PDK1 and breast cancer: While a number of substrates have been proposed for MELK, such as Bcl-G (Lin et al., 2007), CDC25B (Davezac et al., 2002), p53 (Seong and Ha, 2012), and PDK1 (Seong et al., 2012), the substrates that mediate the oncogenic activity of MELK in breast cancer remain to be identified.