Construction and characterization of an equine herpesvirus 1 glycoprotein C negative mutant

An equine herpesvirus 1 (EHV-1) strain RacL11 mutant was constructed that carries the Escherichia coli LacZ gene instead of the open reading frame encoding glycoprotein C (gC). The engineered virus mutant (L11ΔgC) lacked codons 46–440 of the 1404 bp gene. On rabbit kidney cell line Rk13 and equine dermal cell line Edmin337, the L11ΔgC virus grew to titers which were reduced by approximately 5- to 10-fold compared with wild-type RacL11 virus or a repaired virus (R-L11ΔgC). However, when L11ΔgC growth properties were analyzed on primary equine cells a decrease of viral titers was observed such that extracellular L11ΔgC titers were reduced by 48- to 210-fold compared with those of wild-type or repaired virus. Heparin sensitive and heparin resistant attachment was assessed by binding studies using radiolabeled virion preparations. These studies revealed that EHV-1 gC is important for heparin sensitive attachment to the target cell. Similar results were obtained when cellular glycosaminoglycan (GAG) synthesis was inhibited by chlorate treatment or when cells defective in GAG synthesis were used. L11ΔgC also exhibited significantly delayed penetration kinetics on Rk13 and primary equine cells. Infection of mice with L11ΔgC did not cause EHV-1-related disease, whereas mice infected with either RacL11 or R-L11ΔgC exhibited massive bodyweight losses, high virus titers in the lungs, and viremia. Taken together, EHV-1 gC was shown to play important roles in the early steps of infection and in release of virions, especially in primary equine cells, and contributes to EHV-1 virulence.