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Viral replication efficiency is in large part governed by the ability of viruses to counteract pro-apoptotic signals induced by infection of host cells. For HHV-8, viral interferon regulatory factor-1 (vIRF-1) contributes to this process in part via inhibitory interactions with BH3-only protein (BOP) Bim, recently identified as an interaction partner of vIRF-1. Here we recognize that the Bim-binding domain (BBD) of vIRF-1 resembles a region (BH3-B) of Bid, another BOP, which interacts intramolecularly with the functional BH3 domain of Bid to inhibit it pro-apoptotic activity. Indeed, vIRF-1 was found to target Bid in addition to Bim and to interact, via its BBD region, with the BH3 domain of each. In functional assays, BBD could substitute for BH3-B in the context of Bid, to suppress Bid-induced apoptosis in a BH3-binding-dependent manner, and vIRF-1 was able to protect transfected cells from apoptosis induced by Bid. While vIRF-1 can mediate nuclear sequestration of Bim, this was not the case for Bid, and inhibition of Bid and Bim by vIRF-1 could occur independently of nuclear localization of the viral protein. Consistent with this finding, direct BBD-dependent inactivation by vIRF-1 of Bid-induced mitochondrial permeabilization was demonstrable in vitro and isolated BBD sequences were also active in this assay. In addition to Bim and Bid BH3 domains, BH3s of BOPs Bik, Bmf, Hrk, and Noxa also were found to bind BBD, while those of both pro- and anti- apoptotic multi-BH domain Bcl-2 proteins were not. Finally, the significance of Bid to virus replication was demonstrated via Bid-depletion in HHV-8 infected cells, which enhanced virus production. Together, our data demonstrate and characterize BH3 targeting and associated inhibition of BOP pro-apoptotic activity by vIRF-1 via Bid BH3-B mimicry, identifying a novel mechanism of viral evasion from host cell defenses. [ABSTRACT FROM AUTHOR]

Recombinant Towne CMV expressing luciferase under the control of CMV-DNA polymerase (POL) or the late pp28 (UL99) promoters were evaluated for potential application in high-throughput screening of anti-viral compounds. POL-and pp28-luciferase displayed maximal expression 48 and 72 hours post infection, respectively. The pp28- luciferase virus achieved a wider dynamic range of luciferase expression (6-7 logs) and was selected for testing of inhibition by five anti-viral compounds. Luciferase expression highly correlated with plaque reduction and real-time PCR. The pp28-luciferase reporter system is rapid, reproducible, and highly sensitive. It may be applied to screening of novel anti-CMV compounds. [ABSTRACT FROM AUTHOR]

Human herpesvirus 6 (HHV-6) is a recently recognized human herpesvirus isolated from lymphoid cells and thought to be the causative agent for exanthem subitum. Using dot blot hybridization, the HHV-6 sensitivity pattern to several antivirals was compared with those of herpes simplex virus type 1 and human cytomegalovirus. HHV-6 most closely resembled cytomegalovirus in that it was relatively resistant to the antiviral effects of acyclovir and bromovinyl-deoxyuridine but sensitive to ganciclovir and phosphonoacetic acid. From these results, it appears more likely that HHV-6 infections would respond to ganciclovir and foscarnet than to acyclovir should treatment deemed be advisable, although the low toxicity of acyclovir may allow for its use at doses that might affect replication of HHV-6. [ABSTRACT FROM PUBLISHER]

Three temperature-sensitive (ts) mutants of mouse cytomegalovirus (MCMV) were compared with parent virus for their ability to produce acute infection, to stimulate protection against a lethal challenge with salivary gland MCMV, and to become latent and then be reactivated. During the acute phase of infection, ts mutant virus demonstrated very limited replication. During the later phase of infection (seven to 14 days after challenge), titers of virus in the pancreas and salivary glands in mice infected with parent virus continued to rise, whereas no virus could be detected in mice infected with the ts mutants. Prior infection with parent virus or the ts mutants protected susceptible mice from a lethal dose of salivary gland MCMV. One year after infection, treatment of mice with an immunosuppressive regimen resulted in reactivation of parent and ts mutant virus. Reactivated virus recovered from mice infected with ts mutant virus remained temperature sensitive. [ABSTRACT FROM PUBLISHER]