REDUCED LEVELS OF IE2 GENE-EXPRESSION AND SHUTDOWN OF EARLY AND LATE VIRAL GENES DURING LATENT INFECTION OF THE GLIOBLASTOMA CELL-LINE U138-MG WITH SELECTABLE RECOMBINANTS OF HUMAN CYTOMEGALOVIRUS

To establish stable culture conditions which support persistence of th e human cytomegalovirus (HCMV) genome in a latent state, the expressio n of the bacterial neomycin phosphotransferase (neo) from HCMV recombi nants was used for selection. Different cell lines were Infected with HCMV recombinants. The human glioblastoma line U138-MG was rendered re sistant to G418 and retained the viral genome. More than 90% of the ce lls expressed the viral IE1 protein of 72 kDa for a culture period of 18 months. Many fewer cells expressed IE2-encoded proteins. No late ge ne expression or infectious virus was detectable. IE2 gene expression in latently infected cells appeared to be restricted at the level of R NA accumulation. Treatment with TPA or retinoic acid led to enhanced e xpression of the IE2 gene and the early genes encoding pp65 (UL83) and p52 (UL44). Superinfection with wild-type HCMV led to replication of neo-recombinant virus, indicating that replication-competent virus had been retained in latently infected U138-MG and that the cells had kep t their permissive phenotype. Latent HCMV infection in U138-MG cells p rovides a useful model system for studying the role of particular vira l and cellular genes in latent and permissive infections, (C) 1994 Aca demic Press, Inc.