Neutrophil apoptosis:: Selective regulation by different ligands of integrin αMβ2

Neutrophils undergo spontaneous apoptosis, but their survival can be extended during inflammatory responses. alpha(M)beta(2) is reported either to delay or accelerate neutrophil apoptosis, but the mechanisms by which this integrin can support such diametrically opposed responses are poorly understood. The abilities of closely related alpha(M)beta(2) ligands, plasminogen and angiostatin, derived from plasminogen, as well as fibrinogen and its two derivative alpha(M)beta(2), recognition peptides, PI and P2-C, differed markedly in their effects on neutrophil apoptosis. Plasminogen, fibrinogen, and P2-C suppressed apoptosis via activation of Akt and ERK1/2 kinases, while angiostatin and PI failed to activate these prosurvival pathways and did not prevent neutrophil apoptosis. Using cells transfected with alpha(M)beta(2) or its individual alpha(M) or beta(2) subunits, and purified receptors and its constituent chains, we show that engagement of both subunits with prosurvival ligands is essential for induction of the prosurvival response. Hence, engagement of a single integrin by closely related ligands can induce distinct signaling pathways, which can elicit distinct cellular responses.