MST1 (STK3) and MST2 (STK4) are the mammalian homologs of Drosophila Hippo (Hpo), and are core components of the Hippo pathway, which is essentially a kinase cascade whose terminal output regulates the activities of the transcriptional coactivators which control expression of a diverse set of genes that are involved in cell proliferation, survival, and migration. In short, the mammalian Hippo pathway flows from MST1/2 (kinases) -> LATS1/2 (kinases) -> YAP (YY1AP1) and TAZ (WWTR1) (transcriptional coactivators) -> TEA domain (TEAD) 1-4 (transcription factors)-induced gene expression, but a total of more than 30 components have been implicated at the nodes along this complex signalling network.

Hippo signalling has traditionally been viewed as a key regulator of organ growth and development, tissue homeostasis and tumour suppression in multiple organisms [3]. More recent studies have identified new roles for the Hippo pathway in immune cell development and differentiation, autoimmunity and anti-cancer immune responses[1-2,4-5].

1. Du X, Wen J, Wang Y, Karmaus PWF, Khatamian A, Tan H, Li Y, Guy C, Nguyen TM, Dhungana Y et al.. (2018) Hippo/Mst signalling couples metabolic state and immune function of CD8α⁺ dendritic cells. Nature, 558 (7708): 141-145. [PMID:29849151]

2. Hong L, Li X, Zhou D, Geng J, Chen L. (2018) Role of Hippo signaling in regulating immunity. Cell Mol Immunol, 15 (12): 1003-1009. [PMID:29568120]

3. Meng Z, Moroishi T, Guan KL. (2016) Mechanisms of Hippo pathway regulation. Genes Dev, 30 (1): 1-17. [PMID:26728553]

4. Taha Z, J Janse van Rensburg H, Yang X. (2018) The Hippo Pathway: Immunity and Cancer. Cancers (Basel), 10 (4). [PMID:29597279]

5. Yamauchi T, Moroishi T. (2019) Hippo Pathway in Mammalian Adaptive Immune System. Cells, 8 (5). DOI: 10.3390/cells8050398 [PMID:31052239]