Selective inhibition of hepatitis B virus and human immunodeficiency virus sequence-promoted gene expression by cotransfected poly(I):poly(C)

The transient expression of hepatitis B virus (HBV) surface and "e" antigens caused by transfection of human hepatoblastoma HepG2 cells with HBV DNA was markedly inhibited by cotransfection with poly(I):poly(C). Cotransfection with poly(I):poly(C) also inhibited the expression of bacterial chloramphenicol acetyltransferase (CAT) gene which was under the control of either the HBV core promoter or the human immunodeficiency virus (HIV-1) long terminal repeat. This inhibition was much more pronounced on the expression of HBV-promoted CAT than HIV-promoted CAT. The uptake of reporter plasmid was not affected by cotransfected poly(I):poly(C). The inhibition was found to be at the steady-state CAT mRNA level and appeared to be specific for HBV and HIV regulatory sequences since CAT expression directed by other viral and cellular regulatory sequences was not inhibited. Cotransfection with a mixture of equal amounts of poly(I) and poly(C) had similar inhibitory effects whereas cotransfection with poly(I) or poly(C) alone, or other double-stranded ribo- or deoxyribonucleotides, did not have such strong effects. The addition of poly(I):poly(C) to the culture medium of cells transfected with these reporter plasmids caused little inhibition. Transfection with poly(I):poly(C) induced a minimal amount of intracellular interferon-α in HepG2 cells which may be involved in selective inhibition of HBV- and HIV-1-directed gene expression. 2-Aminopurine, an inhibitor of double-stranded RNA activated protein kinase known to block interferon gene induction by poly(I):poly(C), partially reversed the poly(I):poly(C)-induced inhibitory effect on HBV-CAT expression.