Induction of manganese-superoxide dismutase in MRC-5 cells persistently infected with an alphavirus, sindbis.

Sindbis virus (SV), a single-stranded positive-sense RNA virus, multiplies in a variety of cells and causes various outcomes of infection. As we described acute infection of SV induces stress response of small heat shock protein HSP27 and activation of mitogen-activated protein kinase (MAP) signaling pathway (Nakatsue, T., et al., Biochem. Biophys. Res. Commun. 253, 59-64, 1998). In contrast to lytic infection in Vero cells, MRC-5 cells, a human fetus lung cell line, resulted in persistent infection by SV. Here we investigated a cellular factor involved in persistent infection of MRC-5 cells infected with SV. Partial sequence analysis of a 25 kilodalton (kDa) protein, accumulated in large amounts in the cells, showed that manganese-superoxide dismutase (Mn-SOD) was induced during the infections. When Mn-SOD was overexpressed in Vero cells, 20% of the cells survived more than one month, in contrast with the death of 99% of the vehicle-transfected Vero cells at 48 h after infection with SV. These data strongly suggest that a cellular factor which regulates the oxidative pathway modulates the outcome of SV infection.