Accumulation of herpes simplex virus type 1 early and leaky-late proteins correlates with apoptosis prevention in infected human HEp-2 cells

We previously reported that a recombinant ICP27-null virus stimulated, but did not prevent, apoptosis in human HEp-2 cells during infection (M. Aubert and J. A. Blaho, J. Virol. 73:2803-2813, 1999). In the present study, we u sed a panel of 15 recombinant ICP27 mutant viruses to determine which featu res of herpes simplex virus type 1 (HSV-1) replication are required for the apoptosis-inhibitory activity. Each virus was defined experimentally as ei ther apoptotic, partially apoptotic, or nonapoptotic based on infected HEp- 2 cell morphologies, percentages of infected cells with condensed chromatin , and patterns of specific cellular death factor processing. Viruses d27-1, d1-5, d1-2, M11, M15, M16, n504R, n406R, n263R, and n59R are apoptotic or partially apoptotic in HEp-2 cells and severely defective for growth in Ver o cells. Viruses d2-3, d3-4, d4-5, d5-6, and d6-7 are nonapoptotic, demonst rating that ICP27 contains a large amino-terminal region, including its RGG box RNA binding domain, which is not essential for apoptosis prevention. A ccumulations of viral TR, VP16, and go but not gC, ICP22, or ICP4 proteins correlated with prevention of apoptosis during the replication of these vir uses. Of the nonapoptotic viruses, d4-5 did not produce gC, indicating that accumulation of true late gene products is not necessary for the preventio n process. Analyses of viral DNA synthesis in HEp-2 cells indicated that ap optosis prevention by HSV-1 requires that the infection proceeds to the sta ge in which viral DNA replication takes place. Infections performed in the presence of the drug phosphonoacetic acid confirmed that the process of vir al DNA synthesis and the accumulation of true late (gamma (2)) proteins are not required for apoptosis prevention. Based on oar results, we conclude t hat the accumulation of HSV-1 early (beta) and leaky-late (gamma (1)) prote ins correlates with the prevention of apoptosis in infected HEp-2 cells.