Reciprocal antagonism of PIN1-APC/CCDH1 governs mitotic protein stability and cell cycle entry.

Induced oncoproteins degradation provides an attractive anti-cancer modality. Activation of anaphase-promoting complex (APC/CCDH1) prevents cell-cycle entry by targeting crucial mitotic proteins for degradation. Phosphorylation of its co-activator CDH1 modulates the E3 ligase activity, but little is known about its regulation after phosphorylation and how to effectively harness APC/CCDH1 activity to treat cancer. Peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (PIN1)-catalyzed phosphorylation-dependent cis-trans prolyl isomerization drives tumor malignancy. However, the mechanisms controlling its protein turnover remain elusive. Through proteomic screens and structural characterizations, we identify a reciprocal antagonism of PIN1-APC/CCDH1 mediated by domain-oriented phosphorylation-dependent dual interactions as a fundamental mechanism governing mitotic protein stability and cell-cycle entry. Remarkably, combined PIN1 and cyclin-dependent protein kinases (CDKs) inhibition creates a positive feedback loop of PIN1 inhibition and APC/CCDH1 activation to irreversibly degrade PIN1 and other crucial mitotic proteins, which force permanent cell-cycle exit and trigger anti-tumor immunity, translating into synergistic efficacy against triple-negative breast cancer.

MAPK-dependent control of mitotic progression in S. pombe.

BACKGROUND: Mitogen-activated protein kinases (MAPKs) preserve cell homeostasis by transducing physicochemical fluctuations of the environment into multiple adaptive responses. These responses involve transcriptional rewiring and the regulation of cell cycle transitions, among others. However, how stress conditions impinge mitotic progression is largely unknown. The mitotic checkpoint is a surveillance mechanism that inhibits mitotic exit in situations of defective chromosome capture, thus preventing the generation of aneuploidies. In this study, we investigate the role of MAPK Pmk1 in the regulation of mitotic exit upon stress. RESULTS: We show that Schizosaccharomyces pombe cells lacking Pmk1, the MAP kinase effector of the cell integrity pathway (CIP), are hypersensitive to microtubule damage and defective in maintaining a metaphase arrest. Epistasis analysis suggests that Pmk1 is involved in maintaining spindle assembly checkpoint (SAC) signaling, and its deletion is additive to the lack of core SAC components such as Mad2 and Mad3. Strikingly, pmk1Δ cells show up to twofold increased levels of the anaphase-promoting complex (APC/C) activator Cdc20Slp1 during unperturbed growth. We demonstrate that Pmk1 physically interacts with Cdc20Slp1 N-terminus through a canonical MAPK docking site. Most important, the Cdc20Slp1 pool is rapidly degraded in stressed cells undergoing mitosis through a mechanism that requires MAPK activity, Mad3, and the proteasome, thus resulting in a delayed mitotic exit. CONCLUSIONS: Our data reveal a novel function of MAPK in preventing mitotic exit and activation of cytokinesis in response to stress. The regulation of Cdc20Slp1 turnover by MAPK Pmk1 provides a key mechanism by which the timing of mitotic exit can be adjusted relative to environmental conditions.

Genome-Wide Identification and Analysis of APC E3 Ubiquitin Ligase Genes Family in Triticum aestivum.

E3 ubiquitin ligases play a pivotal role in ubiquitination, a crucial post-translational modification process. Anaphase-promoting complex (APC), a large cullin-RING E3 ubiquitin ligase, regulates the unidirectional progression of the cell cycle by ubiquitinating specific target proteins and triggering plant immune responses. Several E3 ubiquitin ligases have been identified owing to advancements in sequencing and annotation of the wheat genome. However, the types and functions of APC E3 ubiquitin ligases in wheat have not been reported. This study identified 14 members of the APC gene family in the wheat genome and divided them into three subgroups (CCS52B, CCS52A, and CDC20) to better understand their functions. Promoter sequence analysis revealed the presence of several cis-acting elements related to hormone and stress responses in the APC E3 ubiquitin ligases in wheat. All identified APC E3 ubiquitin ligase family members were highly expressed in the leaves, and the expression of most genes was induced by the application of methyl jasmonate (MeJA). In addition, the APC gene family in wheat may play a role in plant defense mechanisms. This study comprehensively analyzes APC genes in wheat, laying the groundwork for future research on the function of APC genes in response to viral infections and expanding our understanding of wheat immunity mechanisms.

