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 poo rly understood ECM-associated features of glioblastomas, such as diffu se brain invasion, rarity of extracranial metastasis and marked ECM pr oduction in vitro. We therefore studied TGF-beta(1) expression in glio blastoma biopsy specimens and cell lines by using reverse transcriptio n-polymerase chain reaction (RT-PCR). The cell lines were also examine d 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 phosph orothioate-oligodcoxynucleotides (APO) designed to specifically inhibi t TGF-beta(1) gene expression. Thereafter, collagen synthesis was dete rmined by isotopic labeling with H-3-proline; integrin expression by f low cytometry; adhesion on collagen types I and IV, laminin and fibron ectin by adhesion assays; and invasion through reconstituted basement membrane by invasion assays. We found that TGF-beta(1) was expressed b y all glioma cell lines at protein and mRNA levels. Pretreatment with TGF-beta(1) increased the amount of collagen synthesis/cell, upregulat ed the alpha(5) integrin chain of U-138MG cells, and facilitated adhes ion on all ECM substrates, while invasion of U-138MG cells, but not th at of U-373MG cells, was markedly reduced. Conversely, pretreatment wi th APO reduced TGF-beta(1) protein expression levels, inhibited adhesi on and increased invasion of U-138MG cells, but did not affect collage n synthesis. We conclude that exogenously applied TGF-beta(1) exerts m arked effects on ECM-related features of glioma cells. The secretion o f endogenous TGF-beta(1) by glioma cells is functionally involved in a dhesion and invasion and may contribute to the low metastatic behavior of gliomas. Upregulation of the alpha(5) integrin chain appears to pl ay a central role in mediating some TGF-beta(1) effects on glioma cell s.