ANTI-APOPTOTIC COMPOSITIONS COMPRISING THE R1 SUBUNIT OF HERPES SIMPLEX VIRUS RIBONUCLEOTIDE REDUCTASE OR ITS N-TERMINAL PORTION; AND USES THEREOF

摘要

The R1 subunit of herpes simplex virus (HSV) ribonucleotide reductase, which is expressed very early after viral reactivation, possesses an N-terminal domain of about 350 amino acids of unknown function. Using an adenovirus (Ad) inducible system we had demonstrated that a complete deletion of this domain produces a cytotoxic protein. We now report that apoptotic death induced by this truncated R1 could be completely prevented by coexpression of the full-length R1. The R1 antiapoptotic activity was further substantiated by showing that expression of this protein at low level can completely block apoptosis induced either by TNF-receptor family triggering in the presence of cycloheximide (CHX) or by Fas-L coexpression with an Ad recombinant. In both cases, the protection was lost when inhibiting tTA function with the tetracycline analog doxycycline shut down R1 expression. A level of R1 of 0.005 % total cell protein was sufficient for half-maximal protection against TNF alpha +CHX. By monitoring caspase 8 activation either by immunoblot with an antiserum visualizing the inactive 56-kDa proform and the active 18-kDa species or by an in vitro assay using ETD-AFC as caspase 8 specific fluorescent substrate, we found that the strong activation of caspase 8 induced either by TNF- alpha +CHX or Fas-L expression was prevented by the R1 protein. Finally, using an HSV-1 R1 deletion mutant, ICP6 DELTA , we obtained direct evidence for the importance of HSV-R1 in protecting HSV-infected cells against cytokine-induced apoptosis. These results show that, in addition to its reductase function which is essential for viral reactivation, the HSV R1 could contribute to viral propagation by preventing apoptosis induced by the immune system. The N-terminal domain by itself is as anti-apoptotic as the whole RI protein. An anti-apoptotic agent and a composition derived therefrom are described and claimed.