Li Lab: Research
RNA interference (RNAi) is a naturally occurring pathway in which fragments of double-stranded ribonucleic acid (dsRNA) selectively downregulate genes with complementary sequences to the dsRNA. The ability of RNAi to silence genes by degrading the RNA and preventing protein expression has many advantageous implications for the field of biology. In addition to serving as a valuable genomic tool for the assessment of gene functions, RNAi can also be used as a means of gene therapy to combat various diseases such as viral infections, cancer and neurodegenerative disorders. RNAi silences specific target genes by inducing the cleavage and destruction of mRNA within the cytoplasm. This phenomenon takes place upon the introduction of dsNRA into the cytoplasm, followed by the degradation of dsRNA into siRNA (small interference RNA) consisting of two19-23bp fragments with 2-nucleotide overhangs at the 3’ ends. The siRNA duplexes are then unwound via an ATP-dependent mechanism with one strand (the guided strand) bounded to the RNA-induced silencing complex (RISC), thereby, catalyzing the cleavage of a homologous mRNA. However, in order for RNAi to be effectively used as a therapeutic means, dsRNA must first be successfully incorporated into target cells. siRNA delivery is currently seen as one of the greatest challenge to the development of RNAi-based therapies.
In response to this problem, the laboratory of Dr. Chiang Li has developed a process known as Transkingdom RNA-interference to deliver RNAi to targeted cells. This novel technique uses non-pathogenic bacteria, namely Eschericilia Coli, engineered with the capability to transcribe short hairpin RNA (shRNA) from a TRIP plasmid containing the invasin gene INV and the listeriolysin O gene HlyA. These bacterial factors allow the invasion of E. Coli into mammalian epithelial cells. Once inside the host cells, bacterial lysis releases shRNA, which becomes processed into siRNA, a mediator of the RNAi pathway. This technology has been used successfully in vitro and in vivo and is the subject of an international patent application by the Beth Israel Deaconess Medical Center.
Citations
Shuanglin Xiang, Johannes Fruehauf and Chiang J Li. Short hairpin RNA–expressing bacteria elicit RNA interference in mammals. Nat Biotechnol. 2006 Jun;24(6):697-702. Epub 2006 May 14.
Charles X. Li, Amy Parker, Ellen Menocal, Shuanglin Xiang, Laura Borodyansky, and Johannes H. Fruehauf Delivery of RNA interference. Cell Cycle 5(18): 2103-2109, 2006 September 15
