Decreased replication of human respiratory syncytial virus treated with the proteasome inhibitor MG-132

Many enveloped viruses require components of the host protein ubiquitin system including members of the Paramyxoviridae family of viruses (PIV5, SeV). Until recently, little has been known about the requirements of the subfamily Pneumovirinae. We report here that treatment of Vero cells with the proteasome inhibitor MG-132 results in the reduction of human respiratory syncytial virus (HRSV) titers by as much as 2.2 log10. Inhibition of HRSV by MG-132 was only observed early in infection (4–14 h post-infection). Although Western blots indicated a possible decrease of 52% in virion production, we show by fluorescence microscopy and treatment with cyclohexamide that any apparent inhibition in HRSV budding is the result of decreased viral protein levels and not an inhibition of virus budding. Further, we demonstrate that inhibition of HRSV in Vero cells by MG-132 corresponds with an increase in eIF2α phosphorylation. Phosphorylation of eIF2α during MG-132 treatment only occurred in HRSV infected Vero cells, and not in GFP transfected controls. A combination of HRSV infection and MG-132 treatment may therefore provide sufficient signaling cues to induce inhibition of protein synthesis.