title: Coat Protein Regulation by CK2, CPIP, HSP70, and CHIP Is Required for Potato Virus A Replication and Coat Protein Accumulation.
abstract: We demonstrate here that both coat protein (CP) phosphorylation by protein kinase CK2 and a chaperone system formed by two heat shock proteins, CP-interacting protein (CPIP) and heat shock protein 70 (HSP70), are essential for potato virus A (PVA; genus Potyvirus) replication and that all these host proteins have the capacity to contribute to the level of PVA CP accumulation. An E3 ubiquitin ligase called carboxyl terminus Hsc70-interacting protein (CHIP), which may participate in the CPIP-HSP70-mediated CP degradation, is also needed for robust PVA gene expression. Residue Thr243within the CK2 consensus sequence of PVA CP was found to be essential for viral replication and to regulate CP protein stability. Substitution of Thr243either with a phosphorylation-mimicking Asp (CPADA) or with a phosphorylation-deficient Ala (CPAAA) residue in CP expressed from viral RNA limited PVA gene expression to the level of nonreplicating PVA. We found that both the CPAAAmutant and CK2 silencing inhibited, whereas CPADAmutant and overexpression of CK2 increased, PVA translation. From our previous studies, we know that phosphorylation reduces the RNA binding capacity of PVA CP and an excess of CP fully blocks viral RNA translation. Together, these findings suggest that binding by nonphosphorylated PVA CP represses viral RNA translation, involving further CP phosphorylation and CPIP-HSP70 chaperone activities as prerequisites for PVA replication. We propose that this mechanism contributes to shifting potyvirus RNA from translation to replication.
  
  
  OBJECTIVE
  Host protein kinase CK2, two host chaperones, CPIP and HSP70, and viral coat protein (CP) phosphorylation at Thr243are needed for potato virus A (PVA) replication. Our results show that nonphosphorylated CP blocks viral translation, likely via binding to viral RNA. We propose that this translational block is needed to allow time and space for the formation of potyviral replication complex around the 3' end of viral RNA. Progression into replication involves CP regulation by both CK2 phosphorylation and chaperones CPIP and HSP70.
authors.affiliation: Department of Food and Environmental Sciences, University of Helsinki, Helsinki, Finland.
authors.forename: Andres
authors.initials: A
authors.lastname: Lõhmus
authors.affiliation: Department of Food and Environmental Sciences, University of Helsinki, Helsinki, Finland.
authors.forename: Anders
authors.initials: A
authors.lastname: Hafrén
authors.affiliation: Department of Food and Environmental Sciences, University of Helsinki, Helsinki, Finland kristiina.makinen@helsinki.fi.
authors.forename: Kristiina
authors.identifier: http://orcid.org/0000-0001-8233-8942
authors.initials: K
authors.lastname: Mäkinen
mesh_terms: D036022:Capsid Proteins / Q000235:genetics* / Q000378:metabolism*; D047390:Casein Kinase II / Q000378:metabolism*; D015967:Gene Expression Regulation, Viral; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D010766:Phosphorylation; D017800:Potyvirus / Q000502:physiology*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D017411:Ribonucleoproteins, Small Nuclear / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D014779:Virus Replication
chemical_list: D036022:Capsid Proteins; D018840:HSP70 Heat-Shock Proteins; D017411:Ribonucleoproteins, Small Nuclear; D044767:Ubiquitin-Protein Ligases; D047390:Casein Kinase II; D046988:Proteasome Endopeptidase Complex
keywords: E3 ubiquitin ligase CHIP; HSP70; coat protein; heat shock protein HSP40; potato virus A; potyvirus; protein kinase CK2; translation; viral replication