Benny Wang-Leung Cheung

Mechanisms for HIV Tat upregulation of IL-10 and other cytokine expression: kinase signaling and PKR-mediated immune response.

HIV Tat has been known to have multiple regulatory roles including replication of HIV and modulation of cellular kinases. We investigated whether signaling kinase PKR plays a critical role in mediating Tat‐induced cytokine dysregulation. We showed Tat induction of IL‐10 dysregulation is associated with PKR activation. To examine the mechanism involved, inhibition of PKR activity abrogated the Tat‐induced cytokine induction. We next identified that the MAP kinases including ERK‐1/2 and p38 are downstream of PKR in these Tat‐induced pathways. Thus, PKR may play a critical role in mediating the subversive effects of HIV Tat resulting in IL‐10 induction.

A Role for Double-Stranded RNA-Activated Protein Kinase PKR in Mycobacterium-Induced Cytokine Expression

Following infection of the host by Mycobacterium tuberculosis, induction of cytokines is a major defense mechanism to limit the pathogen invasion. Cytokines interact with each other to form an intertwined network of pathways. For example, IFN and TNF have been shown to interact through common pathways including IFN-inducible, dsRNA-activated serine/threonine protein kinase (PKR) induction. As a signal transducer, it has been conventionally known to regulate the induction of cytokine expression in response to virus infection through NF-κB. In light of the critical role of TNF in immunity and its cytotoxic effects mediated by PKR, we examined the role of the kinase in the regulation of immune response against M. tuberculosis using the interaction of bacillus Calmette-Guérin (BCG) and primary human blood monocytes as a model. Our results showed that BCG stimulates the induction of cytokine expression in human primary blood monocytes including TNF-α, IL-6, and IL-10. With the suppression of PKR by using PKR-mutant gene or 2-aminopurine as PKR inhibitor, we showed that the BCG-induced cytokine expression in human monocytes is regulated by the phosphorylation and activation of PKR. We also demonstrated that downstream of PKR induction is the activation of MAPK and translocation of NF-κB into the nucleus. NF-κB in turn mediates the transcription of specific cytokine genes. Taken together, PKR plays a critical role in the regulation of immune responses to mycobacterial infection and may serve as an important molecule in the innate antimycobacterial defense.

Identification of the bioactive constituent and its mechanisms of action in mediating the anti-inflammatory effects of black cohosh and related Cimicifuga species on human primary blood macrophages.

Cimicifuga species have been used as traditional medicinal herbs to treat inflammation and symptoms associated with menopause in Asia, Europe, and North America. However, the underlying mechanism of their anti-inflammatory effects remains to be investigated. With bioactivity guided purification involving the use of partitioning extraction and high performance liquid chromatography, we isolated one of the key bioactive constituents from the rhizome extracts of Cimicifuga racemosa. By NMR spectroscopy, the molecule was identified to be cimiracemate A (1). This compound (140 muM) suppressed the lipopolysaccharide-induced TNF-alpha production in the blood macrophages by 47 +/- 19% and 58 +/- 30% at LPS concentrations of 1 ng/mL and 10 ng/mL, respectively. The anti-inflammatory activity of compound 1 may be due to its modulation of a signaling mitogen activated protein kinase and transcription factor nuclear factor-kappaB activities. Compound 1 was found in other Cimicifuga species. Our data indicate that compound 1 or its chemical analogues may have the potential to be further developed as a new class of therapeutic agent.

Role for Nonstructural Protein 1 of Severe Acute Respiratory Syndrome Coronavirus in Chemokine Dysregulation

ABSTRACT Severe acute respiratory syndrome (SARS) is an emerging infectious disease caused by a novel coronavirus. Since its associated morbidity and mortality have been postulated to be due to immune dysregulation, we investigated which of the viral proteins is responsible for chemokine overexpression. To delineate the viral and cellular factor interactions, the role of four SARS coronavirus proteins, including nonstructural protein 1 (nsp-1), nsp-5, envelope, and membrane, were examined in terms of cytokine induction. Our results showed that the SARS coronavirus nsp-1 plays an important role in CCL5, CXCL10, and CCL3 expression in human lung epithelial cells via the activation of NF-κB.

