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

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

Mechanism of assembly, activation and lysine selection by the SIN3B histone deacetylase complex

Lysine acetylation in histone tails is a key post-translational modification that controls transcription activation. Histone deacetylase complexes remove histone acetylation, thereby repressing transcription and regulating the transcriptional output of each gene. Although these complexes are drug targets and crucial regulators of organismal physiology, their structure and mechanisms of action are largely unclear. Here, we present the structure of a complete human SIN3B histone deacetylase holo-complex with and without a substrate mimic. Remarkably, SIN3B encircles the deacetylase and contacts its allosteric basic patch thereby stimulating catalysis. A SIN3B loop inserts into the catalytic tunnel, rearranges to accommodate the acetyl-lysine moiety, and stabilises the substrate for specific deacetylation, which is guided by a substrate receptor subunit. Our findings provide a model of specificity for a main transcriptional regulator conserved from yeast to human and a resource of protein-protein interactions for future drug designs.

Long-term use of burosumab for the treatment of tumor-induced osteomalacia

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome caused by tumoral overproduction of FGF-23. Due to local recurrence, we describe the long-term efficacy and safety profile of burosumab, an anti-FGF-23 monoclonal antibody, in a TIO patient after three unsuccessfully surgical attempts.

INTRODUCTION

TIO is a rare paraneoplastic syndrome caused by tumoral overproduction of fibroblast growth factor 23 (FGF23), resulting in hyperphospaturia, hypophosphatemia, and osteomalacia. Surgery is the only definitive treatment, but tumor can locally recur, even after years from primary surgery. Furthermore, some tumors cannot be removed by surgery due to their location.

METHODS

We describe the case of a 54-year-old woman affected by recurrent TIO who, after three unsuccessful surgical attempts of tumor removal, was treated with burosumab, an anti-FGF-23 monoclonal antibody.

RESULTS

The patient was referred to our Bone Unit after experiencing several fractures in different sites, both traumatic and non-traumatic. At the time of first evaluation, at the age of 46, serum-phosphate (SP) was 1.2 mg/dL (reference range (RR) 2.5-4.5), 24-h urinary phosphate was 842 mg (RR 400-1000), and intact-FGF-23 was 117 pg/mL (RR 25-45). Imaging showed a metabolic pre-sacral lesion that firstly underwent to exploratory laparotomy. Then, patient underwent to surgical excision of tumor. After 18 months of well-being, tumor relapsed and even the subsequent surgery was not able to completely remove it. Since 2015, patient was maintained in phosphorus supplements and 1,25(OH)₂vitamin D₃, but SP levels never normalized. In September 2019, she was started on burosumab, initially at the dose of 0.3 mg/kg/month, progressively increased to the current 0.8 mg/kg/month, with great improvement of pain, physical performance, and normalization of SP levels. Burosumab was temporary and cautionary discontinued for COVID-19 pneumonia, with a worsening of SP. After restart of burosumab, biochemistry returned to normal.

CONCLUSIONS

To our knowledge, this is the first European patient affected by TIO treated with burosumab for more than 2 years. Burosumab is a promising therapy in the medical treatment of TIO refractory or not eligible for definitive surgery, with good efficacy and safety profile.

Structure of a nucleosome-bound MuvB transcription factor complex reveals DNA remodelling

Genes encoding the core cell cycle machinery are transcriptionally regulated by the MuvB family of protein complexes in a cell cycle-specific manner. Complexes of MuvB with the transcription factors B-MYB and FOXM1 activate mitotic genes during cell proliferation. The mechanisms of transcriptional regulation by these complexes are still poorly characterised. Here, we combine biochemical analysis and in vitro reconstitution, with structural analysis by cryo-electron microscopy and cross-linking mass spectrometry, to functionally examine these complexes. We find that the MuvB:B-MYB complex binds and remodels nucleosomes, thereby exposing nucleosomal DNA. This remodelling activity is supported by B-MYB which directly binds the remodelled DNA. Given the remodelling activity on the nucleosome, we propose that the MuvB:B-MYB complex functions as a pioneer transcription factor complex. In this work, we rationalise prior biochemical and cellular studies and provide a molecular framework of interactions on a protein complex that is key for cell cycle regulation.

Cell cycle regulation by complex nanomachines

The cell cycle is the essential biological process where one cell replicates its genome and segregates the resulting two copies into the daughter cells during mitosis. Several aspects of this process have fascinated humans since the nineteenth century. Today, the cell cycle is exhaustively investigated because of its profound connections with human diseases and cancer. At the heart of the molecular network controlling the cell cycle, we find the cyclin-dependent kinases (CDKs) acting as an oscillator to impose an orderly and highly regulated progression through the different cell cycle phases. This oscillator integrates both internal and external signals via a multitude of signalling pathways involving posttranslational modifications including phosphorylation, protein ubiquitination and mechanisms of transcriptional regulation. These tasks are specifically performed by multi-subunit complexes, which are intensively studied both biochemically and structurally with the aim to unveil mechanistic insights into their molecular function. The scope of this review is to summarise the structural biology of the cell cycle machinery, with specific focus on the core cell cycle machinery involving the CDK-cyclin oscillator. We highlight the contribution of cryo-electron microscopy, which has started to revolutionise our understanding of the molecular function and dynamics of the key players of the cell cycle.

Molecular mechanisms of APC/C release from spindle assembly checkpoint inhibition by APC/C SUMOylation

The anaphase-promoting complex/cyclosome (APC/C) is an E3 ubiquitin ligase that controls cell cycle transitions. Its regulation by the spindle assembly checkpoint (SAC) is coordinated with the attachment of sister chromatids to the mitotic spindle. APC/C SUMOylation on APC4 ensures timely anaphase onset and chromosome segregation. To understand the structural and functional consequences of APC/C SUMOylation, we reconstituted SUMOylated APC/C for electron cryo-microscopy and biochemical analyses. SUMOylation of the APC/C causes a substantial rearrangement of the WHB domain of APC/C's cullin subunit (APC2WHB). Although APC/CCdc20 SUMOylation results in a modest impact on normal APC/CCdc20 activity, repositioning APC2WHB reduces the affinity of APC/CCdc20 for the mitotic checkpoint complex (MCC), the effector of the SAC. This attenuates MCC-mediated suppression of APC/CCdc20 activity, allowing for more efficient ubiquitination of APC/CCdc20 substrates in the presence of the MCC. Thus, SUMOylation stimulates the reactivation of APC/CCdc20 when the SAC is silenced, contributing to timely anaphase onset.

