RNA interference is a functional pathway with therapeutic potential in human myeloid leukemia cell lines

Background: RNA interference (RNAi) is a cellular pathway of gene silencing in a sequence-specific manner at the messenger RNA level. The basic mechanism behind RNAi is the breaking of a double-stranded RNA (dsRNA) matching a specific gene sequence into short pieces called short interfering RNA, which trigger the degradation of mRNA that matches its sequence. In this study, we explored the effects of RNAi in reducing the target gene expression in human myeloid leukemia cell lines. Methods: Four myeloid leukemia cell lines (HL-60, U937, THP-1, and K562) were transfected with dsRNA duplexes corresponding to the endogenous c-raf and bcl-2genes and the gene expression inhibition was assessed. The effect of RNAi on cell differentiation was studied; the apoptosis induction and the sensitization of the leukemia cell lines to etoposide and daunorubicin were quantified by flowcytometric methods. Results: Transfection of the myeloid leukemia cell lines with dsRNA corresponding to c-raf and bcl-2 genes decreased the expression of Raf-1 and Bcl-2 proteins. RNAi for c-raf gene blocked the appearance of the monocytic differentiation induced by treatment with TPA. Combined RNAi for c-raf and bcl-2 induced apoptosis in HL-60, U937, and THP-1 cells and increased chemosensitivity to etoposide and daunorubicin. Conclusions: RNAi is a functional pathway in human myeloid leukemia cell lines and combined RNAi of c-raf and bcl-2 genes may represent a novel approach to leukemia, providing a means to overcome the resistance to chemotherapeutic agents and ultimately to augment the efficacy of chemotherapy in myeloid leukemia..