Alternative approaches for the application of ribozymes as gene therapies for retroviral infections

Targeting cathepsin L (CL) by specific ribozymes decreases CL protein synthesis and cartilage destruction in rheumatoid arthritis

The present study was undertaken to examine whether ribozymes cleaving specifically cathepsin L (CL) mRNA are able to decrease the synthesis of CL protease in rheumatoid arthritis synovial fibroblasts (RA-SF) and thereby reduce the invasiveness into cartilage both in vitro and in the SCID mouse coimplantation model of RA. Two different ribozymes that cleave CL mRNA specifically at positions 533 (RzCL533) and 790 (RzCL790) were generated. Using retroviral gene transfer, RA-SF were transduced with the ribozyme constructs or the empty vector. To examine the effect of the ribozymes on the mRNA level, quantitative analysis for CL mRNA was performed using real-time PCR. For evaluation on the protein level, ELISA using specific anti-CL antibodies was performed. In addition, transduced RA-SF were examined in vitro in a three-dimensional destruction assay evaluating their ability to degrade extracellular matrix produced by human chondrocytes. Matrix destruction was monitored by the release of soluble glycosaminoglycans (sGAG). Using the in vivo SCID mouse coimplantation model of RA, RzCL533-transduced RA-SF and control cells were coimplanted with human cartilage for 60 days. After being killed, invasion of RA-SF into the cartilage was evaluated by using a semiquantitative score. Transduction of RA-SF with RzCL533 and RzCL790 ribozymes decreased significantly the expression of CL mRNA to 44% (range 25-62%) and 20% (range 1-43%), respectively, when compared to mock-transduced cells. The protein concentration of CL in the cell culture supernatants of transduced RA-SF was decreased from 16.0 ng/ml in the mock constructs to 4.1 and 8.2 ng/ml (mean), respectively. Using the in vitro cartilage destruction assay, the release of sGAG decreased to 46 and 60%, respectively, after 14 days when compared to mock-transduced cells. In the SCID mouse coimplantation model of RA, RzCL533-transduced RA-SF revealed a significant lower cartilage invasion when compared to mock and untransduced cells. Using retroviral gene transfer, ribozymes cleaving CL mRNA inhibit specifically the synthesis of this matrix-degrading enzyme and reduce cartilage destruction in in vitro and in vivo models. Our study therefore suggests that ribozymes targeting CL could be a novel and efficient tool to inhibit joint destruction in RA.

A role for upstream RNA structure in facilitating the catalytic fold of the genomic hepatitis delta virus ribozyme

Hepatitis delta virus (HDV) has a circular RNA genome that replicates by a double rolling-circle mechanism. The genomic and antigenomic versions of HDV contain a ribozyme that undergoes cis-cleavage, thereby processing the transcript into unit-length monomers. A genomic HDV transcript containing 30 nucleotides immediately upstream of the cleavage site was found to have attenuated self-cleavage. Structure mapping and site-directed mutagenesis revealed an inhibitory stretch consisting of upstream nucleotides -24 to -15 that forms a long-range pairing, termed Alt 1, with the 3' strand of P2 (P2(3')) located at the very 3'-end of the ribozyme. Two other alternative pairings were found, Alt 2, which involves upstream nucleotide-ribozyme interactions, and Alt 3, which involves ribozyme-ribozyme interactions. Self-cleavage was rescued 2700 to 20,000-fold by adding DNA oligomers, which sequester the -24/-15 inhibitory stretch in trans. Surprisingly, co-transcriptional self-cleavage occurs when the number of upstream nucleotides is increased to 54. Computer prediction and structure mapping support the existence of an unusually stable upstream hairpin involving nucleotides -54 to -18, termed P(-1)/L(-1), which sequesters the majority of the -24/-15 inhibitory stretch in cis. This hairpin is followed by a stretch of single-stranded pyrimidine-rich nucleotides, termed J(-1/1). Sequence comparison suggests that the P(-1)/L(-1)/J(-1/1) motif is conserved among known genomic HDV isolates, and that the J(-1/1) stretch is conserved among antigenomic HDV isolates. Lastly, the secondary structure of the Alt 1-containing ribozyme provides insight into possible folding intermediates of the ribozyme.