Phosphatidic acid (PA),
lysophosphatidic acid (LPA), and
sphingosine 1-phosphate (SPP) are naturally occurring
phospholipids which induce a variety of effects as extracellular messengers. In this study, we compared the effects of these
phospholipid signaling molecules on the migration of invasive and noninvasive
breast cancer cell lines, an index of the metastatic potential of these cells. As previously demonstrated, invasive MDA-MB-231
breast cancer cells exhibited increased constitutive (nonstimulated) migration in comparison to poorly invasive MCF-7 cells.
Phosphatidic acid employed at nanomolar concentrations markedly potentiated migration of the invasive cells but had no effect on migration of either the noninvasive MCF-7 cells or nonneoplastic human epithelial cells.
Lysophosphatidic acid and
sphingosine 1-phosphate inhibited both the directed (chemotactic) and random (chemokinetic) migration of MDA-MB-231 cells. Experiments were undertaken to characterize the signaling pathway involved in constitutive and PA-stimulated migration of MDA-MB-231 cells. The
tyrosine kinase inhibitors staurosporine and
genistein inhibited constitutive and PA-induced migration in a dose-dependent manner, consistent with a role for
tyrosine phosphorylation in the migratory response. In addition, the
phosphatidylinositol (
PI) 3' kinase inhibitors
wortmannin and
LY294002 strongly inhibited both the constitutive and PA-stimulated migration of the invasive
breast cancer cells, indicating that PI-3'
kinase plays an important role in the metastatic migration of
breast cancer cells. Finally, PA-induced migration of MDA-MB-231 was markedly attenuated by pretreatment of cells with
Clostridium difficile Toxin B,
pertussis toxin and
suramin, implying a role for a Gi receptor-dependent process involving activation of the small
GTP-binding protein Rho. Since an enhanced ability to migrate heightens the metastatic potential of cells within solid
tumors, our results suggest that the metastatic capabilities of
breast cancer cells may be enhanced by a receptor-driven cellular process initiated by
phosphatidic acid or related
lipid phosphate messengers.