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Find video protocols related to scientific articles indexed in Pubmed.
Septins Arrange F-Actin-Containing Fibers on the Chlamydia trachomatis Inclusion and Are Required for Normal Release of the Inclusion by Extrusion.
MBio
PUBLISHED: 10-09-2014
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Chlamydia trachomatis is an obligate intracellular human pathogen that grows inside a membranous, cytosolic vacuole termed an inclusion. Septins are a group of 13 GTP-binding proteins that assemble into oligomeric complexes and that can form higher-order filaments. We report here that the septins SEPT2, -9, -11, and probably -7 form fibrillar structures around the chlamydial inclusion. Colocalization studies suggest that these septins combine with F actin into fibers that encase the inclusion. Targeting the expression of individual septins by RNA interference (RNAi) prevented the formation of septin fibers as well as the recruitment of actin to the inclusion. At the end of the developmental cycle of C. trachomatis, newly formed, infectious elementary bodies are released, and this release occurs at least in part through the organized extrusion of intact inclusions. RNAi against SEPT9 or against the combination of SEPT2/7/9 substantially reduced the number of extrusions from a culture of infected HeLa cells. The data suggest that a higher-order structure of four septins is involved in the recruitment or stabilization of the actin coat around the chlamydial inclusion and that this actin recruitment by septins is instrumental for the coordinated egress of C. trachomatis from human cells. The organization of F actin around parasite-containing vacuoles may be a broader response mechanism of mammalian cells to the infection by intracellular, vacuole-dwelling pathogens.
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ER-stress and apoptosis: molecular mechanisms and potential relevance in infection.
Microbes Infect.
PUBLISHED: 08-27-2014
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During ER-stress, one of the responses a cell can choose is apoptosis. Apoptosis generally is a cell's preferred response when other control mechanisms are overwhelmed. We now have a reasonably clear molecular picture what is happening once the apoptotic apparatus has been started. Unclear however are the majority of the upstream pathways that connect other signalling to apoptosis. During ER-stress, confirmed apoptosis-regulating targets are pro- and anti-apoptotic proteins of the Bcl-2-family, whose concerted action induces apoptosis. I will here discuss how mitochondrial apoptosis is triggered, how this is linked to the ER-stress response and in what way this may be relevant during microbial infections.
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MYC and EGR1 synergize to trigger tumor cell death by controlling NOXA and BIM transcription upon treatment with the proteasome inhibitor bortezomib.
Nucleic Acids Res.
PUBLISHED: 08-21-2014
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The c-MYC (MYC afterward) oncogene is well known for driving numerous oncogenic programs. However, MYC can also induce apoptosis and this function of MYC warrants further clarification. We report here that a clinically relevant proteasome inhibitor significantly increases MYC protein levels and that endogenous MYC is necessary for the induction of apoptosis. This kind of MYC-induced cell death is mediated by enhanced expression of the pro-apoptotic BCL2 family members NOXA and BIM. Quantitative promoter-scanning chromatin immunoprecipitations (qChIP) further revealed binding of MYC to the promoters of NOXA and BIM upon proteasome inhibition, correlating with increased transcription. Both promoters are further characterized by the presence of tri-methylated lysine 4 of histone H3, marking active chromatin. We provide evidence that in our apoptosis models cell death occurs independently of p53 or ARF. Furthermore, we demonstrate that recruitment of MYC to the NOXA as well as to the BIM gene promoters depends on MYC's interaction with the zinc finger transcription factor EGR1 and an EGR1-binding site in both promoters. Our study uncovers a novel molecular mechanism by showing that the functional cooperation of MYC with EGR1 is required for bortezomib-induced cell death. This observation may be important for novel therapeutic strategies engaging the inherent pro-death function of MYC.
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IL-15 regulates Bcl-2 family members Bim and Mcl-1 through JAK/STAT and PI3K/AKT pathways in T cells.
Eur. J. Immunol.
PUBLISHED: 04-03-2014
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Maintenance of T cells is determined by their survival capacity, which is regulated by Bcl-2 proteins. Cytokines signalling through the common gamma chains such as IL-2, IL-7 and IL-15 are important for T-cell survival but how these cytokines determine the expression of Bcl-2-family proteins is not clear. We report signalling events of cytokines that regulate expression of two key Bcl-2 proteins, pro-apoptotic Bim and anti-apoptotic Mcl-1, in resting C57BL/6 mouse T cells. IL-2, IL-7 and IL-15 inhibited apoptosis but paradoxically induced the expression of Bim, countered by concomitant induction of Mcl-1. Bim induction by IL-15 was found at the mRNA and protein levels and depended on both JAK/STAT and PI3K signals. A new STAT5-binding site was identified in the Bim promoter, which was occupied by STAT5 upon IL-15 stimulation. Although it also depended on JAK/STAT- and PI3K signalling, Mcl-1 regulation was independent of Mcl-1 mRNA levels and of regulation of protein stability, suggesting translational regulation. Concurrent CD3 signals inhibited some of the IL-7 effect but not the IL-15 effect on Bcl-2 proteins. The data suggest that cytokines induce Bim and prime T cells for apoptosis, but also inhibit apoptosis by stabilising Mcl-1. Later downregulation of short-lived Mcl-1 may induce efficient, Bim-dependent apoptosis.
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Neutrophil granulocytes recruited upon translocation of intestinal bacteria enhance graft-versus-host disease via tissue damage.
Nat. Med.
