title: A role for Rab5 activity in the biogenesis of endosomal and lysosomal compartments.
abstract: Rab5 is a small GTPase that plays roles in the homotypic fusion of early endosomes and regulation of intracellular vesicle transport. We show here that expression of GFP-tagged GTPase-deficient form of Rab5b (Rab5bQ79L) in NRK cells results in the sequential formation of three morphologically and functionally distinct types of endosomes. Expression of GFP-Rab5bQ79L initially caused a homotypic fusion of early endosomes accompanying a redistribution of the TGN-resident cargo molecules, and subsequent fusion with late endosomes/lysosomes, leading to the formation of giant hybrid organelles with features of early endosomes and late endosomes/lysosomes. Surprisingly, the giant endosomes gradually fragmented and shrunk, leading to the accumulation of early endosome clusters and concurrent reformation of late endosomes/lysosomes, a process accelerated by treatment with a phosphatidylinositol-3-kinase (PI(3)K) inhibitor, wortmannin. We postulate that such sequential processes reflect the biogenesis and maintenance of late endosomes/lysosomes, presumably via direct fusion with early endosomes and subsequent fission from hybrid organelles. Thus, our findings suggest a regulatory role for Rab5 in not only the early endocytic pathway, but also the late endocytic pathway, of membrane trafficking in coordination with PI(3)K activity.
authors.affiliation: Division of Pharmaceutical Cell Biology, Graduate School of Pharmaceutical Sciences, Kyushu University, 3-1-1 Maidashi, Fukuoka 812-8582, Japan.
authors.forename: Yuko
authors.initials: Y
authors.lastname: Hirota
authors.forename: Toshio
authors.initials: T
authors.lastname: Kuronita
authors.forename: Hideaki
authors.initials: H
authors.lastname: Fujita
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Tanaka
mesh_terms: D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D019556:COS Cells; D002451:Cell Compartmentation / Q000187:drug effects; D002522:Chlorocebus aethiops; D011992:Endosomes / Q000187:drug effects / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D008247:Lysosomes / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D051381:Rats; D000077191:Wortmannin; D020696:rab5 GTP-Binding Proteins / Q000502:physiology*
chemical_list: D000730:Androstadienes; D019869:Phosphatidylinositol 3-Kinases; D000077191:Wortmannin; D020696:rab5 GTP-Binding Proteins