title: Cleavage of rabaptin-5 blocks endosome fusion during apoptosis.
abstract: Cells undergoing apoptosis exhibit striking changes in membrane organization, including plasma membrane blebbing and invagination, vacuolation and fragmentation of organelles, and alterations in the surface expression of receptors. The underlying mechanisms for these changes are unknown, though alterations in vesicular fusion are likely to play a role. Using a cell-free system based on Xenopus laevis egg extracts we have found that endosome fusion is blocked during apoptosis. Inhibition of fusion is prevented by Bcl-2 or Bcl-xL, two negative regulators of apoptosis, or by specific inhibitors of members of the caspase family of apoptotic proteases. Selective cleavage of Rabaptin-5, an essential and rate-limiting component of endosome fusion, is responsible for the loss of fusion activity. Cleavage of Rabaptin-5 also occurs in cellular models for apoptosis. These results suggest that inactivation of Rabaptin-5 and inhibition of vesicle transport lead to fragmentation of endosomes and inhibition of the endocytic pathway during the execution phase of apoptosis. We propose that parallel changes to other membrane transport pathways would give rise to general membrane fragmentation in apoptotic cells. These changes are likely to play an important role in the generation of apoptotic bodies and their recognition by phagocytosing cells.
authors.affiliation: Division of Biochemistry, School of Biological Sciences, University of Manchester, Stopford Building, Oxford Road, Manchester M13 9PT, UK.
authors.forename: S C
authors.initials: SC
authors.lastname: Cosulich
authors.forename: H
authors.initials: H
authors.lastname: Horiuchi
authors.forename: M
authors.initials: M
authors.lastname: Zerial
authors.forename: P R
authors.initials: PR
authors.lastname: Clarke
authors.forename: P G
authors.initials: PG
authors.lastname: Woodman
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D001692:Biological Transport; D002474:Cell-Free System; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004705:Endocytosis; D011992:Endosomes / Q000502:physiology*; D006801:Humans; D008561:Membrane Fusion / Q000187:drug effects*; D008565:Membrane Proteins / Q000378:metabolism*; D010063:Ovum; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D013379:Substrate Specificity; D033921:Vesicular Transport Proteins; D014981:Xenopus; D029867:Xenopus Proteins; D051020:bcl-X Protein
chemical_list: C494809:BCL2L1 protein, Xenopus; C494811:BCL2L1 protein, human; D015853:Cysteine Proteinase Inhibitors; D008565:Membrane Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; C097227:RABEP1 protein, human; D033921:Vesicular Transport Proteins; D029867:Xenopus Proteins; D051020:bcl-X Protein; D003546:Cysteine Endopeptidases