Characterization of cell-surface glycopeptides from mouse cerebral cortex that inhibit cell growth and protein synthesis

Abstract

Glycopeptides were isolated from the cell surfaces of mouse brain cortical tissue that inhibited both cell division and protein synthesis by cells in culture. The protein-synthesis inhibition appeared to affect most cells exposed and was equally effective against glycoprotein and protein synthesis. The inhibition of protein metabolism was independent of mRNA synthesis and uptake of labelled precursors into intracellular pools, indicating that it was directed at intracellular translational events. Fractionation of chloroform/methanol-extracted preparations of this brain cell-surface substance on Bio-Gel P-100 revealed the material to be quite heterogenous, although inhibitory activity was found only in fractions of mol.wt. 25000—30000 and 6000—10000. Biochemical analysis of these fractions demonstrated that they were 6% carbohydrate and 94% amino acid by weight. The 25000—30000-mol.wt. glycopeptides were shown to inhibit cell growth at concentrations of 2 microgram/ml in cultured cells and to inhibit protein synthesis by 50% at concentrations of 3 microgram/ml. The 25000—30000-mol.wt. brain-cell-surface-substance glycopeptides were further purified by ultrafiltration and affinity chromatography with Ulex europaeus agglutinin, resulting in a 400-fold increase in specific biological activity. The inhibitor was not lethal to cells and was not species- or tissue-specific.