Deubiquitinase USP13 promotes the epithelial-mesenchymal transition and metastasis in gastric cancer by maintaining Snail protein.

The dynamic balance between ubiquitination and deubiquitination is a key mechanism that regulates protein degradation and maintains cell protein homeostasis. Ubiquitin-specific peptidase 13 (USP13), a deubiquitinase (DUB), regulates various physiological and pathological processes, including cancer. A previous study reported that high USP13 mRNA expression confers poor prognosis in gastric cancer (GC). However, the biological function of USP13 in GC remains unknown. Here, we revealed that USP13 expression was upregulated in GC tissue samples compared to noncancerous tissues. USP13-positive expression was associated with poor differentiation, high invasiveness, and advanced tumor stage. Notably, upregulated USP13 expression was closely correlated with the reduced survival of GC patients. We also confirmed increased USP13 expression in GC cell lines. USP13 knockdown prominently suppressed MGC-803 cell migration and invasion. Conversely, USP13 overexpression markedly enhanced SGC-7901 cell motility. Furthermore, USP13 positively regulates the epithelial-mesenchymal transition (EMT) of GC cells. Interestingly, USP13 remarkably enhanced Snail protein expression but did not affect its mRNA levels in GC cells. We confirmed a positive correlation between USP13 and Snail expression in GC tissues. Mechanistically, USP13 knockdown promoted Snail degradation, which could be blocked by the proteasome inhibitor MG132. USP13 interacted with Snail to deubiquitinate and stabilize Snail in GC cells. Finally, Snail knockdown significantly blocked USP13-induced SGC-7901 cell migration and invasion. In conclusion, USP13 overexpression was frequently detected in GC and contributed to the EMT and metastasis of GC by stabilizing Snail.

The deubiquitinase USP15 modulates cellular redox and is a therapeutic target in acute myeloid leukemia.

Ubiquitin-specific peptidase 15 (USP15) is a deubiquitinating enzyme implicated in critical cellular and oncogenic processes. We report that USP15 mRNA and protein are overexpressed in human acute myeloid leukemia (AML) as compared to normal hematopoietic progenitor cells. This high expression of USP15 in AML correlates with KEAP1 protein and suppression of NRF2. Knockdown or deletion of USP15 in human and mouse AML models significantly impairs leukemic progenitor function and viability and de-represses an antioxidant response through the KEAP1-NRF2 axis. Inhibition of USP15 and subsequent activation of NRF2 leads to redox perturbations in AML cells, coincident with impaired leukemic cell function. In contrast, USP15 is dispensable for human and mouse normal hematopoietic cells in vitro and in vivo. A preclinical small-molecule inhibitor of USP15 induced the KEAP1-NRF2 axis and impaired AML cell function, suggesting that targeting USP15 catalytic function can suppress AML. Based on these findings, we report that USP15 drives AML cell function, in part, by suppressing a critical oxidative stress sensor mechanism and permitting an aberrant redox state. Furthermore, we postulate that inhibition of USP15 activity with small molecule inhibitors will selectively impair leukemic progenitor cells by re-engaging homeostatic redox responses while sparing normal hematopoiesis.

USP1 Promotes GC Metastasis via Stabilizing ID2.

Gastric cancer (GC) is one of the most common malignant tumors all over the world. And recurrence and metastasis are still the main causes of low survival rate for advanced GC. USP1 has been shown overexpressed in multiple cancers, which indicate its important biomarker in tumorigenesis and development. Our study is aimed at defining the exact role of USP1 on GC metastasis and the underlying mechanism. USP1 was firstly found overexpressed in GC tissues and relatively high-expression levels conferred poor survival rates. Then, real-time cellular analysis (RTCA) showed that USP1 knockdown inhibited GC metastasis both in vitro and in vivo. Mechanically, we demonstrated that USP1 promoted GC metastasis via upregulating ID2 expression and further confirmed that USP1 stabilized ID2 expression through deubiquitinating ID2 in GC. In conclusion, our study showed that USP1 promoted GC metastasis via stabilizing ID2 expression, which provides a potential biomarker and therapy target for GC.