A unique binding mode of Nek2A to the APC/C allows its ubiquitination during prometaphase

The anaphase-promoting complex (APC/C) is the key E3 ubiquitin ligase which directs mitotic progression and exit by catalysing the sequential ubiquitination of specific substrates. The activity of the APC/C in mitosis is restrained by the spindle assembly checkpoint (SAC), which coordinates chromosome segregation with the assembly of the mitotic spindle. The SAC effector is the mitotic checkpoint complex (MCC), which binds and inhibits the APC/C. It is incompletely understood how the APC/C switches substrate specificity in a cell cycle-specific manner. For instance, it is unclear how in prometaphase, when APC/C activity towards cyclin B and securin is repressed by the MCC, the kinase Nek2A is ubiquitinated. Here, we combine biochemical and structural analysis with functional studies in cells to show that Nek2A is a conformational-specific binder of the APC/C-MCC complex (APC/CMCC ) and that, in contrast to cyclin A, Nek2A can be ubiquitinated efficiently by the APC/C in conjunction with both the E2 enzymes UbcH10 and UbcH5. We propose that these special features of Nek2A allow its prometaphase-specific ubiquitination.

Mechanism for remodelling of the cell cycle checkpoint protein MAD2 by the ATPase TRIP13

The maintenance of genome stability during mitosis is coordinated by the spindle assembly checkpoint (SAC) through its effector the mitotic checkpoint complex (MCC), an inhibitor of the anaphase-promoting complex (APC/C, also known as the cyclosome)1,2. Unattached kinetochores control MCC assembly by catalysing a change in the topology of the β-sheet of MAD2 (an MCC subunit), thereby generating the active closed MAD2 (C-MAD2) conformer3-5. Disassembly of free MCC, which is required for SAC inactivation and chromosome segregation, is an ATP-dependent process driven by the AAA+ ATPase TRIP13. In combination with p31comet, an SAC antagonist6, TRIP13 remodels C-MAD2 into inactive open MAD2 (O-MAD2)7-10. Here, we present a mechanism that explains how TRIP13-p31comet disassembles the MCC. Cryo-electron microscopy structures of the TRIP13-p31comet-C-MAD2-CDC20 complex reveal that p31comet recruits C-MAD2 to a defined site on the TRIP13 hexameric ring, positioning the N terminus of C-MAD2 (MAD2NT) to insert into the axial pore of TRIP13 and distorting the TRIP13 ring to initiate remodelling. Molecular modelling suggests that by gripping MAD2NT within its axial pore, TRIP13 couples sequential ATP-driven translocation of its hexameric ring along MAD2NT to push upwards on, and simultaneously rotate, the globular domains of the p31comet-C-MAD2 complex. This unwinds a region of the αA helix of C-MAD2 that is required to stabilize the C-MAD2 β-sheet, thus destabilizing C-MAD2 in favour of O-MAD2 and dissociating MAD2 from p31comet. Our study provides insights into how specific substrates are recruited to AAA+ ATPases through adaptor proteins and suggests a model of how translocation through the axial pore of AAA+ ATPases is coupled to protein remodelling.

Pathogenesis of chronic rhinosinusitis in patients affected by β-thalassemia major and sickle cell anaemia post allogenic bone marrow transplant

OBJECTIVES

Sickle cell anemia (SCA) and β -thalassemia major are well-recognized beta-globin gene disorders of red blood cells associated to mortality and morbidity included bone morbidities due to ineffective erythropoiesis and bone marrow expansion, which affect every part of the skeleton. While there are an abundance of described disease manifestations of the head and neck, the manner of paranasal sinuses involvement and its relations to β-thalassemia and SCA process was not studied yet. Therefore, the aim of this study was to investigate a possible increased risk of rhinosinusitis and the real pathogenetic mechanism of it, comparing these two hematological diseases using msCT, gold standard for paranasal sinuses evaluation.

METHODS

A retrospective analysis of 90 patients affected by β-thalassemia major or SCA (respectively 59 and 31) underwent allogeneic bone marrow transplantation (BMT), and 44 control subjects was performed. Both patient categories and control group have been subjected to hematological and radiological evaluation using 64-multidetector-row CT scanner without contrast injection.

RESULTS

Statistical analysis reveals that patients of the two study groups exhibit a significantly increased risk of sinusitis in comparison with the normal controls (RR: 3.55 for β-thalassemic pediatric subjects; RR: 3.35 for SCA pediatric subjects). A significant difference (p < 0,5) was found between the β -thalassemic patients on the one side, and SCA and control group on the other side, with regard to the evaluation of the typical anatomic alteration of maxillary sinus: β-thalassemic children had significant increase in the bone thickness of anterior and lateral sinus walls and significant reduction in volume and density compared to SCA patients and control group, with normal conditions of these parameters.

CONCLUSIONS

In these hematological patients, there is an increased incidence of sinonasal infections due their therapy-induced immunosuppression post transplantation. In β-thalassemic patients, furthermore, the specific anatomical variants play an important confounding factor in radiological interpretation of CT images. Therefore, a cranio-facial CT scan evaluation could be a useful tool in the management of upper airway infections after BMT and should be a routinely exams in order to avoid useless surgical or antibiotic approaches.

