Post-translational regulation of rotavirus protein NSP1 expression in mammalian cells.

The nonstructural rotavirus protein NSP1 binds specifically to viral mRNAs and to interferon regulatory factor 3 (IRF3), inducing IRF3 degradation through a proteasome-dependent pathway. By using a vaccinia virus expression system in mammalian cells, we found that the yield of NSP1 was 8- and 13-fold lower than the viral proteins VP2 or NSP3, respectively; while in the presence of proteasome inhibitors such difference could be reduced to 2- to 2.5-fold, respectively. The susceptibility of NSP1 to proteasome degradation was fully reversed in a dose-dependent manner by transfection with the full complement of 11 molecules of translation-competent rotavirus mRNAs, but this effect was abrogated by the protein synthesis inhibitor cycloheximide. These results demonstrate that NSP1 is degraded through a proteasome-dependent pathway, and viral proteins, alone or in combination with viral mRNAs, interfere with such degradation.