ECT2 and breast cancer: To investigate whether GEF activity of ECT2 is essential for tumor survival, control shRNA or shRNA targeting the 5'UTR region of ECT2 was stably integrated into breast cancer cells stably expressing wild type ECT2 (ECT2/wt) or GEF activity-deficient ECT2 mutant (ECT2/GEFmt, E428A and N608A within the DH domain) 15, 54.