Role of cathepsin B in dengue virus-mediated apoptosis

The HN protein of Newcastle disease virus induces cell apoptosis through the induction of lysosomal membrane permeabilization

Lysosomes are acidic organelles that mediate the degradation and recycling of cellular waste materials. Damage to lysosomes can cause lysosomal membrane permeabilization (LMP) and trigger different types of cell death, including apoptosis. Newcastle disease virus (NDV) can naturally infect most birds. Additionally, it serves as a promising oncolytic virus known for its effective infection of tumor cells and induction of intensive apoptotic responses. However, the involvement of lysosomes in NDV-induced apoptosis remains poorly understood. Here, we demonstrate that NDV infection profoundly triggers LMP, leading to the translocation of cathepsin B and D and subsequent mitochondria-dependent apoptosis in various tumor and avian cells. Notably, the released cathepsin B and D exacerbate NDV-induced LMP by inducing the generation of reactive oxygen species. Additionally, we uncover that the viral Hemagglutinin neuraminidase (HN) protein induces the deglycosylation and degradation of lysosome-associated membrane protein 1 (LAMP1) and LAMP2 dependent on its sialidase activity, which finally contributes to NDV-induced LMP and cellular apoptosis. Overall, our findings elucidate the role of LMP in NDV-induced cell apoptosis and provide novel insights into the function of HN during NDV-induced LMP, which provide innovative approaches for the development of NDV-based oncolytic agents.

Distinct Cleavage Properties of Cathepsin B Compared to Cysteine Cathepsins Enable the Design and Validation of a Specific Substrate for Cathepsin B over a Broad pH Range

The biological and pathological functions of cathepsin B occur in acidic lysosomes and at the neutral pH of cytosol, nuclei, and extracellular locations. Importantly, cathepsin B displays different substrate cleavage properties at acidic pH compared to neutral pH conditions. It is, therefore, desirable to develop specific substrates for cathepsin B that measure its activity over broad pH ranges. Current substrates used to monitor cathepsin B activity consist of Z-Phe-Arg-AMC and Z-Arg-Arg-AMC, but they lack specificity since they are cleaved by other cysteine cathepsins. Furthermore, Z-Arg-Arg-AMC monitors cathepsin B activity at neutral pH and displays minimal activity at acidic pH. Therefore, the purpose of this study was to design and validate specific fluorogenic peptide substrates that can monitor cathepsin B activity over a broad pH range from acidic to neutral pH conditions. In-depth cleavage properties of cathepsin B were compared to those of the cysteine cathepsins K, L, S, V, and X via multiplex substrate profiling by mass spectrometry at pH 4.6 and pH 7.2. Analysis of the cleavage preferences predicted the tripeptide Z-Nle-Lys-Arg-AMC as a preferred substrate for cathepsin B. Significantly, Z-Nle-Lys-Arg-AMC displayed the advantageous properties of measuring high cathepsin B specific activity over acidic to neutral pHs and was specifically cleaved by cathepsin B over the other cysteine cathepsins. Z-Nle-Lys-Arg-AMC specifically monitored cathepsin B activity in neuronal and glial cells which were consistent with relative abundances of cathepsin B protein. These findings validate Z-Nle-Lys-Arg-AMC as a novel substrate that specifically monitors cathepsin B activity over a broad pH range.

Cathepsin B Dipeptidyl Carboxypeptidase and Endopeptidase Activities Demonstrated across a Broad pH Range

Cathepsin B is a lysosomal protease that participates in protein degradation. However, cathepsin B is also active under neutral pH conditions of the cytosol, nuclei, and extracellular locations. The dipeptidyl carboxypeptidase (DPCP) activity of cathepsin B, assayed with the Abz-GIVR↓AK(Dnp)-OH substrate, has been reported to display an acidic pH optimum. In contrast, the endopeptidase activity, monitored with Z-RR-↓AMC, has a neutral pH optimum. These observations raise the question of whether other substrates can demonstrate cathepsin B DPCP activity at neutral pH and endopeptidase activity at acidic pH. To address this question, global cleavage profiling of cathepsin B with a diverse peptide library was conducted under acidic and neutral pH conditions. Results revealed that cathepsin B has (1) major DPCP activity and modest endopeptidase activity under both acidic and neutral pH conditions and (2) distinct pH-dependent amino acid preferences adjacent to cleavage sites for both DPCP and endopeptidase activities. The pH-dependent cleavage preferences were utilized to design a new Abz-GnVR↓AK(Dnp)-OH DPCP substrate, with norleucine (n) at the P3 position, having improved DPCP activity of cathepsin B at neutral pH compared to the original Abz-GIVR↓AK(Dnp)-OH substrate. The new Z-VR-AMC and Z-ER-AMC substrates displayed improved endopeptidase activity at acidic pH compared to the original Z-RR-AMC. These findings illustrate the new concept that cathepsin B possesses DPCP and endopeptidase activities at both acidic and neutral pH values. These results advance understanding of the pH-dependent cleavage properties of the dual DPCP and endopeptidase activities of cathepsin B that function under different cellular pH conditions.

