Avian Reovirus Nonstructural Protein p17-Induced G2/M Cell Cycle Arrest and Host Cellular Protein Translation Shutoff Involve Activation of p53-Dependent Pathways

ABSTRACT The effects of avian reovirus (ARV) p17 protein on cell cycle progression and host cellular protein translation were studied. ARV infection and ARV p17 transfection resulted in the accumulation of infected and/or transfected cells in the G2/M phase of the cell cycle. The accumulation of cells in the G2/M phase was accompanied by upregulation and phosphorylation of the G2/M-phase proteins ATM, p53, p21cip1/waf1, Cdc2, cyclin B1, Chk1, Chk2, and Cdc25C, suggesting that p17 induces a G2/M cell cycle arrest through activation of the ATM/p53/p21cip1/waf1/Cdc2/cyclin B1 and ATM/Chk1/Chk2/Cdc25C pathways. The G2/M cell cycle arrest resulted in increased virus replication. In the present study, we also provide evidence demonstrating that p17 protein is responsible for ARV-induced host cellular protein translation shutoff. Increased phosphorylation levels of the eukaryotic translation elongation factor 2 (eEF2) and initiation factor eIF2α and reduced phosphorylation levels of the eukaryotic translation initiation factors eIF4E, eIF4B, and eIF4G, as well as 4E-BP1 and Mnk-1 in p17-transfected cells, demonstrated that ARV p17 suppresses translation initiation factors and translation elongation factors to induce host cellular protein translation shutoff. Inhibition of mTOR by rapamycin resulted in a decrease in the levels of phosphorylated 4E-BP1, eIF4B, and eIF4G and an increase in the levels eEF2 but did not affect ARV replication, suggesting that ARV replication was not hindered by inhibition of cap-dependent translation. Taken together, our data indicate that ARV p17-induced G2/M arrest and host cellular translation shutoff resulted in increased ARV replication.

Annexin II Incorporated into Influenza Virus Particles Supports Virus Replication by Converting Plasminogen into Plasmin

ABSTRACT For influenza viruses to become infectious, the proteolytic cleavage of hemagglutinin (HA) is essential. This usually is mediated by trypsin-like proteases in the respiratory tract. The binding of plasminogen to influenza virus A/WSN/33 leads to the cleavage of HA, a feature determining its pathogenicity and neurotropism in mice. Here, we demonstrate that plasminogen also promotes the replication of other influenza virus strains. The inhibition of the conversion of plasminogen into plasmin blocked influenza virus replication. Evidence is provided that the activation of plasminogen is mediated by the host cellular protein annexin II, which is incorporated into the virus particles. Indeed, the inhibition of plasminogen binding to annexin II by using a competitive inhibitor inhibits plasminogen activation into plasmin. Collectively, these results indicate that the annexin II-mediated activation of plasminogen supports the replication of influenza viruses, which may contribute to their pathogenicity.

Human Rhinovirus 2A Proteinase Cleavage Sites in Eukaryotic Initiation Factors (eIF) 4GI and eIF4GII Are Different

ABSTRACT Several picornaviruses shut down host cellular protein synthesis by proteolytic cleavage of the eukaryotic initiation factor (eIF) 4GI and eIF4GII isoforms. Viral RNA translation is maintained by a cap-independent mechanism. Here, we identify the human rhinovirus 2 2Apro cleavage site in eIF4GII in vitro as PLLNV699*GSR; this sequence lies seven amino acids C-terminal to the cleavage site previously identified in eIF4GI (LSTR681*GPP).