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

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 [Nistér, M., Heldin, C.‐H., Wasteson, Å. and Westermark, B. (1984) Proc. Nail Acad. Sci. USA 81 , 926‐930]. 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 PDGF‐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.