The Key Role of Lysosomal Protease Cathepsins in Viral Infections

Cathepsins encompass a family of lysosomal proteases that mediate protein degradation and turnover. Although mainly localized in the endolysosomal compartment, cathepsins are also found in the cytoplasm, nucleus, and extracellular space, where they are involved in cell signaling, extracellular matrix assembly/disassembly, and protein processing and trafficking through the plasma and nuclear membrane and between intracellular organelles. Ubiquitously expressed in the body, cathepsins play regulatory roles in a wide range of physiological processes including coagulation, hormone secretion, immune responses, and others. A dysregulation of cathepsin expression and/or activity has been associated with many human diseases, including cancer, diabetes, obesity, cardiovascular and inflammatory diseases, kidney dysfunctions, and neurodegenerative disorders, as well as infectious diseases. In viral infections, cathepsins may promote (1) activation of the viral attachment glycoproteins and entry of the virus into target cells; (2) antigen processing and presentation, enabling the virus to replicate in infected cells; (3) up-regulation and processing of heparanase that facilitates the release of viral progeny and the spread of infection; and (4) activation of cell death that may either favor viral clearance or assist viral propagation. In this review, we report the most relevant findings on the molecular mechanisms underlying cathepsin involvement in viral infection physiopathology, and we discuss the potential of cathepsin inhibitors for therapeutical applications in viral infectious diseases.

Coprophagy Prevention Decreases the Reproductive Performance and Granulosa Cell Apoptosis via Regulation of CTSB Gene in Rabbits

Coprophagy is an instinctive behavior in rabbit with important effects on growth and reproductive performance. The underlying mechanism of this effect in rabbit is unknown. Here, we used Elizabeth circle as a coprophagy preventing model in female rabbits and assess feed intake, growth, and reproductive performance. We found that preventing coprophagy did not affect feed intake but decreased body weight and weight of several organs and tissues and resulted in complete reproductive failure during the late pregnancy period, accompanied by reduced levels of plasma progesterone. RNA-seq analysis of rabbit ovarian tissues revealed that preventing coprophagy affected significantly 241 genes (DEGs), with the large majority being downregulated. Bioinformatic analyses revealed that those DEGs are mostly involved in apoptosis, immune response, and metabolic pathways. Among DEGs, the lysosomal cysteine protease cathepsin B (CTSB) was significantly downregulated in the coprophagy prevention group. Further studies using siRNA and adenovirus overexpression systems revealed that CTSB promotes the proliferation of rabbit granulosa cells (GCS) and prevents apoptosis. Measurement of transcripts coding for proteins related to apoptosis revealed a minor transcriptomic effect of CTSB, indicating that its effect is likely post-transcriptional. Overexpression of CTSB increased secretion of progesterone and estradiol, partly via upregulation of CYP19A1 while inhibition of CTSB decreased progesterone secretion partly via downregulation of the StAR gene. In conclusion, our study demonstrated the detrimental effect on reproduction by preventing coprophagy with a main role for this response played by CTSB on the granulosa cells of the ovary.

