Partial characterization of glioma-derived growth factor 2: A novel mitogenic activity from human cell line D-54 MG

Summary We have shown that several human malignant glioma cell lines are stimulated by bacterial lipopolysaccharide (E. coli 0111B4, 1 g/ml) to produce a high molecular weight (> 200 kD) growth activity for BALB 3T3, clone A31 cells 1, 2]. This glioma-derived growth factor (GDGF-2) acts like a competence factor. Malignant glioma cell line D-54 MG constitutively produced GDGF-2, which we have partially characterized from serumfree conditioned culture medium. GDGF-2 is resistant to heat (100° C, 5 min), acidic (pH 2, 2 hr) or reducing (0.5 M 2 ME, 30 min) conditions as well as exposure to RNases; however, it is sensitive to > 4 freeze-thaw cycles, alkaline (pH 11, 2 hr) conditions or pre-treatment with proteolytic enzymes. GDGF-2 had a pl of 6.8 determined by preparative isoelectric focusing, bound to DEAE, with elution at 35 and 185 mM NaCl and at 43% acetonitrile from a C4 reversed phase column. GDGF-2 activity was not neutralized by antibodies to TGF, TGF, PDGF, VEGF or TNF indicating that it is not immunochemically related to these growth factors. However GDGF-2 co-chromatographed on Superose 12 HPLC (250 × 9 mm; 5% isopropanol, 6 mM CHAPS in PBS) with a substance that suppressed growth of mink lung epithelial cells (Mv1Lu), but not BALB 3T3 cells, and could be neutralized by anti-TGF antibodies. GDGF-2 activity eluted from heparin columns in 0.6 M NaCl; thus, it is not a heparin binding growth factor. D-54 MG cell line produced alpha₂-macroglobulin (₂M), which is known to bind TGF; however, immunoprecipitation of ₂M did not deplete TGF or GDGF-2 activity. Further, neither GDGF-2 or TGF can be dissociated into lower molecular weight active components by chromatography in high salt (2 M NaCl) or 2-ME (0.5 M). GDGF-2 may be a novel autocrine or paracrine mitogen, stimulating mitotic division or interfering with normal cell growth regulation.