PEA15 and breast cancer: Further, MDAMB231 and BT 474 cells stably expressing the nonphosphorylatable mutant of PEA15 were also markedly impaired in their tumor-forming potential compared to WT PEA15-expressing cells (Figure 5C and D), together suggesting that AMPK activation and PEA15 phosphorylation are both necessary for tumor formation by breast cancer cells.