title: Effects of lovastatin on Rho isoform expression, activity, and association with guanine nucleotide dissociation inhibitors.
abstract: 3-Hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase (EC1.1.1.88) inhibitors (statins) reduce cholesterol synthesis and prevent cardiovascular disease; they can also inhibit prenylation of Ras and Rho proteins, and have anti-neoplastic effects. Rho proteins cycle between an active, GTP-bound, and an inactive, GDP-bound form, and Rho prenylation is important for Rho's interaction with upstream regulators and downstream effectors, but the effects of statins on Rho signaling are incompletely understood. We found that the HMG-CoA reductase inhibitor lovastatin markedly induced the expression of RhoA, B, and C in human erythroleukemia (HEL) cells. The drug increased RhoA and C only in their unprenylated forms, but it increased both prenylated and unprenylated RhoB and did not significantly affect N- and K-Ras prenylation, suggesting that it inhibited geranyl-geranylation more efficiently than farnesylation. Quantitative analysis of nucleotides bound to Rho demonstrated a 3.7-fold increase in Rho-GTP and a similar increase in Rho-GDP in lovastatin-treated cells, leaving the fraction of Rho in the active, GTP-bound form constant at 5.8%. Lovastatin reduced Rho association with Rho guanine dissociation inhibitor (RhoGDI)-alpha and -beta, and prenylation-deficient Rho mutants did not associate with RhoGDI. siRNA inhibition of RhoGDIalpha expression increased Rho-GTP, suggesting that decreased Rho/RhoGDIalpha association explained an increase in unprenylated Rho-GTP in lovastatin-treated cells. Unprenylated Rho A, B, and C were partly functional in activating serum response element-dependent transcription. In conclusion, we quantified effects of lovastatin on RhoA, B, and C isoforms, and provide a molecular mechanism whereby statins cause accumulation of unprenylated Rho-GTP.
authors.affiliation: Department of Medicine and Cancer Center, University of California, San Diego, La Jolla, CA 92093-0652, USA.
authors.forename: Stephanie J
authors.initials: SJ
authors.lastname: Turner
authors.forename: Shunhui
authors.initials: S
authors.lastname: Zhuang
authors.forename: Tong
authors.initials: T
authors.lastname: Zhang
authors.forename: Gerry R
authors.initials: GR
authors.lastname: Boss
authors.forename: Renate B
authors.initials: RB
authors.lastname: Pilz
mesh_terms: D045744:Cell Line, Tumor; D020730:Guanine Nucleotide Dissociation Inhibitors / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors / Q000494:pharmacology*; D008148:Lovastatin / Q000494:pharmacology*; D017368:Protein Prenylation; D014158:Transcription, Genetic; D020741:rho GTP-Binding Proteins / Q000378:metabolism*; D062948:rho Guanine Nucleotide Dissociation Inhibitor alpha; D062947:rho-Specific Guanine Nucleotide Dissociation Inhibitors; D020742:rhoA GTP-Binding Protein / Q000378:metabolism*; D020743:rhoB GTP-Binding Protein / Q000378:metabolism*; D000075024:rhoC GTP-Binding Protein
chemical_list: C569638:ARHGDIA protein, human; D020730:Guanine Nucleotide Dissociation Inhibitors; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; D062948:rho Guanine Nucleotide Dissociation Inhibitor alpha; D062947:rho-Specific Guanine Nucleotide Dissociation Inhibitors; C066737:RHOA protein, human; D006160:Guanosine Triphosphate; D008148:Lovastatin; C066690:RHOC protein, human; D020741:rho GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein; D020743:rhoB GTP-Binding Protein; D000075024:rhoC GTP-Binding Protein