Restricted Replication of Herpes Simplex Virus Type 1 in Murine Embryonal Carcinoma Cells

Department of Medicine, University of Ottawa, 451 Smyth Road, Ottawa, Ontario K1H 8M5 and 1 Ecotoxicology Group, National Research Council of Canada, Ottawa, Ontario K1A 0R6, Canada Herpes simplex virus type 1 (HSV-1) has a broad host range but the KOS strain of HSV-1 did not replicate efficiently in murine embryonal carcinoma (EC) cells. The yield of infectious HSV-1 from EC cells was 100- to 1000-fold lower than that from fibroblast cell lines of mouse, monkey or human origin. The thymidine kinase (TK) gene of HSV-1 is expressed early during the infectious cycle. The levels of TK mRNA and of TK activity in infected EC cells were only two- to threefold lower than levels from infected fibroblast cells. Infected EC cells supported replication of about half as much HSV-1 DNA as did fibroblast cells. The reduced yield of infectious virus was consistent with a paucity of virions in infected EC cells examined by electron microscopy, suggesting a major block late during the HSV-1 infectious cycle. We isolated a variant strain of HSV-1, called KOSEC, which replicated as efficiently in EC cells as in mouse fibroblasts. KOSEC infected EC and fibroblast cells, synthesized more TK mRNA, more TK enzyme, and more HSV-1 DNA than did the same cells infected with the KOS stain. Both HSV-1 strains induced similar levels of synthesis of gD, an early viral glycoprotein. By co-infection of EC cells with the KOS and KOSEC virus, both the elevated virus yield and the elevated TK synthesis seen in KOSEC-infected cells appeared to be recessive. Apparently a viral mutation that affects expression of some early viral functions can also overcome the EC cell restriction to HSV-1 replication. Keywords: HSV-1, replication, restricted, EC cells Present address: Department of Biochemistry, McGill University, 3655 Drummond Street, Montreal H3G 1Y6, Canada. Present address: Laboratory Centre for Disease Control, Health and Welfare Canada, Ottawa, Ontario K1A 0L2 Canada. Received 23 April 1986; accepted 28 October 1986.