Avian Reovirus Nonstructural Protein p17-Induced G 2 /M Cell Cycle Arrest and Host Cellular Protein Translation Shutoff Involve Activation of p53-Dependent Pathways

Abstract

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 G 2 /M phase of the cell cycle. The accumulation of cells in the G 2 /M phase was accompanied by upregulation and phosphorylation of the G 2 /M-phase proteins ATM, p53, p21 cip1/waf1 , Cdc2, cyclin B1, Chk1, Chk2, and Cdc25C, suggesting that p17 induces a G 2 /M cell cycle arrest through activation of the ATM/p53/p21 cip1/waf1 /Cdc2/cyclin B1 and ATM/Chk1/Chk2/Cdc25C pathways. The G 2 /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 G 2 /M arrest and host cellular translation shutoff resulted in increased ARV replication.