Anaphase-promoting Complex Research Articles

Counting Degrons: Lessons From Multivalent Substrates for Targeted Protein Degradation.

E3s comprise a structurally diverse group of at least 800 members, most of which target multiple substrates through specific and regulated protein-protein interactions. These interactions typically rely on short linear motifs (SLiMs), called “degrons”, in an intrinsically disordered region (IDR) of the substrate, with variable rules of engagement governing different E3-docking events. These rules of engagement are of importance to the field of targeted protein degradation (TPD), where substrate ubiquitination and destruction require tools to effectively harness ubiquitin ligases (E3s). Substrates are often found to contain multiple degrons, or multiple copies of a degron, contributing to the affinity and selectivity of the substrate for its E3. One important paradigm for E3-substrate docking is presented by the Anaphase-Promoting Complex/Cyclosome (APC/C), a multi-subunit E3 ligase that targets hundreds of proteins for destruction during mitotic exit. APC/C substrate targeting takes place in an ordered manner thought to depend on tightly regulated interactions of substrates, with docking sites provided by the substoichiometric APC/C substrate adaptors and coactivators, Cdc20 or Cdh1/FZR1. Both structural and functional studies of individual APC/C substrates indicate that productive ubiquitination usually requires more than one degron, and that degrons are of different types docking to distinct sites on the coactivators. However, the dynamic nature of APC/C substrate recruitment, and the influence of multiple degrons, remains poorly understood. Here we review the significance of multiple degrons in a number of E3-substrate interactions that have been studied in detail, illustrating distinct kinetic effects of multivalency and allovalency, before addressing the role of multiple degrons in APC/C substrates, key to understanding ordered substrate destruction by APC/C. Lastly, we consider how lessons learnt from these studies can be applied in the design of TPD tools.

The Role of the APC/C and Its Coactivators Cdh1 and Cdc20 in Cancer Development and Therapy.

To sustain genomic stability by correct DNA replication and mitosis, cell cycle progression is tightly controlled by the cyclic activity of cyclin-dependent kinases, their binding to cyclins in the respective phase and the regulation of cyclin levels by ubiquitin-dependent proteolysis. The spindle assembly checkpoint plays an important role at the metaphase-anaphase transition to ensure a correct separation of sister chromatids before cytokinesis and to initiate mitotic exit, as an incorrect chromosome distribution may lead to genetically unstable cells and tumorigenesis. The ubiquitin ligase anaphase-promoting complex or cyclosome (APC/C) is essential for these processes by mediating the proteasomal destruction of cyclins and other important cell cycle regulators. To this end, it interacts with the two regulatory subunits Cdh1 and Cdc20. Both play a role in tumorigenesis with Cdh1 being a tumor suppressor and Cdc20 an oncogene. In this review, we summarize the current knowledge about the APC/C-regulators Cdh1 and Cdc20 in tumorigenesis and potential targeted therapeutic approaches.

The anaphase-promoting complex/cyclosome co-activator, Cdh1, is a novel target of human papillomavirus 16 E7 oncoprotein in cervical oncogenesis.

The transforming properties of the high-risk human papillomavirus (HPV) E7 oncoprotein are indispensable for driving the virus life cycle and pathogenesis. Besides inactivation of the retinoblastoma family of tumor suppressors as part of its oncogenic endeavors, E7-mediated perturbations of eminent cell cycle regulators, checkpoint proteins and proto-oncogenes are considered to be the tricks of its transformative traits. However, many such critical interactions are still unknown. In the present study, we have identified the anaphase-promoting complex/cyclosome (APC) co-activator, Cdh1, as a novel interacting partner and a degradation target of E7. We found that HPV16 E7-induced inactivation of Cdh1 promoted abnormal accumulation of multiple Cdh1 substrates. Such a mode of deregulation possibly contributes to HPV-mediated cervical oncogenesis. Our mapping studies recognized the C-terminal zinc-finger motif of E7 to associate with Cdh1 and interfere with the timely degradation of FoxM1, a bona fide Cdh1 substrate and a potent oncogene. Importantly, the E7 mutant with impaired interaction with Cdh1 exhibited defects in its ability for overriding typical cell cycle transition and oncogenic transformation, thereby validating the functional and pathological significance of the E7-Cdh1 axis during cervical carcinoma progression. Altogether, the findings from our study discover a unique nexus between E7 and APC/C-Cdh1, thereby adding to our understanding of the mechanism of E7-induced carcinogenesis and provide a promising target for the management of cervical carcinoma.

