Human Glioblastoma Cells Produce Granulocyte-macrophage Colony-stimulating Factor In Vitro, but Not In Vivo, Without Expressing Its Receptor

Abstract

Granulocyte-macrophage colony-stimulating factor (GM-CSF) production and receptor expression by human glioblastomas was studied. Enzyme-linked immunosorbent assay showed four of 10 glioblastoma cell lines spontaneously released GM-CSF (2.9-9.2 pg GM-CSF protein/ml culture medium), which was enhanced by stimulation with tumor necrosis factor-α (TNF) (10 U/ml) up to 410 pg/ ml. TNF also induced secretion of GM-CSF by another cell line. Northern blot analysis identified increasing GM-CSF gene expression by cells following TNF stimulation. However, no GM-CSF protein was detectable in the cerebrospinal fluid of three malignant glioma patients. Intratumoral administration of TNF in the patients also failed to stimulate GM-CSF levels in the cerebrospinal fluid. A binding assay using flow cytometry with biotinylated GM-CSF and Scatchard analysis using ¹²⁵I-labeled GM-CSF failed to demonstrate GM-CSF receptor expression on the 13 cell lines. Exogenous GM-CSF stimulation had no effect on production of prostaglandin E₂, interleukin-6, or interleukin-8 by glioma cells. Human glioblastoma cells secrete GM-CSF without expressing the receptor in vitro, but there was no evidence of GM-CSF production in vivo.