Abstract
The unfolded protein response (UPR) is a cellular mechanism that is triggered in order to cope with the stress caused by the accumulation of misfolded proteins in the endoplasmic reticulum (ER). This response is initiated by the endoribonuclease inositol-requiring enzyme 1 (IRE1), activating transcription factor 6 (ATF6), and PKR-like ER kinase, which increase the expression of the genes involved in the folding and degradation processes and decrease the protein input into the ER by inhibiting translation. It has been shown that viruses both induce and manipulate the UPR in order to protect the host cells from an ER stress-mediated death, thus permitting the translation of viral proteins and the efficient replication of the virus. To understand the cellular events that occur during the rotavirus replication cycle, we examined the activation of the three UPR arms following infection, using luciferase reporters driven by promoters of the ER stress-responsive genes and real-time reverse transcription-PCR to determine the levels of the stress-induced mRNAs. Our findings indicated that during rotavirus infection two of the three arms of the UPR (IRE1 and ATF6) become activated; however, these pathways are interrupted at the translational level by the general inhibition of protein synthesis caused by NSP3. This response seems to be triggered by more than one viral protein synthesized during the replication of the virus, but not by the viral double-stranded RNA (dsRNA), since cells transfected with psoralen-inactivated virions, or with naked viral dsRNA, did not induce UPR.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Activating Transcription Factor 6 / genetics
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Activating Transcription Factor 6 / metabolism
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Animals
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Blotting, Western
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Cells, Cultured
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DNA-Binding Proteins / genetics
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DNA-Binding Proteins / metabolism
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Endoplasmic Reticulum / metabolism*
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Endoplasmic Reticulum Chaperone BiP
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Endoribonucleases / genetics
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Endoribonucleases / metabolism
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Epithelial Cells / metabolism
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Epithelial Cells / pathology
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Epithelial Cells / virology
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Heat-Shock Proteins / genetics
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Humans
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Macaca mulatta
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Membrane Proteins / genetics
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Membrane Proteins / metabolism
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Plasmids
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Promoter Regions, Genetic / genetics
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Protein Serine-Threonine Kinases / genetics
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Protein Serine-Threonine Kinases / metabolism
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RNA, Double-Stranded / genetics
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RNA, Messenger / genetics
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Real-Time Polymerase Chain Reaction
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Regulatory Factor X Transcription Factors
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Rotavirus / pathogenicity*
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Rotavirus Infections / metabolism*
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Rotavirus Infections / pathology
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Rotavirus Infections / virology*
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Signal Transduction
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Transcription Factors / genetics
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Transcription Factors / metabolism
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Unfolded Protein Response / physiology*
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Viral Nonstructural Proteins / genetics
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Viral Nonstructural Proteins / metabolism*
Substances
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ATF6 protein, human
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Activating Transcription Factor 6
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DNA-Binding Proteins
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Endoplasmic Reticulum Chaperone BiP
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Heat-Shock Proteins
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Membrane Proteins
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NSP3 protein, Rotavirus
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RNA, Double-Stranded
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RNA, Messenger
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Regulatory Factor X Transcription Factors
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Transcription Factors
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Viral Nonstructural Proteins
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ERN2 protein, human
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Protein Serine-Threonine Kinases
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Endoribonucleases