Design and validation of fibroblast activation protein alpha targeted imaging and therapeutic agents

Background: Cancer-associated fibroblasts (CAFs) comprise a major cell type in the tumor microenvironment where they support tumor growth and survival by producing extracellular matrix, secreting immunosuppressive cytokines, releasing growth factors, and facilitating metastases. Because tumors with elevated CAFs are characterized by poorer prognosis, considerable effort is focused on developing methods to quantitate, suppress and/or eliminate CAFs. We exploit the elevated expression of fibroblast activation protein (FAP) on CAFs to target imaging and therapeutic agents selectively to these fibroblasts in solid tumors. Methods: FAP-targeted optical imaging, radioimaging, and chemotherapeutic agents were synthesized by conjugating FAP ligand (FL) to either a fluorescent dye, technetium-99m, or tubulysin B hydrazide. In vitro and in vivo studies were performed to determine the specificity and selectivity of each conjugate for FAP in vitro and in vivo. Results: FAP-targeted imaging and therapeutic conjugates showed high binding specificity and affinity in the low nanomolar range. Injection of FAP-targeted 99mTc into tumor-bearing mice enabled facile detection of tumor xenografts with little off-target uptake. Optical imaging of malignant lesions was also readily achieved following intravenous injection of FAP-targeted near-infrared fluorescent dye. Finally, systemic administration of a tubulysin B conjugate of FL promoted complete eradication of solid tumors with no evidence of gross toxicity to the animals. Conclusion: In view of the near absence of FAP on healthy cells, we conclude that targeting of FAP on cancer-associated fibroblasts can enable highly specific imaging and therapy of solid tumors.

USP8 ameliorates cognitive and motor impairments via microglial inhibition in a mouse model of sepsis-associated encephalopathy

Sepsis-associated encephalopathy (SAE) is a common and serious complication of sepsis, which is thought to be caused by neuroinflammation. In our previous study, ubiquitin-specific protease 8 (USP8), was reported to regulate inflammation in vitro. In the current study, we investigated whether increased USP8 expression would ameliorate the cognitive and motor impairments induced by cecal ligation and puncture (CLP) in mice, a model of SAE. Male adult mice were randomly divided into four groups: control, sham, CLP, and CLP + USP8 groups. The CLP + USP8 mice showed reduced weight loss on day 4 post-CLP, with a slight increase noted on day 7. The mortality rate in the CLP group was 70% 48 h after CLP; however, USP8 significantly improved survival after CLP. USP8 modulated the neurobehavioral scores in CLP mice. Our results also indicate that USP8 attenuated the CLP-induced cognitive and motor impairments, based on the performance of mice in the Morris water maze (MWM), pole-climbing, and wire suspension tests. USP8 suppressed the release of pro-inflammatory mediators, including prostaglandin E₂(PGE₂) in the serum and nitric oxide (NO) in brain tissue, as well as levels of inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2) in brain tissue. Immunofluorescence experiments revealed that USP8 inhibited CLP-induced increases in microglial size and density in the hippocampus, and protected hippocampal neurons. Our findings indicate that neuroinflammation occurs in the brains of CLP mice, and that USP8 exerts protective effects against CLP-induced neuroinflammation and cognitive and motor impairments, which may aid in the development of novel therapeutic strategies for SAE.

USP8 Deubiquitinates the Leptin Receptor and Is Necessary for Leptin-Mediated Synapse Formation

Leptin has neurotrophic actions in the hippocampus to increase synapse formation and stimulate neuronal plasticity. Leptin also enhances cognition and has antidepressive and anxiolytic-like effects, two hippocampal-dependent behaviors. In contrast, mice lacking leptin or the long form of the leptin receptor (LepRb) have lower cortical volume and decreased memory and exhibit depressive-like behaviors. A number of the signaling pathways regulated by LepRb are known, but how membrane LepRb levels are regulated in the central nervous system is not well understood. Here, we show that the lysosomal inhibitor chloroquine increases LepRb expression in hippocampal cultures, suggesting that LepRb is degraded in the lysosome. Furthermore, we show that leptin increases surface expression of its own receptor by decreasing the level of ubiquitinated LepRbs. This decrease is mediated by the deubiquitinase ubiquitin-specific protease 8 (USP8), which we show is in complex with LepRb. Acute leptin stimulation increases USP8 activity. Moreover, leptin stimulates USP8 gene expression through cAMP response element-binding protein (CREB)-dependent transcription, an effect blocked by expression of a dominant-negative CREB or with short hairpin RNA knockdown of CREB. Increased expression of USP8 causes increased surface localization of LepRb, which in turn enhances leptin-mediated activation of the MAPK kinase/extracellular signal-regulated kinase pathway and CREB activation. Lastly, increased USP8 expression increases glutamatergic synapse formation in hippocampal cultures, an effect dependent on expression of LepRbs. Leptin-stimulated synapse formation also requires USP8. In conclusion, we show that USP8 deubiquitinates LepRb, thus inhibiting lysosomal degradation and enhancing surface localization of LepRb, which are essential for leptin-stimulated synaptogenesis in the hippocampus.

Migration of leukocytes through the vessel wall and beyond

The migration of leukocytes from the vascular lumen to sites of infection and/or injury in the extravascular tissue involves a series of sequential and coordinated molecular and cellular events with the resultant primary response being that of reduced leukocyte velocity within the blood stream, followed by leukocyte firm adhesion to endothelial cells lining the vessel wall and eventually migration through the vessel wall. Despite the growing knowledge of the mechanisms that mediate initial interaction of leukocytes with the endothelium, very little is known about the mechanisms that mediate and regulate leukocyte migration through the venular wall, the endothelium and its associated perivascular basement membrane. This review, whilst giving a brief outline of the stepwise cascade of molecular interactions involved in this process and the methods employed to investigate leukocyte migration in vivo, focuses primarily on mechanisms of leukocyte transmigration, the final step in the process of leukocyte emigration. Furthermore, special emphasis is placed on discussing the process and the mechanisms involved in leukocyte migration through the basement membrane, a structure that presents significant impedance to transmigrating leukocytes but is seldom investigated in the context of leukocyte transmigration in vivo. The review also discusses the growing evidence supporting the concept that leukocyte transmigration is not only a response that describes the passage of leukocytes through the venular wall, but also acts as a means of regulating leukocyte responsiveness beyond the vessel wall, i.e. within the extravascular tissue.

This publication was partially financed by Serono Foundation for the Advancement of Medical Science.

Part of this paper was originally presented at the 2nd International Workshop on New Therapeutic Targets in Vascular Biology from February 6-9, 2003 in Geneva, Switzerland.

Deubiquitinating Enzyme USP9X Suppresses Tumor Growth via LATS Kinase and Core Components of the Hippo Pathway

The core LATS kinases of the Hippo tumor suppressor pathway phosphorylate and inhibit the downstream transcriptional co-activators YAP and TAZ, which are implicated in various cancers. Recent studies have identified various E3 ubiquitin ligases that negatively regulate the Hippo pathway via ubiquitination, yet few deubiquitinating enzymes (DUB) have been implicated. In this study, we report the DUB USP9X is an important regulator of the core kinases of this pathway. USP9X interacted strongly with LATS kinase and to a lesser extent with WW45, KIBRA, and Angiomotin, and LATS co-migrated exclusively with USP9X during gel filtration chromatography analysis. Knockdown of USP9X significantly downregulated and destabilized LATS and resulted in enhanced nuclear translocation of YAP and TAZ, accompanied with activation of their target genes. In the absence of USP9X, cells exhibited an epithelial-to-mesenchymal transition phenotype, acquired anchorage-independent growth in soft agar, and led to enlarged, disorganized, three-dimensional acini. YAP/TAZ target gene activation in response to USP9X knockdown was suppressed by knockdown of YAP, TAZ, and TEAD2. Deletion of USP9X in mouse embryonic fibroblasts resulted in significant downregulation of LATS. Furthermore, USP9X protein expression correlated positively with LATS but negatively with YAP/TAZ in pancreatic cancer tissues as well as pancreatic and breast cancer cell lines. Overall, these results strongly indicate that USP9X potentiates LATS kinase to suppress tumor growth. Cancer Res; 77(18); 4921-33. ©2017 AACR.

