Antiviral activity of RNA molecules containing self-releasing ribozymes targeted to lymphocytic choriomeningitis virus.

Ribozymes catalytically cleave substrate RNA molecules in a sequence-specific manner. Engineered ribozymes can be developed and introduced into tissue culture cells to regulate gene expression and to inhibit viral replication. We have previously reported on the construction of cell lines that constitutively express a single antiviral ribozyme embedded in a lengthy RNA transcript. These cells exhibited a marked reduction in their ability to support viral infection. Here we report the construction of RNA molecules that contain one or two antiviral ribozymes, each specific for a different cleavage site on the genome of the target virus, lymphocytic choriomeningitis virus (LCMV), and each contained in a self-cleavage cassette comprising cis-acting ribozymes designed to release the antiviral molecules from the transcript. In vitro studies showed that both antiviral ribozymes were released properly from the RNAs following cleavage by the flanking ribozymes and that these released ribozymes functioned as expected in cleaving the target virus RNA. These self-cleaving cassettes have been clones into a retroviral vector downstream of, but in the same transcript as, the chloramphenicol acetyltransferase (CAT) gene. Thus, we hoped to employ CAT as a surrogate marker of ribozyme transcription. Stably transformed cell lines were established. Cleavage by the cis-acting ribozymes was incomplete, as assessed by Northern blot analysis and by the ability of transformed cells to produce infectious retroviral particles. Nevertheless, the antiviral ribozyme sequences exerted effects in tissue culture. LCMV RNA levels in ribozyme-expressing cells were suppressed, and infectious virus yields were decreased by up to 95% compared with normal cells and with cells expressing inverted ribozymes. The antiviral effects correlated with CAT levels, but there was no significant difference between cell lines expressing a single ribozymes and those expressing two.