PUBLISHED: 03-03-2014
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Acute graft-versus-host disease (GVHD) considerably limits wider usage of allogeneic hematopoietic cell transplantation (allo-HCT). Antigen-presenting cells and T cells are populations customarily associated with GVHD pathogenesis. Of note, neutrophils are the largest human white blood cell population. The cells cleave chemokines and produce reactive oxygen species, thereby promoting T cell activation. Therefore, during an allogeneic immune response, neutrophils could amplify tissue damage caused by conditioning regimens. We analyzed neutrophil infiltration of the mouse ileum after allo-HCT by in vivo myeloperoxidase imaging and found that infiltration levels were dependent on the local microbial flora and were not detectable under germ-free conditions. Physical or genetic depletion of neutrophils reduced GVHD-related mortality. The contribution of neutrophils to GVHD severity required reactive oxygen species (ROS) because selective Cybb (encoding cytochrome b-245, beta polypeptide, also known as NOX2) deficiency in neutrophils impairing ROS production led to lower levels of tissue damage, GVHD-related mortality and effector phenotype T cells. Enhanced survival of Bcl-xL transgenic neutrophils increased GVHD severity. In contrast, when we transferred neutrophils lacking Toll-like receptor-2 (TLR2), TLR3, TLR4, TLR7 and TLR9, which are normally less strongly activated by translocating bacteria, into wild-type C57BL/6 mice, GVHD severity was reduced. In humans, severity of intestinal GVHD strongly correlated with levels of neutrophils present in GVHD lesions. This study describes a new potential role for neutrophils in the pathogenesis of GVHD in both mice and humans.
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The chlamydial protease CPAF: important or not, important for what?
Microbes Infect.
PUBLISHED: 02-24-2014
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The protease CPAF is only found in Chlamydiales and in at least most bacteria that share with Chlamydia the biphasic life-style in a cytosolic inclusion. CPAF is intriguing: it appears to be secreted from the inclusion across the inclusion membrane into the cytosol. A bacterial protease ravaging in the cytosol of a human cell may cause a plethora of effects. Curiously, very few are known. The current discussion is bogged down by a focus on experimental artifact, while proposed functions of CPAF remain speculative. I here make the attempt to summarize what we know about CPAF.
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Golgi fragmentation and sphingomyelin transport to Chlamydia trachomatis during penicillin-induced persistence do not depend on the cytosolic presence of the chlamydial protease CPAF.
PLoS ONE
PUBLISHED: 01-01-2014
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Chlamydia grows inside a cytosolic vacuole (the inclusion) that is supplied with nutrients by the host through vesicular and non-vesicular transport. It is unclear in many respects how Chlamydia organizes this transport. One model posits that the Chlamydia-induced fragmentation of the Golgi-apparatus is required for normal transport processes to the inclusion and for chlamydial development, and the chlamydial protease CPAF has been controversially implicated in Golgi-fragmentation. We here use a model of penicillin-induced persistence of infection with Chlamydia trachomatis to test this link. Under penicillin-treatment the inclusion grew in size for the first 24 h but after that growth was severely reduced. Penicillin did not reduce the number of infected cells with fragmented Golgi-apparatus, and normal Golgi-fragmentation was found in a CPAF-deficient mutant. Surprisingly, sphingomyelin transport into the inclusion and into the bacteria, as measured by fluorescence accumulation upon addition of labelled ceramide, was not reduced during penicillin-treatment. Thus, both Golgi-fragmentation and transport of sphingomyelin to C. trachomatis still occurred in this model of persistence. The portion of cells in which CPAF was detected in the cytosol, either by immunofluorescence or by immune-electron microscopy, was drastically reduced in cells cultured in the presence of penicillin. These data argue against an essential role of cytosolic CPAF for Golgi-fragmentation or for sphingomyelin transport in chlamydial infection.
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Leukocyte attraction by CCL20 and its receptor CCR6 in humans and mice with pneumococcal meningitis.
PLoS ONE
PUBLISHED: 01-01-2014
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We previously identified CCL20 as an early chemokine in the cerebrospinal fluid (CSF) of patients with pneumococcal meningitis but its functional relevance was unknown. Here we studied the role of CCL20 and its receptor CCR6 in pneumococcal meningitis. In a prospective nationwide study, CCL20 levels were significantly elevated in the CSF of patients with pneumococcal meningitis and correlated with CSF leukocyte counts. CCR6-deficient mice with pneumococcal meningitis and WT mice with pneumococcal meningitis treated with anti-CCL20 antibodies both had reduced CSF white blood cell counts. The reduction in CSF pleocytosis was also accompanied by an increase in brain bacterial titers. Additional in vitro experiments showed direct chemoattractant activity of CCL20 for granulocytes. In summary, our results identify the CCL20-CCR6 axis as an essential component of the innate immune defense against pneumococcal meningitis, controlling granulocyte recruitment.
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Inhibitor of apoptosis proteins (IAPs) are required for effective T cell expansion/survival during anti-viral immunity in mice.
Blood
PUBLISHED: 12-12-2013
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Inhibitor of apoptosis proteins (IAPs) were originally described to regulate apoptosis by direct binding to caspases. More recently, IAPs have been identified as important modulators of canonical and non-canonical NF-?B signalling via their ubiquitin-E3 ligase activity. IAPs are therefore not only gatekeepers of cell death but probably also involved in the regulation of inflammation as well as innate and adaptive immunity. Here we analysed the role of IAPs in T cell immunity during lymphocytic choriomeningitis virus (LCMV) infection by pharmacological targeting with an IAP-antagonist/Smac-mimetic. Expansion of virus-specific CD8 T cells was drastically reduced in LCMV-infected mice exposed to IAP-antagonist. Accordingly, virus control was substantially impaired, indicated by high virus titres in the spleen and spread of LCMV to peripheral organs. The profound negative effect of IAP-antagonists on T cell immunity was partially linked to TNF-mediated cell death of activated T cells and required inhibition of XIAP as well as cIAP1. Thus, IAPs play an important role in T cell expansion and survival in the context of a highly inflammatory environment such as a virus infection, indicating that IAP-antagonists may interfere with immune responses.
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Purulent pericarditis and pneumonia caused by Streptococcus equi subspecies zooepidemicus.
