Inhibitory role of the host apoptogenic gene PKR in the establishment of persistent infection by encephalomyocarditis virus in U937 cells

Persistent infections by viruses such as HIV-1 and hepatitis B virus can po se long-term health hazards. Because establishment of persistent infections involves close interactions and adjustments in both host and virus, it wou ld be informative to establish a paradigm with which a normally cytolytic v iral infection can be easily converted to persistent infection, so that the different stages in developing persistent infection can be examined. Such a model system is described in this paper. Highly cytolytic encephalomyocar ditis virus (EMCV) infection was shifted to persistent infection as a resul t of repressed expression of the double-stranded RNA-dependent protein kina se (PKR) in the promonocytic U937 cells. Because of the apoptogenic potenti al of PKR, a deficiency of PKR resulted in a delay in virus-induced apoptos is in EMCV-infected U937 cells, allowing the eventual establishment of pers istent EMCV infection in these cells (U9K-AV2), That this was a bona fide p ersistent infection was demonstrated by the ability of infected cells to pr opagate as long-term virus-shedding cultures; electron microscopy studies s howing presence of intracellular EMCV virions and chromatin condensation; d etection of virus-induced chromosomal DNA fragmentation and sustained expre ssion of apoptogenic p53 and IL-1 beta converting enzyme; and demonstration of active EMCV transcription by reverse transcription-PCR. In addition, a host-virus coevolution was observed in U9K-AV2 cultures over time: U9K-AV2 cells exhibited slower growth rates, resistance to viral super-infection, a nd cessation of IFN-alpha synthesis, whereas the infectivity of EMCV was dr astically attenuated, Finally, data are presented on the suitability of thi s model to study establishment of persistent infection by other viruses suc h as Sendai virus and reovirus.