Rotavirus Infection Induces the Unfolded Protein Response of the Cell and Controls It through the Nonstructural Protein NSP3

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.

Activation of ERAD Pathway by Human Hepatitis B Virus Modulates Viral and Subviral Particle Production

“…Several viral infection were shown to induce UPR [24], [25] and very recently, an important role of the ERAD pathway in modulating production of infectious HCV, but not of other viruses from the same family, was clearly demonstrated, suggesting a high specificity, with physiological consequences for certain viruses [16].…”

Bacteria, the endoplasmic reticulum and the unfolded protein response: friends or foes?

“…Hepatitis C virus also downregulates the IRE1-XBP1 pathway to promote viral replication 113,114 . Rotavirus can modulate the UPR via sequestration of UPR components 115,116 . Since bacteria that replicate within the ER face a similar environment, they may share some of these strategies for modulation of the UPR with viral pathogens, however additional studies are needed to test this idea.…”

Rotavirus Prevents the Expression of Host Responses by Blocking the Nucleocytoplasmic Transport of Polyadenylated mRNAs

“…Gaussia luciferase mRNA was amplified using the primers Gluc forward and Gluc reverse ( Table 1). The primers used to amplify grp78, grp94, firefly luciferase, Renilla luciferase, and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNAs have been described previously (28)(29)(30). The level of each mRNA was determined by one-step real-time quantitative reverse transcription-PCR (qRT-PCR) as previously reported (29).…”

“…We have previously reported that during rotavirus infection, some genes of the unfolded protein response (UPR), like grp78, become activated so that an increase of at least 4 times in the amount of this mRNA was observed in infected cells. In contrast, other UPR responsive genes, like grp94, did not increase during infection (30). To determine if these cellular mRNAs changed their distribution in the cell, we studied their distribution in nuclear and cellular fractions in virus-infected cells.…”