Ubiquitin-Specific Protease 29 Exacerbates Cerebral Ischemia-Reperfusion Injury in Mice.

Oxidative stress and apoptosis contribute to the progression of cerebral ischemia/reperfusion (I/R) injury. Ubiquitin-specific protease 29 (USP29) is abundantly expressed in the brain and plays critical roles in regulating oxidative stress and cell apoptosis. The purpose of the present study is to investigate the role and underlying mechanisms of USP29 in cerebral I/R injury. Neuron-specific USP29 knockout mice were generated and subjected to cerebral I/R surgery. For USP29 overexpression, mice were stereotactically injected with the adenoassociated virus serotype 9 vectors carrying USP29 for 4 weeks before cerebral I/R. And primary cortical neurons were isolated and exposed to oxygen glucose deprivation/reperfusion (OGD/R) stimulation to imitate cerebral I/R injury in vitro. USP29 expression was elevated in the brain and primary cortical neurons upon I/R injury. Neuron-specific USP29 knockout significantly diminished, whereas USP29 overexpression aggravated cerebral I/R-induced oxidative stress, apoptosis, and neurological dysfunction in mice. In addition, OGD/R-induced oxidative stress and neuronal apoptosis were also attenuated by USP29 silence but exacerbated by USP29 overexpression in vitro. Mechanistically, neuronal USP29 enhanced p53/miR-34a-mediated silent information regulator 1 downregulation and then promoted the acetylation and suppression of brain and muscle ARNT-like protein, thereby aggravating oxidative stress and apoptosis upon cerebral I/R injury. Our findings for the first time identify that USP29 upregulation during cerebral I/R may contribute to oxidative stress, neuronal apoptosis, and the progression of cerebral I/R injury and that inhibition of USP29 may help to develop novel therapeutic strategies to treat cerebral I/R injury.

The Multifaceted Roles of USP15 in Signal Transduction.

Ubiquitination and deubiquitination are protein post-translational modification processes that have been recognized as crucial mediators of many complex cellular networks, including maintaining ubiquitin homeostasis, controlling protein stability, and regulating several signaling pathways. Therefore, some of the enzymes involved in ubiquitination and deubiquitination, particularly E3 ligases and deubiquitinases, have attracted attention for drug discovery. Here, we review recent findings on USP15, one of the deubiquitinases, which regulates diverse signaling pathways by deubiquitinating vital target proteins. Even though several basic previous studies have uncovered the versatile roles of USP15 in different signaling networks, those have not yet been systematically and specifically reviewed, which can provide important information about possible disease markers and clinical applications. This review will provide a comprehensive overview of our current understanding of the regulatory mechanisms of USP15 on different signaling pathways for which dynamic reverse ubiquitination is a key regulator.

USP15 Deubiquitinase Safeguards Hematopoiesis and Genome Integrity in Hematopoietic Stem Cells and Leukemia Cells.

Altering ubiquitination by disruption of deubiquitinating enzymes (DUBs) affects hematopoietic stem cell (HSC) maintenance. However, comprehensive knowledge of DUB function during hematopoiesis in vivo is lacking. Here, we systematically inactivate DUBs in mouse hematopoietic progenitors using in vivo small hairpin RNA (shRNA) screens. We find that multiple DUBs may be individually required for hematopoiesis and identify ubiquitin-specific protease 15 (USP15) as essential for HSC maintenance in vitro and in transplantations and Usp15 knockout (KO) mice in vivo. USP15 is highly expressed in human hematopoietic tissues and leukemias. USP15 depletion in murine progenitors and leukemia cells impairs in vitro expansion and increases genotoxic stress. In leukemia cells, USP15 interacts with and stabilizes FUS (fused in sarcoma), a known DNA repair factor, directly linking USP15 to the DNA damage response (DDR). Our study underscores the importance of DUBs in preserving normal hematopoiesis and uncovers USP15 as a critical DUB in safeguarding genome integrity in HSCs and leukemia cells.

