gms | German Medical Science

Introduction: Glioma cell invasion is a complex and multidimensional process involving a large array of molecules and cell-cell and cell-extracellular matrix (ECM) interactions. These processes allow individual tumor cells to invade the adjacent brain tissue even after total surgical resection leading to failure of current therapeutic modalities. Transforming growth factor-ß2 (TGF-ß2) is a multifunctional cytokine that plays a critical role in malignant progression by inducing invasion, proliferation, angiogenesis and immunosupression. However, the effect of TGF-ß2 on invasion has been described in part in gliomas and other model systems, but a conclusive model does not exist so far. This study was designed to investigate the molecular mechanisms underlying the effect of TGF-ß2 in glioma invasion in vitro and to add knowledge to the complex field of ECM interactions during this process.

Methods: Components of the ECM (tenascin-C, fibronectin, vitronectin, collagens, proteoglycans, laminins, nestin, vimentin) that play critical roles in glioma invasion as well as matrix-metalloproteinases (MMPs) and integrins as cell adhesion receptors were evaluated for their regulatory functions in TGF-ß2-mediated glioma invasion. Expression levels were detected by quantitative polymerase chain reaction at mRNA level and with specific immunoblotting methods at protein level. MMP2 activity was determined by gelatin zymography. Attachment, migration and invasion assays were used to analyse the biological effect of TGF-ß2 in glioma cells.

Results: We demonstrate a concentration-dependent induction of Versican, Collagen1 alpha1, MMP2 and integrin ß3 at mRNA and protein levels in response to TGFß2. MMP2 activity was also up-regulated with TGFß2 in a time and dose-dependent fashion. The functional assays showed that attachment and migration can be reduced by treatment with TGF-ß2, especially in low TGFß2-secreting cell lines. This effect seems dependent of MMP2, as blocking of MMP2 by specific antibodies reverses the effects of TGF-ß2.

Conclusion: We conclude that TGFß2 may substantially alter the migratory behaviour of glioma cell lines by induction of components of the ECM or matrix MMPs, for example by induction of MMP2. Individual cell lines behave differently in response to TGFß2. This may be dependent on the functionality of the Smad pathway in these models. We are on our way to elucidate further the exact mechanisms responsible for these interactions and the reasons for the individual behaviour of individual cell lines.