Both clathrin-positive and -negative coats are involved in endosomal sorting of the EGF receptor.
Sorting of endocytosed EGF receptor (EGFR) to internal vesicles of multivesicular bodies (MVBs) depends on sustained activation and ubiquitination of the EGFR. Ubiquitination of EGFR is mediated by the ubiquitin ligase Cbl, being recruited to the EGFR both directly and indirectly through association with Grb2. Endosomal sorting of ubiquitinated proteins further depends on interaction with ubiquitin binding adaptors like Hrs. Hrs localizes to flat, clathrin-coated domains on the limiting membrane of endosomes. In the present study, we have investigated the localization of EGFR, Cbl and Grb2 with respect to coated and non-coated domains of the endosomal membrane and to vesicles within MVBs. Both EGFR, Grb2, and Cbl were concentrated in coated domains of the limiting membrane before translocation to inner vesicles of MVBs. While almost all Hrs was in clathrin-positive coats, EGFR and Grb2 in coated domains only partially colocalized with Hrs and clathrin. The extent of colocalization of EGFR and Grb2 with Hrs and clathrin varied with time of incubation with EGF. These results demonstrate that both clathrin-positive and clathrin-negative electron dense coats exist on endosomes and are involved in endosomal sorting of the EGFR.
Myromslien
Frøydis D
FD
Institute of Pathology, University of Oslo, Rikshospitalet-Radiumhospitalet HF, 0027 Oslo, Norway.
Grøvdal
Lene Melsaether
LM
Raiborg
Camilla
C
Stenmark
Harald
H
Madshus
Inger Helene
IH
Stang
Espen
E
D002478:Cells, Cultured; D002966:Clathrin / Q000378:metabolism*; D003034:Coated Pits, Cell-Membrane / Q000378:metabolism* / Q000648:ultrastructure; D004705:Endocytosis / Q000502:physiology; D056827:Endosomal Sorting Complexes Required for Transport; D011992:Endosomes / Q000378:metabolism* / Q000648:ultrastructure; D004815:Epidermal Growth Factor / Q000378:metabolism; D066246:ErbB Receptors / Q000378:metabolism* / Q000648:ultrastructure; D051380:GRB2 Adaptor Protein / Q000648:ultrastructure; D006367:HeLa Cells; D006801:Humans; D010750:Phosphoproteins / Q000648:ultrastructure; D021381:Protein Transport; D050721:Proto-Oncogene Proteins c-cbl / Q000648:ultrastructure
D002966:Clathrin; D056827:Endosomal Sorting Complexes Required for Transport; D051380:GRB2 Adaptor Protein; D010750:Phosphoproteins; C096164:hepatocyte growth factor-regulated tyrosine kinase substrate; D004815:Epidermal Growth Factor; D050721:Proto-Oncogene Proteins c-cbl; D066246:ErbB Receptors