A549 cells as a model to study endogenous LPA receptor signaling and regulation.

Lysophosphatidic acid (LPA) modulates the function of many organs, including the lung. A549 is a lung carcinoma-derived cell line, frequently used as a model for type II pneumocytes. Here we show that these cells expressed messenger RNA coding for LPA receptors with the following order of abundance: LPA > LPA > LPA and that LPA was able to increase intracellular calcium, extracellular signal-regulated kinases 1/2 phosphorylation, and cell contraction. These effects were blocked by Ki16425, an antagonist selective for LPA and LPA receptors, and by the LPA-selective antagonist, AM095. Activation of protein kinase C inhibited LPA-induced intracellular calcium increase. This action was blocked by protein kinase C inhibitors and enzyme down-regulation. Phorbol myristate acetate and AM095, but not Ki16425, decreased the baseline intracellular calcium concentration. Ki16425 blocked the effect of AM095 but not that of phorbol myristate acetate. The data indicate that LPA receptors exhibit constitutive activity and that AM095 behaves as an inverse agonist, whereas Ki16425 appears to be a classic antagonist. Furthermore, the LPA agonist, 1-oleoyl-2-O-methyl-rac-glycerophosphothionate, OMPT, induced a weak increase in intracellular calcium, but was able to induce full ERK 1/2 phosphorylation and cell contraction. These effects were blocked by AM095. These data suggest that OMPT is a biased LPA agonist. A549 cells express functional LPA receptors and seem to be a suitable model to study their signaling and regulation.