Glioma-derived PDGF-related protein presents as 17 kd intracellularly and assembled form induces actin reorganization

Abstract

We have electrophoretically obtained platelet-derived growth factor (PDGF)-related protein from human glioma (glioma derived PDGF-related protein: GD-PDGF) and produced rabbit antiserum against the monomer of GD-PDGF. By methods of immunoaffinity chromatography and Western blotting, we analyzed GD-PDGF in cultured human glioma cells and conditioned medium. The intracellular GD-PDGF was only detected at 17 kd molecular weight by the purified rabbit antibody. When the intracellular 17 kd monomer was purified by the IgG-coupled immunoaffinity chromatography, the eluted protein was not detected at 17 kd but at 52 kd. The 52 kd GD-PDGF was spontaneously and immediately converted to 56 kd, which was partly degraded to 32 and 35 kd within 24 hours. On the other hand, in the conditioned media of glioma cell lines GD-PDGF presents mainly as 56 kd. The assembled forms of GD-PDGF exhibited a powerful activity to induce membrane ruffle formation and reorganization of actin filaments in cultured glial cells and glioma cells. These results indicated that GD-PDGF is intracellularly stored as 17 kd monomer and exists extracellularly as assembled forms, which may act as an autocrine and paracrine effect on the surrounding cells.