Loss of UBE2S causes meiosis I arrest with normal spindle assembly checkpoint dynamics in mouse oocytes.

The timely degradation of proteins that regulate the cell cycle is essential for oocyte maturation. Oocytes are equipped to degrade proteins via the ubiquitin-proteasome system. In meiosis, anaphase promoting complex/cyclosome (APC/C), an E3 ubiquitin-ligase, is responsible for the degradation of proteins. Ubiquitin-conjugating enzyme E2 S (UBE2S), an E2 ubiquitin-conjugating enzyme, delivers ubiquitin to APC/C. APC/C has been extensively studied, but the functions of UBE2S in oocyte maturation and mouse fertility are not clear. In this study, we used Ube2s knockout mice to explore the role of UBE2S in mouse oocytes. Ube2s-deleted oocytes were characterized by meiosis I arrest with normal spindle assembly and spindle assembly checkpoint dynamics. However, the absence of UBE2S affected the activity of APC/C. Cyclin B1 and securin are two substrates of APC/C, and their levels were consistently high, resulting in the failure of homologous chromosome separation. Unexpectedly, the oocytes arrested in meiosis I could be fertilized and the embryos could become implanted normally, but died before embryonic day 10.5. In conclusion, our findings reveal an indispensable regulatory role of UBE2S in mouse oocyte meiosis and female fertility.

Functional analysis of Cdc20 reveals a critical role of CRY box in mitotic checkpoint signaling.

Accurate mitosis is coordinated by the spindle assembly checkpoint (SAC) through the mitotic checkpoint complex (MCC), which inhibits the anaphase-promoting complex or cyclosome (APC/C). As an essential regulator, Cdc20 promotes mitotic exit through activating APC/C and monitors kinetochore-microtubule attachment through activating SAC. Cdc20 requires multiple interactions with APC/C and MCC subunits to elicit these functions. Functionally assessing these interactions within cells requires efficient depletion of endogenous Cdc20, which is highly difficult to achieve by RNA interference (RNAi). Here we generated Cdc20 RNAi-sensitive cell lines which display a penetrant metaphase arrest by a single RNAi treatment. In this null background, we accurately measured the contribution of each known motif of Cdc20 on APC/C and SAC activation. The CRY box, a previously identified degron, was found critical for SAC by promoting MCC formation and its interaction with APC/C. These data reveal additional regulation within the SAC and establish a novel method to interrogate Cdc20.

GSK3ß phosphorylates Six1 transcription factor and regulates its APC/CCdh1 mediated proteosomal degradation.

Sine oculis homeobox homolog 1 (Six1) is a developmentally important transcription factor that regulates cellular proliferation, apoptosis, and dissemination during embryogenesis. Six1 overexpression as reported in multiple cancers modulates expression of a repertoire of its target genes causing an increase in proliferation, metastasis and survival of cancer cells. Six1 exists as a cell cycle regulated nuclear phosphoprotein and its cellular turnover is regulated by APC/C (Anaphase promoting complex / Cyclosome) complex mediated proteolysis. However, the kinases that regulate Six1 proteolysis have not been identified and the mechanistic details that cause its overproduction in various cancers are lacking. Here, we report that Six1 is a physiological GSK3ß substrate. GSK3ß interacts with Six1 and phosphorylates it at Ser221 within the conserved consensus sequence in its carboxy terminus. Using pharmacological inhibition, siRNA mediated knockdown and protein overexpression of GSK3ß; we show that GSK3ß regulates Six1 protein stability. Pulse chase analysis of Six1 revealed that GSK3ß regulates its ubiquitin proteolysis such that Six1 phosphomimicking mutant (Six1S221E) for Ser221 site had dramatically increased half-life than its phosphodeficient (Six1S221A) and wild type variants. Furthermore, we demonstrate that GSK3ß rescues Six1 from APC dependent proteolysis by regulating its binding with APC/C co-activator protein Cdh1. Importantly, strong positive correlation exists between GSK3ß and Six1 protein levels throughout the cell cycle and in multiple cancers indicating that GSK3ß activation may in part contribute to Six1 overproduction in a subset of human cancers.