A role for glycogen synthase kinase-3 in antagonizing mycobacterial immune evasion by negatively regulating IL-10 induction

Mtb dysregulates monocyte/macrophage functions to produce a large amount of the immunosuppressive cytokine IL‐10. An important function of IL‐10 in promoting Mtb survival is the suppression of antigen presentation of monocytes/macrophages to T cells. This dampens the host immune responses and provides an opportunity for immune evasion. GSK3 has been shown to control the balance between pro‐ and anti‐inflammatory cytokine productions. Here, we investigated whether GSK3 regulates IL‐10 expression and mediates a protective role upon live mycobacterial challenge using BCG as a model. Our results showed that BCG increased Akt phosphorylation and inhibited GSK3 activity, resulting in increased IL‐10 production. We confirmed further that suppression of GSK3 activities by a specific chemical inhibitor strongly enhanced BCG‐induced IL‐10 production. We also showed that IL‐10 secreted by BCG‐infected human PBMo was a major suppressor of subsequent IFN‐γ production by PBMC and HLA‐DR expression on PBMo in response to BCG. Neutralization of PBMo‐secreted IL‐10 by anti‐IL‐10 antibodies restored the IFN‐γ production and HLA‐DR surface expression. Taken together, GSK3 negatively regulates mycobacteria‐induced IL‐10 production in human PBMo. The kinase may play a role in restoring IFN‐γ secretions and subsequent antigen presentation in response to mycobacterial infection. In conclusion, our results suggest a significant role for GSK3 in guarding against mycobacterial evasion of immunity via IL‐10 induction in the host.

Interferon-γ regulation of TNFα-induced matrix metalloproteinase 3 expression and migration of human glioma T98G cells

Induction of proinflammatory cytokines in response to malignant cells is an integral component of immune response to control tumor development. However, recent evidences have suggested that tumor cells may evade the immune system and exploit inflammatory responses to enhance its own growth. An exemplary example is the highly invasive and tumor necrosis factor (TNF)α‐resistant glioblastoma, whose growth is associated with TNFα expression. We thus examined whether the tumor takes advantage of TNFα overexpression to enhance its invasiveness. To delineate the contribution of inflammation in tumor migration, we demonstrated that the role of proinflammatory cytokines on matrix metalloproteinases‐3 (MMP‐3) expression, and its consequent effects on the invasiveness of a human glioma cell‐line, T98G. By using Matrigel Invasion Chamber, T98G cell migration was significantly enhanced in response to TNFα. In contrast, interferon‐γ (IFNγ) reduced both basal and TNFα‐enhanced cell invasion. To investigate the mechanisms involved, we demonstrated that TNFα upregulated mRNA and protein expression of MMP‐3 in T98G cells, whereas IFNγ downregulated the MMP‐3 expression. The role of MMP‐3 in glioma invasiveness was further confirmed by transfecting MMP‐3 siRNA in T98G to abrogate the TNFα‐enhanced cell invasion. To delineate the mechanisms further, we showed that IFNγ exerts an inhibitory effect on the binding of TNFα‐activated Ets‐1 and NFκB to their respective enhancer elements found in MMP‐3 promoter. In summary, our results indicated that TNFα enhances the invasiveness of T98G glioma cells through MMP‐3 induction, and such enhancement of cell migration can be inhibited by IFNγ.

LOTS: a software DSM supporting large object space

Software DSM provides good programmability for cluster computing, but its performance and limited shared memory space for large applications hinder its popularity. This paper introduces LOTS, a C++ runtime library supporting a large shared object space. With its dynamic memory mapping mechanism, LOTS can map more objects, lazily from the local disk to the virtual memory during access, leaving only a trace of control information for each object in the local process space. To our knowledge, LOTS is the first pure runtime software DSM supporting a shared object space larger than the local process space. Our testing shows that LOTS can utilize all the free hard disk space available to support hundreds of gigabytes of shared objects with a small overhead. The scope consistency memory model and a mixed coherence protocol allow LOTS to achieve better scalability with respect to problem size and cluster size.

A segment-based DSM supporting large shared object space

This paper introduces a software DSM that can extend its shared object space exceeding 4GB in a 32-bit commodity cluster environment. This is achieved through the dynamic memory mapping mechanism, with local hard disks as backing store. We introduce the new concept of segments with intelligent splitting to reduce network traffic, false sharing as well as adapt better to the shared memory access patterns. A priority-based swapping algorithm is designed to reduce disk accesses for efficient dynamic memory mapping, and maximize the use of disk space as shared object space. A new queue-based scheme is also devised for efficient and simple management of memory blocks. The proposed solutions were implemented in LOTS V.2, and it can outperform its previous version when running small applications, while the maximum shared object space is increased to one-third of the total free disk space available among all the nodes