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

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• Neutrophils (PMNs) are key immune cells that combat pathogens through phagocytosis, degranulation, and the formation of neutrophil extracellular traps (NETs).
• Fc receptor gamma (FcγR) engagement, particularly FcγRIIIb cross-linking, can trigger NET formation, distinct from pathways activated by stimuli like Phorbol 12-myristate 13-acetate (PMA).
• The precise signaling cascades downstream of FcγRIIIb leading to NETosis remain incompletely understood, though extracellular signal-regulated kinase (ERK) pathway activation is implicated.

Purpose of the Study:

• To investigate the role of transforming growth factor-β-activated kinase 1 (TAK1) in the FcγRIIIb-mediated signaling pathway that induces NET formation.
• To elucidate the relationship between FcγRIIIb stimulation, TAK1 activation, and the subsequent MEK/ERK signaling cascade in the context of NETosis.

Main Methods:

• FcγRIIIb was stimulated using specific monoclonal antibodies in neutrophil models.
• NET formation was assessed in the presence and absence of pharmacological inhibitors, including a selective TAK1 inhibitor (LL Z1640-2) and a MEK inhibitor.
• Activation of signaling molecules, such as ERK and TAK1, was evaluated through phosphorylation assays.

Main Results:

• The TAK1 inhibitor LL Z1640-2 selectively blocked FcγRIIIb-induced NET formation but did not affect PMA-induced NET formation.
• FcγRIIIb cross-linking, but not PMA stimulation, led to TAK1 phosphorylation, indicating a specific role for TAK1 in the FcγRIIIb pathway.
• While both stimuli induced ERK phosphorylation, only FcγRIIIb-mediated ERK activation was sensitive to TAK1 inhibition, highlighting TAK1's upstream role in this specific pathway.

Conclusions:

• FcγRIIIb cross-linking activates TAK1, establishing it as a critical component of the signaling pathway leading to NETosis.
• TAK1 is essential for initiating the MEK/ERK signaling cascade specifically downstream of FcγRIIIb engagement, differentiating it from other NET-inducing stimuli.
• These findings identify a novel TAK1-dependent signaling mechanism regulating FcγRIIIb-mediated NET formation, offering insights into neutrophil effector functions.