The oscillation of mitotic kinase governs cell cycle latches in mammalian cells.

The mammalian cell cycle alternates between two phases - S-G2-M with high levels of A- and B-type cyclins (CycA and CycB, respectively) bound to cyclin-dependent kinases (CDKs), and G1 with persistent degradation of CycA and CycB by an activated anaphase promoting complex/cyclosome (APC/C) bound to Cdh1 (also known as FZR1 in mammals; denoted APC/C:Cdh1). Because CDKs phosphorylate and inactivate Cdh1, these two phases are mutually exclusive. This 'toggle switch' is flipped from G1 to S by cyclin-E bound to a CDK (CycE:CDK), which is not degraded by APC/C:Cdh1, and from M to G1 by Cdc20-bound APC/C (APC/C:Cdc20), which is not inactivated by CycA:CDK or CycB:CDK. After flipping the switch, cyclin E is degraded and APC/C:Cdc20 is inactivated. Combining mathematical modelling with single-cell timelapse imaging, we show that dysregulation of CycB:CDK disrupts strict alternation of the G1-S and M-G1 switches. Inhibition of CycB:CDK results in Cdc20-independent Cdh1 'endocycles', and sustained activity of CycB:CDK drives Cdh1-independent Cdc20 endocycles. Our model provides a mechanistic explanation for how whole-genome doubling can arise, a common event in tumorigenesis that can drive tumour evolution.

ZmTDM1 encodes a tetratricopeptide repeat domain protein and is required for meiotic exit in maize.

Elaborate cell-cycle control must be adopted to ensure the continuity of the meiotic second division and termination after that. Despite its importance, however, the genetic controls underlying the meiotic cell cycle have not been reported in maize. Here, we characterized a meiotic cell-cycle controller ZmTDM1, which is a homolog of Arabidopsis TDM1 and encodes a canonical tetratricopeptide repeat domain protein in maize. The Zmtdm1 homozygous plants exhibited complete male sterility and severe female abortion. In Zmtdm1 mutants, cell-cycle progression was almost identical to that of wild type from leptotene to anaphase II. However, chromosomes in the tetrad failed meiotic termination at the end of the second division and underwent additional divisions in succession without DNA replication, reducing the ploidy to less than haploid in the product. In addition, two ZmTDM1-like homologs (ZmTDML1 and ZmTDML2) were not functional in meiotic cell-cycle control. Moreover, ZmTDM1 interacted with RING-type E3 ubiquitin ligase, revealing that it acts as a subunit of the APC/C E3 ubiquitin ligase complex. Overall, our results identified a regulator of meiotic cell cycle in maize and demonstrated that ZmTDM1 is essential for meiotic exit after meiosis II.

SETDB2 interacts with BUBR1 to induce accurate chromosome segregation independently of its histone methyltransferase activity.