J. Med. Microbiol.
PUBLISHED: 11-15-2013
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Purulent pericarditis is a life threatening disease that usually manifests following bacteraemia or through spreading from an intrathoracic focus. Only a few cases of this disease have been reported with Lancefield group C streptococci as etiologic agents, and the primary focus in these infections remains unknown. We report a case of purulent pericarditis with septic and cardiogenic shock, caused by Streptococcus equi subspecies zooepidemicus (group C) in a 51-year-old patient. The pathogen was possibly contracted through contact with horses. Most likely, it initially caused pneumonia before spreading to the pericardium, either directly or via the blood stream. A combined therapeutic approach, consisting of antibiotic therapy and repeated pericardial drainage, was necessary to ensure a clinical cure. After discharge, long-term follow-up for development of constrictive pericarditis is considered mandatory.
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Mouse Noxa uses only the C-terminal BH3-domain to inactivate Mcl-1.
Apoptosis
PUBLISHED: 06-05-2013
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Noxa is a member of the pro-apoptotic BH3-only group of Bcl-2 proteins that is known to bind specifically to anti-apoptotic Mcl-1 and A1, antagonizing their function. Mcl-1 has been reported to have a short half-life, and Noxa up-regulation accelerates Mcl-1 degradation by the proteasome. Unlike human Noxa, mouse Noxa has two BH3-domains, which both have affinity for Mcl-1. We here investigate two aspects of the molecular function of Noxa, namely the requirements for the two BH3-domains in mouse Noxa and the role of Noxa in Mcl-1-degradation. We found that only the C-terminal BH3-domain of mouse Noxa is active in neutralizing Mcl-1. This was the result of the targeting of Noxa to the outer mitochondrial membrane through its C-terminal alpha-helix, which allowed Mcl-1-neutralization only when the BH3-domain was immediately N-terminal of the membrane anchor. However, the N-terminal BH3-domain enhanced interaction with Mcl-1 and A1. The Noxa-dependent degradation of Mcl-1 was independent of the kinase GSK3 and the deubiquitinase Usp9x in mouse embryonic fibroblasts. These data show that Noxa is targeted to the mitochondrial membrane where it neutralises Mcl-1 via its C-terminal BH3-domain and suggest that Noxa is co-degraded with Noxa, in a way independent of ubiquitin-modifying enzymes described for Mcl-1.
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Is there, and should there be, apoptosis in bacteria?
Microbes Infect.
PUBLISHED: 03-14-2013
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Apoptosis is a well-studied form of cell death in metazoans, where it has a clear role during the life of the (multicellular) animal. Some situations of cell death in unicellular eukaryotes (protozoa and yeast) have also been referred to as apoptosis. In recent years apoptosis has further been identified in bacteria several times. As a bacterial response to external stimuli, apoptosis could be important not only for the bacteria but also to the host. Here I will discuss why I believe that the term apoptosis should be avoided for these situations in bacteria, no matter how interesting the molecular background or how biologically important the underlying mechanism may be.
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Comparison of (1->3)-?-D-glucan, mannan/anti-mannan antibodies, and Cand-Tec Candida antigen as serum biomarkers for candidemia.
J. Clin. Microbiol.
PUBLISHED: 01-30-2013
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We conducted a case-control study using the Fungitell assay, the novel Platelia Candida Antigen (Ag) Plus and Candida Antibody (Ab) Plus assays, and the Cand-Tec latex agglutination test to evaluate the usefulness of (1?3)-?-D-glucan (BDG), mannan antigen with/without anti-mannan antibody, and Cand-Tec Candida antigen measurement for the diagnosis of candidemia. A total of 56 patients fulfilled the inclusion criteria and were enrolled. One hundred patients with bacteremia and 100 patients with sterile blood cultures served as negative controls. In the candidemia group, median (1?3)-?-D-glucan, mannan antigen, and anti-mannan antibody levels were 427 pg/ml, 190 pg/ml, and 18.6 antibody units (AU)/ml, respectively. All three parameters were significantly elevated in patients with candidemia. The sensitivity and specificity were, respectively, 87.5% and 85.5% for (1?3)-?-D-glucan, 58.9% and 97.5% for mannan antigen, 62.5% and 65.0% for anti-mannan antibody, 89.3% and 63.0% for mannan antigen plus anti-mannan antibody, 89.3% and 85.0% for BDG plus mannan antigen, and 13.0% and 93.9% for Cand-Tec Candida antigen. The low mannan antigen sensitivity was in part caused by Candida parapsilosis and Candida guilliermondii fungemias, which were not detected by the Platelia Candida Ag Plus assay. When the cutoff was lowered from 125 pg/ml to 50 pg/ml, mannan antigen sensitivity increased to 69.6% without severely affecting the specificity (93.5%). Contrary to recently published data, superficial candidiasis was not associated with elevated mannan antigen levels, not even after the cutoff was lowered. Combining procalcitonin (PCT) with (1?3)-?-D-glucan to increase specificity provided a limited advantage because the benefit of the combination did not outweigh the loss of sensitivity. Our results demonstrate that the Cand-Tec Candida antigen and the mannan antigen plus anti-mannan antibody measurements have unacceptably low sensitivity or specificity. Of the four tests compared, (1?3)-?-D-glucan and mannan antigen are the superior biomarkers, depending on whether a sensitivity-driven or specificity-driven approach is used.
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Roscovitine-induced Apoptosis in Neutrophils and Neutrophil Progenitors Is Regulated by the Bcl-2-Family Members Bim, Puma, Noxa and Mcl-1.
PLoS ONE
PUBLISHED: 01-01-2013
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Neutrophil granulocyte (neutrophil) apoptosis plays a key role in determining inflammation in infectious and non-infectious settings. Recent work has shown that inhibitors of cyclin-dependent kinases (cdk) such as roscovitine can potently induce neutrophil apoptosis and reduce inflammation. Using a conditional Hoxb8-expression system we tested the participation of Bcl-2-family proteins to roscovitine-induced apoptosis in mouse neutrophils and in neutrophil progenitor cells. Bcl-2 strongly protected against roscovitine-induced apoptosis in neutrophils. The isolated loss of either Bim or noxa provided significant, partial protection while protection through combined loss of Bim and noxa or Bim and Puma was only slightly greater than this individual loss. The only substantial change in protein levels observed was the loss of Mcl-1, which was not transcriptional and was inhibited by proteasome blockade. In progenitor cells there was no protection by the loss of Bim alone but substantial protection by the loss of both Bim and Puma; surprisingly, strongest protection was seen by the isolated loss of noxa. The pattern of protein expression and Mcl-1-regulation in progenitor cells was very similar to the one observed in differentiated neutrophils. In addition, roscovitine strongly inhibited proliferation in progenitor cells, associated with an accumulation of cells in G2/M-phase.
