Small GTP-binding protein, Rho, both increased and decreased cellular motility, activation of matrix metalloproteinase 2 and invasion of human osteosarcoma cells

Rho, a member of the small GTP-binding proteins, and one of its downstream effectors ROCK (Rho-associated coiled-coil forming protein kinase) play an important role in the invasion of tumor cells. Lysophosphatidic acid (LPA) activates Rho and ROCK and promotes the organization of stress fibers and focal adhesions. However, the effect of LPA on tumor cell invasion is still controversial. In the present study, human osteosarcoma cells treated with a high concentration of LPA (high LPA) showed considerable formation of stress fibers and focal adhesions compared to the cells treated with a low concentration of LPA (low LPA). C3 (inhibitor of Rho) or Y27632 (an inhibitor of ROCK) inhibited the effects of LPA, indicating that LPA activates the Rho-ROCK pathway in the cells. In addition, Rho activation assay showed that the activation level of Rho can be altered by changing the concentration of LPA. Low LPA stimulated the motility and invasion of the cells, while high LPA reduced both. The disruption of extracellular matrix (ECM) by matrix metalloproteinase 2 (MMP2) is also critical for tumor cell invasion. MMP2 is activated by membranous type-1 MMP (MT1-MMP) and type-2 tissue inhibitor of MMP (TIMP2). High LPA suppressed the activation of MMP2 through down-regulation of MT1-MMP and TIMP2. C3 and Y27632 reversed the suppression of the activation of MMP2 and expression of MT1-MMP and TIMP2, suggesting the involvement of the Rho-ROCK pathway in ECM degradation. Tyrosine phosphorylation of focal adhesion kinase (FAK) was also required for the invasion of tumor cells to occur. Low LPA enhanced the tyrosine phosphorylation of FAK whereas high LPA reduced it. In conclusion, we suggest that Rho has a dual effect on the invasion of osteosarcoma cells by modulating the motility, the ability to degrade ECM and tyrosine phosphorylation of FAK.