The Hippo pathway in biological control and cancer development.

The Hippo pathway is an evolutionally conserved protein kinase cascade involved in regulating organ size in vivo and cell contact inhibition in vitro by governing cell proliferation and apoptosis. Deregulation of the Hippo pathway is linked to cancer development. Its first core kinase Warts was identified in Drosophila more than 15 years ago, but it gained much attention when other core components of the pathway were identified 8 years later. Major discoveries of the pathway were made during past several years. The core kinase components Hippo, Salvador, Warts, and Mats in the fly and Mst1/2, WW45, Lats1/2, and Mob1 in mammals phosphorylate and inactivate downstream transcriptional co-activators Yorkie in the fly, Yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ) in mammals, respectively. Phosphorylated Yorkie, YAP, and TAZ are sequestered in the cytoplasm by interaction with 14-3-3 proteins. Here we review recent progresses of this pathway by focusing on how these proteins communicate with each other and how loss of regulation results in cancers.