Visualizing the complex functions and mechanisms of the anaphase promoting complex/cyclosome (APC/C)

The anaphase promoting complex or cyclosome (APC/C) is a large multi-subunit E3 ubiquitin ligase that orchestrates cell cycle progression by mediating the degradation of important cell cycle regulators. During the two decades since its discovery, much has been learnt concerning its role in recognizing and ubiquitinating specific proteins in a cell-cycle-dependent manner, the mechanisms governing substrate specificity, the catalytic process of assembling polyubiquitin chains on its target proteins, and its regulation by phosphorylation and the spindle assembly checkpoint. The past few years have witnessed significant progress in understanding the quantitative mechanisms underlying these varied APC/C functions. This review integrates the overall functions and properties of the APC/C with mechanistic insights gained from recent cryo-electron microscopy (cryo-EM) studies of reconstituted human APC/C complexes.

Molecular basis of APC/C regulation by the spindle assembly checkpoint

In the dividing eukaryotic cell, the spindle assembly checkpoint (SAC) ensures that each daughter cell inherits an identical set of chromosomes. The SAC coordinates the correct attachment of sister chromatid kinetochores to the mitotic spindle with activation of the anaphase-promoting complex (APC/C), the E3 ubiquitin ligase responsible for initiating chromosome separation. In response to unattached kinetochores, the SAC generates the mitotic checkpoint complex (MCC), which inhibits the APC/C and delays chromosome segregation. By cryo-electron microscopy, here we determine the near-atomic resolution structure of a human APC/C–MCC complex (APC/C(MCC)). Degron-like sequences of the MCC subunit BubR1 block degron recognition sites on Cdc20, the APC/C coactivator subunit responsible for substrate interactions. BubR1 also obstructs binding of the initiating E2 enzyme UbcH10 to repress APC/C ubiquitination activity. Conformational variability of the complex enables UbcH10 association, and structural analysis shows how the Cdc20 subunit intrinsic to the MCC (Cdc20(MCC)) is ubiquitinated, a process that results in APC/C reactivation when the SAC is silenced.

Molecular mechanism of APC/C activation by mitotic phosphorylation

In eukaryotes, the anaphase-promoting complex (APC/C, also known as the cyclosome) regulates the ubiquitin-dependent proteolysis of specific cell-cycle proteins to coordinate chromosome segregation in mitosis and entry into the G1 phase. The catalytic activity of the APC/C and its ability to specify the destruction of particular proteins at different phases of the cell cycle are controlled by its interaction with two structurally related coactivator subunits, Cdc20 and Cdh1. Coactivators recognize substrate degrons, and enhance the affinity of the APC/C for its cognate E2 (refs 4-6). During mitosis, cyclin-dependent kinase (Cdk) and polo-like kinase (Plk) control Cdc20- and Cdh1-mediated activation of the APC/C. Hyperphosphorylation of APC/C subunits, notably Apc1 and Apc3, is required for Cdc20 to activate the APC/C, whereas phosphorylation of Cdh1 prevents its association with the APC/C. Since both coactivators associate with the APC/C through their common C-box and Ile-Arg tail motifs, the mechanism underlying this differential regulation is unclear, as is the role of specific APC/C phosphorylation sites. Here, using cryo-electron microscopy and biochemical analysis, we define the molecular basis of how phosphorylation of human APC/C allows for its control by Cdc20. An auto-inhibitory segment of Apc1 acts as a molecular switch that in apo unphosphorylated APC/C interacts with the C-box binding site and obstructs engagement of Cdc20. Phosphorylation of the auto-inhibitory segment displaces it from the C-box-binding site. Efficient phosphorylation of the auto-inhibitory segment, and thus relief of auto-inhibition, requires the recruitment of Cdk-cyclin in complex with a Cdk regulatory subunit (Cks) to a hyperphosphorylated loop of Apc3. We also find that the small-molecule inhibitor, tosyl-l-arginine methyl ester, preferentially suppresses APC/C(Cdc20) rather than APC/C(Cdh1), and interacts with the binding sites of both the C-box and Ile-Arg tail motifs. Our results reveal the mechanism for the regulation of mitotic APC/C by phosphorylation and provide a rationale for the development of selective inhibitors of this state.

Detection of Epstein-Barr virus in leucoreduced blood products

This study examined the prevalence of three human herpesviruses (HHV), namely HHV-4 (Epstein-Barr virus/EBV), HHV-6b and HHV-7 in leucoreduced blood products obtained from the Sainte-Justine Hospital blood bank. A total of 100 specimens, including 34 red blood cell concentrates, 33 platelet bags and 33 plasma units, were collected and screened by a sensitive PCR assay using virus-specific primers. Positive units were then retested by quantitative PCR. Of the 100 specimens, one platelet unit tested positive for EBV.

Structural basis for targeting the chromatin repressor Sfmbt to Polycomb response elements

Polycomb group (PcG) complexes repress developmental regulator genes by modifying their chromatin. However, how PcG proteins assemble into complexes and are recruited to their target genes is poorly understood. Here, Alfieri et al. report the crystal structure of the core of the PcG complex PhoRC, which contains the DNA-binding protein Pho and corepressor Sfmbt. The authors show that tethering of Sfmbt by Pho to Polycomb response elements is essential for Polycomb repression of developmental regulator genes in Drosophila. This study thus reveals the molecular basis for PcG protein complex assembly at specific genomic sites.

Polycomb group (PcG) protein complexes repress developmental regulator genes by modifying their chromatin. How different PcG proteins assemble into complexes and are recruited to their target genes is poorly understood. Here, we report the crystal structure of the core of the Drosophila PcG protein complex Pleiohomeotic (Pho)-repressive complex (PhoRC), which contains the Polycomb response element (PRE)-binding protein Pho and Sfmbt. The spacer region of Pho, separated from the DNA-binding domain by a long flexible linker, forms a tight complex with the four malignant brain tumor (4MBT) domain of Sfmbt. The highly conserved spacer region of the human Pho ortholog YY1 binds three of the four human 4MBT domain proteins in an analogous manner but with lower affinity. Comparison of the Drosophila Pho:Sfmbt and human YY1:MBTD1 complex structures provides a molecular explanation for the lower affinity of YY1 for human 4MBT domain proteins. Structure-guided mutations that disrupt the interaction between Pho and Sfmbt abolish formation of a ternary Sfmbt:Pho:DNA complex in vitro and repression of developmental regulator genes in Drosophila. PRE tethering of Sfmbt by Pho is therefore essential for Polycomb repression in Drosophila. Our results support a model where DNA tethering of Sfmbt by Pho and multivalent interactions of Sfmbt with histone modifications and other PcG proteins create a hub for PcG protein complex assembly at PREs.

