Effect of Siah1 on the clonogenic survival of SKBR3 and MCF-7 cells after IR. Cells transfected with indicated plasmids were irradiated with a single dose of 2, 4 or 6 Gy. Unirradiated cells (0 Gy) were used as control. A: Siah1 and more potently Siah1L decreased clonogenic survival in both irradiated and control cells. Colonies greater than 50 cells were counted and clonogenic survival was determined by crystal violet staining 14 days after IR. Lines, mean of three independent experiments; bars, SD; *, P < 0.05. B: siRNA for Siah1 resulted in reduced radiosensitivity of MCF-7 cells in response to IR. Silencing of Siah1 by siRNA-2 and siRNA-3 revealed results similar to the main Siah1 siRNA. Lines, mean of three independent experiments; bars, SD; *, P < 0.05.