title: AP-2-complex-mediated endocytosis of Drosophila Crumbs regulates polarity by antagonizing Stardust.
abstract: Maintenance of epithelial polarity depends on the correct localization and levels of polarity determinants. The evolutionarily conserved transmembrane protein Crumbs is crucial for the size and identity of the apical membrane, yet little is known about the molecular mechanisms controlling the amount of Crumbs at the surface. Here, we show that Crumbs levels on the apical membrane depend on a well-balanced state of endocytosis and stabilization. The adaptor protein 2 (AP-2) complex binds to a motif in the cytoplasmic tail of Crumbs that overlaps with the binding site of Stardust, a protein known to stabilize Crumbs on the surface. Preventing endocytosis by mutation of AP-2 causes expansion of the Crumbs-positive plasma membrane domain and polarity defects, which can be partially rescued by removing one copy of crumbs. Strikingly, knocking down both AP-2 and Stardust leads to the retention of Crumbs on the membrane. This study provides evidence for a molecular mechanism, based on stabilization and endocytosis, to adjust surface levels of Crumbs, which are essential for maintaining epithelial polarity.
authors.affiliation: Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, Dresden 01307, Germany.
authors.forename: Ya-Huei
authors.initials: YH
authors.lastname: Lin
authors.affiliation: School of Life and Health Sciences, Aston University, Aston Triangle, Birmingham B4 7ET, UK.
authors.forename: Heather
authors.initials: H
authors.lastname: Currinn
authors.affiliation: Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, Dresden 01307, Germany.
authors.forename: Shirin Meher
authors.initials: SM
authors.lastname: Pocha
authors.affiliation: School of Life and Health Sciences, Aston University, Aston Triangle, Birmingham B4 7ET, UK.
authors.forename: Alice
authors.initials: A
authors.lastname: Rothnie
authors.affiliation: School of Life and Health Sciences, Aston University, Aston Triangle, Birmingham B4 7ET, UK.
authors.forename: Thomas
authors.initials: T
authors.lastname: Wassmer
authors.affiliation: Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, Dresden 01307, Germany knust@mpi-cbg.de.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Knust
mesh_terms: D000818:Animals; D016764:Cell Polarity / Q000502:physiology*; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster; D004705:Endocytosis / Q000502:physiology*; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism*; D051528:Guanylate Kinases / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D050656:Transcription Factor AP-2 / Q000235:genetics / Q000378:metabolism*
chemical_list: D029721:Drosophila Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; C493674:TfAP-2 protein, Drosophila; D050656:Transcription Factor AP-2; C064360:crb protein, Drosophila; D051528:Guanylate Kinases; C444479:sdt protein, Drosophila
keywords: AP-2 complex; Crumbs; Endocytosis; Epithelial polarity; PDZ-binding; Stardust