Cnn1 inhibits the interactions between the KMN complexes of the yeast kinetochore

Kinetochores attach the replicated chromosomes to the mitotic spindle and orchestrate their transmission to the daughter cells. Kinetochore-spindle binding and chromosome segregation are mediated by the multi-copy KNL1(Spc105), MIS12(Mtw1) and NDC80(Ndc80) complexes that form the so-called KMN network. KMN-spindle attachment is regulated by the Aurora B(Ipl1) and MPS1(Mps1) kinases. It is unclear whether other mechanisms exist that support KMN activity during the cell cycle. Using budding yeast, we show that kinetochore protein Cnn1 localizes to the base of the Ndc80 complex and promotes a functionally competent configuration of the KMN network. Cnn1 regulates KMN activity in a spatiotemporal manner by inhibiting the interaction between its complexes. Cnn1 activity peaks in anaphase and is driven by the Cdc28, Mps1 and Ipl1 kinases.

Inhibition of IκB kinase by thalidomide increases hepatitis C virus RNA replication

Hepatic fibrosis is an integral element in the progression of chronic liver disease. Elevated hepatic interleukin (IL)-8 is an important contributor to fibrosis in patients chronically infected with the hepatitis C virus (HCV). Thalidomide has been used to reduce liver inflammation and fibrosis in HCV-infected patients, but its impact on HCV replication remains unclear. This study examined the effect of thalidomide on HCV replication in vitro. Results revealed that while thalidomide reduced IL-8 and nuclear factor kappa B (NF-κB) activity by 95% and 46% in Huh-7 cells, increasing concentrations of thalidomide correlated with a linear rise in HCV replication (17-fold at 200 μm). The NF-κB inhibitors, wedelolactone and NF-κB activation inhibitor-1, which mimic the actions of thalidomide by preventing phosphorylation and activation of IκB kinase (IKK) and hence block NF-κB activity, increased HCV RNA by 18- and 19-fold, respectively. During in vitro HCV replication in Huh-7 cells, we observed a 30% increase in IKKα protein and 55% decrease in NF-κB(p65)/RelA protein relative to cellular β-actin. Ectopic expression of IKKα to enhance the inactive form of IKK in cells undergoing virus replication led to a 13-fold increase in HCV RNA. Conversely, enhanced expression of NF-κB(p65)/RelA in infected cells resulted in a 17-fold reduction in HCV RNA. In conclusion, HCV RNA replication was significantly augmented by the inhibition of IKK activation and subsequent NF-κB signalling, whereas a restoration of NF-κB activity by the addition of NF-κB/RelA markedly reduced HCV replication. This study lends added importance to the role of the NF-κB signalling pathway in controlling HCV replication.

Chromatin-modifying complex component Nurf55/p55 associates with histones H3 and H4 and polycomb repressive complex 2 subunit Su(z)12 through partially overlapping binding sites

Drosophila Nurf55 is a component of different chromatin-modifying complexes, including the PRC2 (Polycomb repressive complex 2). Based on the 1.75-Å crystal structure of Nurf55 bound to histone H4 helix 1, we analyzed interactions of Nurf55 (Nurf55 or p55 in fly and RbAp48/46 in human) with the N-terminal tail of histone H3, the first helix of histone H4, and an N-terminal fragment of the PRC2 subunit Su(z)12 using isothermal calorimetry and pulldown experiments. Site-directed mutagenesis identified the binding site of histone H3 at the top of the Nurf55 WD40 propeller. Unmodified or K9me3- or K27me3-containing H3 peptides were bound with similar affinities, whereas the affinity for K4me3-containing H3 peptides was reduced. Helix 1 of histone H4 and Su(z)12 bound to the edge of the β-propeller using overlapping binding sites. Our results show similarities in the recognition of histone H4 and Su(z)12 and identify Nurf55 as a versatile interactor that simultaneously contacts multiple partners.

Recognizing and remodeling the nucleosome

The X-ray structure of the nucleosome core particle (NCP) has been a major milestone in the structural biology of chromatin. Since, our understanding how NCPs interact with multiple partners has been extending from single chromatin-binding domains recognizing post-translational modifications (PTMs) in histone tails towards the recognition of higher-order chromatin structure by multi-subunit chromatin remodeling complexes. The current review summarizes recent progress in the structural biology of nucleosome-recognition from chromatin-binding domains to multi-protein remodeling complexes.

Cleavage of intracellular hepatitis C RNA in the virus core protein coding region by deoxyribozymes

Hepatitis C virus (HCV) infection represents an important global health problem. Current antiviral therapeutics for HCV have proven inadequate in stemming the disease process. A novel therapeutic strategy involves the use of deoxyribozymes, also known as DNA enzymes or DNAzymes. These catalytic DNA molecules, designed to target and cleave specific RNA sequences, have shown promise in in vitro experimental models for various diseases and may serve as an alternative or adjunct to current HCV drug therapy. We designed and tested several deoxyribozymes that can bind and cleave highly conserved RNA sequences encoding the HCV core protein in in vitro systems. One of these deoxyribozymes reduced the level of our HCV RNA target by 32% and 48% after 24 h of cell exposure when tested in human hepatoma and epithelial cell lines, respectively. As this deoxyribozyme showed significant cleavage activity against HCV core protein target RNA in human cells, it may have potential as a therapeutic candidate for clinical trial in HCV infected patients.

The Epstein-Barr virus and post-transplant lymphoproliferative disease: interplay of immunosuppression, EBV, and the immune system in disease pathogenesis

Transplant patients are at particular risk for developing post-transplant lymphoproliferative disease (PTLD) following administration of immunosuppressive therapy. In many cases the PTLD lesions express Epstein-Barr virus (EBV) latent and lytic genes as well as elevated levels of host cytokines. An outline of the potential contributions of EBV, host cytokines and T cells, and the immunosuppressive cyclosporine A, tacrolimus, and anti-CD3 antibody in the mechanism and pathogenesis of this disease is presented and discussed.