Selective Neutral pH Inhibitor of Cathepsin B Designed Based on Cleavage Preferences at Cytosolic and Lysosomal pH Conditions

Cathepsin B is a cysteine protease that normally functions within acidic lysosomes for protein degradation, but in numerous human diseases, cathepsin B translocates to the cytosol having neutral pH where the enzyme activates inflammation and cell death. Cathepsin B is active at both the neutral pH 7.2 of the cytosol and the acidic pH 4.6 within lysosomes. We evaluated the hypothesis that cathepsin B may possess pH-dependent cleavage preferences that can be utilized for design of a selective neutral pH inhibitor by (1) analysis of differential cathepsin B cleavage profiles at neutral pH compared to acidic pH using multiplex substrate profiling by mass spectrometry (MSP-MS), (2) design of pH-selective peptide-7-amino-4-methylcoumarin (AMC) substrates, and (3) design and validation of Z-Arg-Lys-acyloxymethyl ketone (AOMK) as a selective neutral pH inhibitor. Cathepsin B displayed preferences for cleaving peptides with Arg in the P2 position at pH 7.2 and Glu in the P2 position at pH 4.6, represented by its primary dipeptidyl carboxypeptidase and modest endopeptidase activity. These properties led to design of the substrate Z-Arg-Lys-AMC having neutral pH selectivity, and its modification with the AOMK warhead to result in the inhibitor Z-Arg-Lys-AOMK. This irreversible inhibitor displays nanomolar potency with 100-fold selectivity for inhibition of cathepsin B at pH 7.2 compared to pH 4.6, shows specificity for cathepsin B over other cysteine cathepsins, and is cell permeable and inhibits intracellular cathepsin B. These findings demonstrate that cathepsin B possesses pH-dependent cleavage properties that can lead to development of a potent, neutral pH inhibitor of this enzyme.

Cytoprotective effects of taxifolin against cadmium-induced apoptosis in human keratinocytes

Cadmium (Cd) is a heavy metal widely used in industry, and the skin is an important target of this metal. Taxifolin (Tax), a natural source of bioflavonoids found in various conifers, exerts multiple biologic effects on skin cells. However, the mechanisms by which Tax protects keratinocytes against Cd are currently unclear. We investigated the cytoprotective effects of Tax against Cd-induced apoptosis in the human HaCaT keratinocyte. The water-soluble tetrazolium salt (WST-1) assay and Annexin V/propidium iodide double-staining assay results showed that Cd-induced cell death was lower in cells treated with Tax (0–100 μM) than in cells treated with Cd alone. Additionally, a reduction of Cd-induced DNA fragmentation by Tax was shown by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labeling assay. The levels of reactive oxygen species were also lower in Cd/Tax-treated cells than in Cd-treated cells. We employed a two-dimensional electrophoresis-based proteomic analysis to identify treatment-related alterations in protein expression. Tax downregulated cathepsin B and D and upregulated hsp27, cyclophilin A, and peroxiredowin-1. Western blotting confirmed the downregulation of cathepsin B and D and the upregulation of hsp27. The cytoprotective effects of Tax against Cd-induced apoptosis were also characterized by the changes in the activity of caspase 3, -7, poly ADP-ribose polymerase, the cellular proliferation-related ERK1/2, and AKT. Furthermore, the levels of cell cycle-related proteins, such as SP1 and p21, decreased, whereas p53 level increased. We concluded that Tax reduced Cd cytotoxicity and Cd-induced apoptosis by inhibiting the apoptotic pathway.

B cell subset alteration and the expression of tissue homing molecules in dengue infected patients

Background

B cells play an essential role during dengue viral infection. While a major expansion of antibody secreting cells (ASCs) was observed, the importance of these increased frequencies of ASCs remains unclear. The alteration of B cell subsets may result from the expression of tissue specific homing molecules leading to their mobilization and distribution to different target organs during acute dengue viral infection.

Methods

In this study, whole blood samples were obtained from thirty pediatric dengue-infected patients and ten healthy children and then stained with fluorochrome-conjugated monoclonal antibodies against CD3, CD14, CD19, CD20, CD21, CD27, CD38, CD45, CD138 and homing molecules of interest before analyzed by polychromatic flow cytometry. B cell subsets were characterized throughout acute infection period.

Results

Data shows that there were no detectable differences in frequencies of resting, activated and tissue memory cells, whereas the frequency of ASCs was significantly increased and associated with the lower frequency of naïve cells. These results were found from patients with both dengue fever and dengue hemorrhagic fever, suggesting that such change or alteration of B cells was not associated with disease severity. Moreover, several homing molecules (e.g., CXCR3 and CCR2) were found in ASCs, indicating that ASCs may distribute to inflamed tissues and various organs.