Associating transcriptomics data with inflammatory markers to understand tumour microenvironment in hepatocellular carcinoma.

Liver cancer is the fourth leading cause of cancer-related death globally which is estimated to reach more than 1 million deaths a year by 2030. Among liver cancer types, hepatocellular carcinoma (HCC) accounts for approximately 90% of the cases and is known to have a tumour promoting inflammation regardless of its underlying aetiology. However, current promising treatment approaches, such as immunotherapy, are partially effective for most of the patients due to the immunosuppressive nature of the tumour microenvironment (TME). Therefore, there is an urgent need to fully understand TME in HCC and discover new immune markers to eliminate resistance to immunotherapy. We analyse three microarray datasets, using unsupervised and supervised methods, in an effort to discover signature genes. First, univariate, and multivariate, feature selection methods, such as the Boruta algorithm, are applied. Subsequently, an optimisation procedure, which utilises random forest algorithm with three dataset pairs combinations, is performed. The resulting optimal gene sets are then combined and further subjected to network analysis and pathway enrichment analysis so as to obtain information related to their biological relevance. The microarray datasets were analysed via the MCP-counter, CIBERSORT, TIMER, EPIC, and quanTIseq deconvolution methods and an estimation of cell type abundances for each dataset sample were identified. The differences in the cell type abundances, between the adjacent and tumour sample groups, were then assessed using a Wilcoxon Rank Sum test (p-value < 0.05). The optimal gene signature sets, derived from each of the data pairs combination, achieved AUC values ranging from 0.959 to 0.988 in external validation sets using Random Forest model. CLEC1B and PTTG1 genes are retrieved across each optimal set. Among the signature genes, PTTG1, AURKA, and UBE2C genes are found to be involved in the regulation of mitotic sister chromatid separation and anaphase-promoting complex (APC) dependent catabolic process (adjusted p-value < 0.001). Additionally, the application of deconvolution algorithms revealed significant changes in cell type abundances of Regulatory T (Treg) cells, M0 and M1 macrophages, and T CD8+ cells between adjacent and tumour samples. We identified ECM1 gene as a potential immune-related marker acting through immune cell migration and macrophage polarisation. Our results indicate that macrophages, such as M0 macrophage and M1 macrophage cells, undergo significant changes in HCC TME. Moreover, our immune deconvolution approach revealed significant infiltration of Treg cells and M0 macrophages, and a significant decrease in T CD8+ cells and M1 macrophages in tumour samples.

Upregulation of anaphase promoting complex (APC) 7 as a prognostic marker for esophageal squamous cell carcinoma: A hospital based study

Esophageal cancer is the sixth leading cause of cancer death, and esophageal squamous cell carcinoma (ESCC) is the most prevalent type worldwide, with a poor prognosis due to late diagnosis. The search for new molecular prognostic biomarkers revealed that dysregulation of anaphase promoting complex/cyclosome (APC/C) activation due to altered expression of APC molecules might lead to perturbed mitotic progression leading to malignancy. We analyzed the expression of the four different subunits of the APC/C complex—APC3, APC4, APC5 and APC7—by Real Time Polymerase Chain Reaction (RT–PCR). The findings were then correlated with clinicopathological parameters and different lifestyle factors. Significant upregulation of APC7 (tissue and blood: N = 50; 3.72 ± 1.21 and 4.45 ± 1.18, respectively) and APC3 (tissue and blood: N = 52 and 55 and 4.50 ± 1.41 and 4.58 ± 1.06, respectively) suggests their role in uncontrolled cell proliferation. In addition to their association with increasing age, their significant association with tumor size, node stage (only APC7 (p < 0.05)), and dysphagia grade supports a potential role in tumorigenic transformation in ESCC. Furthermore, several exclusive lifestyle-associated factors play a crucial supporting role in the development of ESCC in the Northeast Indian population. Various lifestyle factors, such as the duration of smoking, tobacco and betel nut consumption, and the duration of alcohol consumption, are significantly associated with the expression of APC. Analysis based on Pearson's correlation coefficient indicated a positive correlation among the gene expression levels ofAPC3 (both blood and tissue), APC5 (tissue) and APC3 (tissue), APC7 (tissue) and APC3 (tissue), and APC7 (tissue) and APC3 (blood). Additionally, a positive correlation was found between APC7 expression in blood and tissue samples. However, no significant correlation was found between APC 7 expression and APC4 and APC5 expression in either blood or tissue samples.