SETDB2 is a H3K9 histone methyltransferase required for accurate chromosome segregation. Its H3K9 histone methyltransferase activity was reported to be associated with chromosomes during metaphase. Here, we confirm that SETDB2 is required for mitosis and accurate chromosome segregation. However, these functions are independent of its histone methyltransferase activity. Further analysis showed that SETDB2 can interact with BUBR1, and is required for CDC20 binding to BUBR1 and APC/C complex and CYCLIN B1 degradation. The ability of SETDB2 to regulate the binding of CDC20 to BUBR1 or APC/C complex, and stabilization of CYCLIN B1 are also independent of its histone methyltransferase activity. These results suggest that SETDB2 interacts with BUBR1 to promote binding of CDC20 to BUBR1 and APC3, then degrades CYCLIN B1 to ensure accurate chromosome segregation and mitosis, independently of its histone methyltransferase activity.

REV7 Monomer Is Unable to Participate in Double Strand Break Repair and Translesion Synthesis but Suppresses Mitotic Errors.

Rev7 is a regulatory protein with roles in translesion synthesis (TLS), double strand break (DSB) repair, replication fork protection, and cell cycle regulation. Rev7 forms a homodimer in vitro using its HORMA (Hop, Rev7, Mad2) domain; however, the functional importance of Rev7 dimerization has been incompletely understood. We analyzed the functional properties of cells expressing either wild-type mouse Rev7 or Rev7K44A/R124A/A135D, a mutant that cannot dimerize. The expression of wild-type Rev7, but not the mutant, rescued the sensitivity of Rev7-/- cells to X-rays and several alkylating agents and reversed the olaparib resistance phenotype of Rev7-/- cells. Using a novel fluorescent host-cell reactivation assay, we found that Rev7K44A/R124A/A135D is unable to promote gap-filling TLS opposite an abasic site analog. The Rev7 dimerization interface is also required for shieldin function, as both Rev7-/- cells and Rev7-/- cells expressing Rev7K44A/R124A/A135D exhibit decreased proficiency in rejoining some types of double strand breaks, as well as increased homologous recombination. Interestingly, Rev7K44A/R124A/A135D retains some function in cell cycle regulation, as it maintains an interaction with Ras-related nuclear protein (Ran) and partially rescues the formation of micronuclei. The mutant Rev7 also rescues the G2/M accumulation observed in Rev7-/- cells but does not affect progression through mitosis following nocodazole release. We conclude that while Rev7 dimerization is required for its roles in TLS, DSB repair, and regulation of the anaphase promoting complex, dimerization is at least partially dispensable for promoting mitotic spindle assembly through its interaction with Ran.

TUBA1A licenses APC/C-mediated mitotic progression to drive glioblastoma growth by inhibiting PLK3.

Glioblastoma (GBM) is the most common, aggressive, and chemorefractory primary brain tumor in adults. Identifying novel drug targets is crucial for GBM treatment. Here, we demonstrate that tubulin alpha 1a (TUBA1A) is significantly upregulated in GBM compared to low-grade gliomas (LGG) and normal tissues. High TUBA1A expression is associated with poor survival in GBM patients. TUBA1A knockdown results in mitotic arrest and reduces tumor growth in mice. TUBA1A interacts with the polo-like kinase 3 (PLK3) in the cytoplasm to inhibit its activation. This interaction licenses activation of the anaphase-promoting complex or cyclosome (APC/C) to ensure proper Foxm1-mediated metaphase-to-anaphase transition and mitotic exit. Overall, our findings demonstrate that targeting TUBA1A attenuates GBM cell growth by suppressing mitotic progression in a PLK3-dependent manner.

The anaphase-promoting complex controls a ubiquitination-phosphoprotein axis in chromatin during neurodevelopment.

