Crumbs regulates Salvador/Warts/Hippo signaling in Drosophila via the FERM-domain protein Expanded.
BACKGROUND
Altered expression of apicobasal polarity factors is associated with cancer in vertebrates and tissue overgrowth in invertebrates, yet the mechanisms by which these factors affect growth-regulatory pathways are not well defined. We have tested the basis of an overgrowth phenotype driven by the Drosophila protein Crumbs (Crb), which nucleates an apical membrane complex that functionally interacts with the Par6/Par3/aPKC and Scrib/Dlg/Lgl apicobasal polarity complexes.


RESULTS
We find that Crb-driven growth is dependent upon the Salvador/Warts/Hippo (SWH) pathway and its transcriptional effector Yorkie (Yki). Expression of the Crb intracellular domain elevates Yki activity, and this correlates in tissues and cultured cells with loss of Expanded (Ex), an apically localized SWH component that inhibits Yki. Reciprocally, loss of crb elevates Ex levels, although this excess Ex does not concentrate to its normal location at apical junctions. The Ex-regulatory domain of Crb maps to the juxtamembrane FERM-binding motif (JM), a cytoskeletal interaction domain distinct from the PDZ-binding motif (PBM) through which Crb binds polarity factors. Expression of Crb-JM drives Yki activity and organ growth with little effect on tissue architecture, while Crb-PBM reciprocally produces tissue architectural defects without significant effect on Yki activity.


CONCLUSIONS
These studies identify Crb as a novel SWH regulator via JM-dependent effects on Ex levels and localization and suggest that discrete domains within Crb may allow it to integrate junctional polarity signals with a conserved growth pathway.
Robinson
Brian S
BS
Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322, USA.
Huang
Juang
J
Hong
Yang
Y
Moberg
Kenneth H
KH
D000818:Animals; D030801:Animals, Genetically Modified; D019521:Body Patterning; D002352:Carrier Proteins / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000378:metabolism; D016764:Cell Polarity; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000166:cytology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D005123:Eye / Q000254:growth & development / Q000378:metabolism; D055785:Gene Knockdown Techniques; D017344:Genes, Insect; D051034:Inhibitor of Apoptosis Proteins / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D009687:Nuclear Proteins / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000378:metabolism; D000091102:YAP-Signaling Proteins; D000099317:Hippo Kinases
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D029721:Drosophila Proteins; D051034:Inhibitor of Apoptosis Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D009687:Nuclear Proteins; D011493:Protein Kinase C; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D015534:Trans-Activators; D025521:Tumor Suppressor Proteins; D000091102:YAP-Signaling Proteins; C111891:DIAP1 protein, Drosophila; C517506:RASSF protein, Drosophila; C404683:Scrib protein, Drosophila; C503814:Yki protein, Drosophila; C064360:crb protein, Drosophila; C085090:ex protein, Drosophila; C465504:sav protein, Drosophila; C070350:dlg1 protein, Drosophila; C093503:wts protein, Drosophila; C499474:hpo protein, Drosophila; D000099317:Hippo Kinases; C115015:PKC-3 protein