We have studied the effects of the bioactive
phospholipid lysophosphatidic acid (LPA) on cell lines derived from highly invasive human
glioblastoma multiforme (GBM). Using transwell migration assays, we show that LPA stimulates both chemokinetic and chemotactic migration of
glioma cells. Blood brain barrier breakdown and leakage of serum components that most likely include LPA are common features of GBM. Therefore, the effects of LPA on
glioma cell motility are intriguing given the fact that, in vivo, GBM cells often migrate great distances from the main
tumor, rendering successful therapy extremely difficult. We show here that LPA initiates a variety of signaling cascades in
glioma cells. LPA-enhanced transwell migration was sensitive to
pertussis toxin (PTX) treatment suggesting an important role for G(i) subtype of
G proteins. LPA also stimulated Ca(2+) fluctuations and activation of
extracellular signal-regulated kinases (ERKS) 1 and 2, although blocking either pathway had little effect on
glioma cell migration. Exposure of
glioma cells to LPA resulted in phosphorylation of the regulatory light chain (RLC) of
myosin II and the formation of stress fibers and focal adhesions. These effects were blocked by
Y-27632, an inhibitor of Rho-activated ROCK
kinases. Time-lapse video microscopy revealed that Y-27632-treatment caused cells to assume long thin morphologies that suggested deficiencies in the contractile apparatus. Furthermore, many cells exhibited a conspicuous extension of processes when Rho/ROCK
kinase cascades were inhibited. The above results suggest that LPA/Rho signaling cascades play important roles in
glioma cell motility and that exposure of
tumor cells to LPA in vivo may contribute to their invasive phenotype.