Transforming Growth Factor-β-Activated Kinase 1 Is Required for Human FcγRIIIb-Induced Neutrophil Extracellular Trap Formation

Neutrophils (PMNs) are the most abundant leukocytes in the blood. PMN migrates from the circulation to sites of infection where they are responsible for antimicrobial functions. PMN uses phagocytosis, degranulation, and formation of neutrophil extracellular traps (NETs) to kill microbes. Several stimuli, including bacteria, fungi, and parasites, and some pharmacological compounds, such as Phorbol 12-myristate 13-acetate (PMA), are efficient inducers of NETs. Antigen antibody complexes are also capable of inducing NET formation. Recently, it was reported that Fc gamma RIIIb cross-linking induced NET formation similarly to PMA stimulation. Direct cross-linking of Fc gamma RIIIb or integrins did not promote NET formation. Fc gamma RIIIb-induced NET formation presented different kinetics from PMA-induced NET formation, suggesting differences in signaling. Because Fc gamma RIIIb also induces a strong activation of extracellular signal-regulated kinase (ERK) and nuclear factor Elk-1, and the transforming growth factor activated kinase 1 (TAK1) has recently been implicated in ERK signaling, in the present report, we explored the role of TAK1 in the signaling pathway activated by Fc gamma RIIIb leading to NET formation. Fc gamma RIIIb was stimulated by specific monoclonal antibodies, and NET formation was evaluated in the presence or absence of pharmacological inhibitors. The antibiotic LL Z1640-2, a selective inhibitor of TAK1 prevented Fc gamma RIIIb-induced, but not PMA-induced NET formation. Both PMA and Fc gamma RIIIb cross-linking induced phosphorylation of ERK. But, LL Z1640-2 only inhibited the Fc gamma RIIIb-mediated activation of ERK. Also, only Fc gamma RIIIb, similarly to transforming growth factor-3-induced TAK1 phosphorylation. A MEK (ERK kinase)-specific inhibitor was able to prevent ERK phosphorylation induced by both PMA and Fc gamma RIIIb. These data show for the first time that Fc gamma RIIIb cross-linking activates TAK1, and that this kinase is required for triggering the MEK/ERK signaling pathway to NETosis.