Mutations in the degradative ubiquitin ligase anaphase-promoting complex (APC) alter neurodevelopment by impairing proteasomal protein clearance, but our understanding of their molecular and cellular pathogenesis remains limited. Here, we employ the proteomic-based discovery of APC substrates in APC mutant mouse brain and human cell lines and identify the chromosome-passenger complex (CPC), topoisomerase 2a (Top2a), and Ki-67 as major chromatin factors targeted by the APC during neuronal differentiation. These substrates accumulate in phosphorylated form, suggesting that they fail to be eliminated after mitosis during terminal differentiation. The accumulation of the CPC kinase Aurora B within constitutive heterochromatin and hyperphosphorylation of its target histone 3 are corrected in the mutant brain by pharmacologic Aurora B inhibition. Surprisingly, the reduction of Ki-67, but not H3S10ph, rescued the function of constitutive heterochromatin in APC mutant neurons. These results expand our understanding of how ubiquitin signaling regulates chromatin during neurodevelopment and identify potential therapeutic targets in APC-related disorders.

Spo13/MEIKIN ensures a Two-Division meiosis by preventing the activation of APC/CAma1 at meiosis I.

Genome haploidization at meiosis depends on two consecutive nuclear divisions, which are controlled by an oscillatory system consisting of Cdk1-cyclin B and the APC/C bound to the Cdc20 activator. How the oscillator generates exactly two divisions has been unclear. We have studied this question in yeast where exit from meiosis involves accumulation of the APC/C activator Ama1 at meiosis II. We show that inactivation of the meiosis I-specific protein Spo13/MEIKIN results in a single-division meiosis due to premature activation of APC/CAma1 . In the wild type, Spo13 bound to the polo-like kinase Cdc5 prevents Ama1 synthesis at meiosis I by stabilizing the translational repressor Rim4. In addition, Cdc5-Spo13 inhibits the activity of Ama1 by converting the B-type cyclin Clb1 from a substrate to an inhibitor of Ama1. Cdc20-dependent degradation of Spo13 at anaphase I unleashes a feedback loop that increases Ama1's synthesis and activity, leading to irreversible exit from meiosis at the second division. Thus, by repressing the exit machinery at meiosis I, Cdc5-Spo13 ensures that cells undergo two divisions to produce haploid gametes.

The APC/C E3 ligase subunit ANAPC11 mediates FOXO3 protein degradation to promote cell proliferation and lymph node metastasis in urothelial bladder cancer.

Urothelial bladder cancer (UBC) is one of the most prevalent malignancies worldwide, with striking tumor heterogeneity. Elucidating the molecular mechanisms that can be exploited for the treatment of aggressive UBC is a particularly relevant goal. Protein ubiquitination is a critical post-translational modification (PTM) that mediates the degradation of target protein via the proteasome. However, the roles of aberrant protein ubiquitination in UBC development and the underlying mechanisms by which it drives tumor progression remain unclear. In this study, taking advantage of clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein (Cas) 9 technology, we identified the ubiquitin E3 ligase ANAPC11, a critical subunit of the anaphase-promoting complex/cyclosome (APC/C), as a potential oncogenic molecule in UBC cells. Our clinical analysis showed that elevated expression of ANAPC11 was significantly correlated with high T stage, positive lymph node (LN) metastasis, and poor outcomes in UBC patients. By employing a series of in vitro experiments, we demonstrated that ANAPC11 enhanced the proliferation and invasiveness of UBC cells, while knockout of ANAPC11 inhibited the growth and LN metastasis of UBC cells in vivo. By conducting immunoprecipitation coupled with mass spectrometry, we confirmed that ANAPC11 increased the ubiquitination level of the Forkhead transcription factor FOXO3. The resulting decrease in FOXO3 protein stability led to the downregulation of the cell cycle regulator p21 and decreased expression of GULP1, a downstream effector of androgen receptor signaling. Taken together, these findings indicated that ANAPC11 plays an oncogenic role in UBC by modulating FOXO3 protein degradation. The ANAPC11-FOXO3 regulatory axis might serve as a novel therapeutic target for UBC.

Meiosis II spindle disassembly requires two distinct pathways.