The Coat Protein and NIa Protease of Two Potyviridae Family Members Independently Confer Superinfection Exclusion

Superinfection exclusion (SIE) is an antagonistic virus-virus interaction whereby initial infection by one virus prevents subsequent infection by closely related viruses. Although SIE has been described in diverse viruses infecting plants, humans, and animals, its mechanisms, including involvement of specific viral determinants, are just beginning to be elucidated. In this study, SIE determinants encoded by two economically important wheat viruses, Wheat streak mosaic virus (WSMV; genus Tritimovirus, family Potyviridae) and Triticum mosaic virus (TriMV; genus Poacevirus, family Potyviridae), were identified in gain-of-function experiments that used heterologous viruses to express individual virus-encoded proteins in wheat. Wheat plants infected with TriMV expressing WSMV P1, HC-Pro, P3, 6K1, CI, 6K2, NIa-VPg, or NIb cistrons permitted efficient superinfection by WSMV expressing green fluorescent protein (WSMV-GFP). In contrast, wheat infected with TriMV expressing WSMV NIa-Pro or coat protein (CP) substantially excluded superinfection by WSMV-GFP, suggesting that both of these cistrons are SIE effectors encoded by WSMV. Importantly, SIE is due to functional WSMV NIa-Pro or CP rather than their encoding RNAs, as altering the coded protein products by minimally changing RNA sequences led to abolishment of SIE. Deletion mutagenesis further revealed that elicitation of SIE by NIa-Pro requires the entire protein while CP requires only a 200-amino-acid (aa) middle fragment (aa 101 to 300) of the 349 aa. Strikingly, reciprocal experiments with WSMV-mediated expression of TriMV proteins showed that TriMV CP, and TriMV NIa-Pro to a lesser extent, likewise excluded superinfection by TriMV-GFP. Collectively, these data demonstrate that WSMV- and TriMV-encoded CP and NIa-Pro proteins are effectors of SIE and that these two proteins trigger SIE independently of each other.

IMPORTANCE

Superinfection exclusion (SIE) is an antagonistic virus-virus interaction that prevents secondary invasions by identical or closely related viruses in the same host cells. Although known to occur in diverse viruses, SIE remains an enigma in terms of key molecular determinants and action mechanisms. In this study, we found that Wheat streak mosaic virus (WSMV) and Triticum mosaic virus (TriMV) encode two independently functioning cistrons that serve as effectors of SIE at the protein but not the RNA level. The coat protein and NIa-Pro encoded by these two viruses, when expressed from a heterologous virus, exerted SIE to the cognate viruses. The identification of virus-encoded effectors of SIE and their transgenic expression could potentially facilitate the development of virus-resistant crop plants. Additionally, functional conservation of SIE in diverse virus groups suggests that a better understanding of the underlying mechanisms of SIE could facilitate the development of novel antiviral therapies against viral diseases.

Isocitrate-to-SENP1 signaling amplifies insulin secretion and rescues dysfunctional β cells

Insulin secretion from β cells of the pancreatic islets of Langerhans controls metabolic homeostasis and is impaired in individuals with type 2 diabetes (T2D). Increases in blood glucose trigger insulin release by closing ATP-sensitive K+ channels, depolarizing β cells, and opening voltage-dependent Ca2+ channels to elicit insulin exocytosis. However, one or more additional pathway(s) amplify the secretory response, likely at the distal exocytotic site. The mitochondrial export of isocitrate and engagement with cytosolic isocitrate dehydrogenase (ICDc) may be one key pathway, but the mechanism linking this to insulin secretion and its role in T2D have not been defined. Here, we show that the ICDc-dependent generation of NADPH and subsequent glutathione (GSH) reduction contribute to the amplification of insulin exocytosis via sentrin/SUMO-specific protease-1 (SENP1). In human T2D and an in vitro model of human islet dysfunction, the glucose-dependent amplification of exocytosis was impaired and could be rescued by introduction of signaling intermediates from this pathway. Moreover, islet-specific Senp1 deletion in mice caused impaired glucose tolerance by reducing the amplification of insulin exocytosis. Together, our results identify a pathway that links glucose metabolism to the amplification of insulin secretion and demonstrate that restoration of this axis rescues β cell function in T2D.

How do reducing equivalents increase insulin secretion?

Glucose stimulation of insulin secretion in pancreatic β cells involves cell depolarization and subsequent opening of voltage-dependent Ca2+ channels to elicit insulin granule exocytosis. This pathway alone does not account for the entire magnitude of the secretory response in β cells. In this issue, Ferdaoussi, Dai, and colleagues reveal that insulin secretion is amplified by cytosolic isocitrate dehydrogenase-dependent transfer of reducing equivalents, which generates NADPH and reduced glutathione, which in turn activates sentrin/SUMO-specific protease-1 (SENP1). β Cell-specific deletion of Senp1 in murine models reduced the amplification of insulin exocytosis, resulting in impaired glucose tolerance. Further, their studies demonstrate that restoring intracellular NADPH or activating SENP1 improves insulin exocytosis in human β cells from donors with type 2 diabetes, suggesting a potential therapeutic target to augment insulin production.

Ubiquitin specific protease 2 acts as a key modulator for the regulation of cell cycle by adiponectin and leptin in cancer cells

Adiponectin and leptin, both produced from adipose tissue, cause cell cycle arrest and progression, respectively in cancer cells. Ubiquitin specific protease-2 (USP-2), a deubiquitinating enzyme, is known to impair proteasome-induced degradation of cyclin D1, a critical cell cycle regulator. Herein, we investigated the effects of these adipokines on USP-2 expression and its potential role in the modulation of cell cycle. Treatment with globular adiponectin (gAcrp) decreased, whereas leptin increased USP-2 expression both in human hepatoma and breast cancer cells. In addition, overexpression or gene silencing of USP-2 affected cyclin D1 expression and cell cycle progression/arrest by adipokines. Adiponectin and leptin also modulated in vitro proteasomal activity, which was partially dependent on USP-2 expression. Taken together, our results reveal that modulation of USP-2 expression plays a crucial role in cell cycle regulation by adipokines. Thus, USP-2 would be a promising therapeutic target for the modulation of cancer cell growth by adipokines.

