Effects of lovastatin on Rho isoform expression, activity, and association with guanine nucleotide dissociation inhibitors

Abstract

Abstract3-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, GTPbound, 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 geranylgeranylation 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)-α and -β, and prenylationdeficient Rho mutants did not associate with RhoGDI. siRNA inhibition of RhoGDIα expression increased Rho·GTP, suggesting that decreased Rho/RhoGDIα 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.

Statins induce apoptosis in ovarian cancer cells through activation of JNK and enhancement of Bim expression

“…Based on this, the expectation would be that statins would inhibit the signaling of preny lated G-proteins. Recently, however, lovastatin was shown to induce the expression of Rho A, B and C in human eryth roleukemia cells and to increase the active GTP-bound form of Rho by 3.7 fold [22]. Further, lovastatin did not aVect the prenylation of Ras in erythroleukemia cells, sug gesting that inhibition of geranyl-geranylation was more pronounced than inhibition of farnesylation.…”

“…Although the expectation is that statin would inhibit signaling by these GTPases, recent reports indicate that lovastatin can increase expression of Rho and cause an increase in the active form of Rho:GTP [22]. These GTPases exert similar biological activities in cells.…”

Why drugs fail in clinical trials in pulmonary arterial hypertension, and strategies to succeed in the future

“…The maximum licensed dose of simvastatin is 80mg daily, but this is seldom used due to poor tolerability and increased risk of muscle injury. Doses of 40 to 80mg reduced circulating cholesterol in the clinical studies in PAH, but may be insufficient to effectively inhibit farnesyltransferase (Turner, Zhuang, Zhang, Boss, & Pilz, 2008).…”

Unprenylated RhoA Contributes to IL-1β Hypersecretion in Mevalonate Kinase Deficiency Model through Stimulation of Rac1 Activity

“…However is currently no literature describing signaling for either protein leading to mitochondrial morphology, potential or mitophagy. Further- more, most reports seem to indicate that RhoB and RhoC become active (GTP bound) when unprenylated, while the C3 transferase leaves them inactive (although in different cell types) (33,34). Considering that the same change in mitochondrial morphology is seen with simvastatin treatment and Rho inhibition, where as far as we know the only common factor is RhoA inactivation, we propose that the mitochondrial elongation is a consequence or RhoA inactivation and RhoB and RhoC do not play an important role in the process.…”