Conclusions

Findings from this study provide insight into B cell subset distribution. Furthermore, organ mobilization according to homing molecule expression on different B cell subsets during the course of dengue viral infection also suggests they are distributed to inflamed tissues and various organs.

A transcriptomic survey of the impact of environmental stress on response to dengue virus in the mosquito, Aedes aegypti

Populations of Aedes aegypti naturally exhibit variable susceptibility to dengue viruses. This natural variation can be impacted by nutritional stress resulting from larval-stage crowding, indicating the influence of environment components on the adult mosquito immune response. In particular, larval crowding was previously shown to reduce the susceptibility of adult females of a Trinidad field isolate of A. aegypti to the dengue serotype 2 (JAM1409) virus. Here, we present the first whole transcriptome study to address the impact of environmental stress on A. aegypti response to dengue virus. We examined expression profiles of adult females resulting from crowded and optimum reared larvae from the same Trinidad isolate at two critical early time points-3 and 18 hours post dengue virus infected blood meal. We exposed specimens to either a dengue or naïve blood meal, and then characterized the response in ten gene co-expression modules based on their transcriptional associations with environmental stress and time. We further analyzed the top 30 hub or master regulatory genes in each of the modules, and validated our results via qRT-PCR. These hub genes reveal which functions are critical to the mechanisms that confer dengue virus refractoriness or susceptibility to stress conditioned A. aegypti, as well as the time points at which they are most important.

Cathepsin B aggravates coxsackievirus B3-induced myocarditis through activating the inflammasome and promoting pyroptosis

Cathepsin B (CatB) is a cysteine proteolytic enzyme widely expressed in various cells and mainly located in the lysosomes. It contributes to the pathogenesis and development of many diseases. However, the role of CatB in viral myocarditis (VMC) has never been elucidated. Here we generated the VMC model by intraperitoneal injection of coxsackievirus B3 (CVB3) into mice. At day 7 and day 28, we found CatB was significantly activated in hearts from VMC mice. Compared with the wild-type mice receiving equal amount of CVB3, genetic ablation of CatB (Ctsb^-/-) significantly improved survival, reduced inflammatory cell infiltration, decreased serum level of cardiac troponin I, and ameliorated cardiac dysfunction, without altering virus titers in hearts. Conversely, genetic deletion of cystatin C (Cstc^-/-), which markedly enhanced CatB levels in hearts, distinctly increased the severity of VMC. Furthermore, compared with the control, we found the inflammasome was activated in the hearts of wild-type mice with VMC, which was attenuated in the hearts of Ctsb^-/- mice but was further enhanced in Cstc^-/- mice. Consistently, the inflammasome-initiated pyroptosis was reduced in Ctsb^-/- mice hearts and further increased in Cstc^-/- mice. These results suggest that CatB aggravates CVB3-induced VMC probably through activating the inflammasome and promoting pyroptosis. This finding might provide a novel strategy for VMC treatment.

Severe VMC could lead to sudden cardiac death especially in youths, and is also the most common cause of secondary dilated cardiomyopathy. However, we still lack effective and specific clinical treatments currently. Therefore, further exploration of the pathogenesis and new therapeutic targets are urgently needed. Our results implied that CatB, a cysteine protease mainly located in the lysosome, is activated in the hearts of mice with VMC induced by intraperitoneal injection of CVB3. Genetic deletion of CatB significantly improves survival, attenuates cardiac inflammation, decreases serum cardiac troponin I levels and alleviates cardiac dysfunction, without altering virus titers in hearts. However, ablation of its main endogenous inhibitor, cystatin C, distinctly exaggerates the disease severity. Mechanistically, we found that CatB influences VMC probably by activating the NLRP3 inflammasome and promoting caspase-1-induced pyroptosis. This may provide a potential new therapeutic strategy for VMC.

