DOUBLE-STRANDED-RNA IS A TRIGGER FOR APOPTOSIS IN VACCINIA VIRUS-INFECTED CELLS

The vaccinia virus E3L gene codes for double-stranded RNA (dsRNA) bind ing proteins which can prevent activation of the dsRNA-dependent, inte rferon-induced protein kinase PKR. Activated PKR has been shown to ind uce apoptosis in HeLa cells. HeLa cells infected with vaccinia virus w ith the ML gene deleted have also been shown to undergo apoptosis, whe reas HeLa cells infected with wild-type vaccinia virus do not. In this report, using virus recombinants expressing mutant E3L products or al ternative dsRNA binding proteins, we show that suppression of inductio n of apoptosis correlates with functional binding of proteins to dsRNA . Infection of HeLa cells with ts23, which leads to synthesis of incre ased dsRNA at restrictive temperature, induced apoptosis at restrictiv e but not permissive temperatures. Treatment of cells with cytosine ar abinoside, which blacks the late buildup of dsRNA in vaccinia virus-in fected cells, prevented induction of apoptosis by vaccinia virus with E3L deleted. Cells transfected with dsRNA in the absence of virus infe ction also underwent apoptosis. These results suggest that dsRNA is a trigger that can initiate a suicide response in virus-infected and per haps uninfected cells.