HERPES-SIMPLEX VIRUS TYPE-1 LATENCY-ASSOCIATED TRANSCRIPTS SUPPRESS VIRAL REPLICATION AND REDUCE IMMEDIATE-EARLY GENE MESSENGER-RNA LEVELS IN A NEURONAL CELL-LINE

During herpes simplex virus type 1 (HSV-1) latent infection in human d orsal root ganglia, limited viral transcription, which has been linked to HSV-1 reactivation ability, takes place. To study the involvement of this transcription in HSV-1 replication in neuronal cells and conse quently in viral latency, we constructed stably transfected neuronal c ell lines containing (i) the entire HSV-I latency transcriptionally ac tive DNA fragment, (ii) the same DNA sequence with deletions of the la tency-associated transcript (WT) promoters, or (iii) the DNA coding se quence of the WT domain. Replication of HSV-I or a WT-negative mutant was markedly repressed in the WT-expressing cells, a phenomenon mediat ed by the LATs. To study the mechanism responsible for this effect, we examined WT influence upon expression of HSV-1 immediate-early (IE) g enes ICP0, ICP4, and ICP27, by Northern blot analysis. Following infec tion of a WT-expressing neuronal cell line with a WT-negative mutant, the steady-state levels of all three IE mRNAs were reduced compared to those for control cells, Transient transfections into a neuronal cell line indicated that the WT suppressive effect upon ICP0 mRNA was medi ated directly and was not due to the WT effect upon the ICP0 promoter. We therefore propose that the LATs may repress viral replication in n euronal cells by reducing IE gene mRNA levels and thus facilitate the establishment of HSV-I latency in nervous tissue.