RNAi screen reveals a role of SPHK2 in dengue virus-mediated apoptosis in hepatic cell lines

Hepatic dysfunction is a feature of dengue virus (DENV) infection. Hepatic biopsy specimens obtained from fatal cases of DENV infection show apoptosis, which relates to the pathogenesis of DENV infection. However, how DENV induced liver injury is not fully understood. In this study, we aim to identify the factors that influence cell death by employing an apoptosis-related siRNA library screening. Our results show the effect of 558 gene silencing on caspase 3-mediated apoptosis in DENV-infected Huh7 cells. The majority of genes that contributed to apoptosis were the apoptosis-related kinase enzymes. Tumor necrosis factor superfamily member 12 (TNFSF12), and sphingosine kinase 2 (SPHK2), were selected as the candidate genes to further validate their influences on DENV-induced apoptosis. Transfection of siRNA targeting SPHK2 but not TNFSF12 genes reduced apoptosis determined by Annexin V/PI staining. Knockdown of SPHK2 did not reduce caspase 8 activity; however, did significantly reduce caspase 9 activity, suggesting its involvement of SPHK2 in the intrinsic pathway of apoptosis. Treatment of ABC294649, an inhibitor of SPHK2, reduced the caspase 3 activity, suggesting the involvement of its kinase activity in apoptosis. Knockdown of SPHK2 significantly reduced caspase 3 activity not only in DENV-infected Huh7 cells but also in DENV-infected HepG2 cells. Our results were consistent across all of the four serotypes of DENV infection, which supports the pro-apoptotic role of SPHK2 in DENV-infected liver cells.

Divergent roles of three cytochrome c in CTSB-modulating coelomocyte apoptosis in Apostichopus japonicus

Cytochrome c plays crucial roles in apoptosis and the immune response. We previously demonstrated that cathepsin B from Apostichopus japonicus (AjCTSB) induces coelomocyte apoptosis. However, the mechanistic explanation and the regulation of this process have not been investigated. In the present study, we identified three cytochrome c cDNAs from A. japonicus (designated Ajcytc1, Ajcytc-1, and Ajcytc-2) using expressed sequence tag- (EST) and RACE-based approaches. The deduced amino acid sequences of the three cytochrome isoforms contained conserved CXXCH motifs, which are involved in binding heme and maintaining proteolytic activity. Time course expression analysis in vitro and in vivo revealed that the three cytochrome isoforms were induced upon pathogen challenge and LPS exposure. More importantly, AjCTSB knockdown by siRNA dramatically increased mitochondrial membrane potential (ΔΨm) in a time-dependent manner based on JC-1 fluorescent probe staining. AjCTSB knockdown also resulted in decreased expression of these three cytochromes 24 h after siAjCTSB transfection. Functional analysis using isoform-specific siRNAs revealed that Ajcytc-1, but not Ajcytc1 or Ajcytc-2, is involved in coelomocyte apoptosis. Moreover, the transcript level of Ajcaspase-3, an apoptosis executioner, was also consistently down-regulated upon silencing of Ajcytc-1 but not Ajcytc1 or Ajcytc-2. Collectively, these results indicate that Ajcytc1, Ajcytc-1, and Ajcytc-2 play distinct roles in mediating the immune response to bacteria according to AjCTSB expression. Moreover, Ajcytc-1 could be released upon dissipation of the ΔΨm, which could further trigger coelomocyte apoptosis through the activation of Ajcaspase-3.

Molecular cloning and functional characterization of cathepsin B from the sea cucumber Apostichopus japonicus

Cathepsin B (CTSB), a member of lysosomal cysteine protease, is involved in multiple levels of physiological and biological processes, and also plays crucial roles in host immune defense against pathogen infection in vertebrates. However, the function of CTSB within the innate immune system of invertebrates, particularly in marine echinoderms, has been poorly documented. In this study, the immune function of CTSB in Apostichopus japonicus (designated as AjCTSB), a commercially important and disease vulnerable aquaculture specie, was investigated by integrated molecular and protein approaches. A 2153 bp cDNA representing the full-length of AjCTSB was cloned via overlapping ESTs and RACE fragments. AjCTSB contained an open reading frame of 999 bp encoding a secreted protein of 332 amino acid residues with a predicted molecular mass of 36.8 kDa. The deduced amino acid of AjCTSB shared a typical activity center containing three conserved amino acid residues (Cys¹⁰⁸, His²⁷⁷ and Asn²⁹⁷). Phylogenetic tree analysis also supported that AjCTSB was a new member of CTSB family with clustering firstly with invertebrate CTSBs. Quantitative real time PCR analysis revealed that AjCTSB was ubiquitously expressed in all examined tissues with the highest levels in intestine. The Vibrio splendidus challenged sea cucumber and LPS-exposed coelomocytes could both significantly boost the expression of AjCTSB. Moreover, the purified recombinant AjCTSB exhibited dose-dependent CTSB activities at the concentration ranged from 0 to 0.24 μg μL^-1. Further functional analysis indicated that coelomocytes apoptosis was significantly inhibited by 0.16-fold in vivo and the apoptosis execution Ajcaspase 3 was extremely reduced in Apostichopus japonicus coelomocytes treated with specific AjCTSB siRNA. Collectively, all these results suggested that AjCTSB was an important immune factor and might be served as apoptosis enhancers in pathogen challenged sea cucumber.

