MAPK3 and cancer: Using a panel of probes including p38α, mitogen-activated protein kinase-activated protein kinase 2, extracellular-signal regulated kinases 1/2 (ERK1/2), Akt and protein kinase A, this method has been used to perform activity measurements of individual kinases in a model of skeletal muscle differentiation and cancer tissue samples, providing direct, quantitative readouts of kinase enzymatic activity associated with cellular differentiation and human tumors [41].