Munc13-4 functions as a Ca2+sensor for homotypic secretory granule fusion to generate endosomal exocytic vacuoles
| Autor: | Sang Su Woo, Declan J. James, Thomas Martin |
|---|---|
| Rok vydání: | 2017 |
| Předmět: |
0301 basic medicine
Endosome Endosomes Vacuole Biology Membrane Fusion Exocytosis Cell Line 03 medical and health sciences 0302 clinical medicine Animals Secretion Molecular Biology Total internal reflection fluorescence microscope Secretory Vesicles Proteins Lipid bilayer fusion Articles Cell Biology Secretory Vesicle Rats Cell biology Transport protein Soluble N-Ethylmaleimide-Sensitive Factor Attachment Proteins Protein Transport 030104 developmental biology Membrane Trafficking Vacuoles Calcium Carrier Proteins SNARE Proteins 030217 neurology & neurosurgery |
| Zdroj: | Molecular Biology of the Cell |
| ISSN: | 1939-4586 1059-1524 |
| DOI: | 10.1091/mbc.e16-08-0617 |
| Popis: | Munc13-4, a Ca2+-dependent SNARE/phospholipid-binding protein on secretory granules (SGs), functions as a Ca2+ sensor for SG exocytosis and SG-SG fusion. SG-SG fusion plus fusion with recycling endosomes generates large (>2.4 μm) Munc13-4+/Rab7+/Rab11+ exocytic vacuoles. The results provide insights into multigranular compound exocytosis. Munc13-4 is a Ca2+-dependent SNARE (soluble N-ethylmaleimide–sensitive factor attachment protein receptor)- and phospholipid-binding protein that localizes to and primes secretory granules (SGs) for Ca2+-evoked secretion in various secretory cells. Studies in mast cell–like RBL-2H3 cells provide direct evidence that Munc13–4 with its two Ca2+-binding C2 domains functions as a Ca2+ sensor for SG exocytosis. Unexpectedly, Ca2+ stimulation also generated large (>2.4 μm in diameter) Munc13-4+/Rab7+/Rab11+ endosomal vacuoles. Vacuole generation involved the homotypic fusion of Munc13-4+/Rab7+ SGs, followed by a merge with Rab11+ endosomes, and depended on Ca2+ binding to Munc13-4. Munc13-4 promoted the Ca2+-stimulated fusion of VAMP8-containing liposomes with liposomes containing exocytic or endosomal Q-SNAREs and directly interacted with late endosomal SNARE complexes. Thus Munc13-4 is a tethering/priming factor and Ca2+ sensor for both heterotypic SG-plasma membrane and homotypic SG-SG fusion. Total internal reflection fluorescence microscopy imaging revealed that vacuoles were exocytic and mediated secretion of β-hexosaminidase and cytokines accompanied by Munc13-4 diffusion onto the plasma membrane. The results provide new molecular insights into the mechanism of multigranular compound exocytosis commonly observed in various secretory cells. |
| Databáze: | OpenAIRE |
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