Journal of Cell Biology paper for Cutler and Cramer Group

Actomyosin II contractility expels von Willebrand factor from Weibel-Palade bodies during exocytosis

Authors

Nightingale, T.D., White, I.J., Doyle, E.L., Turmaine, M.,
Harrison-Lavoie, K.J., Webb, K.F., Cramer, L.P., Cutler, D.F.,

Abstract

The study of actin in regulated exocytosis has a long history with many
different results in numerous systems. A major limitation
on identifying precise mechanisms has been the
paucity of experimental systems in which actin function has been
directly assessed
alongside granule content release at distinct steps
of exocytosis of a single secretory organelle with sufficient
spatiotemporal
resolution. Using dual-color confocal microscopy
and correlative electron microscopy in human endothelial cells, we
visually
distinguished two sequential steps of
secretagogue-stimulated exocytosis: fusion of individual secretory
granules (Weibel–Palade
bodies [WPBs]) and subsequent expulsion of von
Willebrand factor (VWF) content. Based on our observations, we conclude
that
for fusion, WPBs are released from cellular sites
of actin anchorage. However, once fused, a dynamic ring of actin
filaments
and myosin II forms around the granule, and
actomyosin II contractility squeezes VWF content out into the
extracellular environment.
This study therefore demonstrates how discrete
actin cytoskeleton functions within a single cellular system explain
actin
filament–based prevention and promotion of specific
exocytic steps during regulated secretion.