Dual specificity mitogen-activated protein kinase kinase 6, also known as MAP kinase kinase 6, MAPKK 6, MAPK / ERK kinase 6, SAPKK3, MAP2K6, and MKK6, is a protein that belongs to the protein kinase superfamily, STE Ser / Thr protein kinase family and MAP kinase kinase subfamily. MAP2K6 / MKK6 contains one protein kinase domain. Mitogen-activated protein kinases are members of a conserved cascade of kinases involved in many signal transduction pathways. They stimulate phosphorylation of transcription factors in response to extracellular signals such as growth factors, cytokines, ultraviolet light, and stress-inducing agents. MAP2K6 / MKK6 exists in a variety of alternatively spliced isoforms with distinct patterns of tissue expression. Isoform 2 of MAP2K6 / MKK6 is only expressed in skeletal muscle. Isoform 1 of MAP2K6 / MKK6 is expressed in skeletal muscle, heart, and to a lesser extent in liver or pancreas.