Bioinformatics analysis based on ferroptosis-related lncRNAs: construction of a clinical prognostic model for nasopharyngeal carcinoma and correlation analysis.

BackgroundA prognostic model of ferroptosis associated with long non-coding RNAs (lncRNAs) in nasopharyngeal carcinoma was established by using The Cancer Genome Atlas (TCGA) database, and immune correlation analysis was conducted for patients classified into high- and low-risk groups by the model. Nasopharyngeal carcinoma is associated with many lncRNA gene mutations, and tumors are often closely related to metabolism, accompanied by obvious characteristics of immune infiltration.MethodsGene expression data and clinical data of nasopharyngeal carcinoma tissues and normal tissues were obtained from TCGA database, and differential lncRNAs related to ferroptosis were screened out. Univariate and multivariate Cox risk regression models were used to screen and establish the lncRNA prognostic risk prediction model. Patients were scored according to the model. The immune-related functions of the high-risk and low-risk groups were compared to obtain immune-related differences between the groups. In this study, the prognostic model was constructed by the intersection of genes related to nasopharyngeal cancer prognosis and genes related to iron death metabolism through Cox regression analysis and R-packet screening, and the area under curve (AUC) was further used to predict and verify the model.ResultsIn this study, a total of 14 differential lncRNAs related to the prognosis of ferroptosis were obtained. Immune correlation analysis showed that the high- and low-risk groups had significant differences in the following factors: dendritic cells, B cells, mast cells, and other immune cells (P=0.0001); anaphase-promoting complex (APC) co-inhibition, chemotactic factor receptor, immune checkpoint, and other immune functions (P=0.002); glutamate cysteine ligase catalytic (GCLC), human endogenous retrovirus-H long terminal repeat-associating protein 2 (HHLA2), cluster of differentiation (CD276), B and T-lymphocyte attenuator (BTLA), and other immune checkpoint related genes (P<0.001). GCLC was highly expressed in NP69/DDP cells (P=0.04). DDP can activate ferroptosis in NP69/DDP cells can inhibit GCLC expression, and the AUC curve (AUC =0.899) indicates that the model has good prediction and accuracy.ConclusionsThe prognostic model based on 16 ferroptosis-related lncRNAs can predict the prognosis of nasopharyngeal carcinoma patients, and the ferroptosis-related lncRNAs involved in the construction of the model obtained in this study may be related to the level of immune infiltration, and may even become new targets for immune checkpoint inhibitor therapy.

Development of a high-throughput assay to identify inhibitors of the ubiquitin-conjugating enzyme UBCH10.

UBCH10 is an ubiquitin-conjugating enzyme (E2) of the anaphase-promoting complex E3 ligase, a key regulator of the cell cycle. The UBCH10 gene and protein are frequently upregulated in multiple solid tumors, associated with an unfavorable outcome. Accumulating evidence from studies of human cancer cell lines, mouse transgenic models, and analyses of clinical samples suggest that UBCH10 is a potential cancer drug target. No small molecule inhibitor of UBCH10 has been reported in the literature. Here, we described the development and optimization of a novel time-resolved fluorescence resonance energy transfer (TR-FRET) UBCH10 assay based on the self-polyubiquitination of the enzyme in the absence of E3. The homogenous assay is robust, sensitive, and scalable to different multi-well formats for high-throughput screening (HTS). We demonstrate the suitability of the TR-FRET assay to identify chemical inhibitors of UBCH10 in a pilot HTS campaign.

