Plays a key role in the Hippo/SWH (Sav/Wts/Hpo) signaling pathway, a signaling pathway that plays a pivotal role in organ size control and tumor suppression by restricting proliferation and promoting apoptosis. The core of this pathway is composed of a kinase cascade wherein Hippo (Hpo), in complex with its regulatory protein Salvador (Sav), phosphorylates and activates Warts (Wts) in complex with its regulatory protein Mats, which in turn phosphorylates and inactivates the Yorkie (Yki) oncoprotein. The Hippo/SWH signaling pathway inhibits the activity of the transcriptional complex formed by Scalloped (sd) and Yki and the target genes of this pathway include cyclin-E (cycE), diap1 and bantam. Phosphorylates Sav, Wts and Th/DIAP1. Regulates the level of Th/DIAP1 apoptosis inhibitor. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Homodimer. Interacts with Sav and Wts. Interacts (via SARAH domain) with Ex. Interacts with Kibra. Expressed in CNS during embryogenesis. In third instar larvae, it is expressed throughout all imaginal disks. Transcriptionally regulated by Gcm (Glial cells missing). Autophosphorylated. Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. STE20 subfamily.