Regulation and functions of mammalian LATS/NDR kinases: looking beyond canonical Hippo signalling

The metazoan Hippo pathway is an essential tumour suppressor signalling cascade that ensures normal tissue growth by co-ordinating cell proliferation, cell death and cell differentiation. Over the past years, various genetic and biochemical studies in Drosophila and mammals have defined a conserved core Hippo signalling module, composed of members of the Ste20-like kinase, the MOB co-activator and the AGC kinase families. In Drosophila, stimulated Hippo kinase phosphorylates and thereby activates the Mats/Warts complex, which consequently phosphorylates and inactivates the transcriptional co-activator Yorkie. In mammals, the counterparts of the Hippo/Mats/Warts/Yorkie cascade, namely MST1/2, MOB1A/B, LATS1/2 and YAP/TAZ, function in a similar fashion. These canonical Hippo pathways are so highly conserved that human MST2, hMOB1A and LATS1 can compensate for the loss of Hippo, Mats and Warts in flies. However, recent reports have shown that Hippo signalling is more diverse and complex, in particular in mammals. In this review, we summarize our current understanding of mammalian LATS1/2 kinases together with their closest relatives, the NDR1/2 kinases. The regulation of the LATS/NDR family of kinases will be discussed, followed by a summary of all currently known LATS/NDR substrates. Last, but not least, the biological roles of LATS/NDR kinases will be reviewed with specific emphasis on recent discoveries of canonical and non-canonical LATS/NDR functions in the extended Hippo pathway.