MAP2K4(mitogen-activated protein kinase kinase 4), which is located on chromosome 17p11.2, with 399-amino acid protein (about 45 kDa), belongs to the family of protein kinases located upstream of the MAP kinases and responsible for their activation has been identified. MEK-4 (also called MEK4/MKK4) activates both p38 and JNK MAP kinases.

MKK4 is a central mediator in the stress activated protein kinase signaling pathway that responds to a number of cellular and environmental stressors. By phosphorylating MAP kinases such as JNK,MKK4 can ultimately transmit stress signals to nuclear transcription factors that mediate various processes including proliferation, apoptosis, and differentiation. Its distinct biological functions have been identified for MKK4 including a role in development, hepatogenesis, and metastasis suppression.