Group B Streptococcus induces macrophage apoptosis by calpain activation

Pro-Inflammatory Cytokines Enhanced In Vitro Cytotoxic Activity of Clostridioides difficile Toxin B in Enteric Glial Cells: The Achilles Heel of Clostridioides difficile Infection?

Bacterial infections are characterized by an inflammatory response, which is essential for infection containment but is also responsible for negative effects on the host. The pathogen itself may have evolved molecular mechanisms to antagonize the antimicrobial effects of an inflammatory response and to enhance its pathogenicity using inflammatory response mediators, such as cytokines. Clostridioides difficile (C. difficile) infection (CDI) causes gastrointestinal diseases with markedly increasing global incidence and mortality rates. The main C. difficile virulence factors, toxin A and B (TcdA/TcdB), cause cytopathic/cytotoxic effects and inflammation. We previously demonstrated that TcdB induces enteric glial cell (EGC) apoptosis, which is enhanced by the pro-inflammatory cytokine tumor necrosis factor alpha plus interferon gamma (CKs). However, it is unknown whether CKs-enhanced TcdB cytotoxicity (apoptosis/necrosis) is affected by the timing of the appearance of the CKs. Thus, we simulated in vitro, in our experimental model with TcdB and EGCs, three main situations of possible interactions between TcdB and the timing of CK stimulation: before TcdB infection, concomitantly with infection, or at different times after infection and persisting over time. In these experimental conditions, which all represent situations of possible interactions between C. difficile and the timing of CK stimulation, we evaluated apoptosis, necrosis, and cell cycle phases. The CKs, in all of these conditions, enhanced TcdB cytotoxicity, which from apoptosis became necrosis when CK stimulation persisted over time, and was most relevant after 48 h of TcdB:EGCs interaction. Particularly, the enhancement of apoptosis by CKs was dependent on the TcdB dose and in a less relevant manner on the CK stimulation time, while the enhancement of necrosis occurred always independently of the TcdB dose and CK stimulation time. However, since in all conditions stimulation with CKs strongly enhanced the TcdB cytotoxicity, it always had a negative impact on C. difficile pathogenicity. This study might have important implications for the treatment of CDI.

The group A Streptococcus interleukin-8 protease SpyCEP promotes bacterial intracellular survival by evasion of autophagy

Autophagy serves an innate immune function in defending the host against invading bacteria, including group A Streptococcus (GAS). Autophagy is regulated by numerous host proteins, including the endogenous negative regulator calpain, a cytosolic protease. Globally disseminated serotype M1T1 GAS strains associated with high invasive disease potential express numerous virulence factors and resist autophagic clearance. Upon in vitro infection of human epithelial cell lines with representative wild-type GAS M1T1 strain 5448 (M1.5448), we observed increased calpain activation linked to a specific GAS virulence factor, the IL-8 protease SpyCEP. Calpain activation inhibited autophagy and decreased capture of cytosolic GAS in autophagosomes. In contrast, the serotype M6 GAS strain JRS4 (M6.JRS4), which is highly susceptible to host autophagy-mediated killing, expresses low levels of SpyCEP and does not activate calpain. Overexpression of SpyCEP in M6.JRS4 stimulated calpain activation, inhibited autophagy and significantly decreased bacterial capture in autophagosomes. These paired loss- and gain-of-function studies reveal a novel role for the bacterial protease SpyCEP in enabling GAS M1 evasion of autophagy and host innate immune clearance.

Clostridioides difficile toxin B alone and with pro-inflammatory cytokines induces apoptosis in enteric glial cells by activating three different signalling pathways mediated by caspases, calpains and cathepsin B

Clostridioides difficile infection (CDI) causes nosocomial/antibiotic-associated gastrointestinal diseases with dramatically increasing global incidence and mortality rates. The main C. difficile virulence factors, toxins A and B (TcdA/TcdB), cause cytopathic/cytotoxic effects and inflammation. We demonstrated that TcdB induces caspase-dependent, mitochondria-independent enteric glial cell (EGC) apoptosis that is enhanced by the pro-inflammatory cytokines TNF-α and IFN-γ (CKs) by increasing caspase-3/7/9 and PARP activation. Because this cytotoxic synergism is important for CDI pathogenesis, we investigated the apoptotic pathways involved in TcdB- and TcdB + CK-induced apoptosis indepth. EGCs were pre-treated with the inhibitors BAF or Q-VD-OPh (pan-caspase), Z-DEVD-fmk (caspase-3/7), Z-IETD-fmk (caspase-8), PD150606 (calpains), and CA-074Me (cathepsin B) 1 h before TcdB exposure, while CKs were given 1.5 h after TcdB exposure, and assays were performed at 24 h. TcdB and TcdB + CKs induced apoptosis through three signalling pathways activated by calpains, caspases and cathepsins, which all are involved both in induction and execution apoptotic signalling under both conditions but to different degrees in TcdB and TcdB + CKs especially as regards to signal transduction mediated by these proteases towards downstream effects (apoptosis). Calpain activation by Ca²⁺ influx is the first pro-apoptotic event in TcdB- and TcdB + CK-induced EGC apoptosis and causes caspase-3, caspase-7 and PARP activation. PARP is also directly activated by calpains which are responsible of about 75% of apoptosis in TcdB and 62% in TcdB + CK which is both effector caspase-dependent and -independent. Initiator caspase-8 activation mediated by TcdB contributes to caspase-3/caspase-7 and PARP activation and is responsible of about 28% of apoptosis in both conditions. Caspase-3/caspase-7 activation is weakly responsible of apoptosis, indeed we found that it mediates 27% of apoptosis only in TcdB. Cathepsin B contributes to triggering pro-apoptotic signal and is responsible in both conditions of about 35% of apoptosis by a caspase-independent manner, and seems to regulate the caspase-3 and caspase-7 cleaved fragment levels, highlighting the complex interaction between these cysteine protease families activated during TcdB-induced apoptosis. Further a relevant difference between TcdB- and TcdB + CK-induced apoptosis is that TcdB-induced apoptosis increased slowly reaching at 72 h the value of 18.7%, while TcdB + CK-induced apoptosis increased strongly reaching at 72 h the value of 60.6%. Apoptotic signalling activation by TcdB + CKs is enriched by TNF-α-induced NF-κB signalling, inhibition of JNK activation and activation of AKT. In conclusion, the ability of C. difficile to activate three apoptotic pathways represents an important strategy to overcome resistance against its cytotoxic activity.

Cisplatin-induced pyroptosis is mediated via the CAPN1/CAPN2-BAK/BAX-caspase-9-caspase-3-GSDME axis in esophageal cancer

Esophageal cancer is the seventh most common cancer globally. Chemotherapy resistance remains a significant challenge in the treatment of esophageal cancer patients. Cisplatin can damage tumor cells by inducing pyroptosis. However, the underlying molecular mechanisms remain unclear. In this work, we aim to investigate pyroptosis-dependent molecular mechanisms underlying cisplatin sensitivity and find potential biomarkers to predict response to cisplatin-based chemotherapy for esophageal cancer patients. Pyroptosis-associated proteins were screened via proteomics for esophageal cancer (n = 124) and bioinformatics analysis. We observed that high calpain-1 (CAPN1) and calpain-2 (CAPN2) expression were associated with favorable clinical outcomes and prolonged survival in esophageal cancer patients. We employed immunohistochemistry to evaluate the expression of CAPN1 and CAPN2 in pretreatment tumor biopsies from 108 patients with esophageal cancer who received concurrent chemoradiotherapy (CCRT). These results suggested that esophageal cancer patients with high expression of both CAPN1 and CAPN2 are likely to experience a complete response to CCRT and have significantly better survival. Western blotting, LDH release, calpain activity and cell viability assays indicated that cisplatin could activate calpain activity, while calpain inhibition or knockout suppressed cisplatin-induced pyroptosis. Mechanistically, we uncovered a novel mechanism whereby cisplatin induced pyroptosis via activation of a CAPN1/CAPN2-BAK/BAX-caspase-9-caspase-3-GSDME signaling axis in esophageal cancer cells. Collectively, this study is the first to explore the effects of calpain on cisplatin-induced pyroptosis in esophageal cancer cells. Further, our findings also imply that the combination of CAPN1 and CAPN2 could be considered as a promising biomarker of cisplatin sensitivity and prognosis in patients with esophageal cancer, providing a possibility to guide individualized treatment.

