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Hippo reprograms the transcriptional response to Ras signalling

ABSTRACT: Mutations that lead to hyperactivation of Ras signaling are hallmarks of carcinomas. During development, signaling via Ras mediates cell fate decisions and cellular differentiation without causing hyper-proliferation. What determines whether Ras activation leads to differentiation or proliferation remains unknown. Here we show that the Hippo pathway reprograms the cellular response to Ras signaling in Drosophila. While hyperactivation of Ras signaling alone promotes cellular differentiation, additional loss of Hippo signaling drives aggressive hyper-proliferation. Transcriptome analysis combined with ChIP-nexus confirmed that the magnitude and specificity of Ras target gene expression strongly depends on the activity status of the Hippo pathway. This is because Hippo signaling directly regulates the expression of two key downstream transcription factors of the Ras pathway: the ETS-domain transcription factor Pointed and the transcriptional repressor Capicua. Our results highlight how independent signaling pathways can impinge on each other at the level of transcription factors, thereby providing a safety mechanism to keep proliferation in check under normal developmental conditions.

ORGANISM(S): Drosophila melanogaster

PROVIDER: GSE96868 | GEO | 2017/09/26

SECONDARY ACCESSION(S): PRJNA379962

REPOSITORIES: GEO

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Project description:Regulation of hepatocyte proliferation and liver morphology is of critical importance to tissue and whole-body homeostasis. However, the molecular mechanisms that underlie this complex process are incompletely understood. Here we describe a novel role for the ubiquitin ligase BRAP in regulation of hepatocyte morphology and turnover via regulation of MST2, a protein kinase in the Hippo pathway. The Hippo pathway has been implicated in control of liver morphology, inflammation and fibrosis. We demonstrate here that liver-specific ablation of Brap in mice results in gross and cellular morphological alterations of the liver. Brap-deficient livers exhibit increased hepatocyte proliferation, cell death, and inflammation. We show that loss of BRAP protein alters Hippo pathway signaling, causing a reduction in phosphorylation of YAP and increased expression of YAP target genes, including those regulating cell growth and interactions with the extracellular environment. Finally, increased Hippo signaling in Brap knockout mice alters the pattern of liver lipid accumulation in dietary models of obesity. These studies identify a role for BRAP as a modulator of the hepatic Hippo pathway with relevance to human liver disease. tissue and whole-body homeostasis. However, the molecular mechanisms that underlie this complex process are incompletely understood. Here we describe a novel role for the ubiquitin ligase BRAP in regulation of hepatocyte morphology and turnover via regulation of MST2, a protein kinase in the Hippo pathway. The Hippo pathway has been implicated in control of liver morphology, inflammation and fibrosis. We demonstrate here that liver-specific ablation of Brap in mice results in gross and cellular morphological alterations of the liver. Brap-deficient livers exhibit increased hepatocyte proliferation, cell death, and inflammation. We show that loss of BRAP protein alters Hippo pathway signaling, causing a reduction in phosphorylation of YAP and increased expression of YAP target genes, including those regulating cell growth and interactions with the extracellular environment. Finally, increased Hippo signaling in Brap knockout mice alters the pattern of liver lipid accumulation in dietary models of obesity. These studies identify a role for BRAP as a modulator of the hepatic Hippo pathway with relevance to human liver disease.

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Hippo reprograms the transcriptional response to Ras signalling

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