ABSTRACT
Versican is a large chondroitin sulphate proteoglycan produced by several tumour cell types, including high-grade glioma. The increased expression of certain versican isoforms in the extracellular matrix (ECM) plays a role in tumour cell growth, adhesion and migration. Transforming growth factor-beta2 (TGF-beta2) is an important modulator of glioma invasion, partially by remodeling the ECM. However, it is unknown whether it interacts with versican during malignant progression of glioma cells. Here, we analysed the effect of TGF-beta2 on the expression of versican isoforms. The expression of versican V0/V1 was upregulated by TGF-beta2 detected by quantitative polymerase chain reaction and immunoprecipitation, whereas V2 was not induced. Using time-lapse scratch and spheroid migration assays, we observed that the glioma migration rate is significantly increased by exogenous TGF-beta2 and inhibited by TGF-beta2-specific antisense oligonucleotides. Interestingly, an antibody specific for the DPEAAE region of glycosaminoglycan-beta domain of versican was able to reverse the effect of TGF-beta2 on glioma migration in a dose-dependent manner. Taken together, we report here that TGF-beta2 triggers the malignant phenotype of high-grade gliomas by induction of migration, and that this effect is, at least in part, mediated by versican V0/V1.
Subject(s)
Cell Movement/drug effects , Glioma/pathology , Transforming Growth Factor beta2/pharmacology , Versicans/physiology , Disease Progression , Gene Expression Profiling , Gene Expression Regulation, Neoplastic/drug effects , Humans , Neoplasm Invasiveness , Protein Isoforms/physiology , Transforming Growth Factor beta2/genetics , Tumor Cells, Cultured , Versicans/geneticsABSTRACT
The transforming growth factor-beta (TGF-beta) plays a pivotal role in the pathobiology of human gliomas: during carcinogenesis, it turns from a tumor suppressor to a tumor promoter. The traditional Smad pathway and the more recently discovered MAPK pathway are the most important pathways for TGF-beta related intracellular signal transduction mediating differential pathobiological effects. In this study, we investigated the effects of TGF-beta2 and the TGF-beta2 antisense phosphorothioate oligodeoxynucleotide (PTO) AS-11 on the functionality of both the Smad and MAPK pathways in high-grade gliomas. We aimed to correlate the imbalance between the pathways with differences in the behaviour of high-grade glioma cells. Gene and protein expression studies were used to detect levels of members of the Smad and MAPK pathways under regulation of TGF-beta2 and AS-11. Proliferation and migration assays were functional readouts for effects caused by these regulating tools. Gene arrays were used to detect yet unknown regulators of these functional effects. The Smad pathway was functional in the tested cell lines. Exogenous TGF-beta2 inhibited proliferation but enhanced migration. Smad 2 mRNA expression and activation were significantly reduced by incubation with AS-11. K-ras was reduced both in gene arrays and quPCR under treatment with AS-11, but there was no influence of K-ras down-regulation on the activity of ERK. Ubiquitination-related genes also were specifically down-regulated with AS-11. Our results indicate the involvement of K-ras in TGF-beta signaling in high-grade gliomas. ERK, which is a member of the MAPK pathway, was not influenced and seems to be activated through RAS independent cascades in glioma. These results suggest that combined antagonization of the TGF-beta and MAPK pathways might be a promising approach for glioma therapy. An imbalance between these two pathways might be responsible for TGF-beta switching to a tumor promoter protein in high-grade gliomas.