Endonuclease G takes part in AIF-mediated caspase-independent apoptosis in Mycobacterium bovis-infected bovine macrophages

Mycobacterium bovis, the causative agent of bovine tuberculosis encodes different virulence mechanisms to survive inside of host cells. One of the possible outcomes in this host-pathogen interaction is cell death. Previous results from our group showed that M. bovis induces a caspase-independent apoptosis in bovine macrophages with the possible participation of apoptosis inducing factor mitochondria associated 1 (AIFM1/AIF), a flavoprotein that functions as a cell-death regulator. However, contribution of other caspase-independent cell death mediators in M. bovis-infected macrophages is not known. In this study, we aimed to further characterize M. bovis-induced apoptosis, addressing Endonuclease G (Endo G) and Poly (ADP-ribose) polymerase 1 (PARP-1). In order to accomplish our objective, we infected bovine macrophages with M. bovis AN5 (MOI 10:1). Analysis of M. bovis-infected nuclear protein extracts by immunoblot, identified a 15- and 43-fold increase in concentration of mitochondrial proteins AIF and Endo G respectively. Interestingly, pretreatment of M. bovis-infected macrophages with cyclosporine A, a mitochondrial permeability transition pore inhibitor, abolished AIF and Endo G nuclear translocation. In addition, it also decreased macrophage DNA fragmentation to baseline and caused a 26.2% increase in bacterial viability. We also demonstrated that PARP-1 protein expression in macrophages did not change during M. bovis infection. Furthermore, pretreatment of M. bovis-infected bovine macrophages with 3-aminobenzamide, a PARP-1 inhibitor, did not change the proportion of macrophage DNA fragmentation. Our results suggest participation of Endo G, but not PARP-1, in M. bovis-induced macrophage apoptosis. To the best of our knowledge this is the first report associating Endo G with caspase-independent apoptosis induced by a member of the Mycobacterium tuberculosis complex.

A novel benzofuran derivative, ACDB, induces apoptosis of human chondrosarcoma cells through mitochondrial dysfunction and endoplasmic reticulum stress

Chondrosarcoma is one of the bone tumor with high mortality in respond to poor radiation and chemotherapy treatment. Here, we analyze the antitumor activity of a novel benzofuran derivative, 2-amino-3-(2-chlorophenyl)-6-(4-dimethylaminophenyl)benzofuran-4-yl acetate (ACDB), in human chondrosarcoma cells. ACDB increased the cell apoptosis of human chondrosarcomas without harm in chondrocytes. ACDB also enhanced endoplasmic reticulum (ER) stress, which was characterized by varieties in the cytosolic calcium levels and induced the expression of glucose-regulated protein (GRP) and calpain. Furthermore, the ACDB-induced chondrosarcoma apoptosis was associated with the upregulation of the B cell lymphoma-2 (Bcl-2) family members including pro- and anti-apoptotic proteins, downregulation of dysfunctional mitochondria that released cytochrome C, and subsequent activation of caspases-3. In addition, the ACDB-mediated cellular apoptosis was suppressed by transfecting cells with glucose-regulated protein (GRP) and calpain siRNA or treating cells with ER stress chelators and caspase inhibitors. Interestingly, animal experiments illustrated a reduction in the tumor volume following ACDB treatment. Together, these results suggest that ACDB may be a novel tumor suppressor of chondrosarcoma, and this study demonstrates that the novel antitumor agent, ACDB, induced apoptosis by mitochondrial dysfunction and ER stress in human chondrosarcoma cells in vitro and in vivo.

Intrinsic Maturational Neonatal Immune Deficiencies and Susceptibility to Group B Streptococcus Infection

Although a normal member of the gastrointestinal and vaginal microbiota, group B Streptococcus (GBS) can also occasionally be the cause of highly invasive neonatal disease and is an emerging pathogen in both elderly and immunocompromised adults. Neonatal GBS infections are typically transmitted from mother to baby either in utero or during passage through the birth canal and can lead to pneumonia, sepsis, and meningitis within the first few months of life. Compared to the adult immune system, the neonatal immune system has a number of deficiencies, making neonates more susceptible to infection. Recognition of GBS by the host immune system triggers an inflammatory response to clear the pathogen. However, GBS has developed several mechanisms to evade the host immune response. A comprehensive understanding of this interplay between GBS and the host immune system will aid in the development of new preventative measures and therapeutics.

Targeting calpains: A novel immunomodulatory approach for microbial infections

Calpains are a family of Ca²⁺ dependent cytosolic non-lysosomal proteases with well conserved cysteine-rich domains for enzymatic activity. Due to their functional dependency on Ca²⁺ concentrations, they are involved in various cellular processes that are regulated by intracellular ca²⁺ concentration (i.e. embryo development, cell development and migration, maintenance of cellular architecture and structure etc.). Calpains are widely studied proteases in mammalian (i.e. mouse and human) physiology and pathophysiology due to their ubiquitous presence. For example, these proteases have been found to be involved in various inflammatory disorders such as neurodegeneration, cancer, brain and myocardial ischemia and infarction, cataract and muscular dystrophies etc. Besides their role in these sterile inflammatory conditions, calpains have also been shown to regulate a wide range of infectious diseases (i.e. sepsis, tuberculosis, gonorrhoea and bacillary dysentery etc.). One of these regulatory mechanisms mediated by calpains (i.e. calpain 1 and 2) during microbial infections involves the regulation of innate immune response, inflammation and cell death. Thus, the major emphasis of this review is to highlight the importance of calpains in the pathogenesis of various microbial (i.e. bacterial, fungal and viral) diseases and the use of calpain modulators as potential immunomodulators in microbial infections.

Enteric glial cells are susceptible to Clostridium difficile toxin B

Clostridium difficile causes nosocomial/antibiotic-associated diarrhoea and pseudomembranous colitis. The major virulence factors are toxin A and toxin B (TcdB), which inactivate GTPases by monoglucosylation, leading to cytopathic (cytoskeleton alteration, cell rounding) and cytotoxic effects (cell-cycle arrest, apoptosis). C. difficile toxins breaching the intestinal epithelial barrier can act on underlying cells, enterocytes, colonocytes, and enteric neurons, as described in vitro and in vivo, but until now no data have been available on enteric glial cell (EGC) susceptibility. EGCs are crucial for regulating the enteric nervous system, gut homeostasis, the immune and inflammatory responses, and digestive and extradigestive diseases. Therefore, we evaluated the effects of C. difficile TcdB in EGCs. Rat-transformed EGCs were treated with TcdB at 0.1-10 ng/ml for 1.5-48 h, and several parameters were analysed. TcdB induces the following in EGCs: (1) early cell rounding with Rac1 glucosylation; (2) early G2/M cell-cycle arrest by cyclin B1/Cdc2 complex inactivation caused by p27 upregulation, the downregulation of cyclin B1 and Cdc2 phosphorylated at Thr161 and Tyr15; and (3) apoptosis by a caspase-dependent but mitochondria-independent pathway. Most importantly, the stimulation of EGCs with TNF-α plus IFN-γ before, concomitantly or after TcdB treatment strongly increased TcdB-induced apoptosis. Furthermore, EGCs that survived the cytotoxic effect of TcdB did not recover completely and showed not only persistent Rac1 glucosylation, cell-cycle arrest and low apoptosis but also increased production of glial cell-derived neurotrophic factor, suggesting self-rescuing mechanisms. In conclusion, the high susceptibility of EGCs to TcdB in vitro, the increased sensitivity to inflammatory cytokines related to apoptosis and the persistence of altered functions in surviving cells suggest an important in vivo role of EGCs in the pathogenesis of C. difficile infection.