Examining the mechanistic relationship of APC/CCDH1 and its interphase inhibitor EMI1.

Proper protein destruction by the ubiquitin (Ub)-proteasome system is vital for a faithful cell cycle. Hence, the activity of Ub ligases is tightly controlled. The Anaphase-Promoting Complex/Cyclosome (APC/C) is a 1.2 MDa Ub ligase responsible for mitotic progression and G1 maintenance. At the G1/S transition, the APC/C is inhibited by EMI1 to prevent APC/C-dependent polyubiquitination of cell cycle effectors. EMI1 uses several interaction motifs to block the recruitment of APC/C substrates as well as the APC/C-associated E2s, UBE2C, and UBE2S. Paradoxically, EMI1 is also an APC/C substrate during G1. Using a comprehensive set of enzyme assays, we determined the context-dependent involvement of the EMI1 motifs in APC/C-dependent ubiquitination of EMI1 and other substrates. Furthermore, we demonstrated that an isolated C-terminal peptide fragment of EMI1 activates APC/C-dependent substrate priming by UBE2C. Together, these findings reveal the multiple roles of the EMI1 C-terminus for G1 maintenance and the G1/S transition.

PLEKHA5 Regulates Mitotic Progression by Promoting APC/C Localization to Microtubules

Progression through major cell cycle checkpoints involves spatiotemporal coordination of cytoskeletal dynamics with changes in protein activities, chromosomal dynamics, and signaling events. A major role of the ubiquitin–proteasome system is to orchestrate cell cycle progression through temporally controlled protein degradation programs. The anaphase‐promoting complex/cyclosome (APC/C) is the primary E3 ligase controlling all aspects of mitosis, including G2/M transition, early mitosis, the metaphase–anaphase transition, and mitotic exit, via polyubiquitination of important mitotic effector proteins. The temporal control of APC/C‐mediated ubiquitination in these processes is well established, including identities of ubiquitination substrates and accessory factors that modulate E3 ligase activity. Much less is known, however, about the spatial organization of APC/C function, including its potential interplay with the microtubule cytoskeleton, which serves as a signaling platform and whose dynamic behavior is central to advancement through mitosis. Here, we investigate and describe pleckstrin homology domain‐containing family A, member 5 (PLEKHA5) as a new regulator of APC/C function and the ubiquitination pathway in mitosis. We found that PLEKHA5 localized to the microtubule network and interacted with APC/C. PLEKHA5 knockdown antagonized mitotic entry and progression, causing a buildup of APC/C substrates implicated in both the G2/M and metaphase–anaphase transitions, in a manner dependent upon the PLEKHA5 interaction with APC/C. In vitro ubiquitination assays showed that APC/C isolated from mitotic cells lacking PLEKHA5 had lower catalytic activity and a decreased association with its key mitotic co‐activator CDC20. We investigated the dynamic localizations of the APC/C and the potential role of PLEKHA5 in its regulation by developing a TurboID proximity biotinylation tool to assess microtubule localization of endogenous proteins. Microtubule‐targeted TurboIDs revealed that PLEKHA5, APC/C subunits, and the co‐activator CDC20 all localized to microtubules both in interphase and in M phase. Importantly, upon PLEKHA5 knockdown, a pool of APC/C, but not CDC20, lost its microtubule localization, which could explain the decreased APC/C‐CDC20 association. We propose that PLEKHA5 functions as a novel APC/C adaptor to promote its subcellular localization to microtubules and enable APC/C to search for its co‐activator CDC20 more efficiently in one dimension along the microtubule network. In this model PLEKHA5 acts to coordinate the spatial regulation of APC/CCDC20 and facilitate its efficient polyubiquitination of key mitotic effector proteins to ensure proper progression of mitosis.

