Yee Shin Lin

Expression of Cytokine, Chemokine, and Adhesion Molecules during Endothelial Cell Activation Induced by Antibodies against Dengue Virus Nonstructural Protein 1

Vascular dysfunction is a hallmark associated with disease onset in dengue hemorrhagic fever and dengue shock syndrome. In addition to direct viral damage, immune responses to dengue virus (DV) infection may also underlie the pathogenesis of disease. We have proposed a mechanism of molecular mimicry in which Abs directed against DV nonstructural protein 1 (NS1) cross-react with endothelial cells and induce damage. In this study, we demonstrated the inflammatory endothelial cell activation induced by anti-DV NS1 via the transcription factor NF-κB-regulated pathway. Protein phosphorylation and NF-κB activation were observed after anti-DV NS1 stimulation in a human microvascular endothelial cell line-1. The cytokine and chemokine production, including IL-6, IL-8, and MCP-1, but not RANTES, in endothelial cells increased after treatment with anti-DV NS1 Abs. The expression of IL-6, IL-8, and MCP-1 was blocked by the preabsorption of anti-DV NS1 with DV NS1 or by the inhibition of NF-κB activation. Furthermore, the increases in both ICAM-1 expression and the ability of human PBMC to adhere to endothelial cells were also observed, and these effects were inhibited by pretreatment with anti-ICAM-1 or anti-MCP-1 Abs. Therefore, in addition to endothelial cell apoptosis, as previously reported, inflammatory activation occurs in endothelial cells after stimulation by anti-DV NS1 Abs. These results suggest the involvement of anti-DV NS1 Abs in the vasculopathy of DV infection.

Manifestation of thrombocytopenia in dengue-2-virus-infected mice.

Dengue virus infection causes dengue fever, dengue haemorrhagic fever and dengue shock syndrome. No animal model is available that mimics these clinical manifestations. In this study, the establishment is reported of a murine model for dengue virus infection that resembles the thrombocytopenia manifestation. Dengue-2 virus (dengue virus type 2) can infect murine cells either in vitro (primary cell culture) or in vivo. Viraemia detected by RT-PCR was found transiently at 2 days after intravenous injection of dengue-2 virus. Transient thrombocytopenia developed at 10-13 days after primary or secondary infection. Anti-platelet antibody was generated after dengue-2 virus infection. There was strain variation in dengue-2 virus infection; the A/J strain was more sensitive than BALB/c or B6 mice. This dengue-2-virus-infected mouse system accompanied by thrombocytopenia and anti-platelet antibody will be a valuable model to study the pathogenicity of dengue virus infection.

GSK-3β acts downstream of PP2A and the PI 3-kinase-Akt pathway, and upstream of caspase-2 in ceramide-induced mitochondrial apoptosis

The signaling of glycogen synthase kinase-3β (GSK-3β) has been implicated in stress-induced apoptosis. However, the pro-apoptotic role of GSK-3β is still unclear. Here, we show the involvement of GSK-3β in ceramide-induced mitochondrial apoptosis. Ceramide induced GSK-3β activation via protein dephosphorylation at serine 9. We previously reported that ceramide induced caspase-2 and caspase-8 activation, Bid cleavage, mitochondrial damage, and apoptosis. In this study, we found that caspase-2 activation and the subsequent apoptotic events were abolished by the GSK-3β inhibitors lithium chloride and SB216763, and by GSK-3β knockdown using short interfering RNA. We also found that ceramide-activated protein phosphatase 2A (PP2A) indirectly caused GSK-3β activation, and that the PP2A-regulated PI 3-kinase-Akt pathway was involved in GSK-3β activation. These results indicate a role for GSK-3β in ceramide-induced apoptosis, in which GSK-3β acts downstream of PP2A and the PI 3-kinase-Akt pathway, and upstream of caspase-2 and caspase-8.

Molecular mimicry between virus and host and its implications for dengue disease pathogenesis

Numerous infectious agents may trigger autoimmunity or even result in autoimmune diseases. Several mechanisms have been proposed for pathogen-triggered autoimmunity including molecular mimicry, cryptic antigens, epitope spreading, bystander activation and polyclonal activation. In the case of dengue virus infection which causes serious public health problems, the mechanisms regarding the pathogenesis of dengue hemorrhagic syndrome are not fully resolved. Our previous studies suggest a mechanism of molecular mimicry in which antibodies directed against dengue virus non-structural protein 1 (NS1) cross-react with human platelets and endothelial cells and cause their damage and dysfunction, which may be related to the clinical features of dengue disease. Several cell surface proteins recognized by patient serum samples and anti-NS1 antibodies have been identified. Based on proteomic studies and sequence analysis, the C-terminal region of dengue virus NS1 shows sequence homology with target proteins. In addition, different regions of dengue virus proteins including core, prM, E and NS1 proteins show sequence homology with different coagulatory molecules. As an example, the amino acid sequence 101–106 of E protein (WGNGCG) shows sequence homology with factors XI, X, IX, VII, II (thrombin), plasminogen and tissue plasminogen activator. Furthermore, single chain variable region against NS1 can interfere with fibrin formation, which leads to prolonged thrombin time. We hypothesize that molecular mimicry between dengue virus proteins and coagulatory molecules may induce cross-reactive autoantibodies that can interfere with coagulation activation. A molecular mimicry pathogenesis for dengue disease which involves cross-reactivity of dengue virus with human endothelial cells, platelets and coagulatory molecules is proposed.