Exploring Reovirus Plasticity for Improving Its Use as Oncolytic Virus

Reoviruses are non-enveloped viruses with a segmented double stranded RNA genome. In humans, they are not associated with serious disease. Human reoviruses exhibit an inherent preference to replicate in tumor cells, which makes them ideally suited for use in oncolytic virotherapies. Their use as anti-cancer agent has been evaluated in several clinical trials, which revealed that intra-tumoral and systemic delivery of reoviruses are well tolerated. Despite evidence of anti-tumor effects, the efficacy of reovirus in anti-cancer monotherapy needs to be further enhanced. The opportunity to treat both the primary tumor as well as metastases makes systemic delivery a preferred administration route. Several pre-clinical studies have been conducted to address the various hurdles connected to systemic delivery of reoviruses. The majority of those studies have been done in tumor-bearing immune-deficient murine models. This thwarts studies on the impact of the contribution of the immune system to the tumor cell eradication. This review focuses on key aspects of the reovirus/host-cell interactions and the methods that are available to modify the virus to alter these interactions. These aspects are discussed with a focus on improving the reovirus' antitumor efficacy.

Quantitative Proteomics Analysis of the Hepatitis C Virus Replicon High-Permissive and Low-Permissive Cell Lines

Chronic hepatitis C virus (HCV) infection is one of the leading causes of severe hepatitis. The molecular mechanisms underlying HCV replication and pathogenesis remain unclear. The development of the subgenome replicon model system significantly enhanced study of HCV. However, the permissiveness of the HCV subgenome replicon greatly differs among different hepatoma cell lines. Proteomic analysis of different permissive cell lines might provide new clues in understanding HCV replication. In this study, to detect potential candidates that might account for the differences in HCV replication. Label-free and iTRAQ labeling were used to analyze the differentially expressed protein profiles between Huh7.5.1 wt and HepG2 cells. A total of 4919 proteins were quantified in which 114 proteins were commonly identified as differentially expressed by both quantitative methods. A total of 37 differential proteins were validated by qRT-PCR. The differential expression of Glutathione S-transferase P (GSTP1), Ubiquitin carboxyl-terminal hydrolase isozyme L1 (UCHL1), carboxylesterase 1 (CES1), vimentin, Proteasome activator complex subunit1 (PSME1), and Cathepsin B (CTSB) were verified by western blot. And over-expression of CTSB or knock-down of vimentin induced significant changes to HCV RNA levels. Additionally, we demonstrated that CTSB was able to inhibit HCV replication and viral protein translation. These results highlight the potential role of CTSB and vimentin in virus replication.

Evidence of plasticity in the dengue virus: Host cell interaction

Dengue virus (DENV) is the most important mosquito transmitted human viral pathogen. There are four different dengue viruses (DENV 1 to DENV 4) with multiple genotypes and strains. Whether there are significant differences in how these DENVs interact with and modulate the host cell proteome remains unclear. Using a panel of 12 DENVs representative of one isolate for each DENV from three different origins (lab adapted, low passage isolates from dengue fever patients, low passage isolates from dengue hemorrhagic fever patients) LLC-MK2 cells were equally infected and proteomic alterations compared by MALDI-TOF and principal component analysis and a sub-10 kDa peptidome analysis. There was no clear segregation of data with respect to either virus origin or serotype in either the MALDI-TOF or the peptidome analysis. The two isolates with the greatest variation from the other isolates in the MALDI-TOF analysis were a low passage DENV 3 dengue fever isolate and a low passage DENV 4 dengue hemorrhagic fever isolate. Analysis of the sub-10 kda protein fraction by LC-MS/MS identified 128 proteins of which only 28 (20%) were constantly expressed in all infections, while 80% showed variable expression, with no clear relationship with either serotype or virus origin. These results suggest that the interaction between DENV and the host cell is characterized by a degree of plasticity, whereby the end biological processes are not rigorously determined by specific proteome alterations, and that virus strain plays a role in determining the specific proteome changes.

