title: Interplay of autophagy and apoptosis during murine cytomegalovirus infection of RPE cells.
abstract: OBJECTIVE
  Previous studies have demonstrated that autophagy is involved in the pathogenesis of human cytomegalovirus (HCMV) infection. However, whether autophagy is regulated by murine cytomegalovirus (MCMV) infection has not yet been investigated. The purpose of these studies was to determine how autophagy is affected by MCMV infection of the retinal pigment epithelial (RPE) cells and whether there is a functional relationship between autophagy and apoptosis; and if so, how regulation of autophagy impacts apoptosis.
  
  
  METHODS
  RPE cells were isolated from C57BL/6 mice and infected with MCMV K181. The cells were cultured in medium containing rapamycin, chloroquine, or ammonium chloride. Green fluorescent protein-light chain 3 (GFP-LC3) plasmid was transfected to RPE cells, and the GFP-LC3 positive puncta were counted. Electron microscopic (EM) images were taken to visualize the structure of the autophagic vacuoles. Western blot was performed to detect the expression of related proteins. Trypan blue exclusion assay was used to measure the percentage of viable cells.
  
  
  RESULTS
  Although the LC3B-II levels consistently increased during MCMV infection of RPE cells, administration of chloroquine or ammonium chloride increased LC3B-II expression only at the early stage of infection (6 h post-inoculation [p.i.] and 12 h p.i.), not at or after 24 h p.i. The punctate autophagic vacuoles in the GFP-LC3 transfected RPE cells were counted using light microscopy or by EM examination, the number of autophagic vacuoles was significantly increased in the MCMV-infected RPE cells compared to the uninfected controls. Compared to untreated MCMV-infected control cells, rapamycin treatment resulted in a significant decrease in the cleaved caspase 3 levels as well as a significant decrease in the ratio of phosphorylated mammalian target of rapamycin (mTOR) to total mTOR and in the ratio of phosphorylated P70S6K to total P70S6K. In contrast, chloroquine treatment resulted in a significant increase in the cleaved caspase 3 levels in the MCMV-infected RPE cells.
  
  
  CONCLUSIONS
  Autophagic vacuole accumulation was detected during MCMV infection of RPE cells. In contrast, autophagic flux was greatly decreased at or after 24 h p.i. The results suggest that MCMV might have a strategy for inhibiting or blocking autophagy activity by targeting a later autophagy process, such as the formation of autolysosomes or degradation of their content. Our data also suggest that there is a functional relationship between autophagy and apoptosis, which plays an important role during MCMV infection of the RPE.
authors.affiliation: Georgia Regents University, Medical College of Georgia, Department of Cellular Biology and Anatomy, Augusta, GA.
authors.forename: Juan
authors.initials: J
authors.lastname: Mo
authors.affiliation: Georgia Regents University, Medical College of Georgia, Department of Cellular Biology and Anatomy, Augusta, GA.
authors.forename: Ming
authors.initials: M
authors.lastname: Zhang
authors.affiliation: Georgia Regents University, Medical College of Georgia, Department of Cellular Biology and Anatomy, Augusta, GA.
authors.forename: Brendan
authors.initials: B
authors.lastname: Marshall
authors.affiliation: Georgia Regents University, Medical College of Georgia, Department of Cellular Biology and Anatomy, Augusta, GA ; Georgia Regents University, Medical College of Georgia, Department of Ophthalmology, Augusta, GA.
authors.forename: Sylvia
authors.initials: S
authors.lastname: Smith
authors.affiliation: Georgia Regents University, Medical College of Georgia, Department of Cellular Biology and Anatomy, Augusta, GA.
authors.forename: Jason
authors.initials: J
authors.lastname: Covar
authors.affiliation: Georgia Regents University, Medical College of Georgia, Department of Cellular Biology and Anatomy, Augusta, GA.
authors.forename: Sally
authors.initials: S
authors.lastname: Atherton
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D001343:Autophagy / Q000502:physiology*; D053148:Caspase 3 / Q000378:metabolism; D002738:Chloroquine / Q000494:pharmacology; D003586:Cytomegalovirus Infections / Q000473:pathology / Q000821:virology; D004195:Disease Models, Animal; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006566:Herpesviridae Infections / Q000378:metabolism / Q000473:pathology* / Q000821:virology*; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D046529:Microscopy, Electron, Transmission; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism; D018146:Muromegalovirus / Q000472:pathogenicity*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D055213:Retinal Pigment Epithelium / Q000378:metabolism / Q000473:pathology* / Q000821:virology*; D020123:Sirolimus / Q000494:pharmacology; D014162:Transfection; D014617:Vacuoles / Q000648:ultrastructure
chemical_list: C480860:Map1lc3b protein, mouse; D008869:Microtubule-Associated Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D002738:Chloroquine; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020123:Sirolimus