Date Published: January 30, 2008
Publisher: Public Library of Science
Author(s): Han Xiao, Ling Hui Xu, Yoshiyuki Yamada, Ding Xiang Liu, Maria Masucci. http://doi.org/10.1371/journal.pone.0001494
Abstract: In response to viral infection, the expression of numerous host genes, including predominantly a number of proinflammatory cytokines and chemokines, is usually up-regulated at both transcriptional and translational levels. It was noted that in cells infected with coronavirus, transcription and translation of some of these genes were differentially induced. Drastic induction of their expression at the transcriptional level was observed in cells infected with coronavirus. However, induction of the same genes at the translational level was usually found to be minimal to moderate. To investigate the underlying mechanisms, yeast two-hybrid screen was carried out using SARS-CoV proteins as baits, revealing that a subunit of the eukaryotic initiation factor 3 (eIF3), eIF3f, may interact with the N-terminal region of the SARS-CoV spike (S) protein. This interaction was subsequently confirmed by co-immunoprecipitation and immunofluorescent staining. Meanwhile, parallel experiments confirmed that eIF3f could also interact with the S protein of another coronavirus, the avian coronavirus infectious bronchitis virus (IBV). These interactions led to the inhibition of translation of a reporter gene in both in vitro expression system and intact cells. Interestingly, IBV-infected cells stably expressing a Flag-tagged eIF3f showed much higher translation of IL-6 and IL-8, suggesting that the interaction between coronavirus S protein and eIF3f plays a functional role in controlling the expression of host genes, especially genes that are induced during coronavirus infection cycles. This study reveals a novel mechanism exploited by coronavirus to regulate viral pathogenesis.
Partial Text: Activation and induction of host gene expression at both transcriptional and translational levels by virus infection constitute essential steps in host anti-viral response and viral pathogenesis. As one of the major factors that causes tissue damage and viral pathogenesis, induction and over-production of proinflammatory cytokines and chemokines are a common phenomenon in many viral infections –. However, it was frequently observed that the expression of these genes was differentially up-regulated at the transcriptional and translational levels in cells infected with a certain virus. For example, in cells infected with severe acute respiratory syndrome coronavirus (SARS-CoV) and in sera from SARS patients, significant up-regulation of the transcription of proinflammatory cytokines and chemokines, such as CCL1, CCL2, CCL3, CCL5, CCL9, CXCL10, IL-6, IL10 and IL12, was reported , –. However, only a moderate increase of the expression of these genes at the protein level was detected –. This differential up-regulation of the host gene expression at transcriptional and translational levels may simply reflect the relative capacity of host transcription and translation machinery in the infected cells. Alternatively, it would consist of a convenient and clever viral strategy to counteract host cell anti-viral response, as over-production of these host proteins is usually harmful to viruses. In this study, we show a novel mechanism exploited by coronavirus to regulate the translation of virus-induced genes at late stages of the virus infection cycle.
Induction and over-production of proinflammatory cytokines and chemokines, such as IL-6, IL-8, TNF-α and INF-γ, were considered to be main mediators in the pathogenesis of SARS , –. These cytokines and chemokines could promote inflammation by induction of acute cell and tissue injury. Understanding the cellular and viral mechanisms that regulate the induction of these molecules at the transcriptional and translational levels would be essential for understanding the pathogenesis of coronavirus. In this study, the S protein of SARS-CoV and IBV was shown to interact with the initiation factor eIF-3f, leading to the inhibition of general protein synthesis. As the inhibition occurs at late stages of the virus replication cycle, the main effect would be on the translation of virus-induced transcripts, including predominantly proinflammatory cytokines and chemokines. This inhibition may therefore play an important role in regulation of the pathogenesis of coronavirus.