Unraveling the mechanism of sepsis-mediated multiple organ dysfunction syndrome by RNA sequencing analysis in the pediatric population

Abstract Sepsis is a significant healthcare burden, with high morbidities and mortalities and no specific therapy is yet available. More than 42,000 children develop severe sepsis each year in the U.S and 67% of those patients develop multiple organ dysfunction syndrome (MODS). In this study we aim to elucidate the mechanism of sepsis-mediated MODS by RNAseq analysis in PBMCs from the peripheral blood of pediatric patients. Comparison between control and septic patients revealed that transcriptomic signatures associated with receptor-mediated endocytosis (Iglc3, Igkv3d-20), anaphase-promoting complex (APC)-dependent catabolic process (Pttg1, Cdc20) heme-metabolism (Alas2, Slc25a39) and oxygen transport (hemoglobulin pathway) (Hbb, Hba2, Hbq1) were upregulated in sepsis. Heme/hemoglobulin related genes were downregulated in the recovery phase of those patients. In addition, neutrophil chemotaxis (CCL3L1, IL1B, CCL4L2, CCL3), phagocytosis (IGLL5, IGHG1, IGHG2), and interleukin-1 receptor binding (IL1RN, IL1B) pathways were upregulated in the recovery phase, while T cell activation (CD2, ITK, ZAP70, CD8A, TREML2) and differentiation (LCK, IL7R), and negative regulation of NIK/NF-kappaB signaling (SPAN6, CPNE1, ADIPOR1) pathways were downregulated. Many of those genes upregulated in the septic patients are associated with lower survival probability in the adult population, while genes upregulated in the recovery phase are associated with higher survival probability, based on the Biological Information Database of Sepsis (BIDOS). Given data on the pediatric population are scarce, our study reveals unique gene signatures of PBMCs associated with pediatric sepsis that could be novel targets for therapeutic intervention. Supported by R21HD099194-01A1, NICHD The Anesthesia Research Distinguished Trailblazer Award, Boston Children's Hospital

Cdh1 Deficiency Sensitizes TNBC Cells to PARP Inhibitors.

Triple-negative breast cancer (TNBC) is a type of breast tumor that currently lacks options for targeted therapy. Tremendous effort has been made to identify treatment targets for TNBC. Here, we report that the expression level of anaphase promoting complex (APC) coactivator Cdh1 in TNBC is elevated compared to that in the adjacent healthy tissues, and high levels of Cdh1 expression are correlated with poor prognoses, suggesting that Cdh1 contributes to the progression of TNBC. Interfering with the function of Cdh1 can potentiate the cytotoxic effects of PARP inhibitors against BRCA-deficient and BRCA-proficient TNBC cells through inducing DNA damage, checkpoint activation, cell cycle arrest, and apoptosis. Further investigation reveals that Cdh1 promotes BRCA1 foci formation and prevents untangled DNA entering mitosis in response to PARP inhibition (PARPi) in TNBC cells. Collectively, these results suggest that APC/Cdh1 is a potential molecular target for PARPi-based therapies against TNBCs.

Regulated interaction of ID2 with the anaphase-promoting complex links progression through mitosis with reactivation of cell-type-specific transcription

Tissue-specific transcriptional activity is silenced in mitotic cells but it remains unclear whether the mitotic regulatory machinery interacts with tissue-specific transcriptional programs. We show that such cross-talk involves the controlled interaction between core subunits of the anaphase-promoting complex (APC) and the ID2 substrate. The N-terminus of ID2 is independently and structurally compatible with a pocket composed of core APC/C subunits that may optimally orient ID2 onto the APCCDH1 complex. Phosphorylation of serine-5 by CDK1 prevented the association of ID2 with core APC, impaired ubiquitylation and stabilized ID2 protein at the mitosis-G1 transition leading to inhibition of basic Helix-Loop-Helix (bHLH)-mediated transcription. The serine-5 phospho-mimetic mutant of ID2 that inefficiently bound core APC remained stable during mitosis, delayed exit from mitosis and reloading of bHLH transcription factors on chromatin. It also locked cells into a “mitotic stem cell” transcriptional state resembling the pluripotent program of embryonic stem cells. The substrates of APCCDH1 SKP2 and Cyclin B1 share with ID2 the phosphorylation-dependent, D-box-independent interaction with core APC. These results reveal a new layer of control of the mechanism by which substrates are recognized by APC.

