Involvement of glycerophosphodiesterase 7 in the intracellular production of cyclic phosphatidic acid

Abstract

Cyclic phosphatidic acid (cPA) is a lipid mediator present in tissues and plasma, which regulates physiological and pathological processes via the suppression of peroxisome proliferator-activated receptor γ (PPARγ). Glycerophosphodiesterase 7 (GDE7) is an endoplasmic reticulum-localized lysophospholipase D-type enzyme, and mouse GDE7 was reported to catalyze the production of cPA in cell-free systems. However, it remains unknown whether this reaction occurs in living cells. In this study, we found that overexpression of human GDE7 in COS-7 cells increased not only cPA-producing activity in the membrane fraction but also cPA levels in living cells. Furthermore, we demonstrated that active site of human GDE7 is directed toward the luminal side of the endoplasmic reticulum membrane. Mutagenesis revealed that amino acid residues F227 and Y238 of human GDE7 play an important role in cPA production. Finally, GDE7-knockout decreased the cPA levels and derepressed mRNA expression of PPARγ target genes in human mammary MCF-7 cells, suggesting that cPA acts as an intracellular lipid mediator. These findings lead to a better understanding of the biological role of GDE7 and cPA in cells.