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Allosteric modulation of caspases.
Pharmacol. Ther.
PUBLISHED: 06-15-2011
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Caspases are proteolytic enzymes mainly involved in the induction and execution phases of apoptosis. This type of programmed cell death is an essential regulatory process required to maintain the integrity and homeostasis of multicellular organisms. Inappropriate apoptosis is attributed a key role in many human diseases, including neurodegenerative disorders, ischemic damage, autoimmune diseases and cancer. Allosteric modulation of the function of a protein occurs when the regulatory trigger, such as the binding of a small effector or inhibitor molecule, takes place some distance from the proteins active site. In recent years, several caspases have been identified that possess allosteric sites and binding of small molecule to these sites resulted in the modulation of enzyme activities. Regulation of caspase activity by small molecule allosteric modulators is believed to be of great therapeutic importance. In this review we give brief highlights on recent developments in identifying and characterizing natural and synthetic allosteric inhibitors as well as activators of caspases and discuss their potential in drug discovery and protein engineering.
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Indoleamine 2,3-dioxygenase-expressing myeloid dendritic cells and macrophages in infectious and noninfectious cutaneous granulomas.
J. Am. Acad. Dermatol.
PUBLISHED: 04-17-2011
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The enzyme indoleamine 2,3-dioxygenase (IDO) degrades the essential amino acid tryptophan, and this degradation is an immunosuppressive mechanism that is mainly used by antigen-presenting cells. IDO-expressing dendritic cells and macrophages have previously been identified as components of lymph node granulomas after Listeria monocytogenes infection. In this study we undertook an analysis of IDO expression in granulomas of infectious and noninfectious origin in the human skin.
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Induction of Noxa-mediated apoptosis by modified vaccinia virus Ankara depends on viral recognition by cytosolic helicases, leading to IRF-3/IFN-?-dependent induction of pro-apoptotic Noxa.
PLoS Pathog.
PUBLISHED: 04-11-2011
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Viral infection is a stimulus for apoptosis, and in order to sustain viral replication many viruses are known to carry genes encoding apoptosis inhibitors. F1L, encoded by the orthopoxvirus modified vaccinia virus Ankara (MVA) has a Bcl-2-like structure. An MVA mutant lacking F1L (MVA?F1L) induces apoptosis, indicating that MVA infection activates and F1L functions to inhibit the apoptotic pathway. In this study we investigated the events leading to apoptosis upon infection by MVA?F1L. Apoptosis largely proceeded through the pro-apoptotic Bcl-2 family protein Bak with some contribution from Bax. Of the family of pro-apoptotic BH3-only proteins, only the loss of Noxa provided substantial protection, while the loss of Bim had a minor effect. In mice, MVA preferentially infected macrophages and DCs in vivo. In both cell types wt MVA induced apoptosis albeit more weakly than MVA?F1L. The loss of Noxa had a significant protective effect in macrophages, DC and primary lymphocytes, and the combined loss of Bim and Noxa provided strong protection. Noxa protein was induced during infection, and the induction of Noxa protein and apoptosis induction required transcription factor IRF3 and type I interferon signalling. We further observed that helicases RIG-I and MDA5 and their signalling adapter MAVS contribute to Noxa induction and apoptosis in response to MVA infection. RNA isolated from MVA-infected cells induced Noxa expression and apoptosis when transfected in the absence of viral infection. We thus here describe a pathway leading from the detection of viral RNA during MVA infection by the cytosolic helicase-pathway, to the up-regulation of Noxa and apoptosis via IRF3 and type I IFN signalling.
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Targeting of a chlamydial protease impedes intracellular bacterial growth.
PLoS Pathog.
PUBLISHED: 04-04-2011
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Chlamydiae are obligate intracellular bacteria that propagate in a cytosolic vacuole. Recent work has shown that growth of Chlamydia induces the fragmentation of the Golgi apparatus (GA) into ministacks, which facilitates the acquisition of host lipids into the growing inclusion. GA fragmentation results from infection-associated cleavage of the integral GA protein, golgin-84. Golgin-84-cleavage, GA fragmentation and growth of Chlamydia trachomatis can be blocked by the peptide inhibitor WEHD-fmk. Here we identify the bacterial protease chlamydial protease-like activity factor (CPAF) as the factor mediating cleavage of golgin-84 and as the target of WEHD-fmk-inhibition. WEHD-fmk blocked cleavage of golgin-84 as well as cleavage of known CPAF targets during infection with C. trachomatis and C. pneumoniae. The same effect was seen when active CPAF was expressed in non-infected cells and in a cell-free system. Ectopic expression of active CPAF in non-infected cells was sufficient for GA fragmentation. GA fragmentation required the small GTPases Rab6 and Rab11 downstream of CPAF-activity. These results define CPAF as the first protein that is essential for replication of Chlamydia. We suggest that this role makes CPAF a potential anti-infective therapeutic target.
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cIAPs block Ripoptosome formation, a RIP1/caspase-8 containing intracellular cell death complex differentially regulated by cFLIP isoforms.
Mol. Cell
PUBLISHED: 03-20-2011
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The intracellular regulation of cell death pathways by cIAPs has been enigmatic. Here we show that loss of cIAPs promotes the spontaneous formation of an intracellular platform that activates either apoptosis or necroptosis. This 2 MDa intracellular complex that we designate "Ripoptosome" is necessary but not sufficient for cell death. It contains RIP1, FADD, caspase-8, caspase-10, and caspase inhibitor cFLIP isoforms. cFLIP(L) prevents Ripoptosome formation, whereas, intriguingly, cFLIP(S) promotes Ripoptosome assembly. When cIAPs are absent, caspase activity is the "rheostat" that is controlled by cFLIP isoforms in the Ripoptosome and decides if cell death occurs by RIP3-dependent necroptosis or caspase-dependent apoptosis. RIP1 is the core component of the complex. As exemplified by our studies for TLR3 activation, our data argue that the Ripoptosome critically influences the outcome of membrane-bound receptor triggering. The differential quality of cell death mediated by the Ripoptosome may cause important pathophysiological consequences during inflammatory responses.
