Loop III region of platelet-derived growth factor (PDGF) B-chain mediates binding to PDGF receptors and heparin.
Site-directed mutagenesis of the platelet-derived growth factor (PDGF) B-chain was conducted to determine the importance of cationic amino acid residues (Arg160-Lys161-Lys162; RKK) located within the loop III region in mediating the biological and cell-association properties of the molecule. Binding to both PDGF alpha-and beta-receptors was inhibited by the conversion of ... all three cationic residues into anionic glutamates (RKK-->EEE), whereas an RKK-->SSS mutant also exhibited a modest loss in affinity for beta-receptors. Replacements with serine at either Arg160 (RKK-->SKK) or at all three positions (RKK-->SSS) had little effect on binding to alpha-receptors. Replacements with either glutamic or serine residues at any of the three positions also resulted in significant inhibition of heparin-binding activity. Furthermore, the RKK-->EEE mutant exhibited decreased association with the cell surface and accumulated in the culture medium as 29-32 kDa forms. Stable transfection of U87 astrocytoma cells with RKK-->EEE mutants of either the A-chain or the B-chain inhibited malignant growth in athymic nude mice. Despite altered receptor-binding activities, each of the loop III mutants retained full mitogenic activity when applied to cultured Swiss 3T3 cells. CD spectrophotometric analysis of the RKK-->EEE mutant revealed a secondary structure indistinguishable from the wild type, with a high degree of beta-sheet structure and random coil content (50% and 43% respectively). These findings indicate an important role of the Arg160-Lys161-Lys162 sequence in mediating the biological and cell-associative activities of the PDGF-BB homodimer, and reveal that the mitogenic activity of PDGF-BB is insufficient to mediate its full oncogenic properties.
Mesh Terms:
Animals, Astrocytoma, Binding Sites, CHO Cells, Cell Division, Cricetinae, Heparin, Humans, Macromolecular Substances, Mutagenesis, Site-Directed, Phosphorylation, Platelet-Derived Growth Factor, Protein Conformation, Proto-Oncogene Proteins, Proto-Oncogene Proteins c-sis, Receptor, Platelet-Derived Growth Factor alpha, Receptor, Platelet-Derived Growth Factor beta, Receptors, Platelet-Derived Growth Factor, Tumor Cells, Cultured
Animals, Astrocytoma, Binding Sites, CHO Cells, Cell Division, Cricetinae, Heparin, Humans, Macromolecular Substances, Mutagenesis, Site-Directed, Phosphorylation, Platelet-Derived Growth Factor, Protein Conformation, Proto-Oncogene Proteins, Proto-Oncogene Proteins c-sis, Receptor, Platelet-Derived Growth Factor alpha, Receptor, Platelet-Derived Growth Factor beta, Receptors, Platelet-Derived Growth Factor, Tumor Cells, Cultured
Biochem. J.
Date: Aug. 01, 1998
PubMed ID: 9677323
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