PtdIns(3,4)P2, Lamellipodin, and VASP coordinate actin dynamics during phagocytosis in macrophages

Class I PI 3-kinase is required for phagocytosis. This study investigates the role of PI3,4P2 produced downstream of PI 3-Kinase in phagocytosis. PI3,4P2, its effector-binding protein Lamellipodin, and VASP are required to support actin-driven pseudopod extension and engulfment of IgG opsonized particles. Phosphoinositides are pivotal regulators of vesicular traffic and signaling during phagocytosis. Phagosome formation, the initial step of the process, is characterized by local membrane remodeling and reorganization of the actin cytoskeleton that leads to formation of the pseudopods that drive particle engulfment. Using genetically encoded fluorescent probes, we found that upon particle engagement a localized pool of PtdIns(3,4)P-2 is generated by the sequential activities of class I phosphoinositide 3-kinases and phosphoinositide 5-phosphatases. Depletion of this locally generated pool of PtdIns(3,4)P-2 blocks pseudopod progression and ultimately phagocytosis. We show that the PtdIns(3,4)P-2 effector Lamellipodin (Lpd) is recruited to nascent phagosomes by PtdIns(3,4)P-2. Furthermore, we show that silencing of Lpd inhibits phagocytosis and produces aberrant pseudopodia with disorganized actin filaments. Finally, vasodilator-stimulated phosphoprotein (VASP) was identified as a key actin-regulatory protein mediating phagosome formation downstream of Lpd. Mechanistically, our findings imply that a pathway involving PtdIns(3,4)P-2, Lpd, and VASP mediates phagocytosis at the stage of particle engulfment.

Automated summary

PI 3-kinase is crucial for phagocytosis, with PI3,4P2, Lamellipodin, and VASP playing essential roles in actin-driven pseudopod extension and particle engulfment. Phosphoinositides are key regulators of vesicular traffic and signaling during phagocytosis, with locally generated PtdIns(3,4)P-2 influencing pseudopod progression and phagocytosis. Lamellipodin and VASP are important actin-regulatory proteins involved in phagosome formation downstream of PtdIns(3,4)P-2.