Acetylation-Dependent Deubiquitinase OTUD3 Controls MAVS Activation in Innate Antiviral Immunity.

Accurate regulation of innate immunity is necessary for the host to efficiently respond to invading pathogens and avoid excessive harmful immune pathology. Here we identified OTUD3 as an acetylation-dependent deubiquitinase that restricts innate antiviral immune signaling. OTUD3 deficiency in mice results in enhanced innate immunity, a diminished viral load, and morbidity. OTUD3 directly hydrolyzes lysine 63 (Lys63)-linked polyubiquitination of MAVS and thus shuts off innate antiviral immune response. Notably, the catalytic activity of OTUD3 relies on acetylation of its Lys129 residue. In response to virus infection, the acetylated Lys129 is removed by SIRT1, which promptly inactivates OTUD3 and thus allows timely induction of innate antiviral immunity. Importantly, acetyl-OTUD3 levels are inversely correlated with IFN-ß expression in influenza patients. These findings establish OTUD3 as a repressor of MAVS and uncover a previously unknown regulatory mechanism by which the catalytic activity of OTUD3 is tightly controlled to ensure timely activation of antiviral defense.

Tumor suppressor OTUD3 induces growth inhibition and apoptosis by directly deubiquitinating and stabilizing p53 in invasive breast carcinoma cells.

BACKGROUND: P53 pathway inactivation plays an important role in the process of breast cancer tumorigenesis. Post-translational protein modification abnormalities have been confirmed to be an important mechanism underlying inactivation of p53. Numerous deubiquitinating enzymes are aberrantly expressed in breast cancer, and a few deubiquitination enzymes can deubiquitinate and stabilize p53. Here, we report that ovarian tumor (OTU) deubiquitinase 3 (OTUD3) is a deubiquitylase of p53 in breast carcinoma (BC). METHODS: Correlations between the mRNA expression levels of OTUD3, TP53 and PTEN and the prognosis of BC were assessed with the Kaplan-Meier Plotter tool. OTUD3 protein expression in 80 pairs of specimens in our cohort was examined by immunohistochemistry and western blotting. The relationship among OTUD3, p53, and p21 proteins was analyzed. Half-life analysis and ubiquitylation assay were performed to elucidate the molecular mechanism by which OTUD3 stabilizes p53. The interaction between OTUD3 and p53 in BC cells was verified by a co-immunoprecipitation assay and GST pulldown experiments. MTS assay for proliferation detection, detection of apoptosis induced by cisplatin and colony formation assay were employed to investigate the functional effects of OTUD3 on breast cancer cells. RESULTS: OTUD3 downregulation is correlated with a poor prognosis in BC patients. OTUD3 expression is decreased in breast cancer tissues and not associated with the histological grade. OTUD3 also inhibits cell proliferation and clone formation and increases the sensitivity of BC cells to apoptosis induced by chemotherapy drugs. Reduced OTUD3 expression accompanied by decreased p53 abundance is correlated with human breast cancer progression. Ectopic expression of wild-type OTUD3, but not its catalytically inactive mutant, stabilizes and activates p53. Mechanistically, OTUD3 interacts directly with p53 through the amino-terminal OTU region. Finally, OTUD3 protects p53 from murine double minute 2 (Mdm2)-mediated ubiquitination and degradation, enabling the deubiquitination of p53 in BC cells. CONCLUSIONS: In summary, we found that OTUD3 may be a potential therapeutic target for restoring p53 function in breast cancer cells and suggest that the OTUD3-p53 signaling axis may play a critical role in tumor suppression.

Zebrafish ubiquitin-specific peptidase 5 (USP5) activates interferon resistance to the virus by increase the expression of RIG-I.

