the NEDD8/CUL pathway.

High-Affinity Peptidomimetic Inhibitors of the DCN1-UBC12 Protein-Protein Interaction

The Cullin-RING ligases (CRLs) regulate the turnover of approximately 20% of the proteins in mammalian cells and are emerging therapeutic targets in human diseases. The activation of CRLs requires the neddylation of their cullin subunit, which is controlled by an activation complex consisting of Cullin-RBX1-UBC12-NEDD8-DCN1. Herein, we describe the design, synthesis, and evaluation of peptidomimetics targeting the DCN1-UBC12 protein-protein interaction. Starting from a 12-residue UBC12 peptide, we have successfully obtained a series of peptidomimetic compounds that bind to DCN1 protein with K_D values of <10 nM. Determination of a cocrystal structure of a potent peptidomimetic inhibitor complexed with DCN1 provides the structural basis for their high-affinity interaction. Cellular investigation of one potent DCN1 inhibitor, compound 36 (DI-404), reveals that it effectively and selectively inhibits the neddylation of cullin 3 over other cullin members. Further optimization of DI-404 may yield a new class of therapeutics for the treatment of human diseases in which cullin 3 CRL plays a key role.

Protein neddylation and its alterations in human cancers for targeted therapy

Neddylation, a post-translational modification that conjugates an ubiquitin-like protein NEDD8 to substrate proteins, is an important biochemical process that regulates protein function. The best-characterized substrates of neddylation are the cullin subunits of Cullin-RING ligases (CRLs), which, as the largest family of E3 ubiquitin ligases, control many important biological processes, including tumorigenesis, through promoting ubiquitylation and subsequent degradation of a variety of key regulatory proteins. Recently, increasing pieces of experimental evidence strongly indicate that the process of protein neddylation modification is elevated in multiple human cancers, providing sound rationale for its targeting as an attractive anticancer therapeutic strategy. Indeed, neddylation inactivation by MLN4924 (also known as pevonedistat), a small molecule inhibitor of E1 NEDD8-activating enzyme currently in phase I/II clinical trials, exerts significant anticancer effects by inducing cell cycle arrest, apoptosis, senescence and autophagy in a cell-type and context dependent manner. Here, we summarize the latest progresses in the field with a major focus on preclinical studies in validation of neddylation modification as a promising anticancer target.

A potent small-molecule inhibitor of the DCN1-UBC12 interaction that selectively blocks cullin 3 neddylation

The Cullin-RING E3 ubiquitin ligases (CRLs) regulate homeostasis of ~20% of cellular proteins and their activation require neddylation of their cullin subunit. Cullin neddylation is modulated by a scaffolding DCN protein through interactions with both the cullin protein and an E2 enzyme such as UBC12. Here we report the development of DI-591 as a high-affinity, cell-permeable small-molecule inhibitor of the DCN1-UBC12 interaction. DI-591 binds to purified recombinant human DCN1 and DCN2 proteins with K i values of 10-12 nM, and disrupts the DCN1-UBC12 interaction in cells. Treatment with DI-591 selectively converts cellular cullin 3 into an un-neddylated inactive form with no or minimum effect on other cullin members. Our data firmly establish a previously unrecognized specific role of the DCN1-UBC12 interaction for cellular neddylation of cullin 3. DI-591 is an excellent probe compound to investigate the role of the cullin 3 CRL ligase in biological processes and human diseases.

Squamous cell carcinoma-related oncogene (SCCRO) neddylates Cul3 protein to selectively promote midbody localization and activity of Cul3KLHL21 protein complex during abscission

Squamous cell carcinoma-related oncogene (SCCRO)/DCUN1D1, a component of the neddylation E3 complex, regulates the activity of the cullin-RING-ligase type of ubiquitination E3s by promoting neddylation of cullin family members. Studies have shown that SCCRO regulates proliferation in vitro and in vivo Here we show that inactivation of SCCRO results in prolonged mitotic time because of delayed and/or failed abscission. The effects of SCCRO on abscission involve its role in neddylation and localization of Cul3 to the midbody. The Cul3 adaptor KLHL21 mediates the effects of SCCRO on abscission, as it fails to localize to the midbody in SCCRO-deficient cells during abscission, and its inactivation resulted in phenotypic changes identical to SCCRO inactivation. Ubiquitination-promoted turnover of Aurora B at the midbody was deficient in SCCRO- and KLHL21-deficient cells, suggesting that it is the target of Cul3^KLHL21 at the midbody. Correction of abscission delays in SCCRO-deficient cells with addition of an Aurora B inhibitor at the midbody stage suggests that Aurora B is the target of SCCRO-promoted Cul3^KLHL21 activity. The activity of other Cul3-anchored complexes, including Cul3^KLHL9/KLHL13, was intact in SCCRO-deficient cells, suggesting that SCCRO selectively, rather than collectively, neddylates cullins in vivo Combined, these findings support a model in which the SCCRO, substrate, and substrate adaptors cooperatively provide tight control of neddylation and cullin-RING-ligase activity in vivo.