LPA₁ receptors mediate stimulation, whereas LPA₂ receptors mediate inhibition, of migration of pancreatic cancer cells in response to lysophosphatidic acid and malignant ascites

Malignant ascites from pancreatic cancer patients has been reported to stimulate migration of pancreatic cancer cells through lysophosphatidic acid (LPA) and LPA₁ receptors. Indeed, ascites- and LPA-induced migration was inhibited by Ki16425, an LPA₁ and LPA₃ antagonist, in Panc-1 cells. Unexpectedly, however, in the presence of Ki16425, ascites and LPA inhibited cell migration in response to epidermal growth factor (EGF). The inhibitory migratory response to ascites and LPA was also observed in the cells treated with pertussis toxin (PTX), a G_i protein inhibitor, and attenuated by a small interfering RNA (siRNA) specific to the LPA₂ receptor. The inhibitory LPA action was reversed by the regulators of G-protein signaling domain of p115RhoGEF, dominant-negative RhoA or C3 toxin. Indeed, LPA activated RhoA, which was attenuated by the siRNA against the LPA₂ receptor. Moreover, LP-105, an LPA₂ agonist, also inhibited EGF-induced migration in the PTX-treated cells. A similar inhibitory migration response through LPA₂ receptors was also observed in YAPC-PD, BxPC-3, CFPAC-1 and PK-1 pancreatic cancer cell lines. LPA also inhibited the invasion of Panc-1 cells in the PTX-treated cells in the in vitro Matrigel invasion assay. We conclude that LPA₂ receptors are coupled to the G_12/13 protein/Rho-signaling pathway, leading to the inhibition of EGF-induced migration and invasion of pancreatic cancer cells.