PtdIns(4,5)P2 is not required for secretory granule docking

Abstract

Phosphoinositides (PtdIns) play important roles in exocytosis and are thought to regulate secretory granule docking by co-clustering with the SNARE protein syntaxin to form a docking receptor in the plasma membrane. Here we tested this idea by high-resolution total internal reflection imaging of EGFP-labeled PtdIns markers or syntaxin-1 at secretory granule release sites in live insulin-secreting cells. In intact cells, PtdIns markers distributed evenly across the plasma membrane with no preference for granule docking sites. In contrast, syntaxin-1 was found clustered in the plasma membrane, mostly beneath docked granules. We also observed rapid accumulation of syntaxin-1 at sites where granules arrived to dock. Acute depletion of plasma membrane phosphatidylinositol (4,5) bisphosphate (PtdIns(4,5)P-2) by recruitment of a 5-phosphatase strongly inhibited Ca2+-dependent exocytosis, but had no effect on docked granules or the distribution and clustering of syntaxin-1. Cell permeabilization by -toxin or formaldehyde-fixation caused PtdIns marker to slowly cluster, in part near docked granules. In summary, our data indicate that PtdIns(4,5)P-2 accelerates granule priming, but challenge a role of PtdIns in secretory granule docking or clustering of syntaxin-1 at the release site.

Keywords

exocytosis; insulin; live cell imaging; phosphoinositides; PtdIns(4,5)P-2; syntaxin clustering; vesicle docking

Published in

Traffic
2018, volume: 19, number: 6, pages: 436-445
Publisher: WILEY

SLU Authors

• Omar Hmeadi, Muhmmad

  • Uppsala University

UKÄ Subject classification

Cell and Molecular Biology

Publication identifier

• DOI: https://doi.org/10.1111/tra.12562

Permanent link to this page (URI)

https://res.slu.se/id/publ/131873