Small noncoding double-stranded RNAs (dsRNA) have been implicated in RNA interference (RNAi) and thereby the silencing of gene expression. Li et al. transfected human prostate cancer cell lines with 21-nucleotide dsRNAs that targeted regions of the E-cadherin promoter and saw an increase in the abundance of E-cadherin mRNA and protein. The increase in E-cadherin mRNA abundance, which occurred within 48 hours and was apparent at dsRNA concentrations as low as 1 nM, was apparent for days and appeared to depend on target location on the promoter. Similar increases in target gene expression were seen in various human cell lines transfected with dsRNA targeting the promoters of the genes encoding vascular endothelial growth factor and p21WAF1/CIP1. Truncation and extension of the 21-nucleotide dsRNAs that stimulated E-cadherin expression suggested that neither 16-nucleotide nor 26-nucleotide dsRNAs were effective in stimulating gene expression. Further, mutational analysis of dsRNAs targeted against E-cadherin and p21 indicated that the 5′ region of the antisense strand was critical for dsRNA-induced gene activation (RNAa). Experiments using siRNA directed against Argonaute proteins indicated that Argonaute 2 (which is required for RNAi) was also necessary for RNAa. Chromatin immunoprecipitation analysis indicated that RNAa was associated with a loss of histone 3 methylation at lysine-9 at dsRNA target sites; however, bisulfite genomic sequencing indicated that changes in DNA methylation status were not involved. Thus, small noncoding RNAs appear to play a role in activating--as well as inhibiting--the expression of target genes.
L. C. Li, S. T. Okino, H. Zhao, D. Pookot, R. F. Place, S. Urakami, H. Enokida, R. Dahiya, Small dsRNAs induce transcriptional activation in human cells. Proc. Natl. Acad. Sci. U.S.A. 103, 17337-17342 (2006). [Abstract] [Full Text]