Impaired Maternal Behavior in Usp46 Mutant Mice: A Model for Trans-Generational Transmission of Maternal Care

Usp46 mutant mice (congenic strain on a B6 genetic background; MT mice) have a low weaning rate and display poor maternal behavior compared to C57BL/6J mice (B6 mice). Based on these observations, we examined how maternal behavior is shaped by cross-fostering and in-fostering MT and B6 mice. The experiments consisted of six groups: B6 mice fostered by their biological mother (B6-CO); MT mice fostered by their biological mother (MT-CO); B6 mice fostered by a different B6 mother (B6-IF); MT mice fostered by a different MT mother (MT-IF); B6 mice fostered by an MT mother (B6-CF); and MT mice fostered by a B6 mother (MT-CF). Maternal behavior was assessed using the pup-retrieval test in adult female offspring, and four parameters, time nursing pups in the nest, time sniffing or licking pups, rearing behavior, and latency to retrieve pups, were measured. Cross-fostering significantly reduced time spent nursing and sniffing/licking pup, and increased the number of instances of rearing in the B6-CF group, and improved three parameters of maternal behaviors (nursing, rearing and latency) in the MT-CF group. These results indicate that the level of maternal care is transmitted to their pups and proper maternal behaviors can be shaped if adequate postpartum maternal care is given, even in genetically vulnerable mice. However, the offspring’s genotype may also influence the development of maternal behaviors in adulthood. Thus, MT mice may prove useful as a model for trans-generational transmission of maternal care, and these findings may provide insight into the mechanisms of maltreating behaviors in human child abuse.

Both the autophagy and proteasomal pathways facilitate the Ubp3p-dependent depletion of a subset of translation and RNA turnover factors during nitrogen starvation in Saccharomyces cerevisiae

Protein turnover is an important regulatory mechanism that facilitates cellular adaptation to changing environmental conditions. Previous studies have shown that ribosome abundance is reduced during nitrogen starvation by a selective autophagy mechanism termed ribophagy, which is dependent upon the deubiquitinase Ubp3p. In this study, we asked whether the abundance of various translation and RNA turnover factors are reduced following the onset of nitrogen starvation in Saccharomyces cerevisiae. We found distinct differences in the abundance of the proteins tested following nitrogen starvation: (1) The level of some did not change; (2) others were reduced with kinetics similar to ribophagy, and (3) a few proteins were rapidly depleted. Furthermore, different pathways differentially degraded the various proteins upon nitrogen starvation. The translation factors eRF3 and eIF4GI, and the decapping enhancer Pat1p, required an intact autophagy pathway for their depletion. In contrast, the deadenylase subunit Pop2p and the decapping enzyme Dcp2p were rapidly depleted by a proteasome-dependent mechanism. The proteasome-dependent depletion of Dcp2p and Pop2p was also induced by rapamycin, suggesting that the TOR1 pathway influences this pathway. Like ribophagy, depletion of eIF4GI, eRF3, Dcp2p, and Pop2p was dependent upon Ubp3p to varying extents. Together, our results suggest that the autophagy and proteasomal pathways degrade distinct translation and RNA turnover factors in a Ubp3p-dependent manner during nitrogen starvation. While ribophagy is thought to mediate the reutilization of scarce resources during nutrient limitation, our results suggest that the selective degradation of specific proteins could also facilitate a broader reprogramming of the post-transcriptional control of gene expression.

Significance of proteolytic activity in 1,25-(OH)2D3-induced differentiation of HL-60 cells

Two types of HL-60 cells, 1,25-(OH)2D3-responsive ATCC HL-60 cells and 1,25-(OH)2D3-resistant LG HL-60 cells were used. Despite the presence of enough amounts of normal 1,25-(OH)2D3 receptors, only 22% of LG cells matured after a 4-day treatment with 10(-7) M 1,25-(OH)2D3, while 80% of ATCC cells differentiated. However, 1,25-(OH)2D3 inhibited the proliferation of LG cells to the same degree as that of ATCC cells. 1,25-(OH)2D3 also induced (1) the ability to metabolize 1,25-(OH)2D3 to 1,24,25-(OH)3D3, and (2) up-regulation of the 1,25-(OH)2D3 receptor in LG as well as ATCC cells. Furthermore, the proportion of mature LG cells was 78% after treatment with 10(-7) M 1,25-(OH)2D3 for the first 48 h and 10(-7) M dbcAMP for the second 48 h, which was greater than that when treated only with 10(-7) M dbcAMP for the second 48 h (24.2%). These results indicate that 1,25-(OH)2D3 receptor complexes function normally in LG cells at commitment step in cell differentiation. ATCC cells had a serine proteinase to destroy specific 1,25-(OH)2D3-binding activity of the unoccupied receptor and digest 53-kD receptor to a small fragment with a MW of 16.3 kD, while not affecting the level of the specific binding of the occupied receptor. Other cells, such as murine leukemia cells, M1, and human chronic myeloid leukemia cells, the differentiation of which is induced by 1,25-(OH)2D3, seemed to have the same type of proteinase, suggesting the physiological significance of this proteinase in 1,25-(OH)2D3-induced cell differentiation.

Taspase1-dependent TFIIA cleavage coordinates head morphogenesis by limiting Cdkn2a locus transcription

Head morphogenesis requires complex signal relays to enable precisely coordinated proliferation, migration, and patterning. Here, we demonstrate that, during mouse head formation, taspase1-mediated (TASP1-mediated) cleavage of the general transcription factor TFIIA ensures proper coordination of rapid cell proliferation and morphogenesis by maintaining limited transcription of the negative cell cycle regulators p16Ink4a and p19Arf from the Cdkn2a locus. In mice, loss of TASP1 function led to catastrophic craniofacial malformations that were associated with inadequate cell proliferation. Compound deficiency of Cdkn2a, especially p16Ink4a deficiency, markedly reduced the craniofacial anomalies of TASP1-deficent mice. Furthermore, evaluation of mice expressing noncleavable TASP1 targets revealed that TFIIA is the principal TASP1 substrate that orchestrates craniofacial morphogenesis. ChIP analyses determined that noncleaved TFIIA accumulates at the p16Ink4a and p19Arf promoters to drive transcription of these negative regulators. In summary, our study elucidates a regulatory circuit comprising proteolysis, transcription, and proliferation that is pivotal for construction of the mammalian head.

Cell cycle-dependent expression of Dub3, Nanog and the p160 family of nuclear receptor coactivators (NCoAs) in mouse embryonic stem cells

Pluripotency of embryonic stem cells (ESC) is tightly regulated by a network of transcription factors among which the estrogen-related receptor β (Esrrb). Esrrb contributes to the relaxation of the G1 to S-phase (G1/S) checkpoint in mouse ESCs by transcriptional control of the deubiquitylase Dub3 gene, contributing to Cdc25A persistence after DNA damage. We show that in mESCs, Dub3 gene expression is cell cycle regulated and is maximal prior G1/S transition. In addition, following UV-induced DNA damage in G1, Dub3 expression markedly increases in S-phase also suggesting a role in checkpoint recovery. Unexpectedly, we also observed cell cycle-regulation of Nanog expression, and not Oct4, reaching high levels prior to G1/S transition, finely mirroring Cyclin E1 fluctuations. Curiously, while Esrrb showed only limited cell-cycle oscillations, transcript levels of the p160 family of nuclear receptor coactivators (NCoAs) displayed strong cell cycle-dependent fluctuations. Since NCoAs function in concert with Esrrb in transcriptional activation, we focussed on NCoA1 whose levels specifically increase prior onset of Dub3 transcription. Using a reporter assay, we show that NCoA1 potentiates Esrrb-mediated transcription of Dub3 and we present evidence of protein interaction between the SRC1 splice variant NCoA1 and Esrrb. Finally, we show a differential developmental regulation of all members of the p160 family during neural conversion of mESCs. These findings suggest that in mouse ESCs, changes in the relative concentration of a coactivator at a given cell cycle phase, may contribute to modulation of the transcriptional activity of the core transcription factors of the pluripotent network and be implicated in cell fate decisions upon onset of differentiation.

