REGULATION OF REACTIVE-OXYGEN-SPECIES GENERATION IN FIBROBLASTS BY RAC1

In a variety of non-phagocytic cell types, there is a marked increase in intracellular levels of reactive oxygen species (ROS), including su peroxide and H2O2, after ligand stimulation. We demonstrate that in NI H 3T3 cells transient expression of constitutively activated forms of the small GTP-binding proteins Ras or Rac1 leads to a significant incr ease in intracellular ROS. An increase in intracellular ROS is also de monstrated after growth factor [platelet-derived growth factor (PDGF) or epidermal growth factor (EGF)] or cytokine [tumour necrosis factor- alpha (TNF-alpha) or interleukin (IL)-1 beta] stimulation of NIH 3T3 c ells. Expression of a dominant negative allele of Rac1 inhibits the ri se in ROS seen after Ras expression or after stimulation by either gro wth factors or cytokines, These results provide the first demonstratio n of the pathway by which ligand stimulation of ROS occurs in non-phag ocytic cells and suggest that the family of Ras-related small GTP-bind ing proteins may function as regulators of the intracellular redox sta te.