Dithiothreitol enhanced arsenic-trioxide-induced cell apoptosis in cultured oral cancer cells via mitochondrial dysfunction and endoplasmic reticulum stress

Arsenic is naturally occurring toxic metalloid and drinking As₂ O₃ containing water are recognized to be related to increased risk of neurotoxicity, liver injury, blackfoot disease, hypertension, and cancer. On the contrary, As₂ O₃ has been an ancient drug used in traditional Chinese medicine with substantial anticancer activities, especially in the treatment of acute promyelocytic leukemia as well as chronic wound healing. However, the cytotoxicity and detail mechanisms of As₂ O₃ action in solid cancer cells, such as oral cancer cells, are largely unknown. In this study, we have primarily cultured four pairs of tumor and nontumor cells from the oral cancer patients and treated the cells with As₂ O₃ alone or combined with dithiothreitol (DTT). The results showed that 0.5 μM As₂ O₃ plus 20 μM DTT caused a significant cell death of oral cancer cells but not the nontumor cells. Also As₂ O₃ plus DTT upregulated Bax and Bak, downregulated Bcl-2 and p53, caused a loss of mitochondria membrane potential in oral cancer cells. On the other way, As₂ O₃ also triggered endoplasmic reticulum stress and increased the levels of glucose-regulated protein 78, calpain 1 and 2. Our results suggest that DTT could synergistically enhance the effects of As₂ O₃ on killing oral cancer cells while nontoxic to the nontumor cells. The combination is promising for clinical practice in oral cancer therapy and worth further investigations. © 2015 Wiley Periodicals, Inc. Environ Toxicol 32: 17-27, 2017.

Critical role of calpain in inflammation

Calpains are a family of cysteine proteases, implicated in a wide range of cellular calcium-regulated functions. Evidence from previous studies using an inhibitor of calpain indicates that calpain activation is involved in the process of numerous inflammation-associated diseases. As a result of in-depth studies, calpains have been proposed to influence the process of inflammation via a variety of mechanisms. The aim of the present study is to provide an overview of recent reports regarding the role of calpain in the process of inflammation, including regulation of immune cell migration, modulation of the activation of inflammatory mediators, degradation of certain associated proteins and induction of cell apoptosis. Understanding these mechanisms may contribute to the investigation of novel therapeutic targets for inflammation-associated diseases.

Recombinant Trichinella spiralis 53-kDa protein activates M2 macrophages and attenuates the LPS-induced damage of endotoxemia

Sepsis is a serious clinical condition of excessive systemic immune response to microbial infection. The pro-inflammatory stage of sepsis is generally launched by innate cells such as macrophages. They release inflammatory cytokines, activate other immune cells and cause severe tissue/organ damage. In this study, we have revealed that recombinant Trichinella spiralis (TS) excretory-secretory protein (rTsP53) exhibited anti-inflammatory properties and rescued mice from LPS-induced endotoxemia, which is a common model for sepsis study, potentially through the induction of M2 macrophages. rTsP53 treatment significantly decreased inflammatory cytokines (IL-6, IFN-γ and TNF-α) and increased IL-4, IL-10, IL-13 and TGF-β secretion, both in circulation and in tissues. rTsP53 also induced the activation and infiltration of F4/80(+)CD163(+) macrophages to inflammatory tissues, increased M2 macrophage-related Arg1 and Fizz1 expression, and decreased M1 macrophage-related iNOS expression. PCR array showed that rTsP53 activated several genes that involve the survival of macrophages and also anti-inflammatory genes such as SOCS3. Together, our results show that rTsP53 activates M2 macrophages, which has strong anti-inflammatory potential to prevent LPS-induced lethal sepsis.

A streptococcal lipid toxin induces membrane permeabilization and pyroptosis leading to fetal injury

Group B streptococci (GBS) are Gram-positive bacteria that cause infections in utero and in newborns. We recently showed that the GBS pigment is hemolytic and increased pigment production promotes bacterial penetration of human placenta. However, mechanisms utilized by the hemolytic pigment to induce host cell lysis and the consequence on fetal injury are not known. Here, we show that the GBS pigment induces membrane permeability in artificial lipid bilayers and host cells. Membrane defects induced by the GBS pigment trigger K⁺ efflux leading to osmotic lysis of red blood cells or pyroptosis in human macrophages. Macrophages lacking the NLRP3 inflammasome recovered from pigment-induced cell damage. In a murine model of in utero infection, hyperpigmented GBS strains induced fetal injury in both an NLRP3 inflammasome-dependent and NLRP3 inflammasome-independent manner. These results demonstrate that the dual mechanism of action of the bacterial pigment/lipid toxin leading to hemolysis or pyroptosis exacerbates fetal injury and suggest that preventing both activities of the hemolytic lipid is likely critical to reduce GBS fetal injury and preterm birth.

Inhibition of microvesiculation sensitizes prostate cancer cells to chemotherapy and reduces docetaxel dose required to limit tumor growth in vivo

Microvesicles shed from cells carry constituents of the cell cytoplasm, including, of importance in multidrug resistance to cancer chemotherapy, drugs that the tumor cell attempts to efflux. To see whether such drugs could be used at lower concentrations with the same efficacy, it was first shown that microvesiculation of prostate cancer (PCa) cells, PC3, could be inhibited pharmacologically with calpeptin (calpain inhibitor) and by siRNA (CAPNS1). In cells treated with docetaxel (DTX), this inhibition resulted in a third-fold increase in intracellular concentrations of DTX. As a result, 20-fold lower concentrations of DTX (5 nM) could be used, in the presence of calpeptin (20 μM) inducing the same degree of apoptosis after 48 h in PC3 cells, as 100 nM of DTX alone. Inhibition of microvesiculation similarly improved combination chemotherapy (DTX and methotrexate). In a mouse xenograft model of PCa, DTX (0.1 mg/kg) together with calpeptin (10 mg/kg), administered i.p., significantly reduced tumor volumes compared to DTX alone (0.1 mg/kg) and brought about the same reductions in tumor growth as 10 mg/kg of DTX alone. As well as further reducing vascularization, it also increased apoptosis and reduced proliferation of PC3 cells in tumor xenografts.

α1-antitrypsin modulates microglial-mediated neuroinflammation and protects microglial cells from amyloid-β-induced toxicity

Background

One hallmark of Alzheimer disease is microglial activation. Therapeutic approaches for this neurodegenerative disease include the modulation of microglial cells. α₁-antitrypsin (A1AT) has been shown to exert anti-inflammatory effects on macrophages and lung epithelial cells and an inhibition of calpain activity in neutrophil granulocytes. Nothing is known about the effect of A1AT on microglial-mediated neuroinflammation. Our aim was to investigate the effect of A1AT on amyloid-β (Aβ)- and LPS-treated microglial cells in vitro with respect to cytokine production, stress pathways, cell viability, phagocytotic abilities and the underlying mechanisms.

Methods

Primary microglial cells were isolated from Swiss Webster mouse embryos on embryonic day 13.5. Cytokines in the supernatants of treated primary microglial cells were analyzed with ELISAs, and accumulated nitrite was detected with Griess reagents. Intracellular stress pathways were investigated in cell lysates using western blotting. Intracellular calcium levels were detected in BV-2 microglial cells loaded with the Ca²⁺-sensitive (fluorescent) dye Fluo-4. Calpain activity in primary microglial cells was assessed by using a calpain activity assay. Cell viability of Aβ-treated microglial cells was analyzed using MTT assay. Phagocytosis of Aβ was evaluated with western blot analysis.

Results

Upon co-administration, A1AT reduced pro-inflammatory mediators induced by LPS or Aβ. Interestingly, we detected a reduction in calpain activity and in the concentration of intracellular calcium that might mediate the anti-inflammatory effects of A1AT. Inhibition of the classic activation pathways, such as phosphorylation of mitogen-activated protein kinases or activation of protein kinase A were excluded as a mechanism of A1AT-mediated effects. In addition, A1AT increased the viability of Aβ-treated microglial cells and reduced Aβ phagocytosis.

Conclusions

We provide evidence on the mechanism of action of A1AT on microglial-mediated neuroinflammation in vitro. Our in vitro data indicate that A1AT treatment modulates microglial cells in inflammatory conditions and that this modulation is due to an inhibition of calpain activity and intracellular calcium levels. The underlying mechanisms of the effects observed here are promising for future therapeutic strategies and should thus be further pursued in transgenic mouse models of Alzheimer disease.

