title: Downregulation of Mdm2 and Mdm4 enhances viral gene expression during adenovirus infection.
abstract: Successful viral replication entails elimination or bypass of host antiviral mechanisms. Here, we show that shRNA-mediated knockdown of murine double minute (Mdm2) and its paralog Mdm4 enhanced the expression of early and late viral gene products during adenovirus (HAdV) infection. Remarkably, whereas the expression of HAdV genes was low in p53-deficient mouse embryonic fibroblasts (p53KO MEFs), the HAdV early gene products were efficiently expressed in Mdm2/p53 double-knockout (DKO) and Mdm4/p53 DKO MEFs, and viral capsid proteins were produced in Mdm2/p53 DKO MEFs. Thus, Mdm2 and Mdm4 seem to have potent antiviral property. In cells infected with wt HAdV or a mutant virus lacking the E1B-55K gene (dl 1520), both Mdm2 and Mdm4 were rapidly depleted, whereas replication-deficient mutant viruses (Ad-GFP) or ΔpTP with deletions within the coding sequence of preterminal binding protein failed to induce their downregulation. Reduced expression of Mdm2 and Mdm4 was not due to general shutoff of host protein synthesis. Additionally, expression of a dominant-negative mutant of Cul5 did not affect Mdm2/Mdm4 downregulation. Thus, viral replication but not the presence of E1B-55K is required for Mdm2/Mdm4 degradation. Surprisingly, treatment of HAdV-infected cells with proteasome inhibitor MG132 only partially restored the protein levels of Mdm2 and Mdm4, suggesting that they may also be downregulated through an additional mechanism independent of proteasome. Interestingly, cyclin D1 and p21 appear to be downregulated similarly during HAdV infection. Collectively, our work provides the first biochemical evidence for antiviral function of Mdm2 and Mdm4 and that viruses employ efficient countermeasure to ensure viral replication.
authors.affiliation: Department of Anatomy and Cell Biology, University of Florida Shands Cancer Center, University of Florida College of Medicine, Gainesville, FL, USA.
authors.forename: Heng
authors.initials: H
authors.lastname: Yang
authors.forename: Zhi
authors.initials: Z
authors.lastname: Zheng
authors.forename: Lisa Y
authors.initials: LY
authors.lastname: Zhao
authors.forename: Qiang
authors.initials: Q
authors.lastname: Li
authors.forename: Daiqing
authors.initials: D
authors.lastname: Liao
mesh_terms: D000256:Adenoviridae / Q000235:genetics*; D000257:Adenoviridae Infections / Q000378:metabolism*; D017501:Adenovirus E1B Proteins / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002460:Cell Line; D044842:Cullin Proteins / Q000378:metabolism; D056741:Cyclin D / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D015536:Down-Regulation; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism / Q000821:virology; D015967:Gene Expression Regulation, Viral / Q000187:drug effects; D045325:HCT116 Cells; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology; D051379:Mice; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D051736:Proto-Oncogene Proteins c-mdm2 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D014779:Virus Replication
chemical_list: D017501:Adenovirus E1B Proteins; D044842:Cullin Proteins; D056741:Cyclin D; D050759:Cyclin-Dependent Kinase Inhibitor p21; D015853:Cysteine Proteinase Inhibitors; D007976:Leupeptins; C461497:Mdm4 protein, mouse; D061988:Proteasome Inhibitors; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering; D016159:Tumor Suppressor Protein p53; C531145:cullin5 protein, mouse; C497207:Mdm2 protein, mouse; D051736:Proto-Oncogene Proteins c-mdm2; D044767:Ubiquitin-Protein Ligases; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde