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Department of Microbiology and Immunology, Emory University, Atlanta, Georgia 30322; and Department of Veterinary Biosciences, The Ohio State University, Columbus, Ohio 43210
Human cytomegalovirus (HCMV) is a ubiquitous herpesvirus that is able to persist for decades in its host. HCMV has evolved protean countermeasures for anti-HCMV cellular immunity that facilitate establishment of persistence. Recently it has been shown that HCMV inhibits interferon
(IFN-)–stimulated MHC class II expression, but the mechanism for this effect is unknown. IFN- signal transduction (Jak/Stat pathway) and class II transactivator (CIITA) are required components for IFN-–stimulated MHC class II expression. In this study, we demonstrate that both a clinical isolate and a laboratory strain of HCMV inhibit inducible MHC class II expression at the cell surface and at RNA level in human endothelial cells and fibroblasts. Moreover, reverse transcriptase polymerase chain reaction and Northern blot analyses demonstrate that neither CIITA nor interferon regulatory factor 1 are upregulated in infected cells. Electrophoretic mobility shift assays reveal a defect in IFN- signal transduction, which was shown by immunoprecipitation to be associated with a striking decrease in Janus kinase 1 (Jak1) levels. Proteasome inhibitor studies with carboxybenzyl-leucyl-leucyl-leucine vinyl sulfone suggest an HCMV-associated enhancement of Jak1 protein degradation. This is the first report of a mechanism for the HCMV-mediated disruption of inducible MHC class II expression and a direct virus-associated alteration in Janus kinase levels. These findings are yet another example of the diverse mechanisms by which HCMV avoids immunosurveillance and establishes persistence.
activation factor; GAS, IFN- activation sequence; HCMV, human cytomegalovirus; IE, immediate-early; IP, immunoprecipitation; IRF, IFN regulatory factor; Jak, Janus kinase; L, late; PFA, phosphonoformic acid; RT, reverse transcribed; Stat, signal transducers and activators of transcription; Z-L3VS, carboxybenzyl-leucyl-leucyl-leucine vinyl sulfone. 1Abbreviations used in this paper: CIITA, class II transactivator; E, early; EC, endothelial cell; EMSA, electrophoretic mobility shift assay; g, glycoprotein; GAF, IFN-
activation factor; GAS, IFN- activation sequence; HCMV, human cytomegalovirus; IE, immediate-early; IP, immunoprecipitation; IRF, IFN regulatory factor; Jak, Janus kinase; L, late; PFA, phosphonoformic acid; RT, reverse transcribed; Stat, signal transducers and activators of transcription; Z-L3VS, carboxybenzyl-leucyl-leucyl-leucine vinyl sulfone. We thank Anna-Maris Colberg-Poley for her generous gift of gB and IE1 plasmids. We thank Hidde Ploegh for graciously supplying the proteasome inhibitor Z-L3VS. Also, we appreciate the helpful suggestions of Robert Schreiber regarding the IFN-
R immunoprecipitation experiments. We are grateful to Deborah Knight, Soraya Rofagha, and Jason Eckles for their technical assistance. This study was supported by National Institutes of Health RO1 grant AI-38452-02. Daniel M. Miller is a Howard Hughes Medical Institute Predoctoral Fellow.
Address correspondence to Daniel D. Sedmak, 139 Hamilton Hall, 1645 Neil Avenue, Columbus, Ohio 43210. Phone: 614-292-4692; Fax: 614-292-7072; E-mail: sedmak.2{at}osu.edu
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