Brucella infection inhibits macrophages apoptosis via Nedd4-dependent degradation of calpain2

The calcium-dependent protease calpain2 is involved in macrophages apoptosis. Brucella infection-induced up-regulation of intracellular calcium level is an essential factor for the intracellular survival of Brucella within macrophages. Here, we hypothesize that calcium-dependent E3 ubiquitin ligase Nedd4 ubiquitinates calpain2 and inhibits Brucella infection-induced macrophage apoptosis via degradation of calpain2.Our results reveal that Brucella infection induces increases in Nedd4 activity in an intracellular calcium dependent manner. Furthermore, Brucella infection-induced degradation of calpain2 is mediated by Nedd4 ubiquitination of calpain2. Brucella infection-induced calpain2 degradation inhibited macrophages apoptosis. Treatment of Brucella infected macrophages with calcium chelator BAPTA or Nedd4 knock-down decreased Nedd4 activity, prevented calpain2 degradation, and resulted in macrophages apoptosis.

Group B streptococcal haemolysin and pigment, a tale of twins

Group B streptococcus [(GBS or Streptococcus agalactiae)] is a leading cause of neonatal meningitis and septicaemia. Most clinical isolates express simultaneously a β-haemolysin/cytolysin and a red polyenic pigment, two phenotypic traits important for GBS identification in medical microbiology. The genetic determinants encoding the GBS haemolysin and pigment have been elucidated and the molecular structure of the pigment has been determined. The cyl operon involved in haemolysin and pigment production is regulated by the major two-component system CovS/R, which coordinates the expression of multiple virulence factors of GBS. Genetic analyses indicated strongly that the haemolysin activity was due to a cytolytic toxin encoded by cylE. However, the biochemical nature of the GBS haemolysin has remained elusive for almost a century because of its instability during purification procedures. Recently, it has been suggested that the haemolytic and cytolytic activity of GBS is due to the ornithine rhamnopolyenic pigment and not to the CylE protein. Here we review and summarize our current knowledge of the genetics, regulation and biochemistry of these twin GBS phenotypic traits, including their functions as GBS virulence factors.

Glyoxalase I inhibition induces apoptosis in irradiated MCF-7 cells via a novel mechanism involving Hsp27, p53 and NF-κB

BACKGROUND

Glyoxalase I (GI) is a cellular defence enzyme involved in the detoxification of methylglyoxal (MG), a cytotoxic byproduct of glycolysis, and MG-derived advanced glycation end products (AGEs). Argpyrimidine (AP), one of the major AGEs coming from MG modifications of proteins arginines, is a pro-apoptotic agent. Radiotherapy is an important modality widely used in cancer treatment. Exposure of cells to ionising radiation (IR) results in a number of complex biological responses, including apoptosis. The present study was aimed at investigating whether, and through which mechanism, GI was involved in IR-induced apoptosis.

METHODS

Apoptosis, by TUNEL assay, transcript and protein levels or enzymatic activity, by RT-PCR, western blot and spectrophotometric methods, respectively, were evaluated in irradiated MCF-7 breast cancer cells, also in experiments with appropriate inhibitors or using small interfering RNA.

RESULTS

Ionising radiation induced a dramatic reactive oxygen species (ROS)-mediated inhibition of GI, leading to AP-modified Hsp27 protein accumulation that, in a mechanism involving p53 and NF-κB, triggered an apoptotic mitochondrial pathway. Inhibition of GI occurred at both functional and transcriptional levels, the latter occurring via ERK1/2 MAPK and ERα modulation.

CONCLUSIONS

Glyoxalase I is involved in the IR-induced MCF-7 cell mitochondrial apoptotic pathway via a novel mechanism involving Hsp27, p53 and NF-κB.

Role of calmodulin-calmodulin kinase II, cAMP/protein kinase A and ERK 1/2 on Aeromonas hydrophila-induced apoptosis of head kidney macrophages

The role of calcium (Ca²⁺) and its dependent protease calpain in Aeromonas hydrophila-induced head kidney macrophage (HKM) apoptosis has been reported. Here, we report the pro-apoptotic involvement of calmodulin (CaM) and calmodulin kinase II gamma (CaMKIIg) in the process. We observed significant increase in CaM levels in A. hydrophila-infected HKM and the inhibitory role of BAPTA/AM, EGTA, nifedipine and verapamil suggested CaM elevation to be Ca²⁺-dependent. Our studies with CaM-specific siRNA and the CaM inhibitor calmidazolium chloride demonstrated CaM to be pro-apoptotic that initiated the downstream expression of CaMKIIg. Using the CaMKIIg-targeted siRNA, specific inhibitor KN-93 and its inactive structural analogue KN-92 we report CaM-CaMKIIg signalling to be critical for apoptosis of A. hydrophila-infected HKM. Inhibitor studies further suggested the role of calpain-2 in CaMKIIg expression. CaMK Kinase (CaMKK), the other CaM dependent kinase exhibited no role in A. hydrophila-induced HKM apoptosis. We report increased production of intracellular cAMP in infected HKM and our results with KN-93 or KN-92 implicate the role of CaMKIIg in cAMP production. Using siRNA to PKACA, the catalytic subunit of PKA, anti-PKACA antibody and H-89, the specific inhibitor for PKA we prove the pro-apoptotic involvement of cAMP/PKA pathway in the pathogenicity of A. hydrophila. Our inhibitor studies coupled with siRNA approach further implicated the role of cAMP/PKA in activation of extracellular signal-regulated kinase 1 and 2 (ERK 1/2). We conclude that the alteration in intracellular Ca²⁺ levels initiated by A. hydrophila activates CaM and calpain-2; both pathways converge on CaMKIIg which in turn induces cAMP/PKA mediated ERK 1/2 phosphorylation leading to caspase-3 mediated apoptosis of infected HKM.

Aeromonas hydrophila is a natural fish pathogen and is known to induce apoptosis of HKM. Head kidney is an important immune-organ in fish and HKM are critical for immunity against the invading pathogen. The mechanisms of cell death induced by A. hydrophila are incompletely characterized. We have studied the role of Ca²⁺-dependent signalling pathways in the induction of A. hydrophila-induced HKM apoptosis. We observed that A. hydrophila infection led to increased CaM expression in infected HKM which was Ca²⁺-dependent. The inhibitor and siRNA studies suggested CaM to be pro-apoptotic and triggered CaMKIIg expression in the infected HKM. Calpain-2 appeared to influence CaMKIIg expression. However, further studies are needed to understand the process. We report that the CaM-CaMKIIg pathway is important for initiating cAMP production within the infected HKM. The pro-apoptotic activation of cAMP dependent PKA was quite evident. The activation of ERK 1/2 was observed in the HKM and results clearly suggested the pro-active role of cAMP/PKA in the process. Thus we conclude that CaM-CaMKIIg initiates the cAMP/PKA pathway that induces ERK 1/2 phosphorylation to promote caspase-3 mediated apoptosis of the A. hydrophila-infected HKM.

Group B streptococcal infection of the choriodecidua induces dysfunction of the cytokeratin network in amniotic epithelium: a pathway to membrane weakening

Early events leading to intrauterine infection remain poorly defined, but may hold the key to preventing preterm delivery. To determine molecular pathways within fetal membranes (chorioamnion) associated with early choriodecidual infection that may progress to preterm premature rupture of membranes (PPROM), we examined the effects of a Group B Streptococcus (GBS) choriodecidual infection on chorioamnion in a nonhuman primate model. Ten chronically catheterized pregnant monkeys (Macaca nemestrina) at 118–125 days gestation (term = 172 days) received choriodecidual inoculation of either GBS (n = 5) or saline (n = 5). Cesarean section was performed in the first week after GBS or saline inoculation. RNA extracted from chorioamnion (inoculation site) was profiled by microarray. Single gene, Gene Set, and Ingenuity Pathway Analysis results were validated using qRT-PCR (chorioamnion), Luminex (amniotic fluid, AF), immunohistochemistry, and transmission electron microscopy (TEM). Despite uterine quiescence in most cases, significant elevations of AF cytokines (TNF-α, IL-8, IL-1β, IL-6) were detected in GBS versus controls (p<0.05). Choriodecidual infection resolved by the time of cesarean section in 3 of 5 cases and GBS was undetectable by culture and PCR in the AF. A total of 331 genes were differentially expressed (>2-fold change, p<0.05). Remarkably, GBS exposure was associated with significantly downregulated expression of multiple cytokeratin (CK) and other cytoskeletal genes critical for maintenance of tissue tensile strength. Immunofluorescence revealed highly significant changes in the CK network within amniocytes with dense CK aggregates and retraction from the cell periphery (all p = 0.006). In human pregnancies affected by PPROM, there was further evidence of CK network retraction with significantly shorter amniocyte foot processes (p = 0.002). These results suggest early choriodecidual infection results in decreased cellular membrane integrity and tensile strength via dysfunction of CK networks. Downregulation of CK expression and perturbations in the amniotic epithelial cell intermediate filament network occur after GBS choriodecidual infection, which may contribute to PPROM.

