The U(S)3 protein kinase blocks apoptosis induced by the d120 mutant of herpes simplex virus 1 at a premitochondrial stage

Earlier studies have shown that the d120 mutant of herpes simplex virus 1, which lacks both copies of the alpha4 gene, induces caspase-3-dependent apo ptosis in HEp-2 cells, Apoptosis was also induced by the alpha4 rescuant bu t was blocked by the complementation of rescuant with a DNA fragment encodi ng the U(S)3 protein kinase (R, Leopardi and B, Roizman, Proc. Natl, Acad. Sci, USA 93:9583-9587, 1996, and R. Leopardi, C, Van Sant, and B, Roizman, Proc. Natl, Acad. Sci, USA 94:7891-7896, 1997), To investigate its role in the apoptotic cascade, the U(S)3 open reading frame was cloned into a bacul ovirus (Bac-U(S)3) under the control of the human cytomegalovirus immediate -early promoter, We report the following, (i) Bac-U(S)3 blocks processing o f procaspase-3 to active caspase, Procaspase-3 levels remained unaltered if superinfected with Bac-U(S)3 at 3 h after d120 mutant infection, but signi ficant amounts of procaspase-3 remained in cells superinfected with Bac-Us3 at 9 h postinfection with d120 mutant, (ii) The U(S)3 protein kinase block s the proapoptotic cascade upstream of mitochondrial involvement inasmuch a s Bac-U(S)3 blocks release of cytochrome c in cells infected with the d120 mutant, (iii) Concurrent infection of HEp-2 cells with Sac-U(S)3 and the d1 20 mutant did not alter the pattern of accumulation or processing of ICP0, -22, or -27, acid therefore U(S)3 does not appear to block apoptosis by tar geting these proteins.