Extracellular matrix mineralization in periodontal tissues: Noncollagenous matrix proteins, enzymes, and relationship to hypophosphatasia and X-linked hypophosphatemia

As broadly demonstrated for the formation of a functional skeleton, proper mineralization of periodontal alveolar bone and teeth - where calcium phosphate crystals are deposited and grow within an extracellular matrix - is essential for dental function. Mineralization defects in tooth dentin and cementum of the periodontium invariably lead to a weak (soft or brittle) dentition in which teeth become loose and prone to infection and are lost prematurely. Mineralization of the extremities of periodontal ligament fibers (Sharpey's fibers) where they insert into tooth cementum and alveolar bone is also essential for the function of the tooth-suspensory apparatus in occlusion and mastication. Molecular determinants of mineralization in these tissues include mineral ion concentrations (phosphate and calcium), pyrophosphate, small integrin-binding ligand N-linked glycoproteins and matrix vesicles. Amongst the enzymes important in regulating these mineralization determinants, two are discussed at length here, with clinical examples given, namely tissue-nonspecific alkaline phosphatase and phosphate-regulating gene with homologies to endopeptidases on the X chromosome. Inactivating mutations in these enzymes in humans and in mouse models lead to the soft bones and teeth characteristic of hypophosphatasia and X-linked hypophosphatemia, respectively, where the levels of local and systemic circulating mineralization determinants are perturbed. In X-linked hypophosphatemia, in addition to renal phosphate wasting causing low circulating phosphate levels, phosphorylated mineralization-regulating small integrin-binding ligand N-linked glycoproteins, such as matrix extracellular phosphoglycoprotein and osteopontin, and the phosphorylated peptides proteolytically released from them, such as the acidic serine- and aspartate-rich-motif peptide, may accumulate locally to impair mineralization in this disease.

The deubiquitylase USP37 links REST to the control of p27 stability and cell proliferation

The RE1 silencing transcription factor (REST) is a repressor of neuronal differentiation and its elevated expression in neural cells blocks neuronal differentiation. In this study, we demonstrate a role for REST in the control of proliferation of medulloblastoma cells. REST expression decreased the levels of cyclin-dependent kinase (CDK)NIB/p27, a CDK inhibitor and a brake of cell proliferation in these cells. The reciprocal relationship between REST and p27 was validated in human tumor samples. REST knockdown in medulloblastoma cells derepessed a novel REST target gene encoding the deubiquitylase ubiquitin (Ub)-specific peptidase 37 (USP37). Ectopically expressed wild-type USP37 formed a complex with p27, promoted its deubiquitination and stabilization and blocked cell proliferation. Knockdown of REST and USP37 prevented p27 stabilization and blocked the diminution in proliferative potential that normally accompanied REST loss. Unexpectedly, wild-type USP37 expression also induced the expression of REST-target neuronal differentiation genes even though REST levels were unaffected. In contrast, a mutant of USP37 carrying a site-directed change in a conserved cysteine failed to rescue REST-mediated p27 destabilization, maintenance of cell proliferation and blockade to neuronal differentiation. Consistent with these findings, a significant correlation between USP37 and p27 was observed in patient tumors. Collectively, these findings provide a novel connection between REST and the proteasomal machinery in the control of p27 and cell proliferation in medulloblastoma cells.

Nonclassical renin-angiotensin system and renal function

The renin-angiotensin system (RAS) constitutes one of the most important hormonal systems in the physiological regulation of blood pressure through renal and nonrenal mechanisms. Indeed, dysregulation of the RAS is considered a major factor in the development of cardiovascular pathologies, including kidney injury, and blockade of this system by the inhibition of angiotensin converting enzyme (ACE) or blockade of the angiotensin type 1 receptor (AT1R) by selective antagonists constitutes an effective therapeutic regimen. It is now apparent with the identification of multiple components of the RAS within the kidney and other tissues that the system is actually composed of different angiotensin peptides with diverse biological actions mediated by distinct receptor subtypes. The classic RAS can be defined as the ACE-Ang II-AT1R axis that promotes vasoconstriction, water intake, sodium retention, and other mechanisms to maintain blood pressure, as well as increase oxidative stress, fibrosis, cellular growth, and inflammation in pathological conditions. In contrast, the nonclassical RAS composed primarily of the AngII/Ang III-AT2R pathway and the ACE2-Ang-(1-7)-AT7R axis generally opposes the actions of a stimulated Ang II-AT1R axis through an increase in nitric oxide and prostaglandins and mediates vasodilation, natriuresis, diuresis, and reduced oxidative stress. Moreover, increasing evidence suggests that these non-classical RAS components contribute to the therapeutic blockade of the classical system to reduce blood pressure and attenuate various indices of renal injury, as well as contribute to normal renal function.

The SUMO protease SENP1 is required for cohesion maintenance and mitotic arrest following spindle poison treatment

SUMO conjugation is a reversible posttranslational modification that regulates protein function. SENP1 is one of the six SUMO-specific proteases present in vertebrate cells and its altered expression is observed in several carcinomas. To characterize SENP1 role in genome integrity, we generated Senp1 knockout chicken DT40 cells. SENP1(-/-) cells show normal proliferation, but are sensitive to spindle poisons. This hypersensitivity correlates with increased sister chromatid separation, mitotic slippage, and apoptosis. To test whether the cohesion defect had a causal relationship with the observed mitotic events, we restored the cohesive status of sister chromatids by introducing the TOP2α(+/-) mutation, which leads to increased catenation, or by inhibiting Plk1 and Aurora B kinases that promote cohesin release from chromosomes during prolonged mitotic arrest. Although TOP2α is SUMOylated during mitosis, the TOP2α(+/-) mutation had no obvious effect. By contrast, inhibition of Plk1 or Aurora B rescued the hypersensitivity of SENP1(-/-) cells to colcemid. In conclusion, we identify SENP1 as a novel factor required for mitotic arrest and cohesion maintenance during prolonged mitotic arrest induced by spindle poisons.

RNF20 and USP44 regulate stem cell differentiation by modulating H2B monoubiquitylation

Embryonic stem cells (ESCs) maintain high genomic plasticity, which is essential for their capacity to enter diverse differentiation pathways. Posttranscriptional modifications of chromatin histones play a pivotal role in maintaining this plasticity. We now report that one such modification, monoubiquitylation of histone H2B on lysine 120 (H2Bub1), catalyzed by the E3 ligase RNF20, increases during ESC differentiation and is required for efficient execution of this process. This increase is particularly important for the transcriptional induction of relatively long genes during ESC differentiation. Furthermore, we identify the deubiquitinase USP44 as a negative regulator of H2B ubiquitylation, whose downregulation during ESC differentiation contributes to the increase in H2Bub1. Our findings suggest that optimal ESC differentiation requires dynamic changes in H2B ubiquitylation patterns, which must occur in a timely and well-coordinated manner.

Separase sensor reveals dual roles for separase coordinating cohesin cleavage and cdk1 inhibition

Complete dissociation of sister chromatid cohesion and subsequent induction of poleward movement of disjoined sisters are two essential events underlying chromosome segregation; however, how cells coordinate these two processes is not well understood. Here, we developed a fluorescence-based sensor for the protease separase that mediates cohesin cleavage. We found that separase undergoes an abrupt activation shortly before anaphase onset in the vicinity of chromosomes. This activation profile of separase depends on the abilities of two of its binding proteins, securin and cyclin B1, to inhibit its protease activity and target it to chromosomes. Subsequent to its proteolytic activation, separase then binds to and inhibits a subset of cyclin B1-cdk1, which antagonizes cdk1-mediated phosphorylation on chromosomes and facilitates poleward movement of sisters in anaphase. Therefore, by consecutively acting as a protease and a cdk1 inhibitor, separase coordinates two key processes to achieve simultaneous and abrupt separation of sister chromatids.