Group B Streptococcus (GBS) is one cause of preterm birth, stillbirth, and fetal brain injury. GBS is present in the vagina and is thought to ascend into the uterus of some women where it can cause placental inflammation and preterm birth. Understanding the earliest events in the placenta that lead to preterm birth is elusive in humans, because the placenta cannot be studied until after birth. Here, we use a nonhuman primate model to show that an early GBS infection can damage the structural support of the fetal membranes, specifically the cytokeratin network in the epithelium of the amnion (one part of the membranes). Next, we obtained human placentas to show that this cytokeratin network was also damaged in human patients that had preterm premature rupture of the membranes, a major cause of preterm birth. Our work is important in understanding why fetal membranes may rupture prematurely, which may lead to early interventions to prevent membrane damage after placental infection and preterm birth.

Calpains promote neutrophil recruitment and bacterial clearance in an acute bacterial peritonitis model

Activation of the innate immune system is critical for clearance of bacterial pathogens to limit systemic infections and host tissue damage. Here, we report a key role for calpain proteases in bacterial clearance in mice with acute peritonitis. Using transgenic mice expressing Cre recombinase primarily in innate immune cells (fes-Cre), we generated conditional capns1 knockout mice. Consistent with capns1 being essential for stability and function of the ubiquitous calpains (calpain-1, calpain-2), peritoneal cells from these mice had reduced levels of calpain-2/capns1, and reduced proteolysis of their substrate selenoprotein K. Using an acute bacterial peritonitis model, we observed impaired bacterial killing within the peritoneum and development of bacteremia in calpain knockout mice. These defects correlated with significant reductions in IL-1α release, neutrophil recruitment, and generation of reactive oxygen species in calpain knockout mice with acute bacterial peritonitis. Peritoneal macrophages from calpain knockout mice infected with enterobacteria ex vivo, were competent in phagocytosis of bacteria, but showed impaired clearance of intracellular bacteria compared with control macrophages. Together, these results implicate calpains as key mediators of effective innate immune responses to acute bacterial infections, to prevent systemic dissemination of bacteria that can lead to sepsis.

Protein degradation systems in platelets

Protein synthesis and degradation are essential processes that allow cells to survive and adapt to their surrounding milieu. In nucleated cells, the degradation and/or cleavage of proteins is required to eliminate aberrant proteins. Cells also degrade proteins as a mechanism for cell signalling and complex cellular functions. Although the last decade has convincingly shown that platelets synthesise proteins, the roles of protein degradation in these anucleate cytoplasts are less clear. Here we review what is known about protein degradation in platelets placing particular emphasis on the proteasome and the cysteine protease calpain.

Glyoxalase 1-419C>A variant is associated with oxidative stress: implications in prostate cancer progression

Glyoxalase 1 is a scavenging enzyme of potent precursors in reactive oxygen species formation and is involved in the occurrence and progression of human malignancies. Glyoxalase I A111E polymorphism has been suggested to influence its enzymatic activity. The present study was aimed at investigating the association of this polymorphism with oxidative stress and its implications in prostate cancer progression or survival. The polymorphism was genotyped in human differently aggressive and invasive prostate cancer cell lines, in 571 prostate cancer or 588 benign prostatic hyperplasia patients, and 580 healthy subjects by Polymerase Chain Reaction/Restriction Fragment Length Polymorphism. Glyoxalase 1 activity, the pro-oxidant Glyoxalase 1-related Argpyrimidine and oxidative stress biomarkers were evaluated by biochemical analyses. Glyoxalase 1 polymorphism was associated with an increase in Glyoxalase 1-related pro-oxidant Argpyrimidine and oxidative stress levels and cancer progression. The mutant A allele conferred a modest risk of prostate cancer, a marked risk of prostate cancer progression and a lower survival time, compared to the wild C allele. The results of our exploratory study point out a significant role for Glyoxalase 1 in prostate cancer progression, providing an additional candidate for risk assessment in prostate cancer patients and an independent prognostic factor for survival. Finally, we provided evidence of the biological plausibility of Glyoxalase 1 polymorphism, either alone or in combination with other ones, all related to oxidative stress control that represents a key event in PCa development and progression.

Impairment of brain mitochondrial functions by β-hemolytic Group B Streptococcus. Effect of cardiolipin and phosphatidylcholine

Group B Streptococcus (GBS) causes severe infection in the central nervous system. In this study, brain mitochondrial function was investigated by simulating infection of isolated mitochondria with GBS, which resulted in loss of mitochondrial activity. The β-hemolysin expressing strains GBS-III-NEM316 and GBS-III-COH31, but not the gGBS-III-COH31 that does not express β-hemolysin, caused dissipation of preformed mitochondrial membrane potential (Δψm). This indicates that β-hemolysin is responsible for decreasing of the reducing power of mitochondria. GBS-III-COH31 interacted with mitochondria causing increase of oxygen consumption, due to uncoupling of respiration, blocking of ATP synthesis, and cytochrome c release outside mitochondria. Moreover, the mitochondrial systems contributing to the control of cellular Ca(2+) uptake were lost. In spite of these alterations, mitochondrial phospholipid content and composition did not change significantly, as evaluated by MALDI-TOF mass spectrometry. However, exogenous cardiolipin (CL) and dipalmitoylphosphatidylcholine (DPPC) attenuated the uncoupling effect of GBS-III-COH31, although with different mechanisms. CL was effective only when fused to the inner mitochondrial membrane, probably reducing the extent of GBS-induced proton leakage. DPPC, which is not able to fuse with mitochondrial membranes, exerted its effect outside mitochondria, likely by shielding mitochondria against GBS β-hemolysin attack.

Trichodermin induces cell apoptosis through mitochondrial dysfunction and endoplasmic reticulum stress in human chondrosarcoma cells

Chondrosarcoma is the second most common primary bone tumor, and it responds poorly to both chemotherapy and radiation treatment. Nalanthamala psidii was described originally as Myxosporium in 1926. This is the first study to investigate the anti-tumor activity of trichodermin (trichothec-9-en-4-ol, 12,13-epoxy-, acetate), an endophytic fungal metabolite from N. psidii against human chondrosarcoma cells. We demonstrated that trichodermin induced cell apoptosis in human chondrosarcoma cell lines (JJ012 and SW1353 cells) instead of primary chondrocytes. In addition, trichodermin triggered endoplasmic reticulum (ER) stress protein levels of IRE1, p-PERK, GRP78, and GRP94, which were characterized by changes in cytosolic calcium levels. Furthermore, trichodermin induced the upregulation of Bax and Bid, the downregulation of Bcl-2, and the dysfunction of mitochondria, which released cytochrome c and activated caspase-3 in human chondrosarcoma. In addition, animal experiments illustrated reduced tumor volume, which led to an increased number of terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL)-positive cells and an increased level of cleaved PARP protein following trichodermin treatment. Together, this study demonstrates that trichodermin is a novel anti-tumor agent against human chondrosarcoma cells both in vitro and in vivo via mitochondrial dysfunction and ER stress.

