Specific inhibition of gene expression and transactivation functions of hepatitis B virus X protein and c-myc by small interfering RNAs

With a view to developing therapeutic strategies against hepatocellular carcinoma (HCC), we have recently shown that co-expression of c-myc and the X protein of hepatitis B virus (HBx) resulted in the development of HCC in the X-myc transgenic mice [Lakhtakia et al., J. Gastroenterol. Hepatol. 18 (2003) 80-91]. We now show in cell culture-based studies that small interfering RNA (siRNA) corresponding to HBx and c-myc can regulate expression and transactivation of the target genes. Expression vectors for small hairpin RNAs (shRNAs) against two different regions each of the HBx and c-myc open reading frames were constructed and their regulatory effects were investigated in COS-1 cells. A dose-dependent specific inhibition in the expression levels of HBx and c-myc was observed with individual shRNAs. Further, the recombinantly expressed shRNAs also blocked the transactivation functions of their cognate genes. Though each shRNA worked at a different efficiency, the inhibitory effects with two different shRNAs were cumulative. These results appear promising for developing a siRNA-based therapy for HCC. (C) 2004 Published by Elsevier B.V. on behalf of the Federation of European Biochemical Societies.