MODIFIED ENTRY AND SYNCYTIUM FORMATION BY HERPES-SIMPLEX VIRUS TYPE-1MUTANTS SELECTED FOR RESISTANCE TO HEPARIN INHIBITION

Herpes simplex virus type 1 (HSV-1) mutants were selected by passage o f HSV-1(KOS) in HEp-2 cells such that binding and penetration occurred in the presence of heparin. Analysis of selected uncloned virus pools revealed that approximately 95% of virus formed syncytia and greater than 58% were gC-negative. Plaque-purified gC-negative syncytial mutan ts were more resistant than HSV-1(KOS) to heparin inhibition, as was a n engineered nonsyncytial recombinant deleted for gC, Delta gC6. Thus, absence of gC was sufficient to explain the enrichment for gC-negativ e mutants. The syncytial phenotype of most mutants mapped to a mutatio n in gK. Transfer of this mutation to HSV-1(KOS) resulted in a recombi nant that induced fusion of Vero cells but not HEp-2 cells and was mor e sensitive to heparin inhibition of entry, revealing a previously und escribed phenotype of mutations in gK. Engineered gC-negative virus co ntaining the gK syncytial mutation induced fusion of both cell lines a nd was as resistant to heparin inhibition as was Delta gC6. Because de letion of gC reduces infectivity of HSV-1 in the absence of heparin, m utations in gC combined with the syncytial mutation could have provide d a selective advantage. Thus, absence of gC reduced heparin inhibitio n of binding and penetration while the combination of the gC and gK mu tations enhanced spread through the HEp-2 cell monolayer by cell fusio n. Because extreme selective pressure was required to favor these muta tions and such mutations are rare in clinical isolates, the wild-type forms of gC and gK must provide for optimal viral replication and prop agation in cell culture as well as in vivo, despite the view that gC i s dispensable in cultured cells. (C) 1996 Academic Press, Inc.