Syk-Mediated Translocation of PI3Kd to the Leading Edge Controls Lamellipodium Formation and Migration

The non-receptor tyrosine kinase Syk is mainly expressed in the hematopoietic system and plays an essential role in b2 integrin-mediated leukocyte activation. To elucidate the signaling pathway downstream of Syk during b2 integrin (CD11/ CD18)-mediated migration and extravasation of polymorphonuclear neutrophils (PMN), we generated neutrophil-like differentiated HL-60 (dHL-60) cells expressing a fluorescently tagged Syk mutant lacking the tyrosine residue at the position 323 (Syk-Tyr323) that is known to be required for the binding of the regulatory subunit p85 of the phosphatidylinositol 3-kinase (PI3K) class IA. Syk-Tyr 323 was found to be critical for the enrichment of the catalytic subunit p110d of PI3K class IA as well as for the generation of PI3K products at the leading edge of the majority of polarized cells. In accordance, the translocation of PI3K p110d to the leading edge was diminished in Syk deficient murine PMN. Moreover, the expression of EGFP-Syk Y323F interfered with proper cell polarization and it impaired efficient migration of dHL-60 cells. In agreement with a major role of b2 integrins in the recruitment of phagocytic cells to sites of lesion, mice with a Syk-deficient hematopoietic system demonstrated impaired PMN infiltration into the wounded tissue that was associated with prolonged cutaneous wound healing. These data imply a novel role of Syk via PI3K p110d signaling for b2 integrin-mediated migration which is a prerequisite for efficient PMN recruitment in vivo