During exit from meiosis II, cells undergo several structural rearrangements, including disassembly of the meiosis II spindles and cytokinesis. Each of these changes is regulated to ensure that they occur at the proper time. Previous studies have demonstrated that both SPS1, which encodes a STE20-family GCKIII kinase, and AMA1, which encodes a meiosis-specific activator of the Anaphase Promoting Complex, are required for both meiosis II spindle disassembly and cytokinesis in the budding yeast Saccharomyces cerevisiae. We examine the relationship between meiosis II spindle disassembly and cytokinesis and find that the meiosis II spindle disassembly failure in sps1Δ and ama1∆ cells is not the cause of the cytokinesis defect. We also see that the spindle disassembly defects in sps1Δ and ama1∆ cells are phenotypically distinct. We examined known microtubule-associated proteins Ase1, Cin8, and Bim1, and found that AMA1 is required for the proper loss of Ase1 and Cin8 on meiosis II spindles while SPS1 is required for Bim1 loss in meiosis II. Taken together, these data indicate that SPS1 and AMA1 promote distinct aspects of meiosis II spindle disassembly, and that both pathways are required for the successful completion of meiosis.

SIRT1 ubiquitination is regulated by opposing activities of APC/C-Cdh1 and AROS during stress-induced premature senescence.

SIRT1, a member of the mammalian sirtuin family, is a nicotinamide adenosine dinucleotide (NAD)-dependent deacetylase with key roles in aging-related diseases and cellular senescence. However, the mechanism by which SIRT1 protein homeostasis is controlled under senescent conditions remains elusive. Here, we revealed that SIRT1 protein is significantly downregulated due to ubiquitin-mediated proteasomal degradation during stress-induced premature senescence (SIPS) and that SIRT1 physically associates with anaphase-promoting complex/cyclosome (APC/C), a multisubunit E3 ubiquitin ligase. Ubiquitin-dependent SIRT1 degradation is stimulated by the APC/C coactivator Cdh1 and not by the coactivator Cdc20. We found that Cdh1 depletion impaired the SIPS-promoted downregulation of SIRT1 expression and reduced cellular senescence, likely through SIRT1-driven p53 inactivation. In contrast, AROS, a SIRT1 activator, reversed the SIRT1 degradation induced by diverse stressors and antagonized Cdh1 function through competitive interactions with SIRT1. Furthermore, our data indicate opposite roles for Cdh1 and AROS in the epigenetic regulation of the senescence-associated secretory phenotype genes IL-6 and IL-8. Finally, we demonstrated that pinosylvin restores downregulated AROS (and SIRT1) expression levels in bleomycin-induced mouse pulmonary senescent tissue while repressing bleomycin-promoted Cdh1 expression. Overall, our study provides the first evidence of the reciprocal regulation of SIRT1 stability by APC/C-Cdh1 and AROS during stress-induced premature senescence, and our findings suggest pinosylvin as a potential senolytic agent for pulmonary fibrosis.

BUB-1-bound PLK-1 directs CDC-20 kinetochore recruitment to ensure timely embryonic mitoses.

During mitosis, chromosomes assemble kinetochores to dynamically couple with spindle microtubules.1,2 Kinetochores also function as signaling hubs directing mitotic progression by recruiting and controlling the fate of the anaphase promoting complex/cyclosome (APC/C) activator CDC-20.3,4,5 Kinetochores either incorporate CDC-20 into checkpoint complexes that inhibit the APC/C or dephosphorylate CDC-20, which allows it to interact with and activate the APC/C.4,6 The importance of these two CDC-20 fates likely depends on the biological context. In human somatic cells, the major mechanism controlling mitotic progression is the spindle checkpoint. By contrast, progression through mitosis during the cell cycles of early embryos is largely checkpoint independent.7,8,9,10 Here, we first show that CDC-20 phosphoregulation controls mitotic duration in the C. elegans embryo and defines a checkpoint-independent temporal mitotic optimum for robust embryogenesis. CDC-20 phosphoregulation occurs at kinetochores and in the cytosol. At kinetochores, the flux of CDC-20 for local dephosphorylation requires an ABBA motif on BUB-1 that directly interfaces with the structured WD40 domain of CDC-20.6,11,12,13 We next show that a conserved "STP" motif in BUB-1 that docks the mitotic kinase PLK-114 is necessary for CDC-20 kinetochore recruitment and timely mitotic progression. The kinase activity of PLK-1 is required for CDC-20 to localize to kinetochores and phosphorylates the CDC-20-binding ABBA motif of BUB-1 to promote BUB-1-CDC-20 interaction and mitotic progression. Thus, the BUB-1-bound pool of PLK-1 ensures timely mitosis during embryonic cell cycles by promoting CDC-20 recruitment to the vicinity of kinetochore-localized phosphatase activity.

