N-acyl-phosphatidylethanolamine (NAPE) is known to be a precursor for various bioactive N-acylethanolamines including the endocannabinoid anandamide. NAPE is produced in mammals through the transfer of an acyl chain from certain glycerophospholipids to phosphatidylethanolamine (PE) by Ca2+-dependent or -independent N-acyltransferases. The ε isoform of mouse cytosolic phospholipase A2 (cPLA2ε) was recently identified as a Ca2+-dependent N-acyltransferase (Ca-NAT). In the present study, we first showed that two isoforms of human cPLA2ε function as Ca-NAT. We next purified both mouse recombinant cPLA2ε and its two human orthologues to examine their catalytic properties. The enzyme absolutely required Ca2+ for its activity and the activity was enhanced by phosphatidylserine (PS). PS enhanced the activity 25-fold in the presence of 1 mM CaCl2 and lowered the EC50 value of Ca2+ >8-fold. Using a PS probe, we showed that cPLA2ε largely co-localizes with PS in plasma membrane and organelles involved in the endocytic pathway, further supporting the interaction of cPLA2ε with PS in living cells. Finally, we found that the Ca2+-ionophore ionomycin increased [14C]NAPE levels >10-fold in [14C]ethanolamine-labeled cPLA2ε-expressing cells while phospholipase A/acyltransferase-1, acting as a Ca2+-independent N-acyltransferase, was insensitive to ionomycin for full activity. In conclusion, PS potently stimulated the Ca2+-dependent activity and human cPLA2ε isoforms also functioned as Ca-NAT.
Keywords: Endocannabinoid; N-acyl-phosphatidylethanolamine; N-acylethanolamine; N-acyltransferase; Phosphatidylserine; Phospholipase A(2).
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