Analysis of VSV pseudotype virus infection mediated by rubella virus envelope proteins

Sakata, Masafumi; Tani, Hideki; Anraku, Masaki; Kataoka, Michiyo; Nagata, Noriyo; Seki, Fumio; Tahara, Maino; Otsuki, Noriyuki; Okamoto, Kiyoko; Takeda, Makoto; Mori, Yoshio

VSV-RV/CE2E1 undergoes a similar entry process to the authentic RV. Infection of VSV FLuc -RV/ CE2E1, but not VSV FLuc -G, which has the VSV-G protein, was inhibited by anti-RV serum in a dose-dependent manner (Fig. 3A, B) , confirming the functional contribution of RV proteins in VSV FLuc -RV/CE2E1 infections. RV enters cells through receptor-binding-mediated endocytosis and subsequent low pH-triggered viral-host membrane fusion [34] [35] [36] . To analyze the entry process of VSV FLuc -RV/CE2E1, the effects of endosomal acidification inhibitors on VSV FLuc -RV/CE2E1-infections were examined. Vero cells were pretreated with various concentrations of bafilomycin A1 and chloroquine, and infected with VSV FLuc -RV/CE2E1 and three control pseudotype VSVs bearing envelope proteins of VSV, murine leukemia virus (MLV), and measles virus (MV) (VSV FLuc -G, VSV FLuc -MLV/Env, and VSV FLuc -MV/FH, respectively). Similar to RV, entry of the authentic VSV occurs in endosomes under low pH conditions 37 , while MLV and MV enter cells in the plasma membrane under neutral pH [38] [39] [40] . As expected, the inhibitors blocked VSV FLuc -G infections in a dose-dependent manner, but did not block VSV FLuc -MLV/Env and VSV FLuc -MV/FH infections (Fig. 3C, D) . The effect of the inhibitors on VSV FLuc -RV/ CE2E1 was similar to that on VSV FLuc -G. Another feature of RV entry is its Ca 2+ dependency 35 . Hence, the Ca 2+ requirements of VSV GFP -RV/CE2E1 infection were assessed. The number of VSV GFP -RV/CE2E1-infected cells declined severely when the level of CaCl 2 in the culture media was lowered (Fig. 3E) . VSV GFP -MV/FH infectivity, which was used as a control, was reduced by only ~20% at a maximum. All these data suggest that VSV GFP -RV/ CE2E1 undergoes a similar entry process to the authentic RV.