Lysosomal ceramide generated by acid sphingomyelinase triggers cytosolic cathepsin B-mediated degradation of X-linked inhibitor of apoptosis protein in natural killer/T lymphoma cell apoptosis

We previously reported that IL-2 deprivation induced acid sphingomyelinase-mediated (ASM-mediated) ceramide elevation and apoptosis in an NK/T lymphoma cell line KHYG-1. However, the molecular mechanism of ASM–ceramide-mediated apoptosis during IL-2 deprivation is poorly understood. Here, we showed that IL-2 deprivation induces caspase-dependent apoptosis characterized by phosphatidylserine externalization, caspase-8, -9, and -3 cleavage, and degradation of X-linked inhibitor of apoptosis protein (XIAP). IL-2 re-supplementation rescued apoptosis via inhibition of XIAP degradation without affecting caspase cleavage. However, IL-2 deprivation induced ceramide elevation via ASM in lysosomes and activated lysosomal cathepsin B (CTSB) but not cathepsin D. A CTSB inhibitor CA-074 Me and knockdown of CTSB inhibited ceramide-mediated XIAP degradation and apoptosis. Inhibition of ceramide accumulation in lysosomes using an ASM inhibitor, desipramine, decreased cytosolic activation of CTSB by inhibiting its transfer into cytosol from the lysosome. Knockdown of ASM also inhibited XIAP degradation and apoptosis. Furthermore, cell permeable N-acetyl sphingosine (C₂-ceramide), which increases mainly endogenous d18:1/16:0 and d18:1/24:1 ceramide-like IL-2 deprivation, induced caspase-dependent apoptosis with XIAP degradation through CTSB. These findings suggest that lysosomal ceramide produced by ASM mediates XIAP degradation by activation of cytosolic CTSB and caspase-dependent apoptosis. The ASM–ceramide–CTSB signaling axis is a novel pathway of ceramide-mediated apoptosis in IL-2-deprived NK/T lymphoma cells.

Molecular characterization of the cathepsin B of turbot (Scophthalmus maximus)

Cathepsin B is an enzymatic protein belonging to the peptidase C1 family. It is involved in diverse physiological and pathological functions that include immune response. In this study, we identified and characterized a cathepsin B homolog (SmCatB) from turbot (Scophthalmus maximus). SmCatB is composed of 330 amino acid residues and possesses typical domain architecture of cathepsin B, which contains a propeptide region and a cysteine protease domain, and the latter processes four conserved residues (Q101, C107, H277, and N297) in the active site. SmCatB shares 80.6-87.6% overall sequence identities with the cathepsin B of a number of teleost. SmCatB expression was detected in a wide range of tissues and upregulated by bacterial infection in a time-dependent manner. Recombinant SmCatB (rSmCatB-WT) purified from Escherichia coli exhibited apparent protease activity, which was optimal at 50 °C and pH 5.5. Compared to rSmCatB-WT, the mutant proteins rSmCatB-C107S, rSmCatB-H277A, and rSmCatB-N297A, which bear C107S, H277A, and N297A mutations, respectively, were significantly reduced in protease activity, with the highest reduction observed with rSmCatB-N297A. These results indicate that SmCatB is a bioactive protease that depends on the conserved structural features and that SmCatB is involved in pathogen-induced immune response.

CTSB promotes porcine preadipocytes differentiation by degrading fibronectin and attenuating the Wnt/β-catenin signaling pathway

The process of preadipocytes differentiation plays a vital role in adipose tissue expansion and many factors are involved in this event. Cathepsin B (CTSB), secreted from lysosome, has been reported in regulating a variety of physiological processes. In this study, we demonstrated CTSB promotes lipid accumulation and adipogenic genes expression in porcine primary preadipocytes by degrading fibronectin (Fn), a key component of extracellular matrix. Lithium chloride (LiCl) is an activator of Wnt/β-catenin signaling through stabilizing β-catenin. We found that CTSB can relieve the anti-adipogenic effects of LiCl, indicating that CTSB could impact Wnt/β-catenin signaling pathway. Interestingly, Fn is an important target gene of Wnt/β-catenin. So we considered that CTSB promote preadipocytes differentiation by suppressing these two pathways.

