Coupling cell growth, proliferation, and death. Hippo weighs in.

Four recent papers describe the characterization in Drosophila of Hippo, a serine/threonine kinase of the Sterile 20 (STE20) group, resembling Mst1 and Mst2. Hippo restricts cell growth and cell proliferation, promotes cell death, and interacts with the tumor suppressors Salvador and Warts. This, together with the ability of Mst2 to rescue hippo mutant phenotypes, argues that Mst/Hippo proteins are tumor suppressors.