The SNARE protein vti1a functions in dense-core vesicle biogenesis

• Published in: The EMBO journal Vol. 33; no. 15; pp. 1681 - 1697
• Main Authors: Walter, Alexander M, Kurps, Julia, de Wit, Heidi, Schöning, Susanne, Toft-Bertelsen, Trine L, Lauks, Juliane, Ziomkiewicz, Iwona, Weiss, Annita N, Schulz, Alexander, Fischer von Mollard, Gabriele, Verhage, Matthijs, Sørensen, Jakob B
• Format: Journal Article
• Language: English
• Published: London Blackwell Publishing Ltd 01.08.2014; Nature Publishing Group UK; BlackWell Publishing Ltd
• Subjects: adrenal chromaffin cells; Animals; Biosynthesis; Ca2+-channels; Calcium Channels - metabolism; Cell Nucleus Structures - metabolism; Cellular biology; Chromaffin Cells - metabolism; EMBO20; EMBO27; exocytosis; Exocytosis - physiology; Kinetics; Mice; Mice, Mutant Strains; Neurotransmitters; Proteins; Qa-SNARE Proteins - metabolism; Qb-SNARE Proteins - genetics; Qb-SNARE Proteins - metabolism; Secretory Vesicles - metabolism; SNARE; Upstream; vesicle biogenesis; Vesicle-Associated Membrane Protein 2 - metabolism; exocytosis; vesicle biogenesis; channels; adrenal chromaffin cells; Ca; SNARE; Ca2+‐channels
• ISSN: 0261-4189; 1460-2075
• DOI: 10.15252/embj.201387549

The SNARE protein vti1a is proposed to drive fusion of intracellular organelles, but recent data also implicated vti1a in exocytosis. Here we show that vti1a is absent from mature secretory vesicles in adrenal chromaffin cells, but localizes to a compartment near the trans‐Golgi network, partially overlapping with syntaxin‐6. Exocytosis is impaired in vti1a null cells, partly due to fewer Ca 2+ ‐channels at the plasma membrane, partly due to fewer vesicles of reduced size and synaptobrevin‐2 content. In contrast, release kinetics and Ca 2+ ‐sensitivity remain unchanged, indicating that the final fusion reaction leading to transmitter release is unperturbed. Additional deletion of the closest related SNARE, vti1b, does not exacerbate the vti1a phenotype, and vti1b null cells show no secretion defects, indicating that vti1b does not participate in exocytosis. Long‐term re‐expression of vti1a (days) was necessary for restoration of secretory capacity, whereas strong short‐term expression (hours) was ineffective, consistent with vti1a involvement in an upstream step related to vesicle generation, rather than in fusion. We conclude that vti1a functions in vesicle generation and Ca 2+ ‐channel trafficking, but is dispensable for transmitter release. Synopsis Neurotransmitter release depends on the SNARE protein vti1a, which is unexpectedly not required for final fusion of dense‐core vesicles, but for their generation. In adrenal chromaffin cells, vti1a localizes to a compartment near the trans ‐Golgi‐network, partly overlapping with syntaxin‐6, but is absent from secretory granules. In the absence of vti1a, secretory amplitude is reduced, fewer Ca 2+ ‐channels are present in the plasma membrane, and the cells contain fewer vesicles of reduced size and synaptobrevin‐2/VAMP2 content. Release kinetics and Ca 2+ ‐sensitivity remain unchanged in vti1a nulls, indicating that the final fusion reaction is independent of vti1a. Long‐term re‐expression of vti1a (days) is necessary for restoration of secretory capacity, consistent with vti1a involvement in an upstream step related to vesicle generation. Graphical Abstract Neurotransmitter release depends on the SNARE protein vti1a, which is unexpectedly not required for final fusion of dense‐core vesicles, but for their generation.