Effects of Transforming Growth Factor-β1 on Collagen Synthesis, Integrin Expression, Adhesion an Invasion of Glioma Cells

ABSTRACTTransforming growth factor-β1 (TGF-β1) as a potent modulator of cell-extracellular matrix (ECM) interactions may be related to poorly understood ECM-associated features of glioblasomas, such as diffuse brain invasion, rarity of extracranial metastasis and marked ECM production in vitro. We therefore studied TGF-β1 expression in glioblastoma biopsy specimens and cell lines by using reverse transcription-polymerase chain reaction (RT-PCR). The cell lines were also examined by Western blotting and immunocytochemistry. To determine effects of TGF-β1, glioma cell lines U-138MG and U-373MG were incubated for 48 hours with TGF-β1 (0.1, 1, 10 ng/ml) or with antisense phosphorathioate-oligodeoxynucleotides (APO) designed to specifically inhibit TGF-β1 gene expression. Thereafter, collagen synthesis was determined by isotopic labeling with H-proline; integrin expression by flow cytometry; adhesion on collagen types I and IV, laminins and fibronectin by adhesion assays; and invasion through reconstituted basement mambrane by invasion assays. We found that TGF-β1 was expressed by all glioma cell lines at protein and mRNA levels. Pretreatment with TGF-β1 increased the amount of collagen synthesis/cell, upregulated the α5 integrin chain of U-138MG cells, and facilitated adhesion on all ECM substracts, while invasion of U-138MG cells, but not that of U-138MG cells, was markedly reduced. Conversely, pretreatment with APO reduced TGF-β1 protein expression levels, inhinited adhesion and increased invasion of U-138MG cells, but did not affect collagen synthesis. We conclude that exogenously applied TGF-β1 exerts marked effects on ECM-related features of glioma cells. The secretion of endogenous TGF-β1 by glioma cells is functionally involved in adhesion and invasion and may contribute to the low metastatic behavior of gliomas. Upregulation of the α5 integrin chain appears to play a central role in mediating some TGF-β1 effects on glioma cells.