CHARACTERIZATION OF A RECEPTOR SUBTYPE-SELECTIVE LYSOPHOSPHATIDIC ACID MIMETIC

Despite an intriguing cell biology and the suggestion of a role in pat hophysiological responses, the mechanism of action of such lipid phosp horic acid mediators as lysophosphatidic acid (LPA) remains obscure, i n part because of an underdeveloped medicinal chemistry. We report now the agonist activity of a synthetic phospholipid in which the glycero l backbone of LPA is replaced by L-serine. Like LPA, the L-serine-base d lipid mobilizes calcium and inhibits activation of adenylyl cyclase in the human breast cancer cell line MDA MB231. Treatment with LPA des ensitizes MDA MB231 cells to subsequent application of the L-serine co mpound; when the order of application is reversed, however, the L-seri ne compound does not prevent calcium mobilization by LPA, which might indicate the existence of two LPA receptors in these cells. The analog ous D-serine-based phospholipid was distinctly less potent than the L- isomer in those assays; this finding demonstrates stereoselectivity by an LPA receptor. Unlike LPA, the L-serine-based lipid does not evoke a chloride conductance in Xenopus laevis oocytes, but injection of pol y(A)+ RNA from HEK 293 cells confers this phenotype on the oocyte. The latter result has practical importance in that it allows use of the f rog oocyte for expression cloning of an LPA receptor DNA, an assay sys tem made problematic by the oocyte's strong endogenous response to LPA .