Survivin Silencing Through RNAi

Carvalho et al. (43) first used RNAi to specifically repress survivin in HeLa cells. These authors showed that survivin was no longer detectable in cultures a few days after transfection with specific siRNA and that survivin-depleted cells were delayed in mitosis and accumulated in prometaphase with misaligned chromosomes. In this model, loss of survivin activated the mitotic checkpoint, which was mediated by induction of p53 and was associated with the increase of its downstream target, p21Waf1. Survivin ablation also caused loss of mitochondrial membrane potential, enhanced caspase-9 proteolytic activation and spontaneous apoptosis (43). More recently, survivin downregulation, accomplished through the use of siRNAs, was seen to reduce clonogenic potential and increase the percentage of multinucleated cells in a panel of human sarcoma cell lines independently of p53 gene status (84). Moreover, survivin knockdown caused radio-sensitization, which was paralleled by an increased activity of caspase-3 and caspase-7, in wild-type-p53 but not in mutant-p53 sarcoma cells (85). An enhanced apoptotic response to APO2L/TRAIL treatment was also observed in melanoma and renal carcinoma cell lines transfected with survivin-specific siRNAs (86). Finally, Coma et al. (87) recently demonstrated that transfection of endothelial cells with survivin specific siRNAs induced a marked increase in the apoptotic rate, a dose-dependent inhibition of their migration on vitronectin and a decrease in capillary formation.

To prevent nonphysiological responses associated with persistent suppression of a gene that is essential for cell survival and cell cycle progression such as survivin, systems allowing an inducible regulation of RNAi have been developed. Coumoul et al. (88) recently demonstrated that inducible suppression of survivin was efficiently achieved in ES cells by regulating RNAi using a Cre-LoxP approach, as indicated by the decrease level of gene expression and reduced proliferative potential.

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