Cooperation between classical and alternative NF-κB pathways regulates proinflammatory responses in epithelial cells

Area of Science:

• Immunology
• Cell Biology
• Respiratory Medicine

Background:

• Nuclear factor-kappa B (NF-κB) is implicated in inflammatory lung diseases.
• Two NF-κB pathways exist: classical (IKKβ/RelA/p50) and alternative (IKKα/RelB/p52).
• The role of the alternative pathway in innate immunity, particularly in lung epithelial cells, is unclear.

Purpose of the Study:

• To investigate the significance of the alternative NF-κB pathway in lung epithelial cells' proinflammatory responses.
• To understand how both NF-κB pathways contribute to inflammatory signaling in the lungs.

Main Methods:

• Utilized C10 murine alveolar and primary murine tracheal epithelial cells.
• Stimulated cells with diverse agents and lipopolysaccharide (LPS).
• Assessed NF-κB pathway activation via nuclear translocation of RelA, p50, RelB, and p52.
• Employed small interfering (si) RNA to knock down IKKα, RelA, and RelB.
• Investigated effects of constitutively active (CA)-IKKα and CA-IKKβ.
• Disrupted the IKK signalsome.

Main Results:

• Both classical and alternative NF-κB pathways were activated by stimuli, with distinct kinetics for RelA and RelB nuclear translocation.
• siRNA-mediated knockdown of IKKα, RelA, or RelB reduced multiple LPS-induced proinflammatory cytokines.
• Surprisingly, IKKα or RelB knockdown increased IL-6 production in response to LPS.
• Co-expression of CA-IKKα and CA-IKKβ synergistically enhanced proinflammatory mediators.
• Inhibition of the IKK signalsome blocked both NF-κB pathways.

Conclusions:

• Both NF-κB pathways are activated in lung epithelial cells.
• The coordinated activation of classical and alternative NF-κB pathways is crucial for regulating the intensity and characteristics of lung inflammation.
• This study elucidates a complex interplay between NF-κB pathways in innate immune responses within the lung.