The biology of GM-CSF: regulation of production and interaction with its receptor.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a small glycoprotein growth factor which stimulates the production and function of neutrophils, eosinophils and monocytes. GM-CSF can be produced by a wide variety of tissue types, including fibroblasts, endothelial cells, T cells, macrophages, mesothelial cells, epithelial cells and many types of tumor cells. In most of these tissues, inflammatory mediators, such as interleukin 1, interleukin 6, tumor necrosis factor or endotoxin, are potent inducers of GM-CSF gene expression, which occurs at least partly by post-transcriptional stabilization of the GM-CSF mRNA. The biological effects of GM-CSF are mediated through binding to cell surface receptors, which appear to be widely expressed by hematopoietic cells and also by some non-hematopoietic cells, such as endothelial cells. Receptor expression is characterized by low number (20-200/cell) and high affinity (Kd = 20-100 pM). At least two different functional classes of GM-CSF receptor have been identified. The neutrophil GM-CSF receptor exclusively binds GM-CSF, while interleukin 3 competes for binding of GM-CSF to a second class of receptors detected on some leukemic cell lines, such as KG1 and MO-7E. Signal transduction involves activation of a tyrosine kinase and possibly G protein-coupled stimulation of Na+/H+ exchange. The exact relationship of the two receptors needs further clarification.