Amyloid-β Induces Cdh1-Mediated Rock2 Stabilization Causing Neurodegeneration

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by progressive cognitive decline, which is causally related to the accumulation of abnormally folded amyloid-β (Aβ) peptide and hyperphosphorylated tau protein aggregates. The dendritic spine regulator Rho protein kinase 2 (Rock2) accumulates in the brain at the earliest stages of AD and remains increased during disease progression. However, the molecular mechanism that upregulates Rock2 in AD, and its role in the disease progression, are unknown. Here, we found that oligomers of the amyloidogenic fragment 25–35 of the Aβ peptide (Aβ25-35) trigger Rock2 accumulation and activation in mouse cortical neurons in primary culture and in mouse hippocampus in vivo. Neuronal apoptotic death and memory impairment caused by Aβ25-35 administration were rescued by genetic and pharmacological inhibition of Rock2 activity. Mechanistically, Aβ25-35 elicited cyclin dependent kinase-5 (Cdk5)-mediated phosphorylation of Cdh1, a cofactor that is essential for the activity of the E3 ubiquitin ligase anaphase-promoting complex/cyclosome (APC/C) in neurons. Notably, phosphorylated Cdh1 was disassembled from the APC/C complex, causing its inactivation and subsequent Rock2 protein stabilization and activation. Moreover, Aβ25-35-induced neuronal apoptosis was prevented by expressing a phosphodefective form of Cdh1, but not by a phosphomimetic Cdh1. Finally, Cdh1 inactivation, using both genetic and pharmacological approaches, enhanced Aβ25-35-mediated neuronal death through a mechanism that was prevented by inhibition of Rock2 activity. These results indicate that the Cdk5-Cdh1 signaling pathway accounts for the increased Rock2 activity by amyloidogenic Aβ peptides and that this mechanism may contribute to neurodegeneration and memory loss in AD.

The Plant Anaphase-Promoting Complex/Cyclosome.

The anaphase-promoting complex/cyclosome (APC/C) represents a large multisubunit E3-ubiquitin ligase complex that controls the unidirectional progression through the cell cycle by the ubiquitination of specific target proteins, marking them for proteasomal destruction. Although the APC/C's role is largely conserved among eukaryotes, its subunit composition and target spectrum appear to be species specific. In this review, we focus on the plant APC/C complex, whose activity correlates with different developmental processes, including polyploidization and gametogenesis. After an introduction into proteolytic control by ubiquitination, we discuss the composition of the plant APC/C and the essential nature of its core subunits for plant development. Subsequently, we describe the APC/C activator subunits and interactors, most being plant specific. Finally, we provide a comprehensive list of confirmed and suspected plant APC/C target proteins. Identification of growth-related targets might offer opportunities to increase crop yield and resilience of plants to climate change by manipulating APC/C activity.

Ubiquitin ligases and a processive proteasome facilitate protein clearance during the oocyte-to-embryo transition in Caenorhabditis elegans.

