Phosphatidylinositol 4‐phosphate dynamics during phagocytosis

Abstract

Phosphoinositide levels undergo acute changes during the course of phagocytosis; phosphatidylinositol 4,5‐bisphosphate [PtdIns(4,5)P2], phosphatidylinositol 3,4,5‐trisphosphate and phosphatidylinositol 3‐phosphate (PtdIns3P) undergo marked changes. However, the fate of phosphatidylinositol 4‐phosphate (PtdIns4P) has not been investigated. Recently, a genetically encoded biosensor was developed to visualize PtdIns4P in live cells. The probe, called P4M2x, consists of two copies of the PtdIns4P‐binding domain of SidM, a Legionella pneumophila effector, tagged with a fluorescent protein. Expression of P4M2x in macrophages revealed tri‐phasic changes of PtdIns4P during phagocytosis. PtdIns4P, normally present in the plasma membrane, underwent a transient, moderate increase as the phagosome sealed, coinciding with the disappearance of PtdIns(4,5)P2. This initial increase was followed by the virtual disappearance of PtdIns4P, which coincided with accumulation of PtdIns3P. At the time when PtdIns3P disappeared, a gradual reacquisition of PtdIns4P was observed, exceeding the levels normally found at the plasma membrane. This reappearance of PtdIns4P was preceded by the sequential acquisition of Rab5 followed by Rab7 –early and late maturation indicators, respectively. The reacquisition of PtdIns4P was accompanied by the appearance of P4M2x‐positive tubules that extended dynamically between phagosomes and the pericentriolar Golgi area.