Effect of spironolactone and its metabolites on contractile property of isolated rat aorta rings

Spironolactone and its active metabolites canrenone and potassium canrenoate are normally used as antihypertensive drugs. Although they are classified as antagonists of aldosterone, their mechanism of action cannot be ascribed solely to the regulation of ion transport in the distal tubule of nephrons. Here we have evaluated the effects of spironolactone, canrenone, and potassium canrenoate on contractile properties of isolated rat aorta rings. Spironolactone (1-300 microM), canrenone (1-300 microM), and potassium canrenoate (0.01-10 mM), in a concentration-dependent manner, relaxed rat aorta rings precontracted with phenylephrine (1 microM) or KCl (40 mM). These relaxant effects were not affected by prior treatment with either aldosterone (100 microM), glibenclamide (10 microM), or tetraethylammonium (10 mM), excluding the possibility that these drugs can be involved in either the nongenomic effect of aldosterone or on activation of potassium channels. Spironolactone and canrenone at concentrations of 30 and 100 microM, but not at 10 microM, and potassium canrenoate at concentrations of 0.3 and 1 mM, but not at 0.1 mM, significantly inhibited the phenylephrine (0.001-3 microM) concentration-response curve. Conversely, all tested concentrations of spironolactone (10, 30, and 100 microM), canrenone (10, 30, and 100 microM), and potassium canrenoate (0.1, 0.3, and 1 mM) significantly inhibited the concentration-response curve induced by cumulative concentrations of KCI (10-80 mM). Because both phenylephrine- and KCl-induced contractions imply an intracellular Ca2+ influx, we suggest that these drugs could act through an inhibition of voltage-dependent Ca2+ channels.

Activation of transcription factors NF-kappaB and NF-IL-6 by human immunodeficiency virus type 1 protein R (Vpr) induces interleukin-8 expression

Human immunodeficiency virus (HIV)-positive individuals express elevated levels of interleukin-8 (IL-8), which is believed to be responsible for some of the clinical manifestations occurring during AIDS. We report here that virion-derived HIV type 1 (HIV-1) protein R (Vpr) increased IL-8 expression in primary T cells and macrophages, as well as in the T-cell line Jurkat, the monocytic cell line U937, and the epithelial cell line A549. Vpr appeared to increase IL-8 expression and IL-8 promoter activity by activating transcription factors NF-kappaB and NF-IL-6. Elevated Vpr was also shown to increase transcription of the NF-kappaB and NF-IL-6 enhancer-containing viral promoters for HIV, cytomegalovirus, and simian virus 40, as well as increase the expression of IL-6 and IL-10 in primary macrophages and in A549 cells, tumor necrosis factor alpha expression in primary T cells, and IL-6 and gamma interferon expression in U937 cells. These results suggest a new role for Vpr in the pathogenesis of HIV infection, namely, the activation of transcription factors NF-IL-6 and NF-kappaB.

Epstein-Barr virus induces Fas (CD95) in T cells and Fas ligand in B cells leading to T-cell apoptosis

Epstein-Barr virus (EBV) acute infectious mononucleosis (AIM) is characterized by transient immunosuppression in vivo and increased T-cell apoptosis after ex vivo culture of AIM peripheral blood mononuclear cells. We undertook experiments to test whether EBV or purified virion envelope glycoprotein gp350 could contribute to Fas-mediated T-cell apoptosis. Our in vitro results indicate that EBV increased Fas expression in CD4(+) T cells and Fas ligand (FasL) expression in B cells and macrophages. Purified gp350 was also shown to significantly increase CD95 expression in CD4(+) T cells. When T-cell CD95 was cross-linked, EBV-stimulated T cells underwent apoptosis. The induction of T-cell CD95 by EBV followed by CD95 cross-linking with anti-CD95 monoclonal antibody resulted in a loss in the number of T cells responding to the T-cell mitogens, anti-CD3 antibody, and interleukin-2. These results indicate that, in addition to serving as a principal ligand for the attachment of virus to target cells, gp350 may also act as an immunomodulatory molecule that promotes T-cell apoptosis.

Natural history of Epstein-Barr virus infection in a prospective pediatric cohort born to human immunodeficiency virus-infected mothers

To determine whether Epstein-Barr virus (EBV) constitutes a contributing factor in AIDS and, conversely, whether the human immunodeficiency virus (HIV) alters the course of primary EBV infection in a pediatric population, 62 children born to HIV-infected mothers and prospectively followed were evaluated. EBV infection was documented by EBV-specific serology and polymerase chain reaction and by clinical history. HIV infection status was determined according to the Centers for Disease Control and Prevention pediatric classification system. Demographics from HIV-infected and HIV-uninfected children were comparable. The data suggest that HIV-infected children may acquire primary EBV infection earlier in life. The incidence of accompanying splenomegaly or hepatomegaly (or both) around the time of EBV seroconversion was higher among HIV-infected children than among HIV-uninfected children. In contrast, HIV disease progression and HIV-1 RNA load did not seem to be influenced by primary EBV infection.

Anti-interleukin-10 antibodies in patients with chronic active Epstein-Barr virus infection

The Epstein-Barr virus (EBV) genome encodes a protein in its BamHI C restriction fragment rightward open-reading frame-1 (designated BCRF1 or viral interleukin-10 [vIL-10]) that shares protein homology and biologic properties with human IL-10. Several EBV disorders are characterized by prolonged active EBV infection. Because continued EBV replication could allow for increased vIL-10, ELISA and immunoprecipitation were used to determine whether vIL-10 expression during chronic active EBV infection resulted in vIL-10 and IL-10 antibodies. IL-10 antibodies were assayed in patients diagnosed with chronic and acute infectious mononucleosis (CIM, AIM), nasopharyngeal carcinoma (NPC), and EBV-associated lymphoproliferative disease (LPD), as well as from healthy organ transplant patients and EBV-negative or EBV-positive persons. Whether anti-IL-10 antibodies could inhibit IL-10 biologic activity was determined. vIL-10 antibodies were found in CIM, NPC, and LPD patients and antibodies reactive to IL-10 were found in CIM patients. One CIM patient had IL-10 antibodies that neutralized IL-10 bioactivity in vitro.