Pleiotropic effects of deubiquitinating enzyme Ubp5 on growth and pathogenesis of Cryptococcus neoformans

Ubiquitination is a reversible protein modification that influences various cellular processes in eukaryotic cells. Deubiquitinating enzymes remove ubiquitin, maintain ubiquitin homeostasis and regulate protein degradation via the ubiquitination pathway. Cryptococcus neoformans is an important basidiomycete pathogen that causes life-threatening meningoencephalitis primarily in the immunocompromised population. In order to understand the possible influence deubiquitinases have on growth and virulence of the model pathogenic yeast Cryptococcus neoformans, we generated deletion mutants of seven putative deubiquitinase genes. Compared to other deubiquitinating enzyme mutants, a ubp5Δ mutant exhibited severely attenuated virulence and many distinct phenotypes, including decreased capsule formation, hypomelanization, defective sporulation, and elevated sensitivity to several external stressors (such as high temperature, oxidative and nitrosative stresses, high salts, and antifungal agents). Ubp5 is likely the major deubiquitinating enzyme for stress responses in C. neoformans, which further delineates the evolutionary divergence of Cryptococcus from the model yeast S. cerevisiae, and provides an important paradigm for understanding the potential role of deubiquitination in virulence by other pathogenic fungi. Other putative deubiquitinase mutants (doa4Δ and ubp13Δ) share some phenotypes with the ubp5Δ mutant, illustrating functional overlap among deubiquitinating enzymes in C. neoformans. Therefore, deubiquitinating enzymes (especially Ubp5) are essential for the virulence composite of C. neoformans and provide an additional yeast survival and propagation advantage in the host.

Ubiquitin-specific peptidase 46 (Usp46) regulates mouse immobile behavior in the tail suspension test through the GABAergic system

The tail suspension test (TST) is widely recognized as a useful experimental paradigm for assessing antidepressant activity and depression-like behavior. We have previously identified ubiquitin-specific peptidase 46 (Usp46) as a quantitative trait gene responsible for decreasing immobility time in the TST in mice. This Usp46 mutation has a 3-bp deletion coding for lysine in the open reading frame, and we indicated that Usp46 is implicated in the regulation of the GABAergic system. However, it is not known precisely how the immobile behavior is regulated by the GABAergic system. Therefore, in the present study, we examined whether the immobility time is influenced by drugs affecting the action mediated by GABA_A receptor using both 3-bp deleted (the Usp46 mutant) and null Usp46 (Usp46 KO) mice. Nitrazepam, an agonist at the benzodiazepine-binding site of the GABA_A receptor, which potentiates the action of GABA, produced a dose-dependent increase in TST immobility time in the Usp46 mutant mice without affecting general behaviors. The Usp46 KO mice exhibited short immobility times comparable to the Usp46 mutant mice, which was also increased by nitrazepam administration. The effects of nitrazepam in the Usp46 mutant and KO mice were antagonized by flumazenil. These results indicate that the 3-bp deleted Usp46 mutation causes a loss-of-function phenotype, and that the GABA_A receptor might participate in the regulation of TST immobility time.

SUMO-specific protease 1 is critical for early lymphoid development through regulation of STAT5 activation

Small ubiquitin-like modifier (SUMO) modification has emerged as an important regulatory mechanism during embryonic development. However, it is not known whether SUMOylation plays a role in the development of the immune system. Here, we show that SUMO-specific protease 1 (SENP1) is essential for the development of early T and B cells. STAT5, a key regulator of lymphoid development, is modified by SUMO-2 and is specifically regulated by SENP1. In the absence of SENP1, SUMO-2 modified STAT5 accumulates in early lymphoid precursors, resulting in a block in its acetylation and subsequent signaling. These results demonstrate a crucial role of SENP1 in the regulation of STAT5 activation during early lymphoid development.

Functional diversification of thylakoidal processing peptidases in Arabidopsis thaliana

Thylakoidal processing peptidase (TPP) is responsible for removing amino-terminal thylakoid-transfer signals from several proteins in the thylakoid lumen. Three TPP isoforms are encoded by the nuclear genome of Arabidopsis thaliana. Previous studies showed that one of them termed plastidic type I signal peptidase 1 (Plsp1) was necessary for processing three thylakoidal proteins and one protein in the chloroplast envelope in vivo. The lack of Plsp1 resulted in seedling lethality, apparently due to disruption of proper thylakoid development. The physiological roles of the other two TPP homologs remain unknown. Here we show that the three A. thaliana TPP isoforms evolved to acquire diverse functions. Phylogenetic analysis revealed that TPP may have originated before the endosymbiotic event, and that there are two groups of TPP in seed plants: one includes Plsp1 and another comprises the other two A. thaliana TPP homologs, which are named as Plsp2A and Plsp2B in this study. The duplication leading to the two groups predates the gymnosperm-angiosperm divergence, and the separation of Plsp2A and Plsp2B occurred after the Malvaceae-Brassicaceae diversification. Quantitative reverse transcription-PCR assay revealed that the two PLSP2 genes were co-expressed in both photosynthetic tissues and roots, whereas the PLSP1 transcript accumulated predominantly in photosynthetic tissues. Both PLSP2 genes were expressed in the aerial parts of the plsp1-null mutant at levels comparable to those in wild-type plants. The seedling-lethal phenotype of the plsp1-null mutant could be rescued by a constitutive expression of Plsp1 cDNA but not by that of Plsp2A or Plsp2B. These results indicate that Plsp1 and Plsp2 evolved to function differently, and that neither of the Plsp2 isoforms is necessary for proper thylakoid development in photosynthetic tissues.

Lysine 92 amino acid residue of USP46, a gene associated with 'behavioral despair' in mice, influences the deubiquitinating enzyme activity

Deubiquitinating enzymes (DUBs) regulate diverse cellular functions by their activity of cleaving ubiquitin from specific protein substrates. Ubiquitin-Specific Protease 46 (USP46) has recently been identified as a quantitative trait gene responsible for immobility in the tail suspension test and forced swimming test in mice. Mice with a lysine codon (Lys 92) deletion in USP46 exhibited loss of ‘behavioral despair’ under inescapable stresses in addition to abnormalities in circadian behavioral rhythms and the GABAergic system. However, whether this deletion affects enzyme activity is unknown. Here we show that USP46 has deubiquitinating enzyme activity detected by USP cleavage assay using GST-Ub52 as a model substrate. Interestingly, compared to wild type, the Lys 92 deletion mutant resulted in a decreased deubiquitinating enzyme activity of 27.04%. We also determined the relative expression levels of Usp46 in rat tissues using real-time RT-PCR. Usp46 mRNA was expressed in various tissues examined including brain, with the highest expression in spleen. In addition, like rat USP46, both human and mouse USP46 are active toward to the model substrate, indicating the USP cleavage assay is a simple method for testing the deubiquitinating enzyme activity of USP46. These results suggest that the Lys 92 deletion of USP46 could influence enzyme activity and thereby provide a molecular clue how the enzyme regulating the pathogenesis of mental illnesses.

The catalytic activity of Ubp6 enhances maturation of the proteasomal regulatory particle

The 26S proteasome is a 2.5 MDa macromolecular machine responsible for targeted protein degradation. Recently, four chaperones were identified that promote the assembly of the 19S regulatory particle (RP). Here, we probe the dynamic architecture of the proteasome by applying quantitative proteomics and mass spectrometry (MS) of intact complexes to provide a detailed characterization of how Ubp6 assists this assembly process. Our MS data demonstrate stoichiometric binding of chaperones and Ubp6 to the basal part of the RP. Genetic interactions of Ubp6 with Hsm3, but not with the other chaperones, indicate a functional overlay with Hsm3. Our biochemical data identified Ubp6 as an additional member of the Hsm3 module. Deletions of ubp6 with hsm3 perturb 26S proteasome assembly, which we attribute to an accumulation of ubiquitylated substrates on these assembly precursors. We therefore propose that Ubp6 facilitates proteasomal assembly by clearing ubiquitylated substrates from assembly precursors by its deubiquitylating activity.

