RNA Interference: A Novel Alternative Approach in Nephrotoxicity Studies

RNA interference (RNAi) is a term used to describe the sequence-specific suppression of genes, initiated by doublestranded RNA (dsRNA) oligonucleotides homologous to the sequence of the silenced gene (Hammond et al., 2001). RNAi was first observed in Caenorhabditis elegans as a response to exogenously introduced long double-stranded RNA (dsRNA) (Fire et al., 1998). While the mechanism of RNAi has yet to be fully characterised, silencing appears to be mediated by duplexes of 21-23 nucleotides (nt), called small interfering RNAs (siRNAs), which are degradation products of longer double-stranded RNAs, cleaved by the RNAse III-like enzyme Dicer. The resulting siRNAs are incorporated into a multi-component complex known as RISC (RNA-induced silencing complex) that targets and cleaves mRNA complementary to the siRNAs (Hamilton et al., 1999; Tuschl et al., 1999; Zamore et al., 2000; Bernstein et al., 2001; Elbashir et al., 2001; Hammond et al., 2001). An overview of the RNAi mechanism is shown in fig. 1. More recently, short endogenous RNAs sharing similarity to siRNAs, called microRNAs (miRNAs), have been identified as key post-transcriptional regulators in such varied organisms as plants, nematodes and mammals (Lagos-Quintana et al., 2001; Lau et al., 2001; Lee et al., 2001; Reinhart et al., 2002). These miRNAs are initially transcribed as a long RNA and then processed to a pre-miRNA of ~70 nt (Lee et al., 2002). This premiRNA forms an imperfect hairpin structure, which is then processed by Dicer enzyme to produce the mature, single-strand ~21-23 nt miRNA (Grishok et al., 2001; Hutvagner et al., 2001; Ketting et al., 2001). While this is an innate process in cells, most probably an evolutionary mechanism to protect against cellular attack from invasive viral RNAs, the mechanism provides researchers with RNA Interference: A Novel Alternative Approach in Nephrotoxicity Studies