Reduced seed region-based off-target activity with lentivirus-mediated RNAi

Along with silencing intended target genes, transfected siRNAs regulate numerous unintended transcripts through a mechanism in which the equivalent of a microRNA-like seed region in the siRNA recognizes complementary sequences in transcript 39 UTRs. Amelioration of this off-target silencing would lead to more accurate interpretation of RNA interference ( RNAi) experiments and thus greatly enhance their value. We tested whether lentivirus-mediated delivery of shRNA is prone to the sequence-based off-target activity prevalent in siRNA experiments. We compared target gene silencing and overall impact on global gene expression caused by multiple sequences delivered as both transfected siRNAs and lentivirus vector-expressed shRNAs. At equivalent levels of target gene silencing, signatures induced by shRNAs were significantly smaller than those induced by cognate siRNAs and arose less frequently from seed region activity. Interestingly, the low level of seed region-based off-target activity exhibited by shRNAs resulted in down-regulation of transcripts that were largely distinct from those regulated by siRNAs. On the basis of these observations, we recommend lentivirus-mediated RNAi for pathway profiling experiments that measure whole genome transcriptional readouts as well as for large-scale screens when resources for extensive follow up are limited.