Cleavage of cohesin rings coordinates the separation of centrioles and chromatids

Cohesin pairs sister chromatids by forming a tripartite Scc1-Smc1-Smc3 ring around them. In mitosis, cohesin is removed from chromosome arms by the phosphorylation-dependent prophase pathway. Centromeric cohesin is protected by shugoshin 1 and protein phosphatase 2A (Sgo1-PP2A) and opened only in anaphase by separase-dependent cleavage of Scc1 (refs 4-6). Following chromosome segregation, centrioles loosen their tight orthogonal arrangement, which licenses later centrosome duplication in S phase. Although a role of separase in centriole disengagement has been reported, the molecular details of this process remain enigmatic. Here, we identify cohesin as a centriole-engagement factor. Both premature sister-chromatid separation and centriole disengagement are induced by ectopic activation of separase or depletion of Sgo1. These unscheduled events are suppressed by expression of non-cleavable Scc1 or inhibition of the prophase pathway. When endogenous Scc1 is replaced by artificially cleavable Scc1, the corresponding site-specific protease triggers centriole disengagement. Separation of centrioles can alternatively be induced by ectopic cleavage of an engineered Smc3. Thus, the chromosome and centrosome cycles exhibit extensive parallels and are coordinated with each other by dual use of the cohesin ring complex.

Deubiquitinating enzymes AtUBP12 and AtUBP13 and their tobacco homologue NtUBP12 are negative regulators of plant immunity

• Signalling by ubiquitination is implicated in diverse aspects of the plant lifecycle, and enzymes of ubiquitin metabolism are overrepresented in the Arabidopsis genome compared with other model eukaryotes. Despite the importance of ubiquitination in the regulation of signalling, little is known about deubiquitinating enzymes, which reverse the process of ubiquitination. • Transgenic RNA interference-based cosuppression and the isolation of Atubp12/13 double mutants collectively provides the first report that AtUBP12 and AtUBP13 are functionally redundant and are required for immunity against virulent Pseudomonas syringae pv tomato in Arabidopsis. The Solanaceous AtUBP12 orthologue NtUBP12 was identified. Viral-induced gene silencing and transient gain-of-function assays were employed to establish that the NtUBP12 protein functions as a negative regulator of the Cf-9-triggered hypersensitive response. • Here, we demonstrate that NtUBP12 and AtUBP12 are bona fide deubiquitinating enzymes capable of cleaving lysine-48-linked ubiquitin chains. AtUBP12 and NtUBP12 are functionally interchangeable and their deubiquitinating activity is required to suppress plant cell death. • Overall, our data implicate AtUBP12- and NtUBP12-dependent deubiquitination in the stabilization of common substrates across Solanaceae and Brassicaceae which regulate disease resistance.

RAS-converting enzyme 1-mediated endoproteolysis is required for trafficking of rod phosphodiesterase 6 to photoreceptor outer segments

Prenylation is the posttranslational modification of a carboxyl-terminal cysteine residue of proteins that terminate with a CAAX motif. Following prenylation, the last three amino acids are cleaved off by the endoprotease, RAS-converting enzyme 1 (RCE1), and the prenylcysteine residue is methylated. Although it is clear that prenylation increases membrane affinity of CAAX proteins, less is known about the importance of the postprenylation processing steps. RCE1 function has been studied in a variety of tissues but not in neuronal cells. To approach this issue, we generated mice lacking Rce1 in the retina. Retinal development proceeded normally in the absence of Rce1, but photoreceptor cells failed to respond to light and subsequently degenerated in a rapid fashion. In contrast, the inner nuclear and ganglion cell layers were unaffected. We found that the multimeric rod phosphodiesterase 6 (PDE6), a prenylated protein and RCE1 substrate, was unable to be transported to the outer segments in Rce1-deficient photoreceptor cells. PDE6 present in the inner segment of Rce1-deficient photoreceptor cells was assembled and functional. Synthesis and transport of transducin, and rhodopsin kinase 1 (GRK1), also prenylated substrates of RCE1, was unaffected by Rce1 deficiency. We conclude that RCE1 is essential for the intracellular trafficking of PDE6 and survival of photoreceptor cells.

Peptidoglycan crosslinking relaxation plays an important role in Staphylococcus aureus WalKR-dependent cell viability

The WalKR two-component system is essential for viability of Staphylococcus aureus, a major pathogen. We have shown that WalKR acts as the master controller of peptidoglycan metabolism, yet none of the identified regulon genes explain its requirement for cell viability. Transmission electron micrographs revealed cell wall thickening and aberrant division septa in the absence of WalKR, suggesting its requirement may be linked to its role in coordinating cell wall metabolism and cell division. We therefore tested whether uncoupling autolysin gene expression from WalKR-dependent regulation could compensate for its essential nature. Uncoupled expression of genes encoding lytic transglycosylases or amidases did not restore growth to a WalKR-depleted strain. We identified only two WalKR-regulon genes whose expression restored cell viability in the absence of WalKR: lytM and ssaA. Neither of these two genes are essential under our conditions and a ΔlytM ΔssaA mutant does not present any growth defect. LytM is a glycyl–glycyl endopeptidase, hydrolyzing the pentaglycine interpeptide crossbridge, and SsaA belongs to the CHAP amidase family, members of which such as LysK and LytA have been shown to have D-alanyl-glycyl endopeptidase activity, cleaving between the crossbridge and the stem peptide. Taken together, our results strongly suggest that peptidoglycan crosslinking relaxation through crossbridge hydrolysis plays a crucial role in the essential requirement of the WalKR system for cell viability.

Evidence for OTUD-6B participation in B lymphocytes cell cycle after cytokine stimulation

Deubiquitinating enzymes (DUBs) are important regulators of cell proliferation. Here we identified a functional deubiquitinating enzyme, ovarian tumor domain-containing 6B (OTUD-6B). Mutation of the conserved Cys residue abolished its deubiquitinating activity in vitro. Otud-6b expression was induced with cytokine stimulation in both mouse Ba/F3 cells and primary B lymphocytes followed a rapid decrease. This rapid decrease was partially facilitated by tristetraprolin (TTP) destabilization of Otud-6b mRNA through AU-rich motifs. Enforced expression of OTUD-6B in Ba/F3 cells could block cell proliferation by arresting cells in G1 phase. In addition, cyclin D2 level was down-regulated when OTUD-6B WT was overexpressed. Therefore, down-regulation of Otud-6b expression after prolonged cytokine stimulation may be required for cell proliferation in B lymphocytes.

