title: Ultrastructural characterization of giant endosomes induced by GTPase-deficient Rab5.
abstract: The small GTPase Rab5 controls the fusogenic properties of early endosomes through GTP-dependent recruitment and activation of effector proteins. Expression of a GTPase-defective mutant, Rab5(Q79L), is known to cause formation of enlarged early endosomes. The ability of Rab5-GTP to recruit multiple effectors raises the question whether the Rab5(Q79L)-induced giant endosomes simply represent enlarged early endosomes or whether they have a more complex phenotype. In this report, we have addressed this issue by generating a HEp2 cell line with inducible expression of Rab5(Q79L) and performing ultrastructural analysis of Rab5(Q79L)-induced endosomes. We find that Rab5(Q79L) not only induces formation of enlarged early endosomes but also causes enlargement of later endocytic profiles. Most strikingly, Rab5(Q79L) causes formation of enlarged multivesicular endosomes with a large number of intraluminal vesicles, and endosomes that contain both early and late endocytic markers are frequently observed. In addition, we observe defects in the sorting of the EGF receptor and the transferrin receptor through this compartment.
authors.affiliation: Department of Biochemistry, Institute for Cancer Research, The Norwegian Radium Hospital, Oslo University Hospital, Montebello, Oslo, Norway.
authors.forename: Catherine Sem
authors.initials: CS
authors.lastname: Wegner
authors.forename: Catherine Sem
authors.initials: CS
authors.lastname: Wegener
authors.forename: Lene
authors.initials: L
authors.lastname: Malerød
authors.forename: Nina Marie
authors.initials: NM
authors.lastname: Pedersen
authors.forename: Cinzia
authors.initials: C
authors.lastname: Progida
authors.forename: Cinzia
authors.initials: C
authors.lastname: Prodiga
authors.forename: Oddmund
authors.initials: O
authors.lastname: Bakke
authors.forename: Harald
authors.initials: H
authors.lastname: Stenmark
authors.forename: Andreas
authors.initials: A
authors.lastname: Brech
mesh_terms: D045744:Cell Line, Tumor; D011992:Endosomes / Q000378:metabolism / Q000648:ultrastructure*; D066246:ErbB Receptors / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000172:deficiency*; D006801:Humans; D020696:rab5 GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D066246:ErbB Receptors; D020558:GTP Phosphohydrolases; D020696:rab5 GTP-Binding Proteins