Involvement of the γ Isoform of cPLA(2) in the Biosynthesis of Bioactive N-Acylethanolamines

Arachidonylethanolamide (anandamide) acts as an endogenous ligand of cannabinoid receptors, while other N-acylethanolamines (NAEs), such as palmitylethanolamide and oleylethanolamide, show analgesic, anti-inflammatory, and appetite-suppressing effects through other receptors. In mammalian tissues, NAEs, including anandamide, are produced from glycerophospholipid via N-acyl-phosphatidylethanolamine (NAPE). The ɛ isoform of cytosolic phospholipase A(2) (cPLA(2)) functions as an N-acyltransferase to form NAPE. Since the cPLA(2) family consists of six isoforms (α, β, γ, δ, ɛ, and ζ), the present study investigated a possible involvement of isoforms other than ɛ in the NAE biosynthesis. Firstly, when the cells overexpressing one of the cPLA(2) isoforms were labeled with [(14)C]ethanolamine, the increase in the production of [(14)C]NAPE was observed only with the ɛ-expressing cells. Secondly, when the cells co-expressing ɛ and one of the other isoforms were analyzed, the increase in [(14)C]N-acyl-lysophosphatidylethanolamine (lysoNAPE) and [(14)C]NAE was seen with the combination of ɛ and γ isoforms. Furthermore, the purified cPLA(2)γ hydrolyzed not only NAPE to lysoNAPE, but also lysoNAPE to glycerophospho-N-acylethanolamine (GP-NAE). Thus, the produced GP-NAE was further hydrolyzed to NAE by glycerophosphodiesterase 1. These results suggested that cPLA(2)γ is involved in the biosynthesis of NAE by its phospholipase A(1)/A(2) and lysophospholipase activities.