MELK is an atypical member of the snf1/AMPK family of serine/threonine kinases that has also been shown to be enriched in triple-negative breast cancer. This family is largely associated with cell survival under conditions of environmental challenge, such as nutrient starvation. MELK, also known as murine protein serine/threonine kinase 38 (MPK38) and Eg3 protein (pEg3), was originally identified as a signal transduction factor. MELK is also a cell cycle-dependent protein kinase that belongs to the KIN1/PAR-1/MARK family. Unlike most members of this family only functioning in cell survival under metabolically challenging conditions, MELK physically interacts with apoptosis signal-regulating kinase 1 (ASK1), and the activity of ASK1 is either positively or negatively regulated by its interacting molecules, including tumor necrosis receptor-associated factor, Daxx, JNK/stress-activated protein kinase-associated protein 1/JNK-interacting protein 3, thioredoxin, glutaredoxin, heat shock protein 72, Raf-1, Akt/PKB, PP5, and 14-3-3 protein. MELK, as an upstream kinase of ASK1, phosphorylates threonine 838 in an activation loop of human ASK1, thereby stimulating ASK1 kinase activity. Interestingly, this interaction enhances JNK-mediated transactivation and H2O2-induced apoptosis. MELK also physically interacts with p53 and enhances of p53-dependent apoptosis and cell cycle arrest. MELK is considered as a regulator of cell proliferation, differentiation, and apoptosis.

References

1.Jiang P,et al. Int J Mol Sci. 2013;14(11):21551–21560.