Mammalian Sterile20-like kinase 1 and the regulation of apoptosis

Mammalian Sterile20-like kinase 1 (Mst1) is a ubiquitously expressed serine/threonine kinase which represents a member of the rapidly expanding family of enzymes related to the yeast Sterile20 kinase. Although the physiological function of Mst1 and its role in intracellular signalling is still unclear, reports to date suggest that Mst1, similar to its yeast homologue, operates in the MAR (mitogen-activated protein kinase) pathway and, in this capacity, may represent a putative MAR kinase kinase kinase. Moreover, there is abundant evidence for a role of this enzyme in apoptosis, where not only is it a target for caspases, but may also serve as an activator of these proteases to amplify the apoptotic signalling pathway. This paper reviews the investigations that have led to our current understanding of the mechanisms by which Mst1 may be activated and thereby contribute to apoptosis.