Vol. 58, Issue 6, 1389-1397, December 2000

Inhibition of Protein Isoprenylation Impairs Rho-Regulated Early Cellular Response to Genotoxic Stress

Renate Gnad, Klaus Aktories, Bernd Kaina, and Gerhard Fritz

Division of Applied Toxicology, Institute of Toxicology, University of Mainz, Mainz, Germany (R.G., B.K., G.F.); and Institute of Pharmacology and Toxicology, University of Freiburg, Freiburg, Germany (K.A.)

Activation of c-Jun N-terminal kinases (JNKs) and nuclear factor-B (NF-B) are early cellular responses to genotoxic stress involved in the regulation of gene expression. Pretreatment of cells with the hydroxymethyl glutaryl-CoA reductase inhibitor lovastatin blocked stimulation of JNK1 activity by UV irradiation and by treatment with the alkylating compound methyl methanesulfonate but did not affect activation of extracellular signal-regulated kinase 2 by UV light. Lovastatin also attenuated UV-induced degradation of the NF-B inhibitor IB. The effects of lovastatin on UV-triggered stimulation of JNK1 as well as on IB degradation were reverted by cotreatment with geranylgeranylpyrophosphate but not with farnesylpyrophosphate. Both a geranylgeranyltransferase type I inhibitor and a farnesyltransferase inhibitor blocked JNK1 stimulation by UV irradiation without impairing signaling to NF-B. This indicates that different types of isoprenylated proteins impair UV-induced signaling to JNK1 and NF-B, respectively. Since lovastatin caused a rapid decrease in the level of membrane-bound Rho GTPases, we hypothesize that Rho signaling is inhibited by lovastatin. In line with this hypothesis, Rho-inactivating toxin B from Clostridium difficile abolished both JNK1 activation and IB degradation evoked by UV irradiation. In summary, lovastatin-mediated inhibition of protein isoprenylation abrogates cellular stress responses involving JNK- and NF-B-regulated pathways, which seems to be caused by inactivation of Rho GTPases.