Cisplatin and siRNA interference with structure and function of Wnt-5a mRNA: design and in vitro evaluation of targeting AU-rich elements in the 3' UTR.

Wnt-5a is a secreted glycoprotein which has been shown to be involved in the regulation of cell adhesion and motility, processes which are of importance in metastasis formation by cancer cells. We here present an initial study aiming at evaluating whether small interfering RNA (siRNA) in combination with cisplatin can be used to modulate protein expression levels under in vitro conditions. For this purpose, an AU-rich region corresponding to the initial 260 bases of the Wnt-5a 3' untranslated region was chosen as the target. The effect of four different siRNAs was evaluated by analysis of protein suppression levels in rabbit reticulocyte lysate (RRL) and an immortalized noncancerous mammary epithelial (HB2) cell line by monitoring the activity of transiently expressed luciferase. The specificity and kinetics for hybridization of the siRNA with the messenger RNA target were followed by digestion techniques and analysis by polyacrylamide gel electrophoresis. Specific and temperature-dependent hybridization was observed, with a half-life of approximately 0.5 h at 4 degrees C. Significant downregulation of luciferase activity was obtained in the micromolar and nanomolar range, for RRL and HB2, respectively. In addition, the downregulation of protein production caused by addition of cisplatin could be further potentiated by addition of siRNA in a selective manner. The latter observation suggests that combined use of cisplatin and siRNA could be a method to decrease therapeutically used cisplatin concentrations. Thus, toxic side effects could be minimized while key proteins are targeted in a highly specific manner.