Antibody and antibody-dependent cellular cytotoxicity responses against the BamHI A rightward open-reading frame-1 protein of Epstein-Barr virus (EBV) in EBV-associated disorders

Antibody-dependent cellular cytotoxicity (ADCC) is an important antiviral effector mechanism. ADCC to the protein encoded by the Epstein-Barr virus (EBV) BamHI A rightward open-reading frame-1 (BARF1) was studied by transducing Raji-tk- cells with the BARF1 gene using a retroviral expression vector. The transduced Raji cells expressed BARF1 on the cell surface, as determined by flow cytometry. Sera from chronic and acute infectious mononucleosis and nasopharyngeal carcinoma patients were found to contain antibodies that react with the BARF1 protein. When BARF1-expressing Raji cells were used as targets for ADCC, sera from several nasopharyngeal carcinoma patients demonstrated significant ADCC reactivity, whereas sera from healthy EBV-seronegative and -seropositive persons lacked such reactivity. BARF1-specific ADCC activity could be competitively inhibited with recombinant BARF1 protein. The level of anti-BARF1 antibody activity in sera of patients with EBV-associated diseases suggests that the BARF1 protein may serve as a target on EBV-infected cells for ADCC.

Antibody responses to two Epstein-Barr virus (EBV) nuclear antigens (EBNA-1 and EBNA-2) during EBV primary infection in children born to mothers infected with human immunodeficiency virus

A variety of antibody response patterns to the latent Epstein-Barr nuclear antigen (EBNA) family have been described in different groups of subjects infected with Epstein-Barr virus (EBV). The purpose of this study was to characterize the immune response to two EBNA proteins, EBNA-1 and EBNA-2, in a population of children who were born to mothers infected with HIV and who underwent EBV seroconversion. Serial serum specimens from 33 children (nine were infected with HIV, and 24 were not infected) were evaluated for the presence of antibodies to EBNA-1 and EBNA-2 by anticomplement immunofluorescence. All the EBNA serology profiles observed for children in our study who were not infected with HIV were consistent with those described for immunocompetent hosts with acute EBV infection, i.e., development of antibodies to EBNA-1, often preceded by the appearance of a humoral immune response to EBNA-2. In contrast, following EBV primary infection in HIV-infected children, antibodies to EBNA-2 arose after antibodies to EBNA-1 and tended to persist. Further studies are needed to investigate the role of EBNA-2 serology as a prognostic marker in HIV-infected children.

Diagnosis of cytomegalovirus (CMV) infection in pediatric transplant patients by the antigenemia, shell vial, and conventional culture assays performed on blood: correlation with CMV disease

BACKGROUND

Human cytomegalovirus (CMV) is a significant cause of morbidity and mortality in transplant recipients. Isolation of CMV from blood leukocytes (CMV viremia) is considered predictive of CMV disease in transplant recipients. Therefore, investigation of methods for the rapid detection of CMV in the blood is important for diagnosis and management of these patients.

OBJECTIVE

To compare three techniques for the diagnosis and monitoring of CMV infection in a pediatric transplant population through the quantitative detection of CMV in peripheral blood leukocytes (PBL).

METHODS

Serial blood specimens were obtained for most patients. After separation of the PBL from each specimen, aliquots of the PBL were used for direct detection of CMV antigenemia by immunoperoxidase staining of acetone-fixed cells (CMV-vue kit, INCSTAR), and by immunofluorescence staining of formaldehyde-fixed cells (Complete 1C3 kit, Biosoft Argene). PBL were also inoculated into conventional cell culture tubes and shell vials. Patients' medical records were reviewed to ascertain the clinical significance of the results.

RESULTS

A total of 154 specimens obtained from 38 pediatric transplant recipients were evaluated. CMV was detected in 16 specimens obtained from eight patients: 11 specimens were found positive with the CMV-vue kit, 10 with the Complete 1C3 kit, four by conventional culture, and one by the shell vial assay. Seven of the eight patients with CMV-positive PBL had clinical signs and other laboratory evidence of active CMV infection. In general, a high-level antigenemia was demonstrated in the presence of clinical disease, but there were exceptions.

CONCLUSIONS

The two antigenemia kits were more sensitive than conventional culture and the shell vial assay for the detection of CMV in the blood of pediatric transplant patients. Our results suggest that CMV antigenemia is a sensitive and specific rapid method for the diagnosis and monitoring of CMV infection in our patient population.

Interactions involving cyclosporine A, interleukin-6, and Epstein-Barr virus lead to the promotion of B-cell lymphoproliferative disease

Post-transplant patients undergoing prolonged Cyclosporine A (CsA) immunosuppressive therapy were reported to have an increased incidence of Epstein-Barr virus (EBV)-associated lymphoproliferative disorders. EBV-infected B cells cultured with CsA demonstrated increased EBV B-cell out-growth as compared to those cultured without CsA. Peripheral blood mononuclear cells (PBMC), following infection with EBV and CsA treatment, demonstrated increased IL-6 activity in the culture supernatant. The induction of IL-6 appeared to differ within the various lymphocyte populations. In monocytes and B cells, IL-6 expression was preferentially induced by EBV, and initiated by the binding of the two major virion glycoproteins, gp350 and gp220, to CD21, or a CD21-like receptor. Expression of IL-6 in T cells appeared to be due mainly to CsA. B cells also expressed IL-6 following EBV exposure, but not following CsA treatment. EBY-immortalized B-cell lines cultured with CsA exhibited both an increased number of cells expressing viral lytic-cycle antigens and increased amounts of lytic-cycle proteins. IL-6, which was induced by CsA in PBMC, was also capable of inducing the lytic viral cycle in several EBV-immortalized cells. When IL-6 was expressed, it was shown to act as an autocrine growth factor for B cells and to inhibit the immune system allowing for the promotion of B-cell tumors by impairing lymphokine-activated killer cells. Thus CsA treatment, in promoting both increased numbers of lytic EBV B cells and expression of the EBV paracrine growth factor, IL-6, within the microenvironment of EBV B:T cell and EBV B:monocyte interactions, may lead to increased EBV B-cell immortalization and ultimately result in the promotion of B-cell lymphomas in immunosuppressed patients.

