Rho GTPases are involved in the regulation of NF-kappaB by genotoxic stress

A common cellular response to genotoxic agents and inflammatory cytokines is the activation of NF-kappaB. Here, we addressed the question of whether small GTPases of the Rho family are involved in the stimulation of NF-kappaB signaling by genotoxic agents or TNFalpha in HeLa cells. Inhibition of isoprenylation of Rho proteins by use of the HMG-CoA reductase inhibitor lovastatin attenuated UV-, doxorubicin-, and TNFalpha-induced degradation of IkappaBalpha as well as drug-stimulated DNA binding activity of NF-kappaB. Furthermore, NF-kappaB-regulated gene expression stimulated by either UV irradiation or treatment with TNFalpha was abrogated by lovastatin pretreatment. This indicates that isoprenylated regulatory proteins participate in the regulation of NF-kappaB by DNA-damaging agents as well as by TNFalpha. Specific blockage of Rho signaling by Clostridium difficile toxin B attenuated UV- and doxorubicin-induced activation of NF-kappaB, but did not affect stimulation of NF-kappaB by TNFalpha. Obviously, signaling to NF-kappaB by genotoxic and nongenotoxic stimuli occurs via different molecular mechanisms, either involving Rho GTPases or not. Based on the data, we suggest Rho GTPases to be essentially required for genotoxic stress-induced signaling to NF-kappaB.