title: Herpes Simplex Virus 1 UL41 Protein Suppresses the IRE1/XBP1 Signal Pathway of the Unfolded Protein Response via Its RNase Activity.
abstract: During viral infection, accumulation of viral proteins can cause stress in the endoplasmic reticulum (ER) and trigger the unfolded protein response (UPR) to restore ER homeostasis. The inositol-requiring enzyme 1 (IRE1)-dependent pathway is the most conserved of the three UPR signal pathways. Upon activation, IRE1 splices out an intron from the unspliced inactive form of X box binding protein 1 [XBP1(u)] mRNA and produces a transcriptionally potent spliced form [XBP1(s)]. Previous studies have reported that the IRE1/XBP1 pathway is inhibited upon herpes simplex virus 1 (HSV-1) infection; however, the underlying molecular mechanism is still elusive. Here, we uncovered a role of the HSV-1 UL41 protein in inhibiting the IRE1/XBP1 signal pathway. Ectopic expression of UL41 decreased the expression of XBP1 and blocked XBP1 splicing activation induced by the ER stress inducer thapsigargin. Wild-type (WT) HSV-1, but not the UL41-null mutant HSV-1 (R2621), decreased XBP1 mRNA induced by thapsigargin. Nevertheless, infection with both WT HSV-1 and R2621 without drug pretreatment could reduce the mRNA and protein levels of XBP1(s), and additional mechanisms might contribute to this inhibition of XBP1(s) during R2621 infection. Taking these findings together, our results reveal XBP1 as a novel target of UL41 and provide insights into the mechanism by which HSV-1 modulates the IRE1/XBP1 pathway.
  
  
  
  During viral infection, viruses hijack the host translation apparatus to produce large amounts of viral proteins, which leads to ER stress. To restore ER homeostasis, cells initiate the UPR to alleviate the effects of ER stress. The IRE1/XBP1 pathway is the most conserved UPR branch, and it activates ER-associated protein degradation (ERAD) to reduce the ER load. The IRE1/XBP1 branch is repressed during HSV-1 infection, but little is known about the underlying molecular mechanism. Our results show for the first time that UL41 suppresses the IRE1/XBP1 signal pathway by reducing the accumulation of XBP1 mRNA, and characterization of the underlying molecular mechanism provides new insight into the modulation of UPR by HSV-1.
authors.affiliation: Soochow University, Institutes of Biology and Medical Sciences, Suzhou, China.
authors.forename: Pengchao
authors.initials: P
authors.lastname: Zhang
authors.affiliation: Soochow University, Institutes of Biology and Medical Sciences, Suzhou, China.
authors.forename: Chenhe
authors.initials: C
authors.lastname: Su
authors.affiliation: Soochow University, Institutes of Biology and Medical Sciences, Suzhou, China.
authors.forename: Zhangtao
authors.initials: Z
authors.lastname: Jiang
authors.affiliation: Soochow University, Institutes of Biology and Medical Sciences, Suzhou, China zheng.alan@hotmail.com.|Department of Microbiology, Immunology and Infectious diseases, University of Calgary, Calgary, AB, Canada.
authors.forename: Chunfu
authors.initials: C
authors.lastname: Zheng
mesh_terms: D002460:Cell Line; D000066630:Ectopic Gene Expression; D004722:Endoribonucleases / Q000378:metabolism*; D004789:Enzyme Activation; D006561:Herpes Simplex / Q000235:genetics / Q000378:metabolism* / Q000821:virology*; D018259:Herpesvirus 1, Human / Q000502:physiology*; D006801:Humans; D007783:Lactones / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D012326:RNA Splicing; D012333:RNA, Messenger / Q000235:genetics; D012717:Sesquiterpenes / Q000378:metabolism; D015398:Signal Transduction; D056811:Unfolded Protein Response; D014764:Viral Proteins / Q000378:metabolism*; D000071717:X-Box Binding Protein 1 / Q000235:genetics / Q000378:metabolism*
chemical_list: D007783:Lactones; D012333:RNA, Messenger; D012717:Sesquiterpenes; C081688:Ul41 protein, Human herpesvirus 1; D014764:Viral Proteins; D000071717:X-Box Binding Protein 1; C046319:thapsigargicin; C528229:ERN1 protein, human; D017346:Protein Serine-Threonine Kinases; D004722:Endoribonucleases
keywords: HSV-1; UL41; UPR; XBP1