Epstein-Barr virus transmission from a blood donor to an organ transplant recipient with recovery of the same virus strain from the recipient's blood and oropharynx

A previous study (Savoie et al, Blood 83:2715, 1994) identified eight transplant patients who acquired Epstein-Barr virus (EBV) infection during the peritransplant period. Three of these patients subsequently developed B-cell lymphoproliferative disease within 4 months of transplantation. Among these, there was a 16-year-old liver transplant patient who was negative for EBV at the time of transplant and who received an EBV-negative organ. After transplant, this patient was transfused with 9 U of packed red blood cells. Eight of the donors were EBV-positive and one was EBV-negative. We succeeded in obtaining spontaneous lymphoblastoid cell lines (LCLs) from the blood of three of these donors, one of whom also yielded a cord-blood line established with his throat-wash EBV. Blood from a fourth donor did not yield an LCL, but his throat washing did have transforming activity when inoculated onto cord-blood leukocytes. We initially could establish spontaneous LCLs only from the recipient's blood. However, a throat-wash sample taken 11 weeks later did show transforming activity. The recipient was shown to have acquired the EBV infection from one of eight EBV-seropositive blood donors. Analysis of fragment length polymorphisms after polymerase chain reaction amplification of the EBV BamHI-K fragment was used to establish strain identity. Western blot analysis for existence of size polymorphisms in three classes of Epstein-Barr nuclear antigens (EBNA-1, EBNA-2, and EBNA-3) confirmed the DNA results. It is noteworthy that the blood donor responsible for transmitting his EBV strain to the recipient had experienced clinical infectious mononucleosis 15 months before donating blood. Our results may, thus, indicate a requirement for leukodepletion of blood destined for immunosuppressed EBV-negative patients. Finally, blood donors with a recent history of infectious mononucleosis should probably be identified so that their blood is not given to EBV-negative transplant patients.

Induction of interleukin-6 after stimulation of human B-cell CD21 by Epstein-Barr virus glycoproteins gp350 and gp220

The cellular receptor for Epstein-Barr virus (EBV) is the type 2 complement receptor, CD21. At initial infection, EBV virion glycoproteins gp350 and gp220 bind to CD21. We report here that the cross-linking of CD21 by gp350/220 results in increased amounts of interleukin 6 (IL-6) RNA and IL-6 protein. This effect could be blocked with anti-gp350/220 and anti-CD21 monoclonal antibodies. Induction of IL-6 in B cells by EBV could be mimicked by treatment with the protein kinase C (PKC) activator phorbol 12,13-dibutyrate but not with the calcium ionophore ionomycin. IL-6 induction by EBV was inhibited with the PKC-specific inhibitor bisindolylmaleimide or the protein tyrosine kinase inhibitors methyl 2,5-dihydroxycinnamate and herbimycin A, indicating that the induction of IL-6 following CD21 cross-linking is mediated through PKC- and protein tyrosine kinase-dependent pathways.

A solitary plasmacytoma of donor origin arising 14 years after kidney allotransplantation

Allotransplantation of solid organs transfers passenger leucocytes which may give rise to a state of persistent microchimaerism. In this report we describe the case of a patient who developed a solitary plasmacytoma in a transplanted kidney more than 10 years after allografting. The diagnosis was established on the basis of the presence of a monoclonal IgG kappa peak in the serum, and light chain proteinuria, the plasmacytoid features of tumour cells including cell surface expression of IgG, kappa light chains, CD20, CD38 and CD56, the absence of lytic bone lesions and a normal bone marrow biopsy, and the disappearance of the monoclonal IgG peak after graft nephrectomy. A donor origin of the tumour was established by HLA DNA typing of tumour, tumour-free kidney tissue, and peripheral blood leucocytes, respectively.

Direct correlation between the load of Epstein-Barr virus-infected lymphocytes in the peripheral blood of pediatric transplant patients and risk of lymphoproliferative disease

The Epstein-Barr virus (EBV) is known to cause posttransplant lymphoproliferative disease (PTLD) in immunosuppressed transplant patients. The results of this pilot study showed that all EBV- patients pretransplant experienced primary EBV infection within the first 3 months after transplant surgery. Virtually all of these patients had a higher burden of EBV-infected cells in their peripheral blood (PB) after infection by EBV than did the EBV+ pretransplant group when tested at the same intervals posttransplant. Salivary EBV titers also increased in most patients, but the difference between the two groups was statistically significant only at 12 months, whereupon EBV+ patients showed higher titers compared with EBV- (alpha < 0.053). Also, polymerase chain reaction amplification followed by Southern blotting was performed to detect EBV sequences in PB mononuclear cells. This technique allowed confirmation of the blood culture results and constituted a faster alternative compared with the culture assay. The highest increase in the number of EBV-infected lymphocytes at 3 months posttransplant obtained from PB was seen in a patient who developed fatal PTLD and in another with protracted infectious mononucleosis. Thus, the number of EBV-infected cells in PB was found to correlate positively with risk of development of PTLD at 3 months posttransplant in our group of pediatric transplant patients. This study showed that quantitative lymphocyte culture of PB was an accurate index of immunosuppression and a reliable method for assessing the risk of PTLD development.