Increased expression of cytokines, soluble cytokine receptors, soluble apoptosis ligand and apoptosis in dengue

Several studies have been performed to determine biomarkers that define the risk factors to developing severe forms of dengue. In this study, the levels of TNF-α, IL-6, IL-1, IL-17, soluble interleukin-1 receptor like 1 protein (sST2), soluble TNF-related apoptosis-inducing ligand (sTRAIL), IL-12 and soluble receptors for TNF (sTNF-RI and sTNF-RII) were determined by ELISA in dengue patients and monocyte/macrophage cultures. Dengue was classified as dengue without warning symptoms (DNWS), with warning symptoms (DWWS) and severe dengue (SD). High values of IL-6, sTNFRI, sTNFRII and sST2 were observed in DWWS and/or SD and IL-12 and sTRAIL in DNWS. TNF-α and IL-17 were increased not associated to the disease severity. High production of TNF-α, IL-1β, IL-12, IL-17, sST2 and sTRAIL and apoptosis expression were observed in dengue monocyte/macrophage cultures. This study shows that beneficial or deleterious biomarkers can be present in dengue regardless the disease severity and that monocytes may be in part the source of studied molecules.

Characterization of cathepsin B gene from orange-spotted grouper, Epinephelus coioides involved in SGIV infection

The lysosomal cysteine protease cathepsin B of papain family is a key regulator and signaling molecule that involves in various biological processes, such as the regulation of apoptosis and activation of virus. In the present study, cathepsin B gene (Ec-CB) was cloned and characterized from orange-spotted grouper, Epinephelus coioides. The full-length Ec-CB cDNA was composed of 1918 bp and encoded a polypeptide of 330 amino acids with higher identities to cathepsin B of teleosts and mammalians. Ec-CB possessed typical cathepsin B structural features including an N-terminal signal peptide, the propeptide region and the cysteine protease domain which were conserved in other cathepsin B sequences. Phylogenetic analysis revealed that Ec-CB was most closely related to Lutjanus argentimaculatus. RT-PCR analysis showed that Ec-CB transcript was expressed in all the examined tissues which abundant in spleen, kidney and gill. After challenged with Singapore grouper iridovirus (SGIV) stimulation, the mRNA expression of cathepsin B in E. coioides was up-regulated at 24 h post-infection. Subcellular localization analysis revealed that Ec-CB was distributed predominantly in the cytoplasm. When the fish cells (GS or FHM) were treated with the cathepsin B specific inhibitor CA-074Me, the occurrence of CPE induced by SGIV was delayed, and the viral gene transcription was significantly inhibited. Additionally, SGIV-induced typical apoptosis was also inhibited by CA-074Me in FHM cells. Taken together, our results demonstrated that the Ec-CB might play a functional role in SGIV infection.

Dengue virus infection induces autophagy: an in vivo study

BACKGROUND

We and others have reported that autophagy is induced by dengue viruses (DVs) in various cell lines, and that it plays a supportive role in DV replication. This study intended to clarify whether DV infection could induce autophagy in vivo. Furthermore, the effect of DV induced autophagy on viral replication and DV-related pathogenesis was investigated.

RESULTS AND CONCLUSIONS

The physiopathological parameters were evaluated after DV2 was intracranially injected into 6-day-old ICR suckling mice. Autophagy-related markers were monitored by immunohistochemical/immunofluorescent staining and Western blotting. Double-membrane autophagic vesicles were investigated by transmission-electron-microscopy. DV non-structural-protein-1 (NS1) expression (indicating DV infection) was detected in the cerebrum, medulla and midbrain of the infected mice. In these infected tissues, increased LC3 puncta formation, LC3-II expression, double-membrane autophagosome-like vesicles (autophagosome), amphisome, and decreased p62 accumulation were observed, indicating that DV2 induces the autophagic progression in vivo. Amphisome formation was demonstrated by colocalization of DV2-NS1 protein or LC3 puncta and mannose-6-phosphate receptor (MPR, endosome marker) in DV2-infected brain tissues. We further manipulated DV-induced autophagy by the inducer rapamycin and the inhibitor 3-methyladenine (3MA), which accordingly promoted or suppressed the disease symptoms and virus load in the brain of the infected mice.We demonstrated that DV2 infection of the suckling mice induces autophagy, which plays a promoting role in DV replication and pathogenesis.