Ras‐dependent and ‐independent regulation of reactive oxygen species by mitogenic growth factors and TGF‐β1

Abstract

Mitogenic growth factors and transforming growth factor beta1 (TGF-beta1) induce the generation of reactive oxygen species (ROS) in nonphagocytic cells, but their enzymatic source(s) and regulatory mechanisms are largely unknown. We previously reported on the ability of TGF-beta1 to activate a cell surface-associated NADH:flavin:O(2) oxidoreductase (NADH oxidase) that generates extracellular H(2)O(2). In this study, we compared the ROS-generating enzymatic systems activated by mitogenic growth factors and TGF-beta1 with respect to the primary reactive species produced (O(2)(.-) vs. H(2)O(2)), the site of generation (intracellular vs. extracellular) and regulation by Ras. We find that the mitogenic growth factors PDGF-BB, FGF-2, and TGF-alpha (an EGF receptor ligand) are able to rapidly (within 5 min) induce the generation of intracellular O(2)(.-) without detectable NADH oxidase activity or extracellular H(2)O(2) release. In contrast, TGF-beta1 does not stimulate intracellular O(2)(.-) production and the delayed induction of extracellular H(2)O(2) release is not associated with O(2)(.-) production. Expression of dominant-negative Ras (N17Ras) protein by herpes simplex virus-mediated gene transfer blocks mitogen-stimulated intracellular O(2)(.-) generation but has no effect on TGF-beta1-induced NADH oxidase activation/H(2)O(2) production. These results demonstrate that there are at least two distinctly different ROS-generating enzymatic systems in lung fibroblasts regulated by mitogenic growth factors and TGF-beta1 via Ras-dependent and -independent mechanisms, respectively. In addition, these findings suggest that endogenous production of ROS by growth factors/cytokines may have different biological effects depending on the primary reactive species generated and site of production.