Radioimmunoprecipitation in the diagnosis of chronic active Epstein-Barr virus infection

Chronic active Epstein-Barr virus (EBV) infection occurs sporadically in a small fraction of individuals infected with EBV. A clear definition of the disease and an unambiguous diagnostic test are still lacking. In an attempt to identify a serologic marker to facilitate the diagnosis, immunoblot and radioimmunoprecipitation assay (RIPA) were compared with standard immunofluorescence on 39 available sera. Results by RIPA revealed that antibodies to a 120 kDa viral protein correlated with the presence of chronic active EBV infection; these antibodies were not detected in sera from other EBV-seropositive individuals, with the exception of one of two patients with ataxia telangiectasia. Also, RIPA was the most sensitive technique for detecting EBV antibodies in sera weakly or doubtfully positive for antibody to EB viral capsid antigen by indirect immunofluorescence. All these sera had antibodies to the 150 kDa protein, also known as p160, the major viral capsid antigen.

Effect of mycophenolic acid on Epstein-Barr virus infection of human B lymphocytes

The effect of mycophenolic acid (MPA) on the growth of Epstein-Barr virus (EBV)-transformed B cells and on EBV lytic-cycle gene expression was investigated. MPA inhibited the proliferation of newly infected or established EBV-transformed B-cell lines but was not able to block cell growth transformation or the viral lytic cycle. These results suggest that MPA might reduce transformed-cell proliferation in transplant patients and possibly decrease the risk of development of EBV-related lymphoproliferative disorders.

Early events in Epstein-Barr virus infection of human B lymphocytes

The sequence of Epstein-Barr virus (EBV) and B lymphocyte changes in the 3 days following acute infection was analyzed. By 16 hr the average infected lymphocyte had 1 EBV episome. Nuclear protein-2 (EBNA-2) and EBNA-leader protein (-LP) were detected by 12 hr, and by 32 hr were at the levels of stable EBV infection in lymphoblastoid cell lines (LCLs). At 12 hr, all EBNA-LP and EBNA-2 RNAs were initiated from the Pw promoter. By 36 hr a significant EBNA-LP and EBNA-2 RNA fraction initiated from the upstream Pc promoter. Throughout acute infection, a similar fraction of potentially bicistronic EBNA-LP mRNAs had first exon splices which would result in EBNA-LP translation. By 36 hr c-myc RNA was transiently induced, and CD21 and CD23 RNAs were beginning to increase. This coincided with low-level EBNA-1, EBNA-3A, B, and C, and latent membrane protein-1 (LMP-1) expression. By 46 hr, EBNA-1, the EBNA-3s, and LMP-1 were near the levels ordinarily found in LCLs and a substantial fraction of lymphocytes were in S phase. These results are compatible with a key role for EBNA-2 (or EBNA-LP) in regulating virus and cell gene expression. High-level expression of the EBV-encoded small RNAs, EBERs, was delayed beyond 36 hr and may, therefore, be activated by other virus or cell genes. A 65-kDa virion protein persisted in acutely infected cells. This protein could be a mediator of virus or cell gene expression.

Induction of germ-line and mature C epsilon transcripts in human B cells stimulated with rIL-4 and EBV

EBV and rIL-4 induce T cell-independent IgE production by normal human B cells. We demonstrate here that EBV and IL-4 induced the synthesis of IgE by surface IgE-negative B cell precursors isolated by cell sorting. This result suggests that the induction of IgE by EBV and IL-4 results not merely from the expansion of a precommitted surface IgE-positive B cell population but more likely from IL-4-directed switching to IgE. At the molecular level, IL-4 and EBV induced the appearance of 2.0- and of 1.8-kilobase (kb) RNA bands, both of which hybridized with an 0.88-kb HinfI fragment spanning part of the C epsilon 1 exon and the entire C epsilon 2 exon. The 1.8-kb band but not the 2.0-kb band also hybridized with a cloned genomic 0.7-kb SmaI fragment located approximately 2 kb upstream of C epsilon. Thus, EBV and IL-4 induced germline (1.8-kb) as well as mature (2.0-kb) C epsilon transcripts. IL-4 by itself induced germ-line C epsilon transcripts but not mature C epsilon transcripts in purified normal B cells. IL-4 failed to induce IgE synthesis in established EBV B cell lines and failed to induce 2.0-kb mature C epsilon transcripts but induced 1.8-kb germ-line C epsilon transcripts. These data show that IL-4 is sufficient for the induction of C epsilon germ-line transcription. In contrast, the transcription of mature epsilon mRNA requires an additional activating signal, provided by infection with EBV. Established EBV transformation results in a dissociation between germ-line C epsilon transcription and the ability to undergo IgE switching in response to IL-4.

Induction of germ-line and mature C epsilon transcripts in human B cells stimulated with rIL-4 and EBV

EBV and rIL-4 induce T cell-independent IgE production by normal human B cells. We demonstrate here that EBV and IL-4 induced the synthesis of IgE by surface IgE-negative B cell precursors isolated by cell sorting. This result suggests that the induction of IgE by EBV and IL-4 results not merely from the expansion of a precommitted surface IgE-positive B cell population but more likely from IL-4-directed switching to IgE. At the molecular level, IL-4 and EBV induced the appearance of 2.0- and of 1.8-kilobase (kb) RNA bands, both of which hybridized with an 0.88-kb HinfI fragment spanning part of the C epsilon 1 exon and the entire C epsilon 2 exon. The 1.8-kb band but not the 2.0-kb band also hybridized with a cloned genomic 0.7-kb SmaI fragment located approximately 2 kb upstream of C epsilon. Thus, EBV and IL-4 induced germline (1.8-kb) as well as mature (2.0-kb) C epsilon transcripts. IL-4 by itself induced germ-line C epsilon transcripts but not mature C epsilon transcripts in purified normal B cells. IL-4 failed to induce IgE synthesis in established EBV B cell lines and failed to induce 2.0-kb mature C epsilon transcripts but induced 1.8-kb germ-line C epsilon transcripts. These data show that IL-4 is sufficient for the induction of C epsilon germ-line transcription. In contrast, the transcription of mature epsilon mRNA requires an additional activating signal, provided by infection with EBV. Established EBV transformation results in a dissociation between germ-line C epsilon transcription and the ability to undergo IgE switching in response to IL-4.