RAC1, AND NOT RAC2, IS INVOLVED IN THE REGULATION OF THE INTRACELLULAR HYDROGEN-PEROXIDE LEVEL IN HEPG2 CELLS

In order to elucidate the components of the oxygen sensory complex in HepG2 cells which regulates the production of erythropoietin, we have microinjected recombinant variants of the human small GTP-binding prot ein hRac1 and measured their effects on the production of reactive oxy gen species (ROS) by the dihydrorhodamine-123 technique. The dominant- negative mutant hRac1(T17N) inhibits the NADH-stimulated production of ROS in HepG2 cells, whereas the constitutively activated hRac1(G12V) leads to an increase in intracellular ROS concentration. Reverse trans criptase PCR analysis showed that the hRac1, but not the hRac2, gene i s expressed in HepG2 cells. These results demonstrate that hRac1, and not hRac2, is involved in the regulation of ROS production in HepG2 ce lls and suggest that hRac1 specifically functions in the non-phagocyti c NAD(P)H oxidase complex.