SIAH1 induced apoptosis by activation of the JNK pathway and inhibited invasion by inactivation of the ERK pathway in breast cancer cells

Seven in absentia homolog 1 (SIAH1), a homologue of Drosophila seven in absentia (Sina), has emerged as a tumor suppressor and plays an important role in regulating cell apoptosis. To investigate the role and possible mechanism of SIAH1 in breast cancer cells, we up‐regulated the expression of SIAH1 using pcDNA3‐myc‐SIAH1 and knocked down SIAH1 using SIAH1 siRNA. We found that the overexpression of SIAH1 induced cell apoptosis by up‐regulating the level of Bim through the activation of the JNK signaling pathway, and the suppression of SIAH1 expression increased cell invasion via the activation of the ERK signaling pathway in breast cancer cells. All these results indicate that the JNK and ERK signaling pathways may play an important role in the SIAH1‐dependent biological behavior of breast cancer, and it may be a good molecular therapeutic target to increase the expression level of SIAH1 through promoting cell apoptosis and inhibiting cell invasion in human breast cancer. (Cancer Sci 2009)