Autophagy Facilitates IFN-γ-induced Jak2-STAT1 Activation and Cellular Inflammation

Autophagy is regulated for IFN-γ-mediated antimicrobial efficacy; however, its molecular effects for IFN-γ signaling are largely unknown. Here, we show that autophagy facilitates IFN-γ-activated Jak2-STAT1. IFN-γ induces autophagy in wild-type but not in autophagy protein 5 (Atg5−/−)-deficient mouse embryonic fibroblasts (MEFs), and, autophagy-dependently, IFN-γ induces IFN regulatory factor 1 and cellular inflammatory responses. Pharmacologically inhibiting autophagy using 3-methyladenine, a known inhibitor of class III phosphatidylinositol 3-kinase, confirms these effects. Either Atg5−/− or Atg7−/− MEFs are, independent of changes in IFN-γ receptor expression, resistant to IFN-γ-activated Jak2-STAT1, which suggests that autophagy is important for IFN-γ signal transduction. Lentivirus-based short hairpin RNA for Atg5 knockdown confirmed the importance of autophagy for IFN-γ-activated STAT1. Without autophagy, reactive oxygen species increase and cause SHP2 (Src homology-2 domain-containing phosphatase 2)-regulated STAT1 inactivation. Inhibiting SHP2 reversed both cellular inflammation and the IFN-γ-induced activation of STAT1 in Atg5−/− MEFs. Our study provides evidence that there is a link between autophagy and both IFN-γ signaling and cellular inflammation and that autophagy, because it inhibits the expression of reactive oxygen species and SHP2, is pivotal for Jak2-STAT1 activation.

Transforming Growth Factor β1 Signaling via Interaction with Cell Surface Hyal-2 and Recruitment of WWOX/WOX1

Transforming growth factor β (TGF-β) initiates multiple signal pathways and activates many downstream kinases. Here, we determined that TGF-β1 bound cell surface hyaluronidase Hyal-2 on microvilli in type II TGF-β receptor-deficient HCT116 cells, as determined by immunoelectron microscopy. This binding resulted in recruitment of proapoptotic WOX1 (also named WWOX or FOR) and formation of Hyal-2·WOX1 complexes for relocation to the nuclei. TGF-β1 strengthened the binding of the catalytic domain of Hyal-2 with the N-terminal Tyr-33-phosphorylated WW domain of WOX1, as determined by time lapse fluorescence resonance energy transfer analysis in live cells, co-immunoprecipitation, and yeast two-hybrid domain/domain mapping. In promoter activation assay, ectopic WOX1 or Hyal-2 alone increased the promoter activity driven by Smad. In combination, WOX1 and Hyal-2 dramatically enhanced the promoter activation (8–9-fold increases), which subsequently led to cell death (>95% of promoter-activated cells). TGF-β1 supports L929 fibroblast growth. In contrast, transiently overexpressed WOX1 and Hyal-2 sensitized L929 to TGF-β1-induced apoptosis. Together, TGF-β1 invokes a novel signaling by engaging cell surface Hyal-2 and recruiting WOX1 for regulating the activation of Smad-driven promoter, thereby controlling cell growth and death.

Glycogen Synthase Kinase-3β Facilitates IFN-γ-Induced STAT1 Activation by Regulating Src Homology-2 Domain-Containing Phosphatase 2

Glycogen synthase kinase-3β (GSK-3β)-modulated IFN-γ-induced inflammation has been reported; however, the mechanism that activates GSK-3β and the effects of activation remain unclear. Inhibiting GSK-3β decreased IFN-γ-induced inflammation. IFN-γ treatment rapidly activated GSK-3β via neutral sphingomyelinase- and okadaic acid-sensitive phosphatase-regulated dephosphorylation at Ser9, and proline-rich tyrosine kinase 2 (Pyk2)-regulated phosphorylation at Tyr216. Pyk2 was activated through phosphatidylcholine-specific phospholipase C (PC-PLC)-, protein kinase C (PKC)-, and Src-regulated pathways. The activation of PC-PLC, Pyk2, and GSK-3β was potentially regulated by IFN-γ receptor 2-associated Jak2, but it was independent of IFN-γ receptor 1. Furthermore, Jak2/PC-PLC/PKC/cytosolic phospholipase A2 positively regulated neutral sphingomyelinase. Inhibiting GSK-3β activated Src homology-2 domain-containing phosphatase 2 (SHP2), thereby preventing STAT1 activation in the late stage of IFN-γ stimulation. All these results showed that activated GSK-3β synergistically affected IFN-γ-induced STAT1 activation by inhibiting SHP2.