The ubiquitin-mediated degradation of oocyte translational regulatory proteins is a conserved feature of the oocyte-to-embryo transition. In the nematode Caenorhabditis elegans, multiple translational regulatory proteins, including the TRIM-NHL RNA-binding protein LIN-41/Trim71 and the Pumilio-family RNA-binding proteins PUF-3 and PUF-11, are degraded during the oocyte-to-embryo transition. Degradation of each protein requires activation of the M-phase cyclin-dependent kinase CDK-1, is largely complete by the end of the first meiotic division and does not require the anaphase-promoting complex. However, only LIN-41 degradation requires the F-box protein SEL-10/FBW7/Cdc4p, the substrate recognition subunit of an SCF-type E3 ubiquitin ligase. This finding suggests that PUF-3 and PUF-11, which localize to LIN-41-containing ribonucleoprotein particles, are independently degraded through the action of other factors and that the oocyte ribonucleoprotein particles are disassembled in a concerted fashion during the oocyte-to-embryo transition. We develop and test the hypothesis that PUF-3 and PUF-11 are targeted for degradation by the proteasome-associated HECT-type ubiquitin ligase ETC-1/UBE3C/Hul5, which is broadly expressed in C. elegans. We find that several GFP-tagged fusion proteins that are degraded during the oocyte-to-embryo transition, including fusions with PUF-3, PUF-11, LIN-41, IFY-1/Securin, and CYB-1/Cyclin B, are incompletely degraded when ETC-1 function is compromised. However, it is the fused GFP moiety that appears to be the critical determinant of this proteolysis defect. These findings are consistent with a conserved role for ETC-1 in promoting proteasome processivity and suggest that proteasomal processivity is an important element of the oocyte-to-embryo transition during which many key oocyte regulatory proteins are rapidly targeted for degradation.

Emi2 enables centriole amplification during multiciliated cell differentiation.

Massive centriole amplification during multiciliated cell (MCC) differentiation is a notable example of organelle biogenesis. This process is thought to be enabled by a derived cell cycle state, but the key cell cycle components required for centriole amplification in MCC progenitors remain poorly defined. Here, we show that emi2 (fbxo43) expression is up-regulated and acts in MCC progenitors after cell cycle exit to transiently inhibit anaphase-promoting complex/cyclosome (APC/C)cdh1 activity. We find that this inhibition is required for the phosphorylation and activation of a key cell cycle kinase, plk1, which acts, in turn, to promote different steps required for centriole amplification and basal body formation, including centriole disengagement, apical migration, and maturation into basal bodies. This emi2-APC/C-plk1 axis is also required to down-regulate gene expression essential for centriole amplification after differentiation is complete. These results identify an emi2-APC/C-plk1 axis that promotes and then terminates centriole assembly and basal body formation during MCC differentiation.

Anticancer effects of disulfiram in T-cell malignancies through NPL4-mediated ubiquitin-proteasome pathway.

T-cell malignancies, including T-cell acute lymphoblastic leukemia (T-ALL) and T-cell lymphoma (TCL), are characterized by inferior treatment effects, high heterogeneity, poor prognosis, and a lack of specific therapeutic targets and drugs to improve outcome. Disulfiram (DSF) is a drug used to clinically control alcoholism that has recently been shown to be cytotoxic for multiple cancers. However, the underlying effects and mechanisms of DFS treatment in patients with T-cell malignancies are not well characterized. In this study, we report that DSF promotes apoptosis and inhibits the proliferation of malignant T-cell cell lines and primary T-ALL cells. We provide evidence that DSF exerts anticancer activity in T-cell malignancies by targeting the NPL4-mediated ubiquitin-proteasome pathway. Notably, high expression of NPL4 and 2 ubiquitin-proteasome pathway genes, anaphase-promoting complex subunit 1 (ANAPC1) and proteasome 26S subunit ubiquitin receptor, non-ATPase 2 (PSMD2), was significantly associated with unfavorable overall survival (OS) for patients with TCL and T-ALL (p<0.05). More importantly, the weighted combination of NPL4, ANAPC1, and PSMD2 could visually display the 1-, 3-, and 5-year OS rates for patients with T-cell malignancies in a nomogram model and facilitate risk stratification. Specifically, risk stratification was an independent predictor of OS for patients with T-cell malignancies. In conclusion, DSF might induce apoptosis and inhibit the proliferation of malignant T-cells via the NPL4-mediated ubiquitin-proteasome pathway and offer a potential therapeutic option for T-cell malignancies.