Group B Streptococcus induces a caspase-dependent apoptosis in fetal rat lung interstitium

Group B Streptococcus (GBS) is an important pathogen and is associated with sepsis and meningitis in neonates and infants. An ex vivo model that facilitates observations of GBS interactions with multiple host cell types over time was used to study its pathogenicity. GBS infections were associated with profound reductions in fetal lung; explant size, and airway branching. Elevated levels of apoptosis subsequent to GBS infections were observed by whole-mount confocal immunofluorescence using activated-caspase-3-antibodies and terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL) assays. The caspase inhibitor Z-VAD-FMK abolished the increase in TUNEL-positive cells associated with GBS infections, indicating that the GBS-induced apoptosis was caspase-dependent. Digital image analyses revealed that both GBS and the active form of caspase-3 were distributed primarily within the lung interstitium, suggesting that these tissues are important targets for GBS. Antibodies to the active form of caspase-3 colocalized with both macrophage- and erythroblast-markers, suggesting that these hematopoietic cells are vulnerable to GBS-mediated pathogenesis. These studies suggest that GBS infections profoundly alter lung morphology and caspase-dependent hematopoietic cell apoptosis within the lung interstitium play roles in GBS pathophysiology in this model.

Role of glyoxalase I in the proliferation and apoptosis control of human LNCaP and PC3 prostate cancer cells

BACKGROUND

Glyoxalase I (GLOI) detoxifies reactive dicarbonyls, as methylglyoxal (MG) that, directly or through the formation of MG-derived adducts, is a growth inhibitor and apoptosis inducer. GLOI has been considered a general marker of cell proliferation, but a direct link between the two has yet to be demonstrated. The aim of the present work was to clarify whether GLOI was involved in the proliferation control of LNCaP and PC3 human prostate cancer cells or might play a different role in the growth regulation of these cells.

METHODS

RNA interference was used to study the role of GLOI in cell proliferation or apoptosis. Cell proliferation was evaluated by [3H]thymidine incorporation assay and flow cytometry, that was also used to analyze apoptosis. Real-time TaqMan polymerase chain reaction and spectrophotometric analyses were used to study transcript levels or specific activity, respectively. Proteins levels were analyzed by Western blot. MG was measured by high-performance liquid chromatography.

RESULTS

We found that GLOI is not implicated in the proliferation control of LNCaP and PC3 cells but plays a role in the apoptosis of invasive prostate cancer PC3 cells, through a mechanism involving a specific MG-adduct and NF-kB signaling pathway.

CONCLUSIONS

Our data represent the first systematic demonstration that GLOI cannot be considered a general marker of cell proliferation and that acts as a pro-survival factor in invasive PC3 cells by elusing apoptosis. GLOI may be involved in prostate cancer progression, via the control of key molecules in the mitochondrial apoptotic mechanism, through NF-kB signaling pathway.

Immune modulation by group B Streptococcus influences host susceptibility to urinary tract infection by uropathogenic Escherichia coli

Urinary tract infection (UTI) is most often caused by uropathogenic Escherichia coli (UPEC). UPEC inoculation into the female urinary tract (UT) can occur through physical activities that expose the UT to an inherently polymicrobial periurethral, vaginal, or gastrointestinal flora. We report that a common urogenital inhabitant and opportunistic pathogen, group B Streptococcus (GBS), when present at the time of UPEC exposure, undergoes rapid UPEC-dependent exclusion from the murine urinary tract, yet it influences acute UPEC-host interactions and alters host susceptibility to persistent outcomes of bladder and kidney infection. GBS presence results in increased UPEC titers in the bladder lumen during acute infection and reduced inflammatory responses of murine macrophages to live UPEC or purified lipopolysaccharide (LPS), phenotypes that require GBS mimicry of host sialic acid residues. Taken together, these studies suggest that despite low titers, the presence of GBS at the time of polymicrobial UT exposure may be an overlooked risk factor for chronic pyelonephritis and recurrent UTI in susceptible groups, even if it is outcompeted and thus absent by the time of diagnosis.

Aeromonas hydrophila induced head kidney macrophage apoptosis in Clarias batrachus involves the activation of calpain and is caspase-3 mediated

The mechanism of macrophage cytotoxicity induced by Aeromonas hydrophila is yet unresolved. We observed A. hydrophila induces Head Kidney Macrophage (HKM) apoptosis in Clarias batrachus, as evident from Hoechst 33342 and AnnexinV-Propidium Iodide staining and presence of oligonucleosomal DNA ladder. Initiation of apoptosis required the bacteria to be alive, be actively phagocytosed into HKM and was dependent on host proteins. Elevated cytosolic calcium and consequent calpain activity that declined following pre-incubation with EGTA, verapamil and nifedipine implicates the role of calcium influx through voltage gated calcium channels and calpain in A. hydrophila-induced HKM apoptosis. Though, calpain-1 and -2 were involved, calpain-2 appeared to be more important in the process. EGTA, verapamil, nifedipine and calpain-2 inhibitor reduced caspase-3 activity and apoptosis. We conclude that A. hydrophila alters cytosolic calcium homeostasis initiating the activation of calpains, more specifically calpain-2, which leads to caspase-3 mediated HKM apoptosis in C. batrachus.

Group B streptococcus GAPDH is released upon cell lysis, associates with bacterial surface, and induces apoptosis in murine macrophages

Glyceraldehyde 3-phosphate dehydrogenases (GAPDH) are cytoplasmic glycolytic enzymes that, despite lacking identifiable secretion signals, have been detected at the surface of several prokaryotic and eukaryotic organisms where they exhibit non-glycolytic functions including adhesion to host components. Group B Streptococcus (GBS) is a human commensal bacterium that has the capacity to cause life-threatening meningitis and septicemia in newborns. Electron microscopy and fluorescence-activated cell sorter (FACS) analysis demonstrated the surface localization of GAPDH in GBS. By addressing the question of GAPDH export to the cell surface of GBS strain NEM316 and isogenic mutant derivatives of our collection, we found that impaired GAPDH presence in the surface and supernatant of GBS was associated with a lower level of bacterial lysis. We also found that following GBS lysis, GAPDH can associate to the surface of many living bacteria. Finally, we provide evidence for a novel function of the secreted GAPDH as an inducer of apoptosis of murine macrophages.

Calpain mediates epithelial cell microvillar effacement by enterohemorrhagic Escherichia coli

A member of the attaching and effacing (AE) family of pathogens, enterohemorrhagic Escherichia coli (EHEC) induces dramatic changes to the intestinal cell cytoskeleton, including effacement of microvilli. Effacement by the related pathogen enteropathogenic E. coli (EPEC) requires the activity of the Ca⁺²-dependent host protease, calpain, which participates in a variety of cellular processes, including cell adhesion and motility. We found that EHEC infection results in an increase in epithelial (CaCo-2a) cell calpain activity and that EHEC-induced microvillar effacement was blocked by ectopic expression of calpastatin, an endogenous calpain inhibitor, or by pretreatment of intestinal cells with a cell-penetrating version of calpastatin. In addition, ezrin, a known calpain substrate that links the plasma membrane to axial actin filaments in microvilli, was cleaved in a calpain-dependent manner during EHEC infection and lost from its normal locale within microvilli. Calpain may be a central conduit through which EHEC and other AE pathogens induce enterocyte cytoskeletal remodeling and exert their pathogenic effects.

Helicobacter pylori activates calpain via toll-like receptor 2 to disrupt adherens junctions in human gastric epithelial cells

Helicobacter pylori is a risk factor for the development of gastritis, gastroduodenal ulcers, and gastric adenocarcinoma. H. pylori-induced disruption of epithelial adherens junctions (AJs) is thought to promote the development of severe disease; however, the mechanisms whereby H. pylori alters AJ structure remain incompletely understood. The present study demonstrates that H. pylori infection in human patients is associated with elevated serum levels of an 80-kDa E-cadherin ectodomain, whose presence is independent of the presence of serum antibodies against CagA. In vitro, a heat-labile H. pylori surface component activates the host protease calpain in human gastric MKN45 cells independently of the virulence factors CagA and VacA. H. pylori-induced calpain activation results in cleavage of E-cadherin to produce a 100-kDa truncated form and induce relocalization of E-cadherin and β-catenin. Stimulation of MKN45 cells with the toll-like receptor 2 (TLR2) ligand P3C activated calpain and disrupted E-cadherin and β-catenin in a pattern similar to that induced by H. pylori. Inhibition of TLR2 prevented H. pylori-induced calpain activation and AJ disassembly. Together, these findings identify a novel pathway whereby H. pylori activates calpain via TLR2 to disrupt gastric epithelial AJ structure.

