Multicellular organisms have subfamilies of mitogen-activated protein kinases (MAPKs) that control a vast array of physiological processes. Enzymes are regulated by a characteristic phosphorylating system in which mitogen-activated protein kinase-activated protein kinase 5 (MK5) is involved in one of the major signaling pathways in cells. MK5, discovered in 1998 by the groups Houng Ni and Ligou New, was shown to be highly conserved in all vertebrates, as well as in vivo and in vitro. The present review summarizes the role of MK5 in tumor suppression as well as tumor promotion, embryogenesis, locomotion, cell motility, and cell regulation. PubMed and MEDLINE were searched to identify molecular mechanisms and biological and physiological roles of MK5 studies between December 2001 and July 2015 using specified key words. This paper is a systemic review of published literature that discussed the role of MK5 in physiological and pathological cellular processes. The screened articles illustrated different signaling pathways that are regulated by phosphorylation in cells and whether they stimulate or inhibit MK5 activity. Activation or inhibition of MK5 seems to be central in most physiological and pathological processes, including cancer. The protein kinase has therefore become a prime target for drug development. One of the challenges in developing anti-cancer drug therapies is that there is a lack of research assessing the molecular level of these diseases. In the following review, we clarify and report the role of MK5 in signaling pathways that control gene expression, cell division, survival, apoptosis, metabolism, differentiation, and motility.

Keywords: MAP Kinase Kinase 5, Phosphorylation, Protein Interaction Domains and Motifs