title: Identification of the ubiquitin ligase Triad1 as a regulator of endosomal transport.
abstract: The ubiquitin system plays an important role in trafficking of signaling receptors from the plasma membrane to lysosomes. Triad1 is a ubiquitin ligase that catalyzes the formation of poly-ubiquitin chains linked via lysine-48 as well as lysine-63 residues. We show that depletion of Triad1 affects the sorting of both growth hormone and epidermal growth factor. Triad1-depleted cells accumulate both ligands in endosomes. While fluid phase transport to the lysosomes is reduced in the absence of Triad1, growth hormone receptor can recycle back to the plasma membrane together with transferrin. Using immune electron microscopy we show that Triad1 depletion results in enlarged endosomes with enlarged and irregular shaped intraluminal vesicles. The endosomes display prominent clathrin coats and show increased levels of growth hormone label. We conclude that Triad1 is required for the proper function of multivesicular bodies.
authors.affiliation: Department of Cell Biology and Institute of Biomembranes, University Medical Center Utrecht ,  3584 CX Utrecht ,  The Netherlands.
authors.forename: Gerco
authors.initials: G
authors.lastname: Hassink
authors.forename: Johan
authors.initials: J
authors.lastname: Slotman
authors.forename: Viola
authors.initials: V
authors.lastname: Oorschot
authors.forename: Bert A
authors.initials: BA
authors.lastname: Van Der Reijden
authors.forename: Davide
authors.initials: D
authors.lastname: Monteferrario
authors.forename: Sylvie M
authors.initials: SM
authors.lastname: Noordermeer
authors.forename: Peter
authors.initials: P
authors.lastname: Van Kerkhof
authors.forename: Judith
authors.initials: J
authors.lastname: Klumperman
authors.forename: Ger J
authors.initials: GJ
authors.lastname: Strous