Arsenic-induced alteration in intracellular calcium homeostasis induces head kidney macrophage apoptosis involving the activation of calpain-2 and ERK in Clarias batrachus

We had earlier shown that exposure to arsenic (0.50 μM) caused caspase-3 mediated head kidney macrophage (HKM) apoptosis involving the p38-JNK pathway in Clarias batrachus. Here we examined the roles of calcium (Ca(2+)) and extra-cellular signal-regulated protein kinase (ERK), the other member of MAPK-pathway on arsenic-induced HKM apoptosis. Arsenic-induced HKM apoptosis involved increased expression of ERK and calpain-2. Nifedipine, verapamil and EGTA pre-treatment inhibited the activation of calpain-2, ERK and reduced arsenic-induced HKM apoptosis as evidenced from reduced caspase-3 activity, Annexin V-FITC-propidium iodide and Hoechst 33342 staining. Pre-incubation with ERK inhibitor U 0126 inhibited the activation of calpain-2 and interfered with arsenic-induced HKM apoptosis. Additionally, pre-incubation with calpain-2 inhibitor also interfered with the activation of ERK and inhibited arsenic-induced HKM apoptosis. The NADPH oxidase inhibitor apocynin and diphenyleneiodonium chloride also inhibited ERK activation indicating activation of ERK in arsenic-exposed HKM also depends on signals from NADPH oxidase pathway. Our study demonstrates the critical role of Ca(2+) homeostasis on arsenic-induced HKM apoptosis. We suggest that arsenic-induced alteration in intracellular Ca(2+) levels initiates pro-apoptotic ERK and calpain-2; the two pathways influence each other positively and induce caspase-3 mediated HKM apoptosis. Besides, our study also indicates the role of ROS in the activation of ERK pathway in arsenic-induced HKM apoptosis in C. batrachus.

FPTB, a novel CA-4 derivative, induces cell apoptosis of human chondrosarcoma cells through mitochondrial dysfunction and endoplasmic reticulum stress pathways

Chondrosarcoma is a malignant primary bone tumor that responds poorly to both chemotherapy and radiation therapy. The aim of this study was to elucidate the mechanism of the novel Combretastatin A-4 derivative, 2-(furanyl)-5-(pyrrolidinyl)-1-(3,4,5-trimethoxybenzyl)benzoimidazole (FPTB)-induced human chondrosarcoma cells apoptosis. FPTB induced cell apoptosis in human chondrosarcoma cell line but not primary chondrocytes. FPTB induced up-regulation of Bax and Bak, down-regulation of Bcl-2 and Bcl-XL and dysfunction of mitochondria in chondrosarcoma. FPTB also triggered endoplasmic reticulum (ER) stress, as indicated by changes in cytosol-calcium levels. We found that FPTB increased glucose-regulated proteins (GRP)78 but not GRP94 expression. In addition, treatment of cells with FPTB induced calpain expression and activity. Transfection of cells with GRP78 or calpain siRNA reduced FPTB-mediated cell apoptosis. Therefore, FPTB-induced apoptosis in chondrosarcoma cells through the mitochondria dysfunction and involves caspase-9 and caspase-3-mediated mechanism. FPTB also induced cell death mediated by increasing ER stress, GPR78 activation, and Ca(2+) release, which subsequently triggers calpain, caspase-12 and caspase-3 activity, resulting in apoptosis.

The calpain system and cancer

The calpains are a conserved family of cysteine proteinases that catalyse the controlled proteolysis of many specific substrates. Calpain activity is implicated in several fundamental physiological processes, including cytoskeletal remodelling, cellular signalling, apoptosis and cell survival. Calpain expression is altered during tumorigenesis, and the proteolysis of numerous substrates, such as inhibitors of nuclear factor-κB (IκB), focal adhesion proteins (including, focal adhesion kinase and talin) and proto-oncogenes (for example, MYC), has been implicated in tumour pathogenesis. Recent evidence indicates that the increased expression of certain family members might influence the response to cancer therapies, providing justification for the development of novel calpain inhibitors.

Group B Streptococcus (GBS) disrupts by calpain activation the actin and microtubule cytoskeleton of macrophages

Group B Streptococcus (GBS) has evolved several strategies to avoid host defences where macrophages are one of main targets. Since pathogens frequently target the cytoskeleton to evade immune defences, we investigated if GBS manipulates macrophage cytoskeleton. GBS-III-COH31 in a time- and infection ratio-dependent manner induces great macrophage cytoskeleton alterations, causing degradation of several structural and regulatory cytoskeletal proteins. GBS β-haemolysin is involved in cytoskeleton alterations causing plasma membrane permeability defects which allow calcium influx and calpain activation. In fact, cytoskeleton alterations are not induced by GBS-III-COH31 in conditions that suppress β-haemolysin expression/activity and in presence of dipalmitoylphosphatidylcholine (β-haemolysin inhibitor). Calpains, particularly m-calpain, are responsible for GBS-III-COH31-induced cytoskeleton disruption. In fact, the calpain inhibitor PD150606, m-calpain small-interfering-RNA and EGTA which inhibit calpain activation prevented cytoskeleton degradation whereas µ-calpain and other protease inhibitors did not. Finally, calpain inhibition strongly increased the number of viable intracellular GBS-III-COH31, showing that cytoskeleton alterations reduced macrophage phagocytosis. Marked macrophage cytoskeleton alterations are also induced by GBS-III-NEM316 and GBS-V-10/84 through β-haemolysin-mediated plasma membrane permeability defects which allow calpain activation. This study suggests a new GBS strategy to evade macrophage antimicrobial responses based on cytoskeleton disruption by an unusual mechanism mediated by calcium influx and calpain activation.

The novel benzimidazole derivative, MPTB, induces cell apoptosis in human chondrosarcoma cells

Chondrosarcoma is a malignant primary bone tumor that responds poorly to both chemotherapy and radiation therapy. This study is the first to investigate the anti-cancer effects of the new benzimidazole derivative (5-methyl-2(pyridine-3-yl)-1-(3,4,5-trimethoxybenzyl)benzimidazole; MPTB) in human chondrosarcoma cells. MPTB-induced cell apoptosis in two human chondrosarcoma cell lines, JJ012 and SW1353 but not in primary chondrocytes. MPTB-induced upregulation of Bax and Bak and dysfunction of mitochondria in chondrosarcoma. MPTB triggered endoplasmic reticulum (ER) stress, as indicated by changes in cytosol calcium levels, and increased glucose-regulated protein (GRP) expression. MPTB also increased calpain expression. Transfection of cells with GRP78 or calpain siRNA reduced MPTB-mediated cell apoptosis in JJ012 cells. Importantly, animal studies have revealed a dramatic 44% reduction in tumor volume after 21 d of treatment. This study demonstrates novel anti-cancer activity of MPTB against human chondrosarcoma cells and in murine tumor models.

Bacterial pore-forming cytolysins induce neuronal damage in a rat model of neonatal meningitis

BACKGROUND

Group B Streptococcus (GBS) and Streptococcus pneumoniae (SP) are leading causes of bacterial meningitis in neonates and children. Each pathogen produces a pore-forming cytolytic toxin, β-hemolysin/cytolysin (β-h/c) by GBS and pneumolysin by SP. The aim of this study was to understand the role of these pore-forming cytotoxins, in particular of the GBS β-h/c, as potential neurotoxins in experimental neonatal meningitis.

METHODS

Meningitis was induced in 7- and 11-day-old rats by intracisternal injection of wild type (WT) GBS or SP and compared with isogenic β-h/c- or pneumolysin-deficient mutants, or a double mutant of SP deficient in pneumolysin and hydrogen peroxide production.

RESULTS

GBS β-h/c and SP pneumolysin contributed to neuronal damage, worsened clinical outcome and weight loss, but had no influence on the early kinetics of leukocyte influx and bacterial growth in the cerebrospinal fluid. In vitro, β-h/c-induced neuronal apoptosis occurred independently of caspase-activation and was not preventable by the broad spectrum caspase-inhibitor z-VAD-fmk.

CONCLUSIONS

These data suggest that both cytolytic toxins, the GBS β-h/c and SP pneumolysin, contribute to neuronal damage in meningitis and extend the concept of a key role for bacterial pore-forming cytolysins in the pathogenesis and sequelae of neonatal meningitis.

