Lipoxin A4 redistributes myosin IIA and Cdc42 in macrophages:: Implications for phagocytosis of apoptotic leukocytes

Lipoxins (LXs) are endogenously produced anti-inflammatory agents that modulate leukocyte trafficking and stimulate nonphlogistic macrophage phagocytosis of apoptotic neutrophils, thereby promoting the resolution of inflammation. Previous data suggest a role for altered protein phosphorylation and cytoskeletal rearrangement in LX-stimulated phagocytosis but the exact mechanisms remain unclear. In this study we examine the effects of LXA(4) on the protein phosphorylation pattern of THP-1 cells differentiated into a macrophage-like phenotype. THP-1 cells stimulated with LXA(4) (1 nM) exhibit dephosphorylation of a 220-kDa protein. Using mass spectrometry, this protein was identified as MYH9, a nonmuscle myosin H chain 11 isoform A, which is involved in cytoskeleton rearrangement. THP-1 cells treated with LXA(4) adopt a polarized morphology with activated Cdc42 localized toward the leading edge and MYH9 localized at the cell posterior. Polarized distribution of Cdc42 is associated with Akt/PKB-mediated Cdc42 activation. Interestingly, the annexin-derived peptide Ac2-26, a recently described agonist for the LXA4 receptor, also stimulates macrophage phagocytosis, MYH9 dephosphorylation, and MYH9 redistribution. In addition, we demonstrate that LXA4 stimulates the phosphorylation of key polarity organization molecules: Akt, protein kinase C zeta, and glycogen synthase kinase-3 beta. Inhibition of LXA(4)-induced Akt and protein kinase C zeta activity with specific inhibitors prevented LXA(4) stimulated phagocytosis of both apoptotic polymorphonuclear neutrophils and lymphocytes, highlighting a potential use for LXA4 in the treatment of autoimmune diseases. Furthermore, phosphorylation and subsequent inactivation of glycogen synthase kinase-3 beta resulted in an increase in phagocytosis similar to that of LXA4. These data highlight an integrated mechanism whereby LXA4 regulates phagocytosis through facilitative actin cytoskeleton rearrangement and cell polarization.