Serine/threonine protein kinase that plays a role in a variety of different signaling pathways including cytoskeleton regulation, cell migration, proliferation or cell survival. Activation by various effectors including growth factor receptors or active CDC42 and RAC1 results in a conformational change and a subsequent autophosphorylation on several serine and/or threonine residues. Phosphorylates the proto-oncogene RAF and stimulates its kinase activity. Promotes cell survival by phosphorylating the BCL2 antagonist of cell death BAD. Phosphorylates CTNND1, probably to regulate cytoskeletal organization and cell morphology. Keeps microtubules stable through MARK2 inhibition and destabilizes the F-actin network leading to the disappearance of stress fibers and focal adhesions (By similarity). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts tightly with GTP-bound but not GDP-bound CDC42/p21 and RAC1. Interacts with MARK2, leading to inhibit MARK2 independently of kinase activity. Interacts with RHOD and RHOH (By similarity). Shuttles between the nucleus and the mitochondria, and mitochondrial localization is essential for the role in cell survival. An autoinhibitory domain is present in the N-terminal region of the protein. Autophosphorylated when activated by CDC42/p21. Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. STE20 subfamily.