Hydrogen peroxide mediates Rac1 activation of S6K1

Abstract

We previously reported that hydrogen peroxide (H2O2) mediates mitogen activation of ribosomal protein S6 kinase 1 (S6K 1) which plays an important role in cell proliferation and growth. In this study, we investigated a possible role of H2O2 as a molecular linker in Rac1 activation of S6K1. Overexpression of recombinant catalase in NIH-3T3 cells led to the drastic inhibition of H2O2 production by PDGF, which was accompanied by a decrease in S6KI activity. Similarly, PDGF activation of S6K1 was significantly inhibited by transient transfection or stable transfection of the cells with a dominant-negative Rac1 (Rac1N17), while overexpression of constitutively active Rac1 (Rac1V12) in the cells led to an increase in basal activity of S6KI. In addition, stable transfection of Rat2 cells with Rac1N17 dramatically attenuated the H2O2 production by PDGF as compared with that in the control cells. In contrast, Rat2 cells stably transfected with Rac1V12 produced high level of H2O2 in the absence of PDGF, comparable to that in the control cells stimulated with PDGF. More importantly, efirnination of H2O2 produced in Rat2 cells overexpressing Rac1V12 inhibited the Rac1V12 activation of S6K 1, indicating the possible role of H2O2 as a mediator in the activation of S6K 1 by Rac 1. However, H2O2 Could be also produced via other