Abstract 2274 Roles of phosphatidylinositol 3,4-bisphosphate in phagocytosis and bacterial invasion.

Phosphoinositides are pivotal regulators of vesicular traffic and plasma membrane dynamics, including phagosome formation and bacterial invasion. Despite its low abundance, phosphatidylinositol 3,4-bisphosphate PI(3,4)P2 is critical for cell survival and actin dynamics. Not surprisingly, PI(3,4)P2 is used by innate immune cells to facilitate the clearance of opsonized prey and apoptotic cells but also bacterial pathogens who exploit the lipid to promote their own survival. Using genetically encoded probes, we demonstrate that the concerted actions of Class I PI 3-Kinase and phosphoinositide 5-phosphatases produce PI(3,4)P2 during phagosome formation, and this is responsible for the recruitment and activation of Ras-associated and pleckstrin homology domains-containing protein 1 (RAPH1)/lamellipodin and actin dynamics. We also characterize a kinase-independent mechanism used by enteropathogenic bacteria Salmonella and Shigella to produce PI(3,4)P2 in host cells to facilitate their invasion. The results show that the Salmonella effector SopB, previously believed to be a phosphoinositide phosphatase, also possesses phosphotransferase/ phosphoisomerase activity to produce PI(3,4)P2 from the PI(4,5)P2. This instance of convergent evolution demonstrates that PI(3,4)P2 production can be beneficial and exploited in the ongoing struggle between innate immune cells and bacterial invaders. Canadian Institutes of Health Research. Canada Research Chairs