MAPK3 and cardiac hypertrophy: For instance, transgenic mice overexpressing an activated dual specificity mitogen-activated protein kinase kinase 1 (MEK1) mutant under the transcriptional control of the cardiac-specific α-myosin heavy chain promoter were found to induce cardiac hypertrophy in vivo, which constitutively activated ERK1/2 in the heart (Bueno et al., 2000).