Analysis of gene expression in a human cell line stably transduced with herpesvirus saimiri

Herpesvirus saimiri (HVS) is the prototype gamma-2 herpesvirus; it has sign ificant homology to the human gammaherpesviruses Kaposi's sarcoma-associate d virus and Epstein-Barr virus and the murine gammaherpesvirus murine herpe svirus 68. HVS causes a persistent asymptomatic infection in its natural ho st, the squirrel monkey. Both subgroups A and C possess the ability to immo rtalize common marmoset T lymphocytes to interleukin-2-independent prolifer ation. However, only subgroup C is capable of transforming human, rabbit, a nd rhesus monkey lymphocytes in vitro. In addition, HVS can stably transduc e a variety of human cell lines where the virus persists as a nonintegratin g circular episome. In this study, we have developed a system in which the HVS DNA is stably maintained as a nonintegrated circular episome in the hum an lung carcinoma cell line A549. Virus production can be reactivated using chemical inducing agents, including tetradecanoyl phorbol acetate and n-bu tyrate, suggesting that the infection in human A549 cells is latent. To ana lyze virus gene expression in these stably transduced cells, Northern blot analysis was performed using a series of probes produced from restriction f ragments spanning the entire coding region of the HVS genome. This demonstr ated that an adjacent set of genes containing open reading frames (ORFs) 71 to 73 are expressed in this stably transduced cell line. Moreover, these g enes are transcribed as a polycistronic mRNA species produced from a common promoter upstream of ORF 73. This model may serve as a useful tool in the further analysis of the role of ORFs 71 to 73 in gamma-2 herpesvirus latenc y.