High doses of siRNAs induce eri-1 and adar-1 gene expression and reduce the efficiency of RNA interference in the mouse

Abstract

RNAi (RNA interference) is a gene-silencing mechanism that is conserved in evolution from worm to human and has been a powerful tool for gene functional research. It has been clear that the RNAi effect triggered by endogenous or exogenous siRNAs (small interfering RNAs) is transient and dose-dependent. However, there is little information on the regulation of RNAi. Recently, some proteins that regulate the RNA-silencing machinery have been identified. We have observed in previous work that the expression of target genes rebounds after being suppressed for a period of time by siRNAs. In the present study, we used secretory hepatitis B virus surface antigen gene as a reporter and compared its expression level in cell culture and mice challenged by different doses of siRNAs. A quicker and higher rebound of gene expression was observed in mice tail-vein-injected with higher doses of siRNA, and the rebound was associated with an increase in the mRNA level of meri-1 (mouse enhanced RNAi) and adar-1 (adenosine deaminase acting on RNA) genes encoding an exonuclease and RNA-specific adenosine deaminase respectively. Down-regulation of meri-1 by RNAi enhanced the sensitivity and efficiency of siRNA in inhibiting the expression of hepatitis B virus surface antigen. These results indicate that RNAi machinery may be under negative regulation, through the induction of a series of genes coding for destabilizing enzymes, by siRNAs introduced into the cell, and also suggest that a suitable amount of siRNA should be used for research or therapeutic applications.

Silencing of African horse sickness virus VP7 protein expression in cultured cells by RNA interference

“…To date, the advantages of using a combination of siRNAs to improve inhibition remain controversial. In some cases the inhibition has been enhanced [33], whereas other reports have indicated a counter-effect by increasing the dosage [34][35][36]. The decrease in inhibition observed in the present study may have been due to the presence of siVP7-441 that inhibited the ability of the more efficacious openUP (December 2007) siVP7-336 molecule to bind to the RISC complex, perhaps through competition for RISC binding.…”

ADAR-mediated RNA editing in non-coding RNA sequences

“…However, several studies show high doses of siRNA induce ADAR1 expression and reduce the RNAi efficiency in mice [118]. This suggests that the ADAR1 gene may play a negative feedback role in RNAi.…”

Dampening the silencing effect of RNA interference in mammals

“…In this issue of the Biochemical Journal, Hong et al [9] show that gene silencing by RNAi may be negatively regulated by eri-1 and ADAR in mice. HBsAg (hepatitis B virus surface antigen) was used as a marker, and HBsAg was detectable in cells or mice transfected with plasmids expressing HBsAg.…”

“…Hong et al [9] studied further whether the rebound phenomenon was linked to eri-1 and ADAR-1, given that eri-1 and ADAR-1 negatively regulate RNAi in C. elegans and murine fibroblasts. They found that the rebound effect induced by a high dose of siRNA was eliminated by the co-transfection of another siRNA against eri-1.…”

“…The work of Hong et al [9] suggests that the function of eri-1 may be conserved in a wide range of organisms. The notion that eri-1 may suppress RNAi in mice as it does in C. elegans may be biologically significant, as the 'amplification' phenomenon observed in C. elegans has not been reported in mice so far.…”