Bacteria that invade human endothelial cells can be efficiently eliminated in phagolysosomes. We investigated the role of vesicle tethering exocyst complex in maturation and function of endothelial cell phagosomes harbouring staphylococci or latex beads. Exocyst complex proteins (Sec5, -8, -10, Exo70) together with recycling endosome marker Rab11 were detected in vesicles that dynamically interacted and seemingly fused with endothelial cell phagosomes. Knockdown of exocyst proteins Sec8 and Exo70 inhibited the accumulation of Rab11-positive vesicles at the phagosomes. Furthermore, knockdown of exocyst proteins and Rab11 greatly reduced acidification of phagosomes and significantly diminished the elimination of invaded staphylococci in endothelial cells. The inhibitory effect of Exo70 knockdown on bacterial elimination could be rescued by constitutively active Rab11-Q70L. Our data suggest that exocyst complex controls the interaction of recycling endocytic vesicles with phagosomes and this process is involved in maturation and functioning of the phagosomes in endothelial cells.