The ubiquitin specific peptidase (USP) family is involved in many life processes, of which antiviral is also an important basic function. One of the more important ways is to activate interferon. In this study, we reported the antiviral function of the ubiquitin specific peptidase 5(USP5) gene in zebrafish. Evolutionary and comparative protein sequence analysis of the USP5 was performed. The localization of USP5 in FHM cells cytoplasm was determined. Overexpression of USP5 significantly evoked higher expression of mRNA that encode IFNφ1 and ISGs, the promoteractivities of IFNφ1 and IFNstimulated response element (ISRE) were augmented likewise. USP5 was also able to enhance the expression of RIG-I and activate higher levels of IFNφ1 stimulated by Poly (I: C). Viral infection and interference tests demonstrated that USP5 inhibited the replication of SVCV in vitro. In summary, this study reveals that USP5 is able to activate higher levels of interferon by increasing RIG-I protein levels, and thus implement antivirus functions.

LINC00467 enhances head and neck squamous cell carcinoma progression and the epithelial-mesenchymal transition process via miR-299-5p/ubiquitin specific protease-48 axis.

BACKGROUND: Head and neck squamous cell carcinoma (HNSCC) has attracted the attention of researchers as a result of its high incidence around the world. This malignancy occurs in the oral cavity, pharynx and larynx in most cases. A number of lncRNAs have been revealed to regulate the malignant neoplasia of several cancers. Nevertheless, the effects of lncRNA LINC00467 in HNSCC have not yet been reported. METHODS: The expression of LINC00467, miR-299-5p and ubiquitin specific protease-48 (USP48) in HNSCC cells was quantified by a quantitative reverse transcriptase-polymerase chain reaction. The influences of LINC00467 deficiency on HNSCC progression were reflected by cell counting kit-8, colony formation, ethynyl-2-deoxyuridine, wound healing and western blot assays. RIP and luciferase reporter assays were conducted to confirm the interaction among LINC00467, miR-299-5p and USP48. RESULTS: LINC00467 was considerably upregulated in HNSCC cells, and an absence of LINC00467 suppressed cell growth, cell migration and the epithelial-mesenchymal process in HNSCC. In addition, miR-299-5p expression was notably downregulated in HNSCC cells, and miR-299-5p could bind with LINC00467. Furthermore, USP48 was conspicuously overexpressed in HNSCC cells and capable of binding with miR-299-5p. LINC00467 could upregulate USP48 expression via sponging miR-299-5p. Finally, rescue assays proved that USP48 overexpression could compensate for the suppressive effects on HNSCC progression mediated by LINC00467 deficiency. CONCLUSIONS: LINC00467 enhances HNSCC progression by serving as a sponge of miR-299-5p to increase USP48 expression.

RNA-binding protein Roquin negatively regulates STING-dependent innate immune response in Drosophila.

Drosophila melanogaster utilizes innate immune response to defend against exogenous pathogens. The molecular regulation mechanism of the process is evolutionarily conserved. Research of the regulatory mechanisms of Drosophila innate immunity is greatly significant for understanding the modulation of the human innate immunity and the pathogenesis of related diseases. To explore novel regulators in the STING-dependent innate immune response in Drosophila, we utilized the double-stranded RNA-mediated gene expression silencing technique and the dual-luciferase reporter system in knockdown experiments on 9 genes encoding the ubiquitin ligase such as echinus (CG2904), usp16 (CG4165), smurf (CG4943), pellino (CG5212), usp47 (CG5486), diap2 (CG8293), dtraf2 (CG10961), roquin (CG16807) and usp10 (CG32479) in the S2 cells in vitro. The results suggested a negative correlation between CG16807 (roquin) and the STING signaling pathway. Further studies showed that over-expression of roquin in S2 cells significantly inhibited STING innate immune signaling. Meanwhile, Listeria infection experiments showed that knocking down of roquin markedly elevated the expression levels of anti-microbial peptides and inhibited the proliferation of Listeria, thus increasing the survival rates post pathogenic infection. Taken together, our results suggested that the RNA-binding protein Roquin negatively regulates the STING-dependent innate immune response in Drosophila. In view of the high correlation between Drosophila genes and human genes, this study provides a theoretical basis for further development of treatments for STING-related innate immune diseases in humans.

RNA splicing factor USP39 promotes glioma progression by inducing TAZ mRNA maturation.

