Abstract

Reactive oxygen species (ROS) have been shown to stimulate proliferation and growth responses in a variety of mammalian cell types and to act as important mediators in many cellular processes, including hematolymphopoiesis. We examined the effect on primitive murine hematopoietic progenitor cells (HPC) of ROS generated by xanthine plus xanthine oxidase (xanthine/XO) and various antioxidants. Pretreatment of murine HPC (C57BL/6) with xanthine/XO produced a dose-dependent enhancement of clonogenic response to granulocyte/macrophage colony-stimulating factor (GM-CSF) but not to interleukin-3 or granulocyte colony-stimulating factor. Stem cell factor (SCF), a potent comitogen for many hematopoietic growth factors, also synergized with GM-CSF. However, the synergistic enhancement of GM-CSF with xanthine/XO and SCF was not additive, indicating that xanthine/XO and SCF may target the same subpopulation of HPC. Support for this conclusion came from experiments demonstrating that 1) mutant mice strains constitutively lacking a SCF-responsive population of HPC [White spotted (W/WV) and Steel (SI/SId)] are unresponsive to xanthine/XO- and SCF-induced enhancement of GM-CSF and 2) 3,4-epoxybutene, which selectively abrogates SCF synergy with GM-CSF, inhibits xanthine/XO-induced enhancement. As xanthine/XO can mimic SCF in this population of HPC, the possibility exists that ROS also play a role in normal SCF-mediated proliferation of these cells. To test this hypothesis, we used the antioxidants N-tert-butyl-alpha-phenylnitrone, exogenous superoxide dismutase, and catalase. Both N-tert-butyl-alpha-phenylnitrone and superoxide dismutase effectively inhibited SCF and xanthine/XO synergism with GM-CSF, whereas catalase had no effect, indicating that the superoxide anion may be involved. Also, none of these compounds affected SCF synergism with other hematopoietic growth factors, such as interleukin-3 or granulocyte colony-stimulating factor, suggesting a population-specific phenomenon. These findings indicate that xanthine/XO mimics SCF in stimulating a subpopulation of murine HPC to proliferate and that SCF synergy with GM-CSF in this population is sensitive to antioxidant inhibition.