title: A single common portal for clathrin-mediated endocytosis of distinct cargo governed by cargo-selective adaptors.
abstract: Sorting of transmembrane cargo into clathrin-coated vesicles requires endocytic adaptors, yet RNA interference (RNAi)-mediated gene silencing of the AP-2 adaptor complex only disrupts internalization of a subset of clathrin-dependent cargo. This suggests alternate clathrin-associated sorting proteins participate in cargo capture at the cell surface, and a provocative recent proposal is that discrete endocytic cargo are sorted into compositionally and functionally distinct clathrin coats. We show here that the FXNPXY-type internalization signal within cytosolic domain of the LDL receptor is recognized redundantly by two phosphotyrosine-binding domain proteins, Dab2 and ARH; diminishing both proteins by RNAi leads to conspicuous LDL receptor accumulation at the cell surface. AP-2-dependent uptake of transferrin ensues relatively normally in the absence of Dab2 and ARH, clearly revealing delegation of sorting operations at the bud site. AP-2, Dab2, ARH, transferrin, and LDL receptors are all present within the vast majority of clathrin structures at the surface, challenging the general existence of specialized clathrin coats for segregated internalization of constitutively internalized cargo. However, Dab2 expression is exceptionally low in hepatocytes, likely accounting for the pathological hypercholesterolemia that accompanies ARH loss.
authors.affiliation: Department of Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA.
authors.forename: Peter A
authors.initials: PA
authors.lastname: Keyel
authors.forename: Sanjay K
authors.initials: SK
authors.lastname: Mishra
authors.forename: Robyn
authors.initials: R
authors.lastname: Roth
authors.forename: John E
authors.initials: JE
authors.lastname: Heuser
authors.forename: Simon C
authors.initials: SC
authors.lastname: Watkins
authors.forename: Linton M
authors.initials: LM
authors.lastname: Traub
mesh_terms: D033962:Adaptor Protein Complex 2; D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D008078:Cholesterol, LDL / Q000493:pharmacokinetics; D002966:Clathrin / Q000502:physiology*; D022163:Clathrin-Coated Vesicles / Q000378:metabolism*; D003034:Coated Pits, Cell-Membrane / Q000378:metabolism*; D004705:Endocytosis; D006056:Golgi Apparatus / Q000378:metabolism; D006367:HeLa Cells; D022781:Hepatocytes / Q000378:metabolism; D006801:Humans; D021381:Protein Transport; D034622:RNA Interference; D051381:Rats; D011973:Receptors, LDL / Q000378:metabolism; D014162:Transfection; D020703:ras GTPase-Activating Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology
chemical_list: D033962:Adaptor Protein Complex 2; D048868:Adaptor Proteins, Signal Transducing; D008078:Cholesterol, LDL; D002966:Clathrin; C462952:DAB2IP protein, human; C469745:LDLRAP1 protein, human; D011973:Receptors, LDL; D020703:ras GTPase-Activating Proteins