Increasing evidence demonstrates that ubiquitin specific protease 39 (USP39) plays an oncogenic role in various human tumors. Here, using expression analysis of the publicly available Oncomine database, clinical glioma patient samples, and glioma cells, we found that USP39 was overexpressed in human gliomas. Knockdown of USP39 in glioma cells demonstrated that the protein promoted cell growth, invasion and migration in vitro and in a tumor model in nude mice. To identify mediators of USP39 growth-promoting properties, we used luciferase reporter constructs under transcriptional control of various promoters specific to seven canonical cancer-associated pathways. Luciferase activity from a synthetic TEAD-dependent YAP/TAZ-responsive reporter, as a direct readout of the Hippo signaling pathway, was decreased by 92% in cells with USP39 knockdown, whereas the luciferase activities from the other six cancer pathways, including MAPK/ERK, MAPK/JNK, NFκB, Notch, TGFß, and Wnt, remained unchanged. TAZ protein expression however was decreased independent of canonical Hippo signaling. Immunohistochemistry revealed a positive correlation between USP39 and TAZ proteins in orthotopic xenografts derived from modified glioma cells expressing USP39 shRNAs and primary human glioma samples (p < 0.05). Finally, loss of USP39 decreased TAZ pre-mRNA splicing efficiency in glioma cells in vitro, which led to reduced levels of TAZ protein. In summary, USP39 has oncogenic properties that increase TAZ protein levels by inducing maturation of its mRNA. USP39 therefore provides a novel therapeutic target for the treatment of human glioma.

ABRO1 promotes NLRP3 inflammasome activation through regulation of NLRP3 deubiquitination.

Deubiquitination of NLRP3 has been suggested to contribute to inflammasome activation, but the roles and molecular mechanisms are still unclear. We here demonstrate that ABRO1, a subunit of the BRISC deubiquitinase complex, is necessary for optimal NLRP3-ASC complex formation, ASC oligomerization, caspase-1 activation, and IL-1ß and IL-18 production upon treatment with NLRP3 ligands after the priming step, indicating that efficient NLRP3 activation requires ABRO1. Moreover, we report that ABRO1 deficiency results in a remarkable attenuation in the syndrome severity of NLRP3-associated inflammatory diseases, including MSU- and Alum-induced peritonitis and LPS-induced sepsis in mice. Mechanistic studies reveal that LPS priming induces ABRO1 binding to NLRP3 in an S194 phosphorylation-dependent manner, subsequently recruiting the BRISC to remove K63-linked ubiquitin chains of NLRP3 upon stimulation with activators. Furthermore, deficiency of BRCC3, the catalytically active component of BRISC, displays similar phenotypes to ABRO1 knockout mice. Our findings reveal an ABRO1-mediated regulatory signaling system that controls activation of the NLRP3 inflammasome and provide novel potential targets for treating NLRP3-associated inflammatory diseases.

FAM188B enhances cell survival via interaction with USP7.

We have previously reported that FAM188B showed significant differential exon usage in cancers (NCBI GEO GSE30727), but the expression and function of FAM188B is not well characterized. In the present study, we explored the functions of FAM188B by a knockdown strategy, using siRNAs specific for FAM188B in colon cancer cell lines. FAM188B is a novel gene that encodes a protein that is evolutionarily conserved among mammals. Its mRNA has been found to be highly expressed in most solid tumors, including colorectal cancer. FAM188B knockdown induced cell growth inhibition due to an increase in apoptosis in colon cancer cell lines. Interestingly, siFAM188B treatment induced the upregulation and activation of p53, and consequently increased p53-regulated pro-apoptotic proteins, PUMA and BAX. Proteomic analysis of FAM188B immunocomplexes revealed p53 and USP7 as putative FAM188B-interacting proteins. Deletion of the putative USP7-binding motif in FAM188B reduced complex formation of FAM188B with USP7. It is noteworthy that FAM188B knockdown resulted in a decrease in overall ubiquitination in the p53 immunocomplexes, as well as p53 ubiquitination, because USP7 is involved in p53 deubiquitination. FAM188B knockdown inhibited both colony formation and anchorage-independent growth in vitro. In addition, FAM188B knockdown by siRNA reduced tumor growth in xenografted mice, with an increase in p53 proteins. Taken together, our data suggest that FAM188B is a putative oncogene that functions via interaction with USP7. Therefore, control of FAM188B could be a possible target to inhibit tumor growth.