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Solid-phase synthesis of disubstituted N-acylureas from resin-bound ureas and acyl chlorides.
ACS Comb Sci
PUBLISHED: 11-10-2010
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Acylureas (ureides) are valued for their important biological activities. Whereas cyclic acylureas have frequently been the object of solid-phase chemistry, only few reports have focused on the solid-supported preparation of acyclic representatives. We have prepared different types of acylureas on Rink amide resin in three or four steps. The products are either N-acylated (9, 18), N-acylated-N-alkylated (10, 19), or N-acylated-N-alkylated (22). Characteristic NMR parameters of isomeric acylureas 10, 19, and 22 are discussed.
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Cleavage of the NF-?B family protein p65/RelA by the chlamydial protease-like activity factor (CPAF) impairs proinflammatory signaling in cells infected with Chlamydiae.
J. Biol. Chem.
PUBLISHED: 11-01-2010
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Chlamydiae are obligate intracellular bacteria that frequently cause human disease. Chlamydiae replicate in a membranous vacuole in the cytoplasm termed inclusion but have the ability to transport proteins into the host cell cytosol. Chlamydial replication is associated with numerous changes of host cell functions, and these changes are often linked to proteolytic events. It has been shown earlier that the member of the NF-?B family of inflammation-associated transcription factors, p65/RelA, is cleaved during chlamydial infection, and a chlamydial protease has been implicated. We here provide evidence that the chlamydial protease chlamydial protease-like activity factor (CPAF) is responsible for degradation of p65/RelA during infection. This degradation was seen in human and in mouse cells infected with either Chlamydia trachomatis or Chlamydia pneumoniae where it correlated with the expression of CPAF and CPAF activity. Isolated expression of active C. trachomatis or C. pneumoniae CPAF in human or mouse cells yielded a p65 fragment of indistinguishable size from the one generated during infection. Expression of active CPAF in human cells caused a mild reduction in I?B? phosphorylation but a strong reduction in NF-?B reporter activity in response to interleukin-1?. Infection with C. trachomatis likewise reduced this responsiveness. IL-1?-dependent secretion of IL-8 was further reduced by CPAF expression. Secretion of CPAF is, thus, a mechanism that reduces host cell sensitivity to a proinflammatory stimulus, which may facilitate bacterial growth in vivo.
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CXCL16 contributes to neutrophil recruitment to cerebrospinal fluid in pneumococcal meningitis.
J. Infect. Dis.
PUBLISHED: 09-30-2010
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In this study, we analyzed the expression and function of CXCL16 in pneumococcal meningitis. CXCL16 was found to be up‐regulated in RAW264.7 macrophages (but not in neutrophils and endothelial cells) upon pneumococcal stimulation, in the cerebrospinal fluid of patients, and in the brains as well as the cerebrospinal fluid of mice with pneumococcal meningitis. CXCL16 up‐regulation in vivo was dependent on Toll‐like receptor (TLR) 2/TLR4 and MyD88 signaling. Neutralization of CXCL16 in animals before intracisternal pneumococcal infection (using anti‐CXCL16 antibodies) resulted in reduced cerebrospinal fluid pleocytosis. In vitro, murine neutrophils expressed the CXCL16 receptor CXCR6 and showed dose‐dependant migration toward a CXCL16 gradient. Thus, this study implicates CXCL16 as an additional neutrophil chemoattractant in cerebrospinal fluid in early pneumococcal meningitis.
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Direct formation of ring-fused 1,3-thiazine-2,4-dithiones from aromatic o-amino carboxylic acids: observation of a carbon disulfide mediated thionation.
Org. Lett.
PUBLISHED: 07-30-2010
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A facile synthesis of 2H-3,1-benzothiazine-2,4(1H)-dithiones (trithioisatoic anhydrides) or 2H-naphtho[2,3-d][1,3]thiazine-2,4(1H)-dithione solely from anthranilic acids or 3-amino-2-naphthoic acid and carbon disulfide, performed at room temperature in 1,4-dioxane in the presence of Et(3)N, is reported. Corresponding 2-alkylsulfanyl derivatives were obtained in one-pot reactions under the same conditions after addition of alkyl halides. The mechanism of the thiazine cyclization was investigated using (13)C-labeled carbon disulfide to reveal that carbon disulfide was incorporated into the heterocycle and additionally acted as a thionation reagent.
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Raman microspectroscopy reveals long-term extracellular activity of Chlamydiae.
Mol. Microbiol.
PUBLISHED: 06-01-2010
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The phylum Chlamydiae consists exclusively of obligate intracellular bacteria. Some of them are formidable pathogens of humans, while others occur as symbionts of amoebae. These genetically intractable bacteria possess a developmental cycle consisting of replicative reticulate bodies and infectious elementary bodies, which are believed to be physiologically inactive. Confocal Raman microspectroscopy was applied to differentiate between reticulate bodies and elementary bodies of Protochlamydia amoebophila and to demonstrate in situ the labelling of this amoeba symbiont after addition of isotope-labelled phenylalanine. Unexpectedly, uptake of this amino acid was also observed for both developmental stages for up to 3 weeks, if incubated extracellularly with labelled phenylalanine, and P. amoebophila remained infective during this period. Furthermore, P. amoebophila energizes its membrane and performs protein synthesis outside of its host. Importantly, amino acid uptake and protein synthesis after extended extracellular incubation could also be demonstrated for the human pathogen Chlamydia trachomatis, which synthesizes stress-related proteins under these conditions as shown by 2-D gel electrophoresis and MALDI-TOF/TOF mass spectrometry. These findings change our perception of chlamydial biology and reveal that host-free analyses possess a previously not recognized potential for direct experimental access to these elusive microorganisms.
