A human glioma cell line secretes three structurally and functionally different dimeric forms of platelet‐derived growth factor

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Abstract
A human malignant glioma cell line, U-343 MGa Cl 2:6, has previously been shown to secrete platelet-derived-growth-factor(PDGF)-like activity [Nister, M., Heldin, C.-H., Wasteson, A. and Westermark, A. and Westermark, B. (1984) Proc. Natl Acad. Sci. USA 81, 926-93]. We report here that this activity consists of three different molecules separable by reversed-phase chromatography and immobilized-metal-ion affinity chromatography. HPLC reversed-phase chromatography resolved two peaks of activity, which were denoted glioma-derived growth factor-I (GDGF-I) and GDGF-II. GDGF-I was purified to >90% purity; in SDS gel electrophoresis, it appeared as a 31-kDa component which by reduction was converted to 17 kDa. Immunoprecipitation of radiolabeled, reduced and alkylated GDGF-I with antisera made against peptides from the A and B chains of PDGF, gave a specific signal only with antiserum against the A chain. Furthermore, when reduced and alkylated GDGF-I was analyzed by reversed-phase HPLC, it eluted at the position of PDGF A chains. We conclude that GDGF-I is a homodimer of a polypeptide similar to the A chain of PGDF. GDGF-II was found to have higher mitogenic activity than GDGF-I. Analysis by immunoprecipitation with PGDG-chain-specific antisera revealed that GDGF-II contained a polypeptide similar to the B chain of PDGF. Immobilized-metal-ion affinity chromatography revealed that 95% of the mitogenic activity of GDGF-II consisted of a heterodimer of one A and one B chain, whereas 5% consisted of a B-chain homodimer. Thus, U-343 MGa Cl 2:6 cells secrete all three possible dimeric forms of PDGF.