title: Molecules internalized by clathrin-independent endocytosis are delivered to endosomes containing transferrin receptors.
abstract: We have previously demonstrated that the preendosomal compartment in addition to clathrin-coated vesicles, comprises distinct nonclathrin coated endocytic vesicles mediating clathrin-independent endocytosis (Hansen, S. H., K. Sandvig, and B. van Deurs. 1991. J. Cell Biol. 113:731-741). Using K+ depletion in HEp-2 cells to block clathrin-dependent but not clathrin-independent endocytosis, we have now traced the intracellular routing of these nonclathrin coated vesicles to see whether molecules internalized by clathrin-independent endocytosis are delivered to a unique compartment or whether they reach the same early and late endosomes as encountered by molecules internalized with high efficiency through clathrin-coated pits and vesicles. We find that Con A-gold internalized by clathrin-independent endocytosis is delivered to endosomes containing transferrin receptors. After incubation of K(+)-depleted cells with Con A-gold for 15 min, approximately 75% of Con A-gold in endosomes is colocalized with transferrin receptors. Endosomes containing only Con A-gold may be accounted for either by depletion of existing endosomes for transferrin receptors or by de novo generation of endosomes. Cationized gold and BSA-gold internalized in K(+)-depleted cells are also delivered to endosomes containing transferrin receptors. h-lamp-1-enriched compartments are only reached occasionally within 30 min in K(+)-depleted as well as in control cells. Thus, preendosomal vesicles generated by clathrin-independent endocytosis do not fuse to any marked degree with late endocytic compartments. These data show that in HEp-2 cells, molecules endocytosed without clathrin are delivered to the same endosomes as reached by transferrin receptors internalized through clathrin-coated pits.
authors.affiliation: Department of Anatomy, Panum Institute, University of Copenhagen, Denmark.
authors.forename: S H
authors.initials: SH
authors.lastname: Hansen
authors.forename: K
authors.initials: K
authors.lastname: Sandvig
authors.forename: B
authors.initials: B
authors.lastname: van Deurs
mesh_terms: D015703:Antigens, CD; D016477:Artifacts; D001692:Biological Transport; D002451:Cell Compartmentation; D002460:Cell Line; D002966:Clathrin; D003034:Coated Pits, Cell-Membrane; D003208:Concanavalin A / Q000031:analogs & derivatives; D004705:Endocytosis; D006651:Histocytochemistry; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism*; D051907:Lysosomal Membrane Proteins; D008562:Membrane Glycoproteins / Q000302:isolation & purification / Q000378:metabolism; D011191:Potassium Deficiency / Q000378:metabolism; D011990:Receptors, Transferrin / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D015703:Antigens, CD; D002966:Clathrin; D051907:Lysosomal Membrane Proteins; D008562:Membrane Glycoproteins; D011990:Receptors, Transferrin; C083511:concanavalin A-gold; D003208:Concanavalin A