Role of ubiquitin-protein ligase UBR5 in the disassembly of mitotic checkpoint complexes

The mitotic (or spindle assembly) checkpoint system ensures accurate chromosome segregation in mitosis by preventing the onset of anaphase until correct bipolar attachment of sister chromosomes to the mitotic spindle is attained. It acts by promoting the assembly of a mitotic checkpoint complex (MCC), composed of mitotic checkpoint proteins BubR1, Bub3, Mad2, and Cdc20. MCC binds to and inhibits the action of ubiquitin ligase APC/C (anaphase-promoting complex/cyclosome), which targets for degradation regulators of anaphase initiation. When the checkpoint system is satisfied, MCCs are disassembled, allowing the recovery of APC/C activity and initiation of anaphase. Many of the pathways of the disassembly of the different MCCs have been elucidated, but the mode of their regulation remained unknown. We find that UBR5 (ubiquitin-protein ligase N-recognin 5) is associated with the APC/C*MCC complex immunopurified from extracts of nocodazole-arrested HeLa cells. UBR5 binds to mitotic checkpoint proteins BubR1, Bub3, and Cdc20 and promotes their polyubiquitylation invitro. The dissociation of a Bub3*BubR1 subcomplex of MCC is stimulated by UBR5-dependent ubiquitylation, as suggested by observations that this process in mitotic extracts requires UBR5 and α-β bond hydrolysis of adenosine triphosphate. Furthermore, a system reconstituted from purified recombinant components carries out UBR5- and ubiquitylation-dependent dissociation of Bub3*BubR1. Immunodepletion of UBR5 from mitotic extracts slows down the release of MCC components from APC/C and prolongs the lag period in the recovery of APC/C activity in the exit from mitotic checkpoint arrest. We suggest that UBR5 may be involved in the regulation of the inactivation of the mitotic checkpoint.

CDC27-ODC1 Axis Promotes Metastasis, Accelerates Ferroptosis and Predicts Poor Prognosis in Neuroblastoma.

Neuroblastoma (NB) is a devastating malignancy threatening children’s health, and amplification of MYCN is associated with treatment failure and a poor outcome. Here, we aimed to demonstrate the role of cell division cycle 27 (CDC27), an important core subunit of the anaphase-promoting complex, and its clinical significance in NB patients. In functional assays, we illustrated that CDC27 promoted the cell growth, metastasis and sphere-formation ability of NB cells both in vitro and in vivo. To further understand the potential mechanism, SK-N-SH cells were transfected with CDC27 siRNA, and RNA-sequencing was performed. The results revealed that downregulation of CDC27 led to markedly reduced expression of ODC1, which is a well-established direct target of MYCN. Subsequently, we further illustrated that suppression of ODC1 significantly attenuated the promotion effect of CDC27 on the proliferation, metastasis, and sphere-formation ability of NB cells, hinting that CDC27 exerted its biological behavior in NB at least partly in an ODC1-dependent manner. In addition, CDC27 rendered cells more vulnerable to ferroptosis, while knockdown of ODC1 markedly reversed the pro-ferroptotic effect of CDC27. Collectively, our data is the first to report that the CDC27/ODC1 axis promotes tumorigenesis and acts as a positive regulator of ferroptosis in NB, highlighting that CDC27 may represent a novel therapeutic strategy and prognostic biomarker in neuroblastoma.

Glutamine synthetase licenses APC/C-mediated mitotic progression to drive cell growth.

Tumors can reprogram the functions of metabolic enzymes to fuel malignant growth; however, beyond their conventional functions, key metabolic enzymes have not been found to directly govern cell mitosis. Here, we report that glutamine synthetase (GS) promotes cell proliferation by licensing mitotic progression independently of its metabolic function. GS depletion, but not impairment of its enzymatic activity, results in mitotic arrest and multinucleation across multiple lung and liver cancer cell lines, patient-derived organoids and xenografted tumors. Mechanistically, GS directly interacts with the nuclear pore protein NUP88 to prevent its binding to CDC20. Such interaction licenses activation of the CDC20-mediated anaphase-promoting complex or cyclosome to ensure proper metaphase-to-anaphase transition. In addition, GS is overexpressed in human non-small cell lung cancer and its depletion reduces tumor growth in mice and increases the efficacy of microtubule-targeted chemotherapy. Our findings highlight a moonlighting function of GS in governing mitosis and illustrate how an essential metabolic enzyme promotes cell proliferation and tumor development, beyond its main metabolic function.