ABSTRACT
Nontransformed cells depend on growth factors for their survival, proliferation, and differentiation. In addition to polypeptide growth factors, an emerging group of naturally occurring phospholipid growth factors (PLGFs) has been discovered. Lysophosphatidic acid (1-acyl-2-lyso-sn-glycero-3-phosphate, LPA), cyclic-phosphatidic acid (cyclic-PA), plasmalogen-glycerophosphate (alkenyl-GP), phosphatidic acid (PA), lysophosphatidylserine (LPS), sphin-gosine-1-phosphate (SPP), and sphingosylphosphorylcholine (lysosphingomyelin, SPC) are all naturally occurring lipid mediators with growth factor-like actions. The ultraviolet (UV) absorption coefficient of simple phospholipids is low, which is complicated in the far-UV range by the high absorption of organic solvents often used in HPLC. Assaying the functional expression of the stable transfectants is done by monitoring the PLGF-mediated activation of the signal transduction pathways. Measuring changes in second messenger levels and/or the activation of downstream targets can help determine the specific coupling between PLGFRs and the different heterotrimeric G proteins.
