Regulation of Hippo signaling by EGFR-MAPK signaling through Ajuba. Venu Reddy Bommireddy Venkata, Ken Irvine. Waksman Institute, Piscataway, NJ.

   Epidermal growth factor receptor signaling plays an important role in growth control, and inappropriate activation of EGFR signaling has been implicated in several cancers. Likewise, the recently discovered Hippo signaling plays a crucial role both in controlling normal growth during development, and when dysregulated contributes to tumorigenesis. Here, we identify and characterize a conserved link between these pathways. We find that EGFR activates the Hippo pathway transcription factor Yorkie, and demonstrate that Yorkie is required for the influence of EGFR on cell proliferation in both glial cells and wing imaginal discs of Drosophila. We determine that EGFR regulates Yorkie through the Ras-MAPK branch of EGFR signaling. Genetic and biochemical experiments implicate the Ajuba LIM protein Jub as the key target of EGFR-Ras-MAPK signaling within the Hippo pathway, as Jub is epistatic to EGFR and Ras for Yorkie regulation, Jub is subject to MAPK-dependent phosphorylation, and EGFR-Ras-MAPK signaling enhances Jub binding to the Yorkie kinase Warts, and to the scaffolding protein Salvador. We further show that an EGFR-Hippo pathway link is conserved in mammals, as activation of EGFR or RAS results in activation of the Yorkie homologue YAP, and EGFR-RAS-MAPK signaling promotes phosphorylation of the human Ajuba family protein WTIP, and also promote WTIP binding to the Warts and Salvador homologues LATS and WW45. Our observations implicate the Hippo pathway in EGFR-mediated tumorigenesis and identify a novel molecular link between these two pathways.