The deubiquitylase USP15 regulates topoisomerase II alpha to maintain genome integrity.

Ubiquitin-specific protease 15 (USP15) is a widely expressed deubiquitylase that has been implicated in diverse cellular processes in cancer. Here we identify topoisomerase II (TOP2A) as a novel protein that is regulated by USP15. TOP2A accumulates during G2 and functions to decatenate intertwined sister chromatids at prophase, ensuring the replicated genome can be accurately divided into daughter cells at anaphase. We show that USP15 is required for TOP2A accumulation, and that USP15 depletion leads to the formation of anaphase chromosome bridges. These bridges fail to decatenate, and at mitotic exit form micronuclei that are indicative of genome instability. We also describe the cell cycle-dependent behaviour for two major isoforms of USP15, which differ by a short serine-rich insertion that is retained in isoform-1 but not in isoform-2. Although USP15 is predominantly cytoplasmic in interphase, we show that both isoforms move into the nucleus at prophase, but that isoform-1 is phosphorylated on its unique S229 residue at mitotic entry. The micronuclei phenotype we observe on USP15 depletion can be rescued by either USP15 isoform and requires USP15 catalytic activity. Importantly, however, an S229D phospho-mimetic mutant of USP15 isoform-1 cannot rescue either the micronuclei phenotype, or accumulation of TOP2A. Thus, S229 phosphorylation selectively abrogates this role of USP15 in maintaining genome integrity in an isoform-specific manner. Finally, we show that USP15 isoform-1 is preferentially upregulated in a panel of non-small cell lung cancer cell lines, and propose that isoform imbalance may contribute to genome instability in cancer. Our data provide the first example of isoform-specific deubiquitylase phospho-regulation and reveal a novel role for USP15 in guarding genome integrity.

Abro1 maintains genome stability and limits replication stress by protecting replication fork stability.

Protection of the stalled replication fork is crucial for responding to replication stress and minimizing its impact on chromosome instability, thus preventing diseases, including cancer. We found a new component, Abro1, in the protection of stalled replication fork integrity. Abro1 deficiency results in increased chromosome instability, and Abro1-null mice are tumor-prone. We show that Abro1 protects stalled replication fork stability by inhibiting DNA2 nuclease/WRN helicase-mediated degradation of stalled forks. Depletion of RAD51 prevents the DNA2/WRN-dependent degradation of stalled forks in Abro1-deficient cells. This mechanism is distinct from the BRCA2-dependent fork protection pathway, in which stable RAD51 filament formation prevents MRE11-dependent degradation of the newly synthesized DNA at stalled forks. Thus, our data reveal a new aspect of regulated protection of stalled replication forks that involves Abro1.

USP13 negatively regulates antiviral responses by deubiquitinating STING.

STING (also known as MITA) is critical for host defence against viruses and the activity of STING is regulated by ubiquitination. However, the deubiquitination of STING is not fully understood. Here, we show that ubiquitin-specific protease 13 (USP13) is a STING-interacting protein that catalyses deubiquitination of STING. Knockdown or knockout of USP13 potentiates activation of IRF3 and NF-κB and expression of downstream genes after HSV-1 infection or transfection of DNA ligands. USP13 deficiency results in impaired replication of HSV-1. Consistently, USP13 deficient mice are more resistant than wild-type littermates to lethal HSV-1 infection. Mechanistically, USP13 deconjugates polyubiquitin chains from STING and prevents the recruitment of TBK1 to the signalling complex, thereby negatively regulating cellular antiviral responses. Our study thus uncovers a function of USP13 in innate antiviral immunity and provides insight into the regulation of innate immunity.

The Role of the Complex USP1/WDR48 in Differentiation and Proliferation Processes in Cancer Stem Cells.

