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 apoptosis in HEp-2 cells. Apoptosis was also induced by the alpha4 rescuant but was blocked by the complementation of rescuant with a DNA fragment encoding 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 baculovirus (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 of 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 significant 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 blocks the proapoptotic cascade upstream of mitochondrial involvement inasmuch as Bac-U(S)3 blocks release of cytochrome c in cells infected with the d120 mutant. (iii) Concurrent infection of HEp-2 cells with Bac-U(S)3 and the d120 mutant did not alter the pattern of accumulation or processing of ICP0, -22, or -27, and therefore U(S)3 does not appear to block apoptosis by targeting these proteins.
Munger
J
J
The Marjorie B. Kovler Viral Oncology Laboratories, The University of Chicago, Chicago, Illinois 60637, USA.
Chee
A V
AV
Roizman
B
B
D017209:Apoptosis / Q000187:drug effects*; D016367:Baculoviridae / Q000235:genetics / Q000378:metabolism; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D004792:Enzyme Precursors / Q000378:metabolism; D006561:Herpes Simplex / Q000821:virology; D018259:Herpesvirus 1, Human / Q000201:enzymology / Q000235:genetics / Q000472:pathogenicity*; D006801:Humans; D017874:Immediate-Early Proteins / Q000235:genetics* / Q000378:metabolism; D008928:Mitochondria / Q000502:physiology*; D009154:Mutation; D010447:Peptide Hydrolases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism / Q000494:pharmacology*; D014764:Viral Proteins / Q000378:metabolism
D004792:Enzyme Precursors; D017874:Immediate-Early Proteins; D014764:Viral Proteins; C048925:herpes simplex virus, type 1 protein ICP4; D017346:Protein Serine-Threonine Kinases; C095207:US3 protein, Human herpesvirus 1; D010447:Peptide Hydrolases; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; C108711:DEVDase