Phosphoinositide 3-kinase modulation of β3-integrin represents an endogenous “braking” mechanism during neutrophil transmatrix migration

During episodes of inflammation, neutrophils (polymorphonuclear leukocytes [PMNs]) encounter subendothelial matrix substrates that may require additional signaling pathways as directives for movement through the extracellular space. Using an in vitro endothelial and epithelial model, inhibitors of phosphoinositide 3-kinase (PI3K) were observed to promote chemoattractant-stimulated migration by as much as 8 +/- 0.3-fold. Subsequent studies indicated that PMNs respond in a similar manner to RGD-containing matrix substrates and that PMN-matrix interactions are potently inhibited by antibodies directed against beta(3)- but not beta(1)-integrin antibodies, and that PI3K inhibitors block beta(3)-integrin dependence. Biochemical analysis of intracellular beta(3)-integrin uncoupling by PI3K inhibitors revealed diminished beta(3)-integrin tyrosine phosphorylation and decreased association with p72(syk). Similarly, the p72(syk) inhibitor piceatannol promoted PMN transmatrix migration, whereas HIV-tat peptide-facilitated loading of peptides corresponding to the beta(3)-integrin cytoplasmic tail identified the functional tyrosine residues for this activity. These data indicate that PI3K-regulated beta(3)-integrin represents a natural "braking" mechanism for PMNs during transit through the extracellular matrix.