COLONY-STIMULATING FACTORS SIGNAL FOR INCREASED TRANSPORT OF VITAMIN-C IN HUMAN HOST-DEFENSE CELLS

Although serum concentrations of ascorbic acid seldom exceed 150 mu mo l/L, mature neutrophils and mononuclear phagocytes accumulate millimol ar concentrations of vitamin C. Relatively little is known about the m echanisms regulating this process. The colony-stimulating factors (CSF s), which are central modulators of the production, maturation, and fu nction of human granulocytes and mononuclear phagocytes, are known to stimulate increased glucose uptake in target cells. We show here that vitamin C uptake in neutrophils, monocytes, and a neutrophilic HL-60 c ell line is enhanced by the CSFs. Hexose uptake studies and competitio n analyses showed that dehydroascorbic acid is taken up by these cells through facilitative glucose transporters. Human monocytes were found to have a greater capacity to take up dehydroascorbic acid than neutr ophils, related to more facilitative glucose transporters on the monoc yte cell membrane. Ascorbic acid was not transported by these myeloid cells, indicating that they do not express a sodium-ascorbate cotransp orter. Granulocyte (G)- and granulocyte-macrophage colony-stimulating factor (GM-CSF) stimulated increased uptake of vitamin C in human neut rophils, monocytes, and HL-60 neutrophils. In HL-60 neutrophils, GM-CS F increased both the transport of dehydroascorbic acid and the intrace llular accumulation of ascorbic acid. The increase in transport was re lated to a decrease in Km for transport of dehydroascorbic acid withou t a change in Vmax, Increased ascorbic acid accumulation was a seconda ry effect of increased transport. Triggering the neutrophils with the peptide fMetLeuPhe led to enhanced vitamin C uptake by increasing the oxidation of ascorbic acid to the transportable moiety dehydroascorbic acid, and this effect was increased by priming the cells with GM-CSF. Thus, the CSFs act at least at two distinct functional loci to increa se cellular vitamin C uptake: conversion of ascorbic acid to dehydroas corbic acid by enhanced oxidation in the pericellular milieu and incre ased transport of DHA through the facilitative glucose transporters at the cell membrane, These results link the regulated uptake of vitamin C in human host defense cells to the action of CSFs. (C) 1998 by The American Society of Hematology.