ABSTRACT
The Hippo pathway is an evolutionarily conserved regulator of organ growth and tumorigenesis. In Drosophila, oncogenic RasV12 cooperates with loss-of-cell polarity to promote Hippo pathway-dependent tumor growth. To identify additional factors that modulate this signaling, we performed a genetic screen utilizing the Drosophila RasV12/lgl-/- in vivo tumor model and identified Rox8, a RNA-binding protein (RBP), as a positive regulator of the Hippo pathway. We found that Rox8 overexpression suppresses whereas Rox8 depletion potentiates Hippo-dependent tissue overgrowth, accompanied by altered Yki protein level and target gene expression. Mechanistically, Rox8 directly binds to a target site located in the yki 3' UTR, recruits and stabilizes the targeting of miR-8-loaded RISC, which accelerates the decay of yki messenger RNA (mRNA). Moreover, TIAR, the human ortholog of Rox8, is able to promote the degradation of yki mRNA when introduced into Drosophila and destabilizes YAP mRNA in human cells. Thus, our study provides in vivo evidence that the Hippo pathway is posttranscriptionally regulated by the collaborative action of RBP and microRNA (miRNA), which may provide an approach for modulating Hippo pathway-mediated tumorigenesis.
Subject(s)
Drosophila Proteins/genetics , Drosophila melanogaster/genetics , MicroRNAs/genetics , Nuclear Proteins/genetics , RNA, Messenger , RNA-Binding Proteins/genetics , Trans-Activators/genetics , 3' Untranslated Regions , Animals , Cell Proliferation , Fluorescent Antibody Technique , Gene Expression Regulation , Hippo Signaling Pathway , Humans , Models, Biological , Organ Specificity , Protein Serine-Threonine Kinases/metabolism , RNA Interference , RNA Stability , Signal Transduction , YAP-Signaling ProteinsABSTRACT
The Hippo pathway is a central regulator of tissue development and homeostasis, and has been reported to have a role during vascular development. Here we develop a bioluminescence-based biosensor that monitors the activity of the Hippo core component LATS kinase. Using this biosensor and a library of small molecule kinase inhibitors, we perform a screen for kinases modulating LATS activity and identify VEGFR as an upstream regulator of the Hippo pathway. We find that VEGFR activation by VEGF triggers PI3K/MAPK signaling, which subsequently inhibits LATS and activates the Hippo effectors YAP and TAZ. We further show that the Hippo pathway is a critical mediator of VEGF-induced angiogenesis and tumor vasculogenic mimicry. Thus, our work offers a biosensor tool for the study of the Hippo pathway and suggests a role for Hippo signaling in regulating blood vessel formation in physiological and pathological settings.