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Parenchymal cells critically curtail cytotoxic T-cell responses by inducing Bim-mediated apoptosis.
Eur. J. Immunol.
PUBLISHED: 02-04-2010
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To develop cytolytic effector functions, CD8(+) T lymphocytes need to recognize specific Ag/MHC class I complexes in the context of costimuli on Ag-presenting DC. Thereafter they differentiate into effector and memory CTL able to confer protection against pathogen infection. Using transgenic mice with DC-selective MHC class I expression and DC-specific versus ubiquitous vaccination regimen, we found that DC are sufficient to prime CTL responses. However, Ag recognition on parenchymal non-professional APC negatively affected CD8(+) T-cell responses in mice by inducing expression of the pro-apoptotic bcl2-family member bim in CTL. This unexpected induction of apoptosis in the early phase of effector CTL accumulation lead to suboptimal clonal burst size and diminished long-term memory. Thus, our data demonstrate that effector CTL differentiation and apoptosis are regulated independently. Moreover, Ag distribution on cells other than DC critically reduces CTL responses.
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Chemotherapeutic drugs sensitize human renal cell carcinoma cells to ABT-737 by a mechanism involving the Noxa-dependent inactivation of Mcl-1 or A1.
Mol. Cancer
PUBLISHED: 01-12-2010
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Human renal cell carcinoma (RCC) is very resistant to chemotherapy. ABT-737 is a novel inhibitor of anti-apoptotic proteins of the Bcl-2 family that has shown promise in various preclinical tumour models.
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Toxoplasma gondii infection confers resistance against BimS-induced apoptosis by preventing the activation and mitochondrial targeting of pro-apoptotic Bax.
J. Cell. Sci.
PUBLISHED: 09-08-2009
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In order to accomplish their life style, intracellular pathogens, including the apicomplexan Toxoplasma gondii, subvert the innate apoptotic response of infected host cells. However, the precise mechanisms of parasite interference with the mitochondrial apoptotic pathway remain unknown. Here, we used the conditional expression of the BH3-only protein Bim(S) to pinpoint the interaction of T. gondii with the intrinsic pathway of apoptosis. Infection of epithelial cells with T. gondii dose-dependently abrogated Bim(S)-triggered release of cytochrome c from host-cell mitochondria into the cytosol, induction of activity of caspases 3, 7 and 9, and chromatin condensation. Furthermore, inhibition of apoptosis in parasite-infected lymphocytes counteracted death of Toxoplasma-infected host cells. Although total cellular levels and mitochondrial targeting of Bim(S) was not altered by the infection, the activation of pro-apoptotic effector proteins Bax and Bak was strongly impaired. Inhibition of Bax and Bak activation by T. gondii was seen with regard to their conformational changes, the cytosol-to-mitochondria targeting and the oligomerization of Bax but not their cellular protein levels. Blockade of Bax and Bak activation was not mediated by the upregulation of anti-apoptotic Bcl-2-like proteins following infection. Further, the BH3-mimetic ABT-737 failed to overcome the Toxoplasma-imposed inhibition of Bim(S)-triggered apoptosis. These results indicate that T. gondii targets activation of pro-apoptotic Bax and Bak to inhibit the apoptogenic function of mitochondria and to increase host-cell viability.
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Analogs of a 4-aminothieno[2,3-d]pyrimidine lead (QB13) as modulators of P-glycoprotein substrate specificity.
Bioorg. Med. Chem. Lett.
PUBLISHED: 08-05-2009
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P-glycoprotein (P-gp) is an important factor in the development of multidrug resistance (MDR) in cancer cells. In literature reports, a thieno[2,3-d]pyrimidine (QB13) was described as P-gp modulator and opposed effects on the cell accumulation of distinct P-gp substrates were postulated. On the basis of this lead structure, a series of 2-alkylthio-4-aminothieno[2,3-d]pyrimidines was prepared and tested in a daunorubicin accumulation assay. Modulation of substrate specificity was shown for selected compounds in cytotoxicity (MTT) assays.
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Inflammasome-dependent caspase-1 activation in cervical epithelial cells stimulates growth of the intracellular pathogen Chlamydia trachomatis.
J. Biol. Chem.
PUBLISHED: 07-31-2009
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Inflammasomes have been extensively characterized in monocytes and macrophages, but not in epithelial cells, which are the preferred host cells for many pathogens. Here we show that cervical epithelial cells express a functional inflammasome. Infection of the cells by Chlamydia trachomatis leads to activation of caspase-1, through a process requiring the NOD-like receptor family member NLRP3 and the inflammasome adaptor protein ASC. Secretion of newly synthesized virulence proteins from the chlamydial vacuole through a type III secretion apparatus results in efflux of K(+) through glibenclamide-sensitive K(+) channels, which in turn stimulates production of reactive oxygen species. Elevated levels of reactive oxygen species are responsible for NLRP3-dependent caspase-1 activation in the infected cells. In monocytes and macrophages, caspase-1 is involved in processing and secretion of pro-inflammatory cytokines such as interleukin-1beta. However, in epithelial cells, which are not known to secrete large quantities of interleukin-1beta, caspase-1 has been shown previously to enhance lipid metabolism. Here we show that, in cervical epithelial cells, caspase-1 activation is required for optimal growth of the intracellular chlamydiae.
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Aromatic 2-(thio)ureidocarboxylic acids as a new family of modulators of multidrug resistance-associated protein 1: synthesis, biological evaluation, and structure-activity relationships.
