Reovirus Activates a Caspase-Independent Cell Death Pathway

Berger, Angela K.; Danthi, Pranav

Strain-specific differences in cell death induction correlate with caspase activation. Previous studies have suggested that blockade of the prosurvival function of NF-B by T3A but not T1L late following infection controls the differences in the capacity of these two strains to elicit apoptosis (34) . While following up on these studies, we investigated the extent to which T1L and T3D differ in their capacity to block activation of NF-B at late times following infection of L929 cells. We found that each strain inhibits tumor necrosis factor alpha (TNF-␣)-induced NF-B nuclear translocation to an equivalent extent (see Fig. S1A in the supplemental material). To determine if T3D and T1L continue to maintain a difference in their capacity to evoke cell death, we performed acridine orange, ethidium bromide (AOEB) staining on infected cells at 48 h after infection. Rather than subjective determination of the staining pattern of the nuclear material to distinguish between apoptotic and necrotic cells (35) , all cells that stained with EB were counted as dead cells. Evaluation by this method indicated that T3D induced significantly greater cell death than T1L (Fig. 1A) , consistent with previous results (30, 31) . Both T1L and T3D were capable of establishing efficient infection in these cells (Fig. S1B) . Thus, despite efficiently establishing infection and blocking NF-B activation late in infection to an equal extent, T3D induced cell death to a much greater extent in L929 cells than did T1L. These data suggest that unlike that reported for HEK293 cells (34) , differences in the capacity of T3D and T1L to evoke cell death in L929 cells are not related to inhibition of NF-B late in infection.