Enlargeosome, an exocytic vesicle resistant to nonionic detergents, undergoes endocytosis via a nonacidic route.
Enlargeosomes, a new type of widely expressed cytoplasmic vesicles, undergo tetanus toxin-insensitive exocytosis in response to cytosolic Ca(2+) concentration ([Ca(2+)](i)) rises. Cell biology of enlargeosomes is still largely unknown. By combining immunocytochemistry (marker desmoyokin-Ahnak, d/A) to capacitance electrophysiology in the enlargeosome-rich, neurosecretion-defective clone PC12-27, we show that 1) the two responses, cell surface enlargement and d/A surface appearance, occur with similar kinetics and in the same low micromolar [Ca(2+)](i) range, no matter whether induced by photolysis of the caged Ca(2+) compound o-nitrophenyl EGTA or by the Ca(2+) ionophore ionomycin. Thus, enlargeosomes seem to account, at least in large part, for the exocytic processes triggered by the two stimulations. 2. The enlargeosome membranes are resistant to nonionic detergents but distinct from other resistant membranes, rich in caveolin, Thy1, and/or flotillin1. 3. Cell cholesterol depletion, which affects many membrane fusions, neither disrupts enlargeosomes nor affects their regulated exocytosis. 4. The postexocytic cell surface decline is [Ca(2+)](i) dependent. 5. Exocytized d/A-rich membranes are endocytized and trafficked along an intracellular pathway by nonacidic organelles, distinct from classical endosomes and lysosomes. Our data define specific aspects of enlargeosomes and suggest their participation, in addition to cell differentiation and repair, for which evidence already exists, to other physiological and pathological processes.
Vita-Salute University, and San Raffaele Scientific Institute, Excellence Center in Cell Differentiation Pathophysiology, 20132 Milan, Italy.
Emanuele
E
Cocucci
Gabriella
G
Racchetti
Paola
P
Podini
Marjan
M
Rupnik
Jacopo
J
Meldolesi
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002460:Cell Line; D002784:Cholesterol / Q000172:deficiency / Q000494:pharmacology; D003902:Detergents / Q000737:chemistry / Q000494:pharmacology*; D025802:Electric Capacitance; D004705:Endocytosis / Q000187:drug effects; D011992:Endosomes / Q000378:metabolism / Q000648:ultrastructure; D005089:Exocytosis / Q000187:drug effects; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000187:drug effects; D015759:Ionomycin / Q000494:pharmacology; D007477:Ions / Q000737:chemistry; D007700:Kinetics; D008565:Membrane Proteins / Q000378:metabolism; D008854:Microscopy, Electron; D009363:Neoplasm Proteins / Q000378:metabolism; D010782:Photolysis; D051381:Rats
C489573:Ahnak protein, rat; D003902:Detergents; D007477:Ions; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D015759:Ionomycin; D002784:Cholesterol; D002118:Calcium