Hyaluronic acid induces osteopontin via the phosphatidylinositol 3-kinase/Akt pathway to enhance the motility of human glioma cells

Abstract

Hyaluronic acid (HA) binds to cell-surface receptors such as CD44, and seems to be involved in cell adhesion, motility, and tumor progression in brain. To identify gene expression changes that are initiated by HA, we explored human cytokine arrays in U87MG glioma cells and identified osteopontin, a secreted matrix protein, as a transcriptional target of RA. Interestingly, expression of osteopontin was induced by HA in glioma cells lacking functional PTEN, a tumor suppressor gene (U87MG, U251MG, and U373MG), but not in wild-type (wt)-PTEN-harboring cells (LN18 and LN428). To confirm the role of PTEN, adenoviral (Ad)-wt-PTEN was used to induce ectopic expression of wt-PTEN in U87MG cells, leading to reduced RA-mediated osteopontin induction. Reciprocally, transfection with dominant-negative Akt repressed HA-induced osteopontin expression. Furthermore, HA promoted the motility of glioma cells, and down-regulation of induced osteopontin activity via a neutralizing anti-osteopontin antibody repressed RA-induced motility in vitro. Together, these results strongly suggest that induction of osteopontin expression by RA is dependent on activation of the phosphatidylinositol 3-kinase/Akt pathway. Furthermore, our data indicate that PTEN can effectively modulate the expression of osteopontin, and UA-induced osteopontin plays an important role in the motility response induced by HA in human glioma cells.