Protein expression changes induced in murine peritoneal macrophages by Group B Streptococcus

Protein expression changes induced in thioglycolate-elicited peritoneal murine macrophages (M Phi) by infection with type III Group B Streptococcus (GBS) are described. Proteins from control M Phi and M Phi incubated 2 h with live or heat-inactivated GBS were separated by 2-DE. Proteins whose expression was significantly different in infected M Phi, as compared with control cells, were identified by MS/MS analysis. Changes in the expression level of proteins involved in both positive and negative modulation of phagocytic functions, stress response and cell death were induced in M Phi by GBS infection. In particular, expression of enzymes playing a key role in production of reactive oxygen species was lowered in GBS-infected M Phi. Significant alterations in the expression of some metabolic enzymes were also observed, most of the glycolytic and of the pentose-cycle enzymes being down-regulated in M Phi infected with live GBS. Finally, evidence was obtained that GBS infection affects the expression of enzymes or enzyme subunits involved in ATP synthesis and in adenine nucleotides interconversion processes.

Listeriolysin O-dependent bacterial entry into the cytoplasm is required for calpain activation and interleukin-1 alpha secretion in macrophages infected with Listeria monocytogenes

Listeriolysin O (LLO), an hly-encoded cytolysin of Listeria monocytogenes, plays an essential role in the entry of L. monocytogenes into the host cell cytoplasm. L. monocytogenes-infected macrophages produce various proinflammatory cytokines, including interleukin-1 alpha (IL-1 alpha), that contribute to the host immune response. In this study, we have examined IL-1 alpha production in macrophages infected with wild-type L. monocytogenes or a nonescaping mutant strain deficient for LLO (Delta hly). Expression of IL-1 alpha mRNA and accumulation of pro-IL-1 alpha in the cytoplasm were induced by both strains. In contrast, the secretion of the mature form of IL-1 alpha from infected macrophages was observed in infection with wild-type L. monocytogenes but not with the Delta hly mutant. A recovery of the ability to induce IL-1 alpha secretion was shown in a mutant strain complemented with the hly gene. The Toll-like receptor (TLR)/MyD88 signaling pathway was exclusively required for the expression of pro-IL-1 alpha, independently of LLO-mediated cytoplasmic entry of L. monocytogenes. The LLO-dependent secretion of mature IL-1 alpha was abolished by addition of calcium chelators, and only LLO-producing L. monocytogenes strains were able to induce elevation of the intracellular calcium level in infected macrophages. A calcium-dependent protease, calpain, was implicated in the maturation and secretion of IL-1 alpha induced by LLO-producing L. monocytogenes strains based on the effect of calpain inhibitor. Functional activation of calpain was detected in macrophages infected with LLO-producing L. monocytogenes strains but not with a mutant strain lacking LLO. These results clearly indicated that LLO-mediated cytoplasmic entry of bacteria could induce the activation of intracellular calcium signaling, which is essential for maturation and secretion of IL-1 alpha in macrophages during L. monocytogenes infection through activation of a calcium-dependent calpain protease. In addition, recombinant LLO, when added to macrophages infected with the Delta hly strain, could induce calcium influx and IL-1 alpha secretion at doses exhibiting cytolytic activity, suggesting that LLO produced by intracellular L. monocytogenes may be implicated in induction of calcium influx through pore formation.

BFPP, a phloroglucinol derivative, induces cell apoptosis in human chondrosarcoma cells through endoplasmic reticulum stress

Chondrosarcoma is a malignant primary bone tumor that responds poorly to both chemotherapy and radiation therapy. This study is the first to investigate the anticancer effects of the new phloroglucinol derivative (2,4-bis(2-fluorophenylacetyl)phloroglucinol; BFPP) in human chondrosarcoma cells. BFPP induced cell apoptosis in two human chondrosarcoma cell lines, JJ012 and SW1353 but not in primary chondrocytes. BFPP triggered endoplasmic reticulum (ER) stress, as indicated by changes in cytosol calcium levels, and increased glucose-regulated protein 78 (GRP78) expression, but failed to show the same effects on GRP94 expression. BFPP also increased calpain expression and activity. Transfection of cells with GRP78 or calpain siRNA reduced BFPP-mediated cell apoptosis in JJ012 cells. Importantly, animal studies have revealed a dramatic 50% reduction in tumor volume after 21 days of treatment. This study demonstrates novel anticancer activity of BFPP against human chondrosarcoma cells and in murine tumor models.

Pretreatment with pancaspase inhibitor (Z-VAD-FMK) delays but does not prevent intraperitoneal heat-killed group B Streptococcus-induced preterm delivery in a pregnant mouse model

Caspases and apoptosis are thought to play a role in infection-associated preterm-delivery. We have shown that in vitro treatment with pancaspase inhibitor Z-VAD-FMK protects trophoblasts from microbial antigen-induced apoptosis. Objective. To examine whether in vivo administration of Z-VAD-FMK would prevent infection-induced preterm-delivery. Methods. We injected 14.5 day-pregnant-mice with heat-killed group B streptococcus (HK-GBS). Apoptosis within placentas and membranes was assessed by TUNEL staining. Calpain expression and caspase-3 activation were assessed by immunohistochemistry. Preterm-delivery was defined as expulsion of a fetus within 48 hours after injection. Results. Intrauterine (i.u.) or intraperitoneal (i.p.) HK-GBS injection led to preterm-delivery and induced apoptosis in placentas and membranes at 14 hours. The expression of calpain, a caspase-independent inducer of apoptosis, was increased in placenta. Treatment with the specific caspase inhibitor Z-VAD-FMK (i.p.) prior to HK-GBS (i.p.) delayed but did not prevent preterm-delivery. Conclusion. Caspase-dependent apoptosis appears to play a role in the timing but not the occurrence of GBS-induced preterm delivery in the mouse.

Apoptosis of hippocampal pyramidal neurons is virus independent in a mouse model of acute neurovirulent picornavirus infection

Many viruses, including picornaviruses, have the potential to infect the central nervous system (CNS) and stimulate a neuroinflammatory immune response, especially in infants and young children. Cognitive deficits associated with CNS picornavirus infection result from injury and death of neurons that may occur due to direct viral infection or during the immune responses to virus in the brain. Previous studies have concluded that apoptosis of hippocampal neurons during picornavirus infection is a cell-autonomous event triggered by direct neuronal infection. However, these studies assessed neuron death at time points late in infection and during infections that lead to either death of the host or persistent viral infection. In contrast, many neurovirulent picornavirus infections are acute and transient, with rapid clearance of virus from the host. We provide evidence of hippocampal pathology in mice acutely infected with the Theiler's murine encephalomyelitis picornavirus. We found that CA1 pyramidal neurons exhibited several hallmarks of apoptotic death, including caspase-3 activation, DNA fragmentation, and chromatin condensation within 72 hours of infection. Critically, we also found that many of the CA1 pyramidal neurons undergoing apoptosis were not infected with virus, indicating that neuronal cell death during acute picornavirus infection of the CNS occurs in a non-cell-autonomous manner. These observations suggest that therapeutic strategies other than antiviral interventions may be useful for neuroprotection during acute CNS picornavirus infection.

Ca2+ signaling in airway epithelial cells facilitates leukocyte recruitment and transepithelial migration

In airway cells, TLR2 stimulation by bacterial products activates Ca2+ fluxes that signal leukocyte recruitment to the lung and facilitates transepithelial migration into the airway lumen. TLR2 is apically displayed on airway cells, where it senses bacterial stimuli. Biochemical and genetic approaches demonstrate that TLR2 ligands stimulate release of Ca2+ from intracellular stores by activating TLR2 phosphorylation by c-Src and recruiting PI3K and PLCgamma to affect Ca2+ release through IP3Rs. This Ca2+ release plays a pivotal role in signaling TLR2-dependent NF-kappaB activation and chemokine expression to recruit PMNs to the lung. In addition, TLR2-initiated Ca2+ release activates Ca2+-dependent proteases, calpains, which cleave the transmembrane proteins occludin and E-cadherin to promote PMN transmigration. This review highlights recent findings that demonstrate a central role for Ca2+ signaling in airway epithelial cells to induce proinflammatory gene transcription and to initiate junctional changes that accommodate transmigration of recruited PMNs.