The adapter protein FADD provides an alternate pathway for entry into the cell cycle by regulating APC/C-Cdh1 E3 ubiquitin ligase activity.

The E3 ubiquitin ligase APC/C-Cdh1 maintains the G0/G1 state, and its inactivation is required for cell cycle entry. We reveal a novel role for Fas-associated protein with death domain (FADD) in the cell cycle through its function as an inhibitor of APC/C-Cdh1. Using real-time, single-cell imaging of live cells combined with biochemical analysis, we demonstrate that APC/C-Cdh1 hyperactivity in FADD-deficient cells leads to a G1 arrest despite persistent mitogenic signaling through oncogenic EGFR/KRAS. We further show that FADDWT interacts with Cdh1, while a mutant lacking a consensus KEN-box motif (FADDKEN) fails to interact with Cdh1 and results in a G1 arrest due to its inability to inhibit APC/C-Cdh1. Additionally, enhanced expression of FADDWT but not FADDKEN, in cells arrested in G1 upon CDK4/6 inhibition, leads to APC/C-Cdh1 inactivation and entry into the cell cycle in the absence of retinoblastoma protein phosphorylation. FADD's function in the cell cycle requires its phosphorylation by CK1α at Ser-194 which promotes its nuclear translocation. Overall, FADD provides a CDK4/6-Rb-E2F-independent "bypass" mechanism for cell cycle entry and thus a therapeutic opportunity for CDK4/6 inhibitor resistance.

Lactate fuels mitosis.

Cell cycle and metabolism are intimately intertwined, but how metabolites directly regulate cell-cycle machinery remains elusive. Liu et al.1 reveal that glycolysis end-product lactate directly binds and inhibits the SUMO protease SENP1 to govern the E3 ligase activity of the anaphase-promoting complex, leading to efficient mitotic exit in proliferative cells.

The MAD2B-APC/C-MDM2 axis mediates acute kidney injury by modulating p53.

P53 is a master regulator modulating the progression of acute kidney injury (AKI). However, the mechanism underlying p53 regulation in AKI needs further investigation. Mitotic arrest deficient 2 like 2 (MAD2B) is a subunit of DNA polymerase ζ. Its role in AKI remains unclear. Here, we demonstrated that MAD2B acted as an endogenous suppressor of p53. MAD2B conditional knockout augmented the upregulation of p53 in kidneys suffering from cisplatin-induced AKI, therefore promoting the deterioration of renal function, G1 phase arrest and apoptosis of proximal tubular epithelial cells. Mechanistically, MAD2B deficiency activated the anaphase-promoting complex/cyclosome (APC/C), which is an inhibitor of the well-characterized p53-directed E3 ligase MDM2. The decreased MDM2 diminished the degradation of p53, resulting in the upregulation of p53. The APC/C antagonist proTAME ameliorated cisplatin-induced AKI and blocked MAD2B knockdown-induced p53 upregulation and reduced cell cycle arrest and apoptosis in tubular epithelial cells by upregulating MDM2. These results indicate that MAD2B is a novel target for inhibiting p53 and ameliorating AKI.