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Synaptotagmin-7 links fusion-activated Ca(2+) entry and fusion pore dilation

Ca(2+)-dependent regulation of fusion pore dilation and closure is a key mechanism determining the output of cellular secretion. We have recently described ‘fusion-activated’ Ca(2+) entry (FACE) following exocytosis of lamellar bodies in alveolar type II cells. FACE regulates fusion pore expansion a...

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Autores principales: Neuland, Kathrin, Sharma, Neeti, Frick, Manfred
Formato: Online Artículo Texto
Lenguaje:English
Publicado: The Company of Biologists 2014
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4265738/
https://www.ncbi.nlm.nih.gov/pubmed/25344253
http://dx.doi.org/10.1242/jcs.153742
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author Neuland, Kathrin
Sharma, Neeti
Frick, Manfred
author_facet Neuland, Kathrin
Sharma, Neeti
Frick, Manfred
author_sort Neuland, Kathrin
collection PubMed
description Ca(2+)-dependent regulation of fusion pore dilation and closure is a key mechanism determining the output of cellular secretion. We have recently described ‘fusion-activated’ Ca(2+) entry (FACE) following exocytosis of lamellar bodies in alveolar type II cells. FACE regulates fusion pore expansion and facilitates secretion. However, the mechanisms linking this locally restricted Ca(2+) signal and fusion pore expansion were still elusive. Here, we demonstrate that synaptotagmin-7 (Syt7) is expressed on lamellar bodies and links FACE and fusion pore dilation. We directly assessed dynamic changes in fusion pore diameters by analysing diffusion of fluorophores across fusion pores. Expressing wild-type Syt7 or a mutant Syt7 with impaired Ca(2+)-binding to the C(2) domains revealed that binding of Ca(2+) to the C(2)A domain facilitates FACE-induced pore dilation, probably by inhibiting translocation of complexin-2 to fused vesicles. However, the C(2)A domain hampered Ca(2+)-dependent exocytosis of lamellar bodies. These findings support the hypothesis that Syt7 modulates fusion pore expansion in large secretory organelles and extend our picture that lamellar bodies contain the necessary molecular inventory to facilitate secretion during the exocytic post-fusion phase. Moreover, regulating Syt7 levels on lamellar bodies appears to be essential in order that exocytosis is not impeded during the pre-fusion phase.
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spelling pubmed-42657382014-12-23 Synaptotagmin-7 links fusion-activated Ca(2+) entry and fusion pore dilation Neuland, Kathrin Sharma, Neeti Frick, Manfred J Cell Sci Research Article Ca(2+)-dependent regulation of fusion pore dilation and closure is a key mechanism determining the output of cellular secretion. We have recently described ‘fusion-activated’ Ca(2+) entry (FACE) following exocytosis of lamellar bodies in alveolar type II cells. FACE regulates fusion pore expansion and facilitates secretion. However, the mechanisms linking this locally restricted Ca(2+) signal and fusion pore expansion were still elusive. Here, we demonstrate that synaptotagmin-7 (Syt7) is expressed on lamellar bodies and links FACE and fusion pore dilation. We directly assessed dynamic changes in fusion pore diameters by analysing diffusion of fluorophores across fusion pores. Expressing wild-type Syt7 or a mutant Syt7 with impaired Ca(2+)-binding to the C(2) domains revealed that binding of Ca(2+) to the C(2)A domain facilitates FACE-induced pore dilation, probably by inhibiting translocation of complexin-2 to fused vesicles. However, the C(2)A domain hampered Ca(2+)-dependent exocytosis of lamellar bodies. These findings support the hypothesis that Syt7 modulates fusion pore expansion in large secretory organelles and extend our picture that lamellar bodies contain the necessary molecular inventory to facilitate secretion during the exocytic post-fusion phase. Moreover, regulating Syt7 levels on lamellar bodies appears to be essential in order that exocytosis is not impeded during the pre-fusion phase. The Company of Biologists 2014-12-15 /pmc/articles/PMC4265738/ /pubmed/25344253 http://dx.doi.org/10.1242/jcs.153742 Text en © 2014. Published by The Company of Biologists Ltd http://creativecommons.org/licenses/by/3.0 This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed.
spellingShingle Research Article
Neuland, Kathrin
Sharma, Neeti
Frick, Manfred
Synaptotagmin-7 links fusion-activated Ca(2+) entry and fusion pore dilation
title Synaptotagmin-7 links fusion-activated Ca(2+) entry and fusion pore dilation
title_full Synaptotagmin-7 links fusion-activated Ca(2+) entry and fusion pore dilation
title_fullStr Synaptotagmin-7 links fusion-activated Ca(2+) entry and fusion pore dilation
title_full_unstemmed Synaptotagmin-7 links fusion-activated Ca(2+) entry and fusion pore dilation
title_short Synaptotagmin-7 links fusion-activated Ca(2+) entry and fusion pore dilation
title_sort synaptotagmin-7 links fusion-activated ca(2+) entry and fusion pore dilation
topic Research Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4265738/
https://www.ncbi.nlm.nih.gov/pubmed/25344253
http://dx.doi.org/10.1242/jcs.153742
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