BACKGROUND: Recently, some studies identified the Basic-Helix-Loop-Helix (bHLH) transcription factor as a significant regulator for the evolution of neoplasms. The binding between bHLH proteins and DNA is restricted by heterodimerization with Inhibitors of DNA binding (ID). IDs prevent cellular differentiation, promote growth and sustain tumor development. The wide presence of stem cells in cancers suggests that genes ID are essential to cancer stem cells (CSC) progress. The enzyme Ubiquitin-specific protease 1 (USP1) is reported to deubiquitinate and stabilize IDs. Considering the action of the proteins ID, USP1 contributes to prevent differentiation mediated by bHLH and, consequently, keep CSC original characteristics. USP1 has its activity potentiated when bound to protein WD repeat-containing protein (WDR48). OBJECTIVE: To identify the influence of the complex USP1/WDR48 during the CSC tumorigenesis process, and whether this complex is a possible therapeutic target. METHODS: A literature search regarding the role of the complex USP1/WDR48 in inhibiting differentiation and increasing proliferation of CSC was performed, and possible selective molecule inhibitors of these deubiquitinase proteins were investigated. RESULTS: There is evidence that USP1/WDR48 complex promotes stem cell conservation and regulation of DNA damage repair. For this reason, inhibitors as Pimozide, GW7647, C527, SJB2-043, ML323 have been studied to inhibit USPs in cases of treatment intervention. CONCLUSION: It is consolidated in the literature the role of USP1/WDR48 during tumorigenesis. However, these studies are not enough to completely clarify the process; but certainly, the researchers are converging towards a promising direction to provide a new treatment option for cancer.

The Multiple Roles of Ubiquitylation in Regulating Challenged DNA Replication.

DNA replication is essential for the propagation of life and the development of complex organisms. However, replication is a risky process as it can lead to mutations and chromosomal alterations. Conditions challenging DNA synthesis by replicative polymerases or DNA helix unwinding, generally termed as replication stress, can halt replication fork progression. Stalled replication forks are unstable, and mechanisms exist to protect their integrity, which promote an efficient restart of DNA synthesis and counteract fork collapse characterized by the accumulation of DNA lesions and mutagenic events. DNA replication is a highly regulated process, and several mechanisms control replication timing and integrity both during unperturbed cell cycles and in response to replication stress. Work over the last two decades has revealed that key steps of DNA replication are controlled by conjugation of the small peptide ubiquitin. While ubiquitylation was traditionally linked to protein degradation, the complexity and flexibility of the ubiquitin system in regulating protein function have recently emerged. Here we review the multiple roles exerted by ubiquitin-conjugating enzymes and ubiquitin-specific proteases, as well as readers of ubiquitin chains, in the control of eukaryotic DNA replication and replication-coupled DNA damage tolerance and repair.

SUMO proteases: uncovering the roles of deSUMOylation in plants.

Plants have evolved to cope with changing environmental conditions. One way plants achieve this is through post-translational modification of target proteins by ubiquitination and SUMOylation. These post-translational modifiers (PMs) can alter stability, protein-protein interactions, and the overall fate of the protein. Both of these systems have remarkable similarities in terms of the process leading to attachment of the PM to its substrate : having to undertake activation, conjugation, and finally ligation to the target. In the ubiquitin system, there are a vast number of ubiquitin ligase enzymes (E3s) that provide specificity for the attachment of ubiquitin. With the SUMO system, only a small number of SUMO E3 ligases have so far been identified in the fully sequenced plant genomes. In Arabidopsis thaliana, there are only two SUMO E3s, compared to over 1400 ubiquitin E3s, a trend also observed in crop species such as Oryza sativa and Zea mays Recent research indicates that removing SUMO from its substrate by the enzymatically active SUMO proteases is a vital part of this system. A class of SUMO proteases called ubiquitin-like proteases (ULPs) are widespread in all eukaryotes; within plants, both monocot and dicot kingdoms have conserved and divergent ULPs and ULP-like proteases. This paper examines the roles ULPs have in stress responses and highlights the 'fine-tuning' of SUMO attachment/removal in balancing growth versus stress.