[5][6] The central core of each mitogen-activated protein kinase (MAPK) pathway is a conserved cascade of 3 protein kinases: an activated MAPK kinase kinase (MAPKKK) phosphorylates and activates a specific MAPK kinase (MAPKK), which then activates a specific MAPK.

While the ERK MAPKs are activated by mitogenic stimulation, the CSBP2 (p38α) and JNK MAPKs are activated by environmental stresses such as osmotic shock, UV irradiation, wound stress, and inflammatory factors.

This gene encodes a MAPKKK, the MEKK4 protein, also called MTK1.

MEKK4 is a major mediator of environmental stresses that activate the p38 MAPK pathway, and a minor mediator of the JNK pathway.

Two alternatively spliced transcripts encoding distinct isoforms have been described.