Cross-talk between IRAK-4 and the NADPH oxidase

Area of Science:

• Immunology
• Cellular Signaling
• Molecular Biology

Background:

• Neutrophil oxidative responses are crucial for immunity but their regulation is complex.
• Lipopolysaccharide (LPS) stimulates neutrophils via Toll-like receptor 4 (TLR4), activating signaling pathways.
• The precise mechanisms linking TLR4 activation to NADPH oxidase activation remain incompletely understood.

Purpose of the Study:

• To investigate the role of interleukin-1 receptor-associated kinase-4 (IRAK-4) in regulating NADPH oxidase activation.
• To determine if IRAK-4 phosphorylates the cytosolic factor p47phox, a critical component of NADPH oxidase.

Main Methods:

• In vitro kinase assays using purified proteins.
• Mass spectrometry (MS) to identify phosphorylation sites.
• Cellular assays in granulocytes and neutrophils.
• Immunoprecipitation and immunofluorescence microscopy.

Main Results:

• IRAK-4 directly phosphorylates p47phox at novel threonine-rich sites, distinct from protein kinase C (PKC) targets.
• LPS stimulation induces p47phox phosphorylation in neutrophils, which is enhanced by p38 MAPK inhibition.
• IRAK-4 and p47phox interact and co-localize at the plasma membrane upon LPS stimulation.
• IRAK-4 activation and subsequent p47phox phosphorylation (at Thr133, Ser288, Thr356) are essential for NADPH oxidase activation.

Conclusions:

• IRAK-4 is a key regulator of NADPH oxidase activation in neutrophils.
• IRAK-4 phosphorylates p47phox, leading to the activation of the oxidase response to LPS.
• This study elucidates a novel signaling pathway in innate immune responses.