Expression of HCV E1 protein in baculovirus-infected cells: effects on cell viability and apoptosis induction

The molecular mechanisms of pathogenesis in hepatitis C virus (HCV) infection are not yet understood. Recently, we reported that the expression of the envelope protein E1 is toxic for Escherichia coli cells. The toxicity is related to the ability of C-terminal transmembrane (TM) domain of E1 to modify membrane permeability. In this study we expressed the E1 protein, complete (a.a. 192-383) or deleted (a.a. 192-340) of the TM region, fused to the C-terminus of glutathione-S-transferase by two recombinant baculoviruses. Infection of Sf9 insect cells by E1 baculovirus induced a rapid decrease in cell viability in the first 18-24 h postinfection. Premature cytopathic changes and low level of E1 protein expression were also reported. The analysis of DNA isolated from cells revealed a typical internucleosomal ladder pattern characteristic of apoptosis. The DNA degradation was first detected at 18 h postinfection by ethidium bromide gel electrophoresis and was confirmed by TUNEL assay. The results indicated that the C-terminal domain of E1 is essential for apoptosis induction as neither cell death nor DNA degradation were observed following infection with the recombinant baculovirus expressing the C-terminal-deleted E1. These findings support the hypothesis that the TM domain of E1 may play a role in viral pathogenesis.