Identification of distinctive patterns of USP19-mediated growth regulation in normal and malignant cells

We previously reported that the USP19 deubiquitinating enzyme positively regulates proliferation in fibroblasts by stabilizing KPC1, a ubiquitin ligase for p27(Kip1). To explore whether this role of USP19 extends to other cellular systems, we tested the effects of silencing of USP19 in several human prostate and breast models, including carcinoma cell lines. Depletion of USP19 inhibited proliferation in prostate cancer DU145, PC-3 and 22RV1 cells, which was similar to the pattern established in fibroblasts in that it was due to decreased progression from G1 to S phase and associated with a stabilization of the cyclin-dependent kinase inhibitor p27(Kip1). However, in contrast to previous findings in fibroblasts, the stabilization of p27(Kip1) upon USP19 depletion was not associated with changes in the levels of the KPC1 ligase. USP19 could also regulate the growth of immortalized MCF10A breast epithelial cells through a similar mechanism. This regulatory pattern was lost, though, in breast cancer MCF7 and MDA-MB-231 cells and in prostate carcinoma LNCaP cells. Of interest, the transformation of fibroblasts through overexpression of an oncogenic form of Ras disrupted the USP19-mediated regulation of cell growth and of levels of p27(Kip1) and KPC1. Thus, the cell context appears determinant for the ability of USP19 to regulate cell proliferation and p27(Kip1) levels. This may occur through both KPC1 dependent and independent mechanisms. Moreover, a complete loss of USP19 function on cell growth may arise as a result of oncogenic transformation of cells.

Synthetic lethality of rpn11-1 rpn10Δ is linked to altered proteasome assembly and activity

An rpn11-1 temperature-sensitive mutant shows defect in proteolysis, mitochondrial function and proteasome assembly. The Rpn11 protein is a proteasome subunit that deubiquitinates proteolytic substrates. Multiubiquitinated proteins interact with proteasome receptors, such as Rpn10, which intriguingly is also required for promoting proteasome stability. We report here that Rpn10 binds Rpn11, and genetic studies revealed synthetic lethality of an rpn11-1 rpn10Δ double mutant. The carboxy-terminus of Rpn11 is critical for function, as deletion of 7 C-terminal residues prevented suppression of rpn11-1 rpn10Δ. Native gel electrophoresis showed increased levels of the proteasome 20S catalytic particle in rpn11-1 rpn10Δ, and altered assembly. The inviability of rpn11-1 rpn10Δ was suppressed by rpn10(uim), a mutant that can bind the proteasome, but not multiubiquitin chains. rpn10(uim) reduced the levels of free 20S, and increased formation of intact proteasomes. In contrast, rpn10(vwa), which binds multiubiquitin chains but not the proteasome, failed to suppress rpn11-1 rpn10Δ. Moreover, high levels of multiubiquitinated proteins were bound to rpn10(vwa), but were not delivered to the proteasome. Based on these findings, we propose that the lethality of rpn11-1 rpn10Δ results primarily from altered proteasome integrity. It is conceivable that Rpn10/Rpn11 interaction couples proteasome assembly to substrate binding.

The ubiquitin-specific protease 17 is involved in virus-triggered type I IFN signaling

Viral infection initiates a series of signaling cascades that activate the transcription factors nuclear factor kappa B and interferon regulatory factor 3, which collaborate to induce transcription of genes for type I interferons (IFNs) and other cytokines. Here we report that the deubiquitinating enzyme ubiquitin-specific protease 17 (USP17) is required for virus-induced RIG-I- and melanoma differentiation-associated protein-5 (MDA5)-mediated type I IFN signaling. Knockdown of endogenous USP17 inhibited virus-, cytoplasmic poly(I:C)- and poly(dA:dT)-induced activation of the IFN-beta promoter and cellular antiviral responses. We further found that knockdown of USP17 inhibited RIG-I- and MDA5-induced but not downstream activator-induced activation of the IFN-beta promoter, which was correlated with an increase in ubiquitination levels of RIG-I and MDA5. Taken together, our findings suggest that USP17 functions through deubiquitination of RIG-I and MDA5 to regulate virus-induced type I IFN signaling.

Expression and localization of the deubiquitinating enzyme mUBPy in wobbler mouse testis during spermiogenesis

Mouse ubiquitin-specific processing protease (mUBPy) is a deubiquitinating enzyme highly expressed in both brain and testis. In testis, it interacts with the DnaJ protein, MSJ-1; both mUBPy and MSJ-1 are located on the cytoplasmic surface of the developing acrosome and in the centrosomal region during spemiogenesis. Present data show the first appearance in testis of mUbpy mRNA and protein at 10 days post-partum (d.p.p.). In addition, to investigate on a possible role of mUBPy in sperm formation, we took advantage of mutant wr/wr (wobbler) mice characterized by male infertility, which is likely due to the lack of a real, functional acrosome. RT-PCR and Northern blot analyses show that mUbpy is up-regulated in adult wobbler testis. Furthermore, in wild-type testis mUBPy protein is primarily detected by Western blot in the soluble (cytosolic/nuclear) fraction during the first round of spermatogenesis and in the adult. By contrast, mUBPy is primarily detected in membranous/insoluble protein fraction when wobbler phenotype is clearly shown (30 d.p.p.) and in adult wobbler testis. By immunohistochemistry, whereas in wild-type animals mUBPy marks the profile of the acrosomic vesicle in differentiating spermatids, in wobbler mice only a detergent pre-treatment procedure allows to detect mUBPy immunoreactivity, which results in diffuse spotted granules inside the cytoplasm and around the nuclear shape. In conclusion, in wobbler testis expression of mUbpy is up-regulated, while a differential sorting of the protein characterizes wobbler spermatids where acrosome formation is impaired.

A conditional mutation in Arabidopsis thaliana separase induces chromosome non-disjunction, aberrant morphogenesis and cyclin B1;1 stability

The caspase family protease, separase, is required at anaphase onset to cleave the cohesin complex, which joins sister chromatids. However, among eukaryotes, separases have acquired novel functions. Here, we show that Arabidopsis thaliana radially swollen 4 (rsw4), a temperature-sensitive mutant isolated previously on the basis of root swelling, harbors a mutation in At4g22970, the A. thaliana separase. Loss of separase function in rsw4 at the restrictive temperature is indicated by the widespread failure of replicated chromosomes to disjoin. Surprisingly, rsw4 has neither pronounced cell cycle arrest nor anomalous spindle formation, which occur in other eukaryotes upon loss of separase activity. However, rsw4 roots have disorganized cortical microtubules and accumulate the mitosis-specific cyclin, cyclin B1;1, excessive levels of which have been associated with altered microtubules and morphology. Cyclin B1;1 also accumulates in certain backgrounds in response to DNA damage, but we find no evidence for aberrant responses to DNA damage in rsw4. Our characterization of rsw4 leads us to hypothesize that plant separase, in addition to cleaving cohesin, regulates cyclin B1;1, with profound ramifications for morphogenesis.

Emerging roles of deubiquitinases in cancer-associated pathways

Deubiquitinases (DUBs) are emerging as important regulators of many pathways germane to cancer. They may regulate the stability of key oncogenes, exemplified by USP28 stabilisation of c-Myc. Alternatively they can negatively regulate ubiquitin-dependent signalling cascades such as the NF-kappaB activation pathway. We review the current literature that associates DUBs with cancer and discuss their suitability as drug targets of the future.

Towards control of Streptococcus iniae

Streptococcus iniae is an emerging zoonotic pathogen; such infections generally occur through injuries associated with preparing whole fresh fish for cooking. Those infected to date have been of Asian descent, are usually elderly (average age 68 years), and have had >/=1 underlying conditions that may predispose them to infection. Studies of the foundations of growth characteristics of S. iniae and its interactions with piscine host cells have recently been complemented by molecular studies. Advances in molecular biology have allowed research groups to identify numerous virulence factors and to explore their roles in the progression of S. iniae infection. Many of these virulence factors are homologous to those found in the major human pathogen S. pyogenes. An increased understanding of the properties of these factors and their effect on the success of infection is leading to novel approaches to control S. iniae infection; in particular, vaccination programs at fish farms have reduced the reservoir of infection for additional clinical cases.

