Enlargeosome Traffic: Exocytosis Triggered by Various Signals Is Followed by Endocytosis, Membrane Shedding or Both

Traffic. 2007 Jun;8(6):742-57. doi: 10.1111/j.1600-0854.2007.00566.x. Epub 2007 May 4.


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 Ca(2+) 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, Omega-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 microM; 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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphate / pharmacology
  • Animals
  • Clone Cells
  • Detergents / pharmacology
  • Dose-Response Relationship, Drug
  • Endocytosis / drug effects
  • Endocytosis / physiology*
  • Endosomes / drug effects
  • Endosomes / ultrastructure
  • Exocytosis / drug effects
  • Exocytosis / physiology*
  • Intracellular Membranes / drug effects
  • Intracellular Membranes / ultrastructure
  • Ionomycin / pharmacology
  • Ionophores / pharmacology
  • PC12 Cells
  • Rats
  • Tetradecanoylphorbol Acetate / pharmacology


  • Detergents
  • Ionophores
  • Ionomycin
  • Adenosine Triphosphate
  • Tetradecanoylphorbol Acetate