Article
- The EMBO Journal (2006) 25, 5443 - 5456
- doi:10.1038/sj.emboj.7601419
Published online: 2 November 2006
Subject Category:
Annexin2 coating the surface of enlargeosomes is needed for their regulated exocytosis
Anna Lorusso1, Cesare Covino1, Giuseppina Priori2, Angela Bachi1, Jacopo Meldolesi1,2,3 and Evelina Chieregatti2,3
- Scientific Institute San Raffaele, ALEMBIC, Advanced Light and Electron Microscopy BioImaging Center, Milan, Italy
- Department of Neuroscience, Vita-Salute San Raffaele University, Center of Excellence in Cell Development, Milan, Italy
- IIT Research Unit of Molecular Neuroscience, Milan, Italy
Correspondence to:
Evelina Chieregatti, Vita-Salute San Raffaele University, DIBIT, via Olgettina 58, 20132 Milan, Italy. Tel.: +39 022 643 4604; Fax: +39 022 643 4813; E-mail E-mail: chieregatti.evelina@hsr.it
Received 20 June 2006; Accepted 10 October 2006
Abstract
Enlargeosomes are small cytoplasmic vesicles that undergo rapid, Ca2+-dependent exo/endocytosis. The role of the cytoskeleton in these processes was unknown. In PC12-27 cells, microtubule disassembly had little effect on enlargeosomes, whereas microfilament disassembly increased markedly both their resting and stimulated exocytosis, and inhibited their endocytosis. Even at rest enlargeosomes are coated at their cytosolic surface by an actin-associated protein, annexin2, bound by a dual, Ca2+-dependent and Ca2+-independent mechanism. In contrast, the other enlargeosome marker, desmoyokin/Ahnak, is transported across the organelle membrane, apparently by an ABC transporter, and binds to its lumenal face. Annexin2-GFP expression revealed that, upon stimulation, the slow and random enlargeosome movement increases markedly and becomes oriented toward the plasma membrane. After annexin2 downregulation enlargeosome exocytosis induced by both [Ca2+]i rise and cytoskeleton disruption is inhibited, and the NGF-induced differentiation is blocked. Binding of annexin2 to the enlargeosome membrane, the most extensive ever reported (>50% annexin2 bound to 
3% of total membrane area), seems therefore to participate in the regulation of their exocytosis.
Keywords:
- annexin2,
- cytoskeleton,
- enlargeosome,
- exocytosis,
- membrane traffic
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