Current progress in dengue vaccines

Dengue is one of the most important emerging vector-borne viral diseases. There are four serotypes of dengue viruses (DENV), each of which is capable of causing self-limited dengue fever (DF) or even life-threatening dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). The major clinical manifestations of severe DENV disease are vascular leakage, thrombocytopenia, and hemorrhage, yet the detailed mechanisms are not fully resolved. Besides the direct effects of the virus, immunopathological aspects are also involved in the development of dengue symptoms. Although no licensed dengue vaccine is yet available, several vaccine candidates are under development, including live attenuated virus vaccines, live chimeric virus vaccines, inactivated virus vaccines, and live recombinant, DNA and subunit vaccines. The live attenuated virus vaccines and live chimeric virus vaccines are undergoing clinical evaluation. The other vaccine candidates have been evaluated in preclinical animal models or are being prepared for clinical trials. For the safety and efficacy of dengue vaccines, the immunopathogenic complications such as antibody-mediated enhancement and autoimmunity of dengue disease need to be considered.

Glycogen Synthase Kinase-3β Mediates Endoplasmic Reticulum Stress-Induced Lysosomal Apoptosis in Leukemia

Glycogen synthase kinase (GSK)-3β may modulate endoplasmic reticulum (ER) stress-induced apoptosis; however, the mechanism remains unclear. Our data showed that human monocytic leukemia/lymphoma U937 and acute myeloid leukemia HL-60, but not chronic myeloid leukemia K562, cells were susceptible to apoptosis induced by ER stressor tunicamycin, a protein glycosylation inhibitor. Tunicamycin caused early activation of caspase-2, -3, -4, and -8, followed by apoptosis, whereas caspase-9 was slowly activated. Inhibiting caspase-2 reduced activation of caspase-8 and -3 but had no effect on caspase-4. Tunicamycin induced apoptosis independently of the mitochondrial pathway but caused lysosomal destabilization followed by lysosomal membrane permeabilization (LMP), cathepsin B relocation from lysosomes to the cytosol, and caspase-8 and -3 activation. It is notable that caspase-2 mediated lysosomal destabilization. Inhibiting GSK-3β comprehensively reduced lysosomal apoptosis after caspase-2 inhibition. Unlike U937 and HL-60 cells, K562 cells showed nonresponsive ER stress and failure of activation of GSK-3β and caspase-2 in response to tunicamycin. Activating GSK-3β caused K562 cells to be susceptible to tunicamycin-induced apoptosis. Taken together, we show that GSK-3β exhibits a mechanism of ER stress-induced lysosomal apoptosis in leukemia involving caspase-2-induced LMP and cathepsin B relocation, which result in caspase-8 and -3 activation.

Interferon–α–induced serotonin uptake in Jurkat T cells via mitogen–activated protein kinase and transcriptional regulation of the serotonin transporter

Interferon (IFN)-α upregulates serotonin (5-HT) uptake and serotonin transporter (5-HTT) messenger ribonucleic acid (mRNA) expression in immune cells, which implies the mechanism underlying IFN-α-induced depression. However, the signal transduction of this effect remains unclear. We investigated whether the effects of IFN-α on the functions of 5-HTT were related to mitogen-activated protein kinase (MAPK). By performing Western blotting, real-time reverse transcriptase—polymerase chain reaction and [3H]5-HT labelling, we examined MAPK phosphorylation, 5-HTT mRNA expression and 5-HT uptake in Jurkat T cells. The cells had been cultured for different time periods (1) with IFN-α alone and (2) preincubated with either MAPK inhibitors or with the selective serotonin reuptake inhibitor, fluoxetine, and subsequently cultured along with IFN-α. The levels of MAPK phosphorylation, 5-HTT mRNA expression and 5-HT uptake all increased in the IFN-α-treated cells but were blocked in those that were pretreated with MAPK inhibitors and fluoxetine. These results appear to clarify the association of depression with IFN-α-induced 5-HT uptake that reduces the 5-HT levels and IFN-α-regulated transcription of 5-HTT; further, the results suggest the involvement of MAPK in this process.