title: Biphasic regulation of A20 gene expression during human cytomegalovirus infection.
abstract: BACKGROUND
  The A20 ubiquitin-editing enzyme is a target of nuclear factor kappa B (NF-κB) and also plays a key role in regulating the NF-κB signaling pathway. NF-κB activity is increased during human cytomegalovirus (HCMV) infection and HCMV appears to be adapted to this change. To better understand the regulation of NF-κB signaling during HCMV infection, we investigated how A20 expression is controlled during HCMV infection.
  
  
  METHODS
  The expression level of A20 in human fibroblast cells infected with HCMV or UV-inactivated virus (UV-HCMV) was measured by immunoblot analysis, cell staining, and quantitative real-time PCR. Changes of histone modifications on the A20 promoter were determined by chromatin immunoprecipitation assays. Lentiviral vectors were used to knockdown A20 in fibroblast cells.
  
  
  RESULTS
  A20 expression was increased at early times after HCMV infection. This increase of the A20 protein level was promoted by viral gene expression under low viral load conditions. The viral IE1 protein, which is known to activate NF-κB, increased the A20 promoter activity through the upstream NF-κB sites in reporter assays, suggesting that IE1 is at least partly involved in A20 induction. Analysis of A20 expression with a high viral load demonstrated that the A20 regulation by HCMV was biphasic; both A20 protein and mRNA levels were increased at the early stage of infection, but decreased at the late stage. Under high viral load conditions, A20 upregulation was more profound with UV-HCMV than with HCMV, indicating a role of the viral gene product(s) in limiting A20 induction. Consistently, more histone modifications for euchromatin were found on the A20 promoter during UV-HCMV infection than with HCMV infection. A20 knockdown by shRNA reduced HCMV growth.
  
  
  CONCLUSIONS
  These results suggest that the biphasic regulation of A20 expression may be important for productive HCMV infection.
authors.forename: Su Yeon
authors.initials: SY
authors.lastname: Gu
authors.forename: Young-Eui
authors.initials: YE
authors.lastname: Kim
authors.forename: Ki Mun
authors.initials: KM
authors.lastname: Kwon
authors.forename: Tae-Hee
authors.initials: TH
authors.lastname: Han
authors.affiliation: Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, 2066 Seoburo, Suwon 440-746, Republic of Korea. jahn@skku.edu.
authors.forename: Jin-Hyun
authors.initials: JH
authors.lastname: Ahn
mesh_terms: D002460:Cell Line; D003587:Cytomegalovirus / Q000502:physiology*; D003586:Cytomegalovirus Infections / Q000235:genetics* / Q000821:virology*; D004268:DNA-Binding Proteins / Q000235:genetics*; D044127:Epigenesis, Genetic; D005347:Fibroblasts / Q000378:metabolism / Q000821:virology; D015870:Gene Expression; D005786:Gene Expression Regulation; D055785:Gene Knockdown Techniques; D017930:Genes, Reporter; D006657:Histones / Q000378:metabolism; D006801:Humans; D017874:Immediate-Early Proteins / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics*; D016328:NF-kappa B / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics*; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015533:Transcriptional Activation; D000072598:Tumor Necrosis Factor alpha-Induced Protein 3; D019562:Viral Load
chemical_list: D004268:DNA-Binding Proteins; D006657:Histones; C088645:IE1 protein, cytomegalovirus; D017874:Immediate-Early Proteins; D047908:Intracellular Signaling Peptides and Proteins; D016328:NF-kappa B; D009687:Nuclear Proteins; D012333:RNA, Messenger; C076529:TNFAIP3 protein, human; D000072598:Tumor Necrosis Factor alpha-Induced Protein 3