A role for Rab5 activity in the biogenesis of endosomal and lysosomal compartments

Yuko Hirota, Toshio Kuronita, Hideaki Fujita, Yoshitaka Tanaka

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37 Citations (Scopus)


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.

Original languageEnglish
Pages (from-to)40-47
Number of pages8
JournalBiochemical and Biophysical Research Communications
Issue number1
Publication statusPublished - Dec 7 2007

All Science Journal Classification (ASJC) codes

  • Biophysics
  • Biochemistry
  • Molecular Biology
  • Cell Biology


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