SIAH1 and breast cancer: For example, the ubiquitin ligase Siah1/2 and the Skp1-Pam-Fbxo45 complex have been shown to promote ZEB1 ubiquitination and degradation.18,44,45 Moreover, Zhang et al. found that ATM is rapidly activated upon radiation exposure, which phosphorylates and stabilizes ZEB1 protein in radioresistant breast cancer cells.19 However, the molecular mechanisms by which the ZEB1 protein is stabilized remain unclear.