Inhibition by 5′-methylthioadenosine of cell growth and tyrosine kinase activity stimulated by fibroblast growth factor receptor in human gliomas

✓ Stimulation of three human glioma cell lines with basic fibroblast growth factor (bFGF) led to the enhancement of cell growth and the rapid tyrosine phosphorylation of cellular proteins, including major substrates of 90 kD. A methyltransferase inhibitor, 5′-methylthioadenosine (MTA), inhibited dose dependently the bFGF-stimulated cell growth and protein tyrosine phosphorylation in glioma cells by blocking both receptor autophosphorylation and substrate phosphorylation, as shown by immunoblotting with antiphosphotyrosine antibodies and cross-linking bFGF to receptors. The antiproliferative activity of MTA correlated quantitatively with its potency as an inhibitor of bFGF-stimulated protein tyrosine kinase activity. The methyltransferase inhibitor MTA had no effect on either epidermal growth factor— or platelet-derived growth factor—stimulated protein tyrosine phosphorylation in glioma cells, but inhibited specifically bFGF-stimulated protein tyrosine kinase activity. The concentration of MTA required for...