MAPK3 and breast cancer: As we have used three different breast cancer cell lines, first, we have compared steady state levels of phosphorylated form of ERK1/2 in three cell populations and found that MCF-7 cells are 92.2% phospho-ERK1/2-negative, MDA-MB-231 cells are 89.7% phospho-ERK1/2-positive and SK-BR-3 cells are 49.7% phospho-ERK1/2-positive in the control conditions (Fig. 8).