EFFECTS OF TRANSFORMING GROWTH FACTOR-BETA(1) ON COLLAGEN-SYNTHESIS, INTEGRIN EXPRESSION, ADHESION AND INVASION OF GLIOMA-CELLS

Transforming growth factor-beta(1) (TGF-beta(1)) as a potent modulator of cell-extracellular matrix (ECM) interactions may be related to poorly understood ECM-associated features of glioblastomas, such as diffuse brain invasion, rarity of extracranial metastasis and marked ECM production in vitro. We therefore studied TGF-beta(1) 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-beta(1), glioma cell lines U-138MG and U-373MG were incubated for 48 hours with TGF-beta(1) (0.1, 1, 10 ng/ml) or with antisense phosphorothioate-oligodcoxynucleotides (APO) designed to specifically inhibit TGF-beta(1) gene expression. Thereafter, collagen synthesis was determined by isotopic labeling with H-3-proline; integrin expression by flow cytometry; adhesion on collagen types I and IV, laminin and fibronectin by adhesion assays; and invasion through reconstituted basement membrane by invasion assays. We found that TGF-beta(1) was expressed by all glioma cell lines at protein and mRNA levels. Pretreatment with TGF-beta(1) increased the amount of collagen synthesis/cell, upregulated the alpha(5) integrin chain of U-138MG cells, and facilitated adhesion on all ECM substrates, while invasion of U-138MG cells, but not that of U-373MG cells, was markedly reduced. Conversely, pretreatment with APO reduced TGF-beta(1) protein expression levels, inhibited adhesion and increased invasion of U-138MG cells, but did not affect collagen synthesis. We conclude that exogenously applied TGF-beta(1) exerts marked effects on ECM-related features of glioma cells. The secretion of endogenous TGF-beta(1) by glioma cells is functionally involved in adhesion and invasion and may contribute to the low metastatic behavior of gliomas. Upregulation of the alpha(5) integrin chain appears to play a central role in mediating some TGF-beta(1) effects on glioma cells.