Identification of Happyhour/MAP4K as Alternative Hpo/Mst-like Kinases in the Hippo Kinase Cascade

Abstract

In Drosophila and mammals, the canonical Hippo kinase cascade is mediated by Hpo/Mst acting through the intermediary kinase Wts/Lats to phosphorylate the transcriptional coactivator Yki/YAP/TAZ. Despite recent reports linking Yki/YAP/TAZ activity to the actin cytoskeleton, the underlying mechanisms are poorly understood and/or controversial. Using Drosophila imaginal discs as an in vivo model, we show that Wts, but not Hpo, is genetically indispensable for cytoskeleton-mediated subcellular localization of Yki. Through a systematic screen, we identify the Ste-20 kinase Happyhour (Hppy) and its mammalian counterpart MAP4K1/2/3/5 as an alternative kinase that phosphorylates the hydrophobic motif of Wts/Lats in a similar manner as Hpo/Mst. Consistent with their redundant function as activating kinases of Wts/Lats, combined loss of Hpo/Mst and Hppy/MAP4K abolishes cytoskeleton-mediated regulation of Yki/YAP subcellular localization, as well as YAP cytoplasmic translocation induced by contact inhibition. These Hpo/Mst-like kinases provide an expanded view of the Hippo kinase cascade in development and physiology.

Mechanisms of Hippo pathway regulation

“…LATS1/2 subsequently undergo autophosphorylation and are activated (Chan et al 2005) and in turn phosphorylate and inactivate YAP and TAZ . In parallel to MST1/2, two groups of MAP4Ks (mitogen-activated protein kinase kinase kinase kinase), MAP4K1/2/3/5 (homologs of Drosophila Happyhour [Hppy]) and MAP4K4/6/7 (homologs of Drosophila Misshapen [Msn]), can also directly phosphorylate LATS1/2 at their hydrophobic motifs and result in LATS1/2 activation Zheng et al 2015). In HEK293A cells, triple knockout of MAP4K4/6/7 reduces the phosphorylation of YAP/TAZ more dramatically than MST1/2 double knockout under serum deprivation, indicating that MAP4Ks may play a more prominent role than MST in Hippo pathway regulation under certain conditions .…”

Thromboxane A2 Activates YAP/TAZ Protein to Induce Vascular Smooth Muscle Cell Proliferation and Migration

“…MST1/2 phosphorylate and activate LATS1/2 kinases, which in turn phosphorylate and inhibit YAP/TAZ. Recently, MAP4Ks have been shown to be core components of the Hippo pathway, and they function in parallel to MST1/2 to phosphorylate and activate LATS1/2 (26,27). Phosphorylation of YAP at Ser-127 results in cytoplasmic sequestration because of 14-3-3 binding (28,29).…”

“…MST1/2 and MAP4Ks are responsible for LATS kinase activation in response to upstream signals (26,27,46). To test whether MST1/2 or MAP4Ks are involved in I-BOP-induced YAP/TAZ dephosphorylation, we used MST1/2 double knockout (MST1/2 dKO) and combined deletion of MST1/2 and MAP4K1/2/3/4/5/6/7 (MM-9KO) HEK293A cells (supplemental Fig.…”

Osmotic stress‐induced phosphorylation by NLK at Ser128 activates YAP

“…MST1/2 or MAP4Ks activate LATS1/2 by phosphorylating the hydrophobic motif residues in LATS1/2 [8][9][10][11][12][13][14]. Activated LATS1/2 then phosphorylate YAP and TAZ, leading to 14-3-3 binding and cytoplasmic retention [15].…”

“…The mammalian Hippo pathway core kinase cascade consists of Mammalian Ste20-like kinases 1/2 (MST1/2), MAP kinase kinase kinase kinase (MAP4Ks), large tumor suppressor 1/2 (LATS1/2) and the downstream effectors Yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ) [7][8][9]. MST1/2 or MAP4Ks activate LATS1/2 by phosphorylating the hydrophobic motif residues in LATS1/2 [8][9][10][11][12][13][14].…”