title: Endocytosis of megalin by visceral endoderm cells requires the Dab2 adaptor protein.
abstract: Rapid endocytosis of lipoprotein receptors involves NPxY signals contained in their cytoplasmic tails. Several proteins, including ARH and Dab2, can bind these sequences, but their importance for endocytosis may vary in different cell types. The lipoprotein receptor megalin is expressed in the visceral endoderm (VE), a polarized epithelium that supplies maternal nutrients to the early mammalian embryo. Dab2 is also expressed in the VE, and is required for embryo growth and gastrulation. Here, we show that ARH is absent from the VE, and Dab2 is required for uptake of megalin, its co-receptor cubilin, and a cubilin ligand, transferrin, from the brush border of the VE into intracellular vesicles. By making isoform-specific knock-in mice, we show that the p96 splice form of Dab2, which binds endocytic proteins, can fully rescue endocytosis. The more abundant p67 isoform, which lacks some endocytic protein binding sites, only partly rescues endocytosis. Endocytosis of cubilin is also impaired in VE and in mid-gestation visceral yolk sac when p96 is absent. These studies suggest that Dab2 p96 mediates endocytosis of megalin in the VE. In addition, rescue of embryonic viability correlates with endocytosis, suggesting that endocytosis mediated by Dab2 is important for normal development.
authors.affiliation: Division of Basic Sciences and Molecular and Cellular Biology Program, Fred Hutchinson Cancer Research Center, 1100 Fairview Ave N, Seattle, WA 98109, USA.
authors.forename: Meghan E
authors.initials: ME
authors.lastname: Maurer
authors.forename: Jonathan A
authors.initials: JA
authors.lastname: Cooper
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000172:deficiency; D033942:Adaptor Proteins, Vesicular Transport / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D017398:Alternative Splicing / Q000235:genetics; D000818:Animals; D051017:Apoptosis Regulatory Proteins; D002470:Cell Survival; D004622:Embryo, Mammalian / Q000166:cytology / Q000378:metabolism / Q000648:ultrastructure; D047108:Embryonic Development; D004705:Endocytosis; D004707:Endoderm / Q000166:cytology* / Q000378:metabolism*; D026561:Low Density Lipoprotein Receptor-Related Protein-2 / Q000378:metabolism*; D051379:Mice; D009928:Organ Specificity; D020033:Protein Isoforms; D021381:Protein Transport; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism; D019076:Transgenes / Q000235:genetics
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D051017:Apoptosis Regulatory Proteins; C478773:Dab2 protein, mouse; C500241:Ldlrap1 protein, mouse; D026561:Low Density Lipoprotein Receptor-Related Protein-2; D020033:Protein Isoforms; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; C029486:intrinsic factor-cobalamin receptor