IDENTIFICATION OF A NOVEL GROWTH FACTOR-LIKE LIPID, 1-O-CIS-ALK-1'-ENYL-2-LYSO-SN-GLYCERO-3-PHOSPHATE (ALKENYL-GP) THAT IS PRESENT IN COMMERCIAL SPHINGOLIPID PREPARATIONS

Lysophosphatidic acid, a member of the acidic phospholipid autacoid (A PA) family of lipid mediators, elicits diverse cellular effects that r ange from mitogenesis to the prevention of programmed cell death. Sphi ngosine 1-phosphate and sphingosylphosphorylcholine have also been pro posed to be ligands of the APA receptors, However, key observations th at provide the foundation of this hypothesis have not been universally reproducible, leading to a controversy in the field. We provide evide nce that 1-O-cis-alk-1'-enyl-2-lyso-sn-glycero-3-phosphate (alkenyl-GP ) is present in some commercial sphingolipid preparations and is respo nsible for many of their APA-like effects, which were previously attri buted to sphingosylphosphorylcholine. Alkenyl-GP was generated by acid ic and basic methanolysis from ethanolamine lysoplasmalogen, which was present in the sphingomyelin fraction that is used to manufacture sph ingosylphosphorylcholine. We present the structural identification of alkenyl-GP, using H-1 and C-13 NMR, Fourier transform infrared spectro metry, and mass spectrometry. Alkenyl-GP was a potent activator of the mitogen-activated protein kinases ERK1/2 and elicited a mitogenic res ponse in Swiss 3T3 fibroblasts. In contrast, sphingosylphosphorylcholi ne at a concentration of 10 mu M was only a weak mitogen and only weak ly activated the extracellular signal-regulated protein kinases, Alken yl-GP has recently been detected as an injury-induced component in the anterior chamber of the eye (Liliom, K., Guan, Z., Tseng, H., Desider io, D. M., Tigyi, G., and Watsky, M. (1998) Am. J, Physiol. 274, C1065 -C1074), indicating that this lipid is a naturally occurring member of the APA mediator family.