Intracellular shuttling of a Drosophila APC tumour suppressor homolog.
BACKGROUND
The Adenomatous polyposis coli (APC) tumour suppressor is found in multiple discrete subcellular locations, which may reflect sites of distinct functions. In Drosophila epithelial cells, the predominant APC relative (E-APC) is concentrated at the apicolateral adherens junctions. Genetic analysis indicates that this junctional association is critical for the function of E-APC in Wnt signalling and in cellular adhesion. Here, we ask whether the junctional association of E-APC is stable, or whether E-APC shuttles between the plasma membrane and the cytoplasm.


RESULTS
We generated a Drosophila strain that expresses E-APC (dAPC2) tagged with green fluorescent protein (GFP-E-APC) and we analysed its junctional association with fluorescence recovery after photobleaching (FRAP) experiments in live embryos. This revealed that the junctional association of GFP-E-APC in epithelial cells is highly dynamic, and is far less stable than that of the structural components of the adherens junctions, E-cadherin, alpha-catenin and Armadillo. The shuttling of GFP-E-APC to and from the plasma membrane is unaltered in mutants of Drosophila glycogen synthase kinase 3 (GSK3), which mimic constitutive Wingless signalling. However, the stability of E-APC is greatly reduced in these mutants, explaining their apparent delocalisation from the plasma membrane as previously observed. Finally, we show that GFP-E-APC forms dynamic patches at the apical plasma membrane of late embryonic epidermal cells that form denticles, and that it shuttles up and down the axons of the optic lobe.


CONCLUSIONS
We conclude that E-APC is a highly mobile protein that shuttles constitutively between distinct subcellular locations.
Cliffe
Adam
A
MRC Laboratory of Molecular Biology, Hills Road, Cambridge, CB2 2QH, UK. cliffe@embl.de
Mieszczanek
Julius
J
Bienz
Mariann
M
D025601:Adenomatous Polyposis Coli Protein / Q000235:genetics / Q000378:metabolism*; D022005:Adherens Junctions / Q000235:genetics / Q000378:metabolism; D000818:Animals; D003593:Cytoplasm / Q000737:chemistry / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism; D004330:Drosophila / Q000196:embryology / Q000235:genetics*; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism; D004625:Embryo, Nonmammalian; D004847:Epithelial Cells / Q000737:chemistry / Q000378:metabolism; D017491:Genes, APC / Q000502:physiology; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D042541:Intracellular Space / Q000737:chemistry*; D021381:Protein Transport / Q000235:genetics*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
D025601:Adenomatous Polyposis Coli Protein; D003598:Cytoskeletal Proteins; D029721:Drosophila Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins