Lower than that of the non-targeting siRNA-treated cultures respectively. There was a tendency for the siRNA-2- treated cells to form syncytia-like structures in which clusters of cells were joined by long spindle-like projections. Results are representative of two independent experiments. The effect of BIRC6 silencing on cell cycle progression was also examined. The knockdown of BIRC6 in LNCaP cells did not result in significant change in cell cycling. BIRC6 has been reported to play a significant role in apoptosis resistance of a variety of cancers. In the present study we investigated whether it also plays a role in apoptosis resistance of prostate cancer, as this process may underlie the development of castration resistance. In contrast to earlier reports, our study established that the BIRC6 protein is markedly expressed by a variety of conventional malignant prostate cell lines as distinct from benign prostate cell lines, indicating that BIRC6 could have a significant role in prostate cancer. BIRC6 was found to be functionally critical for the survival of prostate cancer cells. Specific reduction of BIRC6 expression by siRNAs led to a marked inhibition of prostate cancer cell viability, which notably was coupled to a marked increase in Annexin-V positive cells and the expression of apoptosis markers. The reduction in population growth induced by nontargeting siRNA is likely due to non-specific toxicity as reported by MK-7622 others ; importantly, it was not associated with an increase in apoptosis marker expression. The results are consistent with reports of a critical role for BIRC6 in the survival of a variety of cancer cells. Cell cycle analysis showed that BIRC6 reduction did not result in significant change in cell cycle distribution, suggesting that the reduction in cell viability was attributable to apoptosis. In this study, a decrease in cell viability induced by BIRC6 reduction did not confine to cells expressing wild-type p53, contrary to previous reports suggesting that apoptosis resulting from BIRC6 knockdown in H460 cells and breast cancer cells requires 24144-92-1 functional p53. We showed that both wild type p53 and p53 null cells were sensitive to BIRC6 siRNA induced growth inhibition. This variation reflec
