Platelet-activating factor (PAF) stimulates the PAF-synthesizing enzyme acetyl-CoA:1-alkyl-sn-glycero-3-phosphocholine O2-acetyltransferase and PAF synthesis in neutrophils | JoVE Visualize

Platelet-activating factor (PAF) stimulates the PAF-synthesizing enzyme acetyl-CoA:1-alkyl-sn-glycero-3-phosphocholine O2-acetyltransferase and PAF synthesis in neutrophils

T W Doebber¹, M S Wu

¹Department of Biochemical Regulation, Merck Sharp & Dohme Research Laboratories, Rahway, NJ 07065-0900.

Proceedings of the National Academy of Sciences of the United States of America|November 1, 1987

View abstract on PubMed

Summary

Platelet activating factor (PAF) rapidly activates neutrophil acetyltransferase, an enzyme crucial for PAF synthesis. This enzyme activation, more sensitive to PAF than degranulation, suggests distinct receptor mechanisms and likely amplifies neutrophil responses.

Area of Science:

Immunology and Cell Biology
Biochemistry and Molecular Biology

Background:

Platelet-activating factor (PAF) is a potent lipid mediator involved in inflammatory and immune responses.
Neutrophils are key effector cells in inflammation, and their activation by PAF leads to various responses, including degranulation and mediator synthesis.

Purpose of the Study:

To investigate the effect of PAF on the biosynthesis of PAF itself in neutrophils.
To characterize the activation of the key enzyme in PAF synthesis, acetyl-CoA:1-alkyl-sn-glycero-3-phosphocholine O2-acetyltransferase, by PAF.

Main Methods:

Isolated rat peritoneal and human peripheral neutrophils were stimulated with PAF.
Acetyltransferase activity and PAF synthesis ([3H]acetate incorporation) were measured.
Enzyme kinetics, receptor antagonist inhibition, and effects of alkaline phosphatase were assessed.

Main Results:

PAF rapidly and potently activated neutrophil acetyltransferase (8-10 fold increase) and degranulation within 30 seconds.
Acetyltransferase activation was more sensitive to PAF (evident at 10(-9) M) than degranulation.
PAF-induced acetyltransferase exhibited a 10-fold higher Vmax compared to basal enzyme, with similar Km for acetyl-CoA.

Conclusions:

PAF stimulates its own synthesis in neutrophils by activating acetyltransferase, likely amplifying the overall neutrophil response.
Differential sensitivity to PAF and receptor antagonists suggests distinct PAF receptor involvement or occupancy requirements for acetyltransferase activation versus degranulation.