Platelet-activating factor induces NF-kappa B activation through a G protein-coupled pathway

Area of Science:

• Cellular and Molecular Biology
• Immunology
• Signal Transduction

Background:

• Platelet-activating factor (PAF) is a potent lipid mediator involved in inflammation and immune responses.
• Transcription factors, such as nuclear factor kappa B (NF-kappa B), play crucial roles in regulating gene expression.

Purpose of the Study:

• To investigate the role of PAF in activating transcription factors.
• To elucidate the signaling pathway involved in PAF-induced transcription factor activation.

Main Methods:

• Utilized stably transfected Chinese hamster ovary cells expressing the PAF receptor (CHO-PAFR).
• Employed gel supershift and UV cross-linking assays to identify DNA-binding proteins.
• Analyzed messenger RNA and protein levels of I kappa B alpha.
• Used PAF receptor antagonist (SR 27417) and bacterial toxins (cholera toxin, pertussis toxin) to probe signaling pathways.
• Confirmed findings in murine macrophage and human B cell lines with endogenous PAF receptors.

Main Results:

• PAF stimulation led to nuclear expression of DNA-binding activity specific to the kappa B sequence in CHO-PAFR cells.
• p50 and p65 proteins, components of NF-kappa B, were identified in these complexes.
• PAF induced changes in I kappa B alpha levels and mRNA, characteristic of NF-kappa B activation.
• PAF-induced kappa B binding activity was rapid, peaking within 30-40 minutes.
• SR 27417 blocked PAF-induced activity, while cholera toxin reduced it, suggesting G protein involvement.
• PAF activated NF-kappa B in cell lines expressing endogenous PAF receptors.

Conclusions:

• PAF activates transcription factor NF-kappa B through a signaling pathway involving G proteins.
• This activation occurs in various cell types, including macrophages and B cells.
• PAF may regulate gene expression via G protein-coupled transcription factor activation.