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Oxidative stress became emerged as a key player in the development and progression of many pathological conditions including virus-induced encephalitis. Heme oxygenase-1 (HO-1) plays a crucial role in defending the body against oxidant-induced injury during inflammatory processes. Therefore, we investigated the induction of HO-1 level in host cells, which may exert a beneficial effect to minimize viral replication in SK-N-SH cells. In this study, we found that enterovirus 71 (EV71) induced the generation of reactive oxygen species (ROS) and activation of NADPH oxidase. EV71-induced ROS generation was mediated through activation of integrin β1, an epidermal growth factor receptor (EGFR), Rac1 and NADPH oxidase which revealed by using selective pharmacological inhibitors or transfection with respective siRNAs. In addition, the reduction of viral load was observed with NADPH oxidase inhibitors (apocynin and diphenyleneiodonium chloride), ROS scavenger (N-acetylcysteine), and transfection with p47(phox) siRNA in Western blot and real-time PCR analyses. Consistently, overexpression of HO-1 attenuated EV71-induced NADPH oxidase/ROS generation and EV71 replication which were abrogated by pretreatment with an HO-1 inhibitor, zinc protoporphyrin IX (ZnPP IX). Moreover, metabolite of HO-1, carbon monoxide (CO), also diminished ROS formation and EV71 replication which were reversed by pretreatment with a CO scavenger (hemoglobin) and a cyclic GMP-dependent protein kinase (PKG) inhibitor (KT5823). These findings suggest that up-regulation of HO-1 exerts as a host cellular defense mechanism against EV71 infection in SK-N-SH cells.

BACKGROUND AND PURPOSEJapanese encephalitis virus (JEV) is a member of the family Flaviviridae and JEV infection is a major cause of acute encephalopathy in children, which destroys cells in the CNS, including astrocytes and neurons. However, the detailed mechanisms underlying the inflammatory action of JEV are largely unclear. EXPERIMENTAL APPROACHThe effect of JEV on the expression of matrix metalloproteinase (MMP)-9 was determined by gelatin zymography, Western blot analysis, real-time PCR and promoter assay. The involvement of the NADPH oxidase and reactive oxygen species (ROS), MAPKs, and the transcription factor NF-kB in these responses was investigated by using selective pharmacological inhibitors and transfection with appropriate siRNAs. KEY RESULTSJEV induced the expression of the pro-form of MMP-9 in rat brain astrocytes (RBA-1 cells). In RBA-1 cells, JEV induced MMP-9 expression and promoter activity, which was inhibited by pretreatment with inhibitors of NADPH oxidase (diphenylene iodonium chloride or apocynin), MAPKs (U0126, SB203580 or SP600125) and a ROS scavenger (N-acetylcysteine), or transfection with siRNAs of p47 phox , ERK1, JNK2 and p38. In addition, JEV-induced MMP-9 expression was reduced by pretreatment with an inhibitor of NF-kB (helenalin) or transfection with p65 siRNA. Moreover, JEV-stimulated NF-kB activation was inhibited by pretreatment with the inhibitors of NADPH oxidase and MAPKs. CONCLUSIONS AND IMPLICATIONSMMP-9 expression induced by JEV infection of RBA-1 cells was mediated through the generation of ROS and activation of p42/p44 MAPK, p38 MAPK and JNK1/2, leading to NF-kB activation. AbbreviationsBBB, blood-brain barrier; BCA, Bicinchoninic acid; COX-2, cyclooxygenase-2; ECM, extracellular matrix; GFAP, glial fibrillary acid protein; HIV, human immunodeficiency virus; iNOS, inducible nitric oxide synthase; IL-8, interleukin-8; JEV, Japanese encephalitis virus; MMP-9, matrix metalloproteinase-9; PBS, phosphate-buffered saline; TNF-a, tumor necrosis factor-a

Sphingosine 1-phosphate (S1P) has been shown to regulate expression of several genes in vascular smooth muscle cells (VSMCs) and contributes to arteriosclerosis. However, the mechanisms regulating epidermal growth factor receptor (EGFR) expression by S1P in aortic VSMCs remain unclear. Western blotting and RT-PCR analyses showed that S1P induced EGFR mRNA and protein expression in a time- and concentration-dependent manner, which was attenuated by inhibitors of MEK1/2 (U0126) and phosphatidylinositide 3-kinase (PI3K; wortmannin), and transfection with dominant negative mutants of ERK and Akt, respectively. These results suggested that S1P-induced EGFR expression was mediated through p42/p44 MAPK and PI3K/Akt pathways in VSMCs. In accordance with these findings, S1P stimulated phosphorylation of p42/p44 MAPK and Akt which was attenuated by U0126 and wortmannin, respectively. Furthermore, S1P-induced EGFR upregulation was blocked by a selective NF-kappaB inhibitor helenalin. Immunofluorescent staining and reporter gene assay revealed that S1P-induced activation of NF-kappaB was blocked by wortmannin, but not by U0126, suggesting that activation of NF-kappaB was mediated through PI3K/Akt. Moreover, S1P-induced EGFR expression was inhibited by an AP-1 inhibitor curcumin and tanshinone IIA. S1P-stimulated AP-1 subunits (c-Jun and c-Fos mRNA) expression was attenuated by U0126 and wortmannin, suggesting that MEK and PI3K/ERK cascade linking to AP-1 was involved in EGFR expression. Upregulation of EGFR by S1P may exert a phenotype modulation of VSMCs. This hypothesis was supported by pretreatment with AG1478 or transfection with shRNA of EGFR that attenuated EGF-stimulated proliferation of VSMCs pretreated with S1P, determined by XTT assay. These results demonstrated that in VSMCs, activation of Akt/NF-kappaB and ERK/AP-1 pathways independently regulated S1P-induced EGFR expression in VSMCs. Understanding the mechanisms involved in S1P-induced EGFR expression on VSMCs may provide potential therapeutic targets in the treatment of arteriosclerosis.

Objection-Thrombin upregulates expression of several proteins in vascular smooth muscle cells (VSMCs) which may contribute to atherosclerosis. Here, we investigated the mechanisms underlying thrombin-induced EGF receptor (EGFR) expression and its effect on VSMCs. Methods and Results-Normal rat VSMCs were used. First, Western blotting and RT-PCR analyses showed that thrombin induces the expression of EGFR at transcription and translation levels in VSMCs. Second, pharmacological inhibitors, dominant negative mutants, and short hairpin RNA interference (shRNA) technology enabled us to demonstrate that thrombin-induced EGFR expression is mediated through PKC(␦)/c-Src-dependent transactivation of EGFR linking to PI3K/Akt and ERK1/2. We further investigated whether the transcription factors AP-1 and NF-B are involved in this response by a promoter assay. Finally, data obtained by using EGFR shRNA technology and XTT assay demonstrated that thrombin-enhanced VSMC proliferation was mediated through upregulation of EGFR. Conclusions-Our