The colony-stimulating factors and molecular transport

Glucose is fundamental to the metabolism and survival of mammalian cells, and its passage across cell membranes is mediated by a family of transport proteins (glucose transporters) located at the cell membrane. We studied the regulation of glucose transport by granulocyte-macrophage colony-stimulating factor (GM-CSF), a hemopoietin that functions in regulating the proliferation, differentiation, maturation and survival of cells of the host defense system. The receptor for GM-CSF is composed of an alpha and beta subunit, and the alpha-beta complex binds GM-CSF with high affinity whereas the isolated alpha subunit binds GM-CSF with low affinity. Using Xenopus laevis oocytes expressing the human GM-CSF receptor alpha subunit, we provided direct evidence indicating that the isolated alpha subunit signals for increased glucose uptake in a phosphorylation-independent manner. We extended these studies to human neutrophils and HL-60 cells and found that signaling for hexose uptake also occurs in a phosphorylation-independent manner in cells expressing the high-affinity GM-CSF receptor. Since the glucose transporters are multifunctional transport proteins, the findings regarding GM-CSF regulation of cellular glucose uptake may have wide import relative to CSF regulation of molecular transport in target cells.