Molecular Mechanism Of C1QBP Inhibits PCV2 Proliferation

Porcine circovirus type 2(PCV2)is primary causative agent of porcine circovirus associated disease(PCVAD).PCV2 is a member of the family Circoviridae,genus Circovirus.PCV2,the genome size of 1767 bp or 1768 bp,a closed single-stranded circular DNA virus,can encode 11 open reading frames(ORFs)at least.ORF1 of PCV2 encodes two replicases Rep and Rep,protein,related to the replication of PCV2.ORF2 encodes nucleocapsid protein Cap,which has multitudes of functions during the replication of PCV2,and can automatically assemble into VLPs.The special argininerich N-terminal(position 1-41)of Cap protein described as a nuclear localization signal(NLS)helps Cap protein enter the nucleus.The proliferation of PCV2 will happen in the nucleus of host cells.Therefore,Cap protein is vital for proliferation of PCV2.We found the Complement component 1q subcomponent binding protein(C1QBP)interacted with Cap protein via yeast two-hybrid experiment.C1 QBP can interact with Cap protein around the nucleus by confocal microscopy,changing the localization of Cap protein.Overexpression C1 QBP can remarkably inhibit proliferation of PCV2,which as result of C1 QBP inhibits Cap protein into the cell nucleus.We use ivermectin,the inhibitor of nuclear import,to inhibit Cap protein entrance the cell nucleus for uncovering the influence of nuclear import for proliferation of PCV2.Exploring the mechanism of C1 QBP inhibits PCV2 proliferation via overexpression Cap and CapNLS protein.Following results were obtained:(1)Ivermectin can inbihit the proliferation of PCV2 in PK-15 cells.PK-15 cells infected with PCV2 after treatment with ivermectin,and the mRNA of PCV2 expression reduce 61% and 81% after treatment 24 h and 48 h.(2)When ivermectin treats the PK-15 cells which overexpression Cap and CapNLS protein,it can inhibit the Cap and CapNLS into the cell nucleus.Therefore,ivermectin will change the localization of Cap and CapNLS,and ivermectin possible play a role on NLS of Cap protein.(3)PK-15 cells which overexpression the C1 QBP can inhibit the proliferation of PCV2,and the mRNA of PCV2 level reduce 59% and 28% after infection 24 h and 48 h.(4)C1QBP inhibits Cap and CapNLS into the cell nucleus via interacting with Cap and CapNLS protein,and the acting site of C1 QBP for Cap protein is possibly CapNSL.(5)Overexpression the CapNLS can increase the proliferation of PCV2 in PK-15 cells,but overexpression CapNLS can inhibit the Cap into the cell nucleus,which explains many complex factors participating the nuclear import of Cap protein.In conclusion,our studies elucidated that C1 QBP and ivermectin inhibite PCV2 proliferation,and the underlying mechanism may be that ivermectin inhibits Cap protein into the nucleus.But overexpression CapNLS can not promote Cap protein into the nucleus,but overexpression CapNLS can increase the proliferation of PCV2,which hints many complex mechanism during the PCV2 proliferation.