Myosin I: A new pip(3) effector in chemotaxis and phagocytosis.

Phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P(3)) is a key signaling molecule in chemotaxis, a directed cell migration toward chemoattractants. PtdIns(3,4,5)P(3) is transiently generated by chemotactic stimulation and activates reorganization of the actin cytoskeleton at the leading edge of migrating cells. In a recent study, we demonstrated that PtdIns(3,4,5)P(3) directly binds to three members of the actin-based motor protein myosin I (myosin ID, IE and IF) in Dictyostelium discoideum and recruits these proteins to the plasma membrane of the leading edge. The PtdIns(3,4,5)P(3)-regulated membrane recruitment of myosin I induced chemoattractant-stimulated actin polymerization and was therefore required for chemotaxis. Similarly, human myosin IF was translocated to the plasma membrane through interactions with PtdIns(3,4,5)P(3) upon chemotactic stimulation in a neutrophil cell line. Interestingly, we also found that the three PtdIns(3,4,5)P(3)-binding myosin I proteins function in phagocytosis, which involves both PtdIns(3,4,5)P(3) signaling and actin cytoskeleton remodeling. Our findings provide an evolutionarily conserved mechanism by which class I myosin transmits PtdIns(3,4,5)P(3) signals to the actin cytoskeleton.