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

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Abstract
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 β3- but not β1-integrin antibodies, and that PI3K inhibitors block β3-integrin dependence. Biochemical analysis of intracellular β3-integrin uncoupling by PI3K inhibitors revealed diminished β3-integrin tyrosine phosphorylation and decreased association with p72syk. Similarly, the p72sykinhibitor piceatannol promoted PMN transmatrix migration, whereas HIV-tat peptide-facilitated loading of peptides corresponding to the β3-integrin cytoplasmic tail identified the functional tyrosine residues for this activity. These data indicate that PI3K-regulated β3-integrin represents a natural “braking” mechanism for PMNs during transit through the extracellular matrix.