STK3, Active

Creasy identified a cDNA encoding STK3, which they called MST2. Sequence analysis indicated that the deduced 491-amino acid STK3 protein contains an N-terminal catalytic domain characteristic of STKs (1). Taylor also isolated cDNAs encoding STK3 (p63) and STK4 (p61) respectively. STK3 and STK4 share 94% amino acid identity in the catalytic domain and 78% identity overall (2). The yeast 'sterile 20' (Ste20) kinase acts upstream of the mitogen-activated protein kinase (MAPK) cascade that is activated under a variety of stress conditions. O'Neill used proteomic analysis of RAF1 signaling complexes to show that RAF1 counteracts apoptosis by suppressing the activation of mammalian sterile 20-like kinase (MST2) (3). MST2 was identified as a kinase that is activated by the proapoptotic agents straurosporine and FAS ligand (2; 4). STK3 activation presumably allows cells to resist unfavorable environmental conditions.