J. Med. Chem.
PUBLISHED: 07-08-2009
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Four series of aromatic carboxylic acids were prepared with a urea or thiourea moiety at the neighboring position to the carboxyl group and benzene or thiophene as aromatic scaffold. Using a calcein AM assay, these compounds were evaluated as inhibitors of multidrug resistance-associated protein 1 (MRP1) and selected compounds were examined toward P-glycoprotein (P-gp) as well as breast cancer resistance protein (BCRP) to assess selectivity for MRP1. Two 2-thioureidobenzo[b]thiophene-3-carboxylic acids (48, 49) were identified as particularly potent inhibitors of MRP1, with IC50 values of around 1 microM. The structural features of this new family of nontoxic MRP1 inhibitors include a (thio)urea disubstituted with preferentially two alkyl groups at the terminal nitrogen and an additional fused aromatic ring.
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Tryptophan deprivation induces inhibitory receptors ILT3 and ILT4 on dendritic cells favoring the induction of human CD4+CD25+ Foxp3+ T regulatory cells.
J. Immunol.
PUBLISHED: 06-17-2009
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Tryptophan catabolism through IDO activity can cause nonresponsiveness and tolerance acting on T cells. Given the crucial importance of dendritic cells (DCs) in the initiation of a T cell response, surprisingly little is known about the impact of IDO activity and tryptophan deprivation on DCs themselves. In the present study, we show that human DCs differentiated under low-tryptophan conditions acquire strong tolerogenic capacity. This effect is associated with a markedly decreased Ag uptake as well as the down-regulation of costimulatory molecules (CD40, CD80). In contrast, the inhibitory receptors ILT3 and ILT4 are significantly increased. Functionally, tryptophan-deprived DCs show a reduced capacity to stimulate T cells, which can be restored by blockade of ILT3. Moreover, ILT3(high)ILT4(high) DCs lead to the induction of CD4(+)CD25(+) Foxp3(+) T regulatory cells with suppressive activity from CD4(+)CD25(-) T cells. The generation of ILT3(high)ILT4(high) DCs with tolerogenic properties by tryptophan deprivation is linked to a stress response pathway mediated by the GCN2 kinase. These results demonstrate that tryptophan degradation establishes a regulatory microenvironment for DCs, enabling these cells to induce T regulatory cells. The impact of IDO thus extends beyond local immune suppression to a systemic control of the immune response.
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Proapoptotic signaling induced by RIG-I and MDA-5 results in type I interferon-independent apoptosis in human melanoma cells.
J. Clin. Invest.
PUBLISHED: 05-13-2009
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The retinoic acid-inducible gene I (RIG-I) and melanoma differentiation-associated antigen 5 (MDA-5) helicases sense viral RNA in infected cells and initiate antiviral responses such as the production of type I IFNs. Here we have shown that RIG-I and MDA-5 also initiate a proapoptotic signaling pathway that is independent of type I IFNs. In human melanoma cells, this signaling pathway required the mitochondrial adapter Cardif (also known as IPS-1) and induced the proapoptotic BH3-only proteins Puma and Noxa. RIG-I- and MDA-5-initiated apoptosis required Noxa but was independent of the tumor suppressor p53. Triggering this pathway led to efficient activation of mitochondrial apoptosis, requiring caspase-9 and Apaf-1. Surprisingly, this proapoptotic signaling pathway was also active in nonmalignant cells, but these cells were much less sensitive to apoptosis than melanoma cells. Endogenous Bcl-xL rescued nonmalignant, but not melanoma, cells from RIG-I- and MDA-5-mediated apoptosis. In addition, we confirmed the results of the in vitro studies, demonstrating that RIG-I and MDA-5 ligands both reduced human tumor lung metastasis in immunodeficient NOD/SCID mice. These results identify an IFN-independent antiviral signaling pathway initiated by RIG-I and MDA-5 that activates proapoptotic signaling and, unless blocked by Bcl-xL, results in apoptosis. Due to their immunostimulatory and proapoptotic activity, RIG-I and MDA-5 ligands have therapeutic potential due to their ability to overcome the characteristic resistance of melanoma cells to apoptosis.
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Apoptosis is essential for neutrophil functional shutdown and determines tissue damage in experimental pneumococcal meningitis.
PLoS Pathog.
PUBLISHED: 04-30-2009
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During acute bacterial infections such as meningitis, neutrophils enter the tissue where they combat the infection before they undergo apoptosis and are taken up by macrophages. Neutrophils show pro-inflammatory activity and may contribute to tissue damage. In pneumococcal meningitis, neuronal damage despite adequate chemotherapy is a frequent clinical finding. This damage may be due to excessive neutrophil activity. We here show that transgenic expression of Bcl-2 in haematopoietic cells blocks the resolution of inflammation following antibiotic therapy in a mouse model of pneumococcal meningitis. The persistence of neutrophil brain infiltrates was accompanied by high levels of IL-1beta and G-CSF as well as reduced levels of anti-inflammatory TGF-beta. Significantly, Bcl-2-transgenic mice developed more severe disease that was dependent on neutrophils, characterized by pronounced vasogenic edema, vasculitis, brain haemorrhages and higher clinical scores. In vitro analysis of neutrophils demonstrated that apoptosis inhibition completely preserves neutrophil effector function and prevents internalization by macrophages. The inhibitor of cyclin-dependent kinases, roscovitine induced apoptosis in neutrophils in vitro and in vivo. In wild type mice treated with antibiotics, roscovitine significantly improved the resolution of the inflammation after pneumococcal infection and accelerated recovery. These results indicate that apoptosis is essential to turn off activated neutrophils and show that inflammatory activity and disease severity in a pyogenic infection can be modulated by targeting the apoptotic pathway in neutrophils.
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Induction of tumor cell apoptosis or necrosis by conditional expression of cell death proteins: analysis of cell death pathways and in vitro immune stimulatory potential.
