Enlargeosome traffic: Exocytosis triggered by various signals is followed by endocytosis, membrane shedding or both

Emanuele Cocucci, Gabriella Racchetti, Paola Podini, Jacopo Meldolesi

Research output: Contribution to journalArticle

Abstract

Enlargeosomes are cytoplasmic organelles discharged by regulated exocytosis, identified by immunofluorescence of their membrane marker, desmoyokin/Ahnak, but never revealed at the ultrastructural level. Among the numerous enlargeosome-positive cells, the richest and most extensively characterized are those of a PC12 clone, PC12-27, defective of classical neurosecretion. By using ultrastructural immunoperoxidase labeling of formaldehyde-fixed, Triton-X-100-permeabilized PC12-27 cells, we have now identified the enlargeosomes as small vesicles scattered in the proximity of, but never docked to, the plasma membrane. Upon stimulation, these vesicles undergo exocytosis [rapid after the Ca2+ ionophore, ionomycin, much slower after either the phorbol ester, phorbol myristate acetate (PMA), or ATP, working through a P2Y receptor], with appearance in the plasma membrane of typical desmoyokin/Ahnak (d/A)-positive, Ω-shaped and open profiles evolving into flat patches. Postexocytic removal of the exocytized d/A-positive membrane occurs by two processes: generation of endocytic vesicles, predominant after ionomycin and ATP 100-500 μM; and shedding of membrane-bound cytoplasmic bodies, predominant after PMA and 1 mM ATP, containing little or no trace of endoplasmic reticulum, Golgi, endo/lysosomes and also of a plasma membrane marker. Depending on the stimulation, therefore, the cell-surface expansion by enlargeosome exocytosis is not always recycled but can induce release of specific membranes, possibly important in the pericellular environment.

Original languageEnglish
Pages (from-to)742-757
Number of pages16
JournalTraffic
Volume8
Issue number6
DOIs
Publication statusPublished - Jun 2007

Keywords

  • ATP
  • Desmoyokin/Ahnak
  • Detergent resistance
  • Endocytosis
  • Exocytosis
  • Ionomycin
  • Membrane shedding
  • P2Y receptors
  • PC12-27
  • PMA

ASJC Scopus subject areas

  • Biochemistry
  • Cell Biology
  • Genetics
  • Molecular Biology
  • Structural Biology

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