[Progress of research in osteoarthritis. An overview of the recent knowledge on osteoarthritis: pathogenesis, evaluation and therapies]

Osteoarthritis (OA) is a degenerative joint disease that causes physical disability in many elderly people. Multiple risk factors, including age, gender, genetics, overuse, trauma and obesity, are involved in the onset and progression of OA. Various biological and molecular events that occur in OA joint have been intensively studied and there is an increasing appreciation of the contribution of joint tissues in addition to cartilage. Recent investigations are further deepening the understanding on the importance of matrix-degrading enzymes, chondrocyte hypertrophy and apoptosis, subchondral bone metabolism, cytokines and inflammation. All these serve as therapeutic targets. However, there are currently no clinical interventions proven to restore cartilage and inhibit disease processes. With research efforts for the identification of better therapeutic target together with reliable imaging and biomarkers for evaluation, we expect to have guide for potential disease-modifying agents.

Polo kinase and separase regulate the mitotic licensing of centriole duplication in human cells

It has been proposed that separase-dependent centriole disengagement at anaphase licenses centrosomes for duplication in the next cell cycle. Here we test whether such a mechanism exists in intact human cells. Loss of separase blocked centriole disengagement during mitotic exit and delayed assembly of new centrioles during the following S phase; however, most engagements were eventually dissolved. We identified Polo-like kinase 1 (Plk1) as a parallel activator of centriole disengagement. Timed inhibition of Plk1 mapped its critical period of action to late G2 or early M phase, i.e., prior to securin destruction and separase activation at anaphase onset. Crucially, when cells exited mitosis after downregulation of both separase and Plk1, centriole disengagement failed completely, and subsequent centriole duplication in interphase was also blocked. Our results indicate that Plk1 and separase act at different times during M phase to license centrosome duplication, reminiscent of their roles in removing cohesin from chromosomes.

Ubiquitin Ligases in Malignant Lymphoma

The highly controlled degradation of proteins via the ubiquitin-proteasome pathway represents a key mechanism for cell regulation and homeostasis. Ubiquitin-dependent proteolysis, carried out in large part by the E3 ubiquitin ligases, is a critical mode of post-translational modification that is important in regulation of cell cycle progression, signal transduction, gene transcription, antigen receptor signaling, immune response and cell differentiation. Recent studies demonstrate that increasing numbers of proteins with ubiquitin ligase activity are being characterized. Identification and characterization of their substrates indicate that they regulate the turnover of key cell cycle proteins (p27Kip1, p21Cip1, p57Kip2, cyclin E), tumor suppressor proteins (p53, RB), signaling kinases (Src, Zap70, PI-3 kinase), apoptosis regulators (Bcl-2, Bax, Bik) and transcription factors (Myc, NF-kappaB, E1F1), all of which have been implicated in the pathogenesis of malignant lymphoma. Studies to determine the functional role of ubiquitin ligases in the pathogenesis of malignant lymphoma represent potential areas of investigation.

A herpesvirus encoded deubiquitinase is a novel neuroinvasive determinant

The neuroinvasive property of several alpha-herpesviruses underlies an uncommon infectious process that includes the establishment of life-long latent infections in sensory neurons of the peripheral nervous system. Several herpesvirus proteins are required for replication and dissemination within the nervous system, indicating that exploiting the nervous system as a niche for productive infection requires a specialized set of functions encoded by the virus. Whether initial entry into the nervous system from peripheral tissues also requires specialized viral functions is not known. Here we show that a conserved deubiquitinase domain embedded within a pseudorabies virus structural protein, pUL36, is essential for initial neural invasion, but is subsequently dispensable for transmission within and between neurons of the mammalian nervous system. These findings indicate that the deubiquitinase contributes to neurovirulence by participating in a previously unrecognized initial step in neuroinvasion.

Subsets of herpesviruses, such as herpes simplex virus and pseudorabies virus, are neuroinvasive pathogens. Upon infection, these viruses efficiently target peripheral nervous system tissue and establish a life-long infection for which there is no cure. Very few pathogens are known that invade the nervous system proficiently, and the mechanism by which herpesviruses achieve neuroinvasion is largely unknown. In this study, we demonstrate that a viral protease plays a critical and specific role allowing the virus to cross the threshold of the nervous system, but is dispensable for subsequent replication and encephalitic spread within the brain.

Shugoshin prevents cohesin cleavage by PP2A(Cdc55)-dependent inhibition of separase

Chromosome segregation is triggered by separase, an enzyme that cleaves cohesin, the protein complex that holds sister chromatids together. Separase activation requires the destruction of its inhibitor, securin, which occurs only upon the correct attachment of chromosomes to the spindle. However, other mechanisms restrict separase activity to the appropriate window in the cell cycle because cohesin is cleaved in a timely manner in securin-deficient cells. We investigated the mechanism by which the protector protein Shugoshin counteracts cohesin cleavage in budding yeast. We show that Shugoshin can prevent separase activation independently of securin. Instead, PP2A(Cdc55) is essential for Shugoshin-mediated inhibition of separase. Loss of both securin and Cdc55 leads to premature sister chromatid separation, resulting in aneuploidy. We propose that Cdc55 is a separase inhibitor that acts downstream from Shugoshin under conditions where sister chromatids are not under tension.

Functional analysis of the porcine USP18 and its role during porcine arterivirus replication

Emerging evidence places deubiquitylation at the core of a multitude of regulatory processes, ranging from cell growth to innate immune response and health, such as cancer, degenerative and infectious diseases. Little is known about deubiquitylation in pig and arterivirus infection. This report provides information on the biochemical and functional role of the porcine USP18 during innate immune response to the porcine respiratory and reproductive syndrome virus (PRRSV). We have shown that UBP gene is the ortholog of the murine USP18 (Ubp43) gene and the human ubiquitin specific protease 18 (USP18) gene and encodes a biochemically functional de-ubiquitin enzyme which inhibits signalling pathways that lead to IFN-stimulating response element (ISRE) promotor regulation. Furthermore we have demonstrated that overexpression of the porcine USP18 leads to reduced replication and/or growth of PRRSV. Our data contrast with the conclusion of numerous reports demonstrating that USP18-deficient mice are highly resistant to viral and bacterial infections and to oncogenic transformation by BCR-ABL, and highlight USP18 as a potential target gene that promotes reduced replication of PRRSV.

Mitotic exit in the absence of separase activity

In budding yeast, three interdigitated pathways regulate mitotic exit (ME): mitotic cyclin-cyclin-dependent kinase (Cdk) inactivation; the Cdc14 early anaphase release (FEAR) network, including a nonproteolytic function of separase (Esp1); and the mitotic exit network (MEN) driven by interaction between the spindle pole body and the bud cortex. Here, we evaluate the contributions of these pathways to ME kinetics. Reducing Cdk activity is critical for ME, and the MEN contributes strongly to ME efficiency. Esp1 contributes to ME kinetics mainly through cohesin cleavage: the Esp1 requirement can be largely bypassed if cells are provided Esp1-independent means of separating sister chromatids. In the absence of Esp1 activity, we observed only a minor ME delay consistent with a FEAR defect. Esp1 overexpression drives ME in Cdc20-depleted cells arrested in metaphase. We have found that this activity of overexpressed Esp1 depended on spindle integrity and the MEN. We defined the first quantitative measure for Cdc14 release based on colocalization with the Net1 nucleolar anchor. This measure indicates efficient Cdc14 release upon MEN activation; release driven by Esp1 in the absence of microtubules was inefficient and incapable of driving ME. We also found a novel role for the MEN: activating Cdc14 nuclear export, even in the absence of Net1.