J. Immunol.
PUBLISHED: 04-04-2009
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For the efficient stimulation of T cells by tumor Ag, tumor-derived material has to be presented by dendritic cells (DC). This very likely involves the uptake of dead tumor cells by DC. Cell death in tumors often occurs through apoptosis, but necrotic cell death may also be prevalent. This distinction is relevant because numerous studies have proposed that apoptotic cells have immunosuppressive effects while necrosis may be stimulatory. However, a system has been lacking that would allow the induction of apoptosis or necrosis without side effects by the death stimuli used experimentally. In this study, we present such a system and test its effects on immune cells in vitro. B16 mouse melanoma cells were generated and underwent cell death through the doxycycline-inducible induction of death proteins. In one cell line, the induction of Bim(S) induced rapid apoptosis, in the other line the induction of the FADD death domain induced nonapoptotic/necrotic cell death. Bim(S)-induced apoptosis was associated with the typical morphological and biochemical changes. FADD death domain induced necrosis occurred through a distinct pathway involving RIP1 and the loss of membrane integrity in the absence of apoptotic changes. Apoptotic and necrotic cells were taken up with comparable efficiency by DC. OVA expressed in cells dying by either apoptosis or necrosis was cross-presented to OT-1 T cells and induced their proliferation. These results argue that it is not the form of cell death but its circumstances that decide the question whether cell death leads to a productive T cell response.
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Endogenous Noxa Determines the Strong Proapoptotic Synergism of the BH3-Mimetic ABT-737 with Chemotherapeutic Agents in Human Melanoma Cells.
Transl Oncol
PUBLISHED: 01-16-2009
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Human melanoma cells are very resistant to treatment with chemotherapeutic agents, and melanoma shows poor response to chemotherapeutic therapy. We describe a strong synergistic proapoptotic effect of the Bcl-2 family inhibitor ABT-737 and the standard antimelanoma drugs, namely, dacarbazine and fotemustine, and the experimental agent, imiquimod. Experiments with human melanoma cells, keratinocytes, and embryonic fibroblasts showed that all three agents activated the mitochondrial apoptosis pathway. ABT-737 on its own was ineffective in melanoma cells unless Mcl-1 was experimentally downregulated. However, ABT-737 strongly enhanced the proapoptotic activity of the chemotherapeutic drugs. Whereas cell death induction by all three agents involved the activity of both BH3-only proteins, Bim and Noxa, the combination with ABT-737 overcame the requirement for Bim. However, the synergism between ABT-737 and imiquimod or dacarbazine required endogenous Noxa, as demonstrated by experiments with Noxa-specific RNAi. Surprisingly, although Bim was activated, it was unable to replace Noxa. Studies of mitochondrial cytochrome c release using BH3 peptides confirmed that a main effect of dacarbazine, fotemustine, and imiquimod was to neutralize Mcl-1, thereby sensitizing mitochondria to the inhibition of other Bcl-2 family members through ABT-737. ABT-737 is thus a promising agent for combination therapy for human melanoma. Importantly, the efficacy of this therapy depends on endogenous Noxa, and the ability of chemotherapeutic drugs to activate Noxa may be a valuable predictor of their synergism with Bcl-2-targeting drugs.
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2-Amino- and 2-alkylthio-4H-3,1-benzothiazin-4-ones: synthesis, interconversion and enzyme inhibitory activities.
Molecules
PUBLISHED: 01-08-2009
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The synthetic access to 2-sec-amino-4H-3,1-benzothiazin-4-ones 2 was explored. Compounds 2 were available from methyl 2-thioureidobenzoates 1, 2-thioureidobenzoic acids 3, and novel 2-thioureidobenzamides 6, respectively, under different conditions. 2-Alkylthio-4H-3,1-benzothiazin-4-ones 5 have been prepared from anthranilic acid following a two step route. Both, benzothiazinones 2 and 5 underwent ring cleavage reactions to produce thioureas 1 and 6, respectively. Twelve benzothiazinones were evaluated as inhibitors against a panel of eight proteases and esterases to identify one selective inhibitor of human cathepsin L, 2b, and one selective inhibitor of human leukocyte elastase, 5i.
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Reversible inhibition of Chlamydia trachomatis infection in epithelial cells due to stimulation of P2X(4) receptors.
Infect. Immun.
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Bacterial infections of the mucosal epithelium are a major cause of human disease. The prolonged presence of microbial pathogens stimulates inflammation of the local tissues, which leads to changes in the molecular composition of the extracellular milieu. A well-characterized molecule that is released to the extracellular milieu by stressed or infected cells is extracellular ATP and its ecto-enzymatic degradation products, which function as signaling molecules through ligation of purinergic receptors. There has been little information, however, on the effects of the extracellular metabolites on bacterial growth in inflamed tissues. Millimolar concentrations of ATP have been previously shown to inhibit irreversibly bacterial infection through ligation of P2X(7) receptors. We show here that the proinflammatory mediator, ATP, is released from Chlamydia trachomatis-infected epithelial cells. Moreover, further stimulation of the infected cells with micromolar extracellular ADP or ATP significantly impairs the growth of the bacteria, with a profile characteristic of the involvement of P2X(4) receptors. A specific role for P2X(4) was confirmed using cells overexpressing P2X(4). The chlamydiae remain viable and return to normal growth kinetics after removal of the extracellular stimulus, similar to responses previously described for persistence of chlamydial infection.
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Inhibitor of apoptosis proteins limit RIP3 kinase-dependent interleukin-1 activation.
Immunity
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Interleukin-1? (IL-1?) is a potent inflammatory cytokine that is usually cleaved and activated by inflammasome-associated caspase-1. To determine whether IL-1? activation is regulated by inhibitor of apoptosis (IAP) proteins, we treated macrophages with an IAP-antagonist "Smac mimetic" compound or genetically deleted the genes that encode the three IAP family members cIAP1, cIAP2, and XIAP. After Toll-like receptor priming, IAP inhibition triggered cleavage of IL-1? that was mediated not only by the NLRP3-caspase-1 inflammasome, but also by caspase-8 in a caspase-1-independent manner. In the absence of IAPs, rapid and full generation of active IL-1? by the NLRP3-caspase-1 inflammasome, or by caspase-8, required the kinase RIP3 and reactive oxygen species production. These results demonstrate that activation of the cell death-inducing ripoptosome platform and RIP3 can generate bioactive IL-1? and implicate them as additional targets for the treatment of pathological IL-1-driven inflammatory responses.
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