Lovastatin inhibits the growth and survival pathway of phosphoinositide 3‐kinase/protein kinase B in immortalized rat brain neuroblasts

Abstract

We previously showed that lovastatin, an HMG-CoA reductase inhibitor, suppresses cell growth by inducing apoptosis in rat brain neuroblasts. Our aim was to study intracellular signalling induced by lovastatin in neuroblasts. Lovastatin significantly decreases the phosphoinositide 3-kinase (PI3-K) activity in a concentration-dependent manner. Expression of p85 subunit and its association with phosphotyrosine-containing proteins are unaffected by lovastatin. Lovastatin decreases protein kinase B (PKB)/Akt phosphorylation, and its downstream effectors, p70 S6K and the eukaryotic initiation factor 4E (eIF4E) regulatory protein 1, 4E-BP1, in a concentration-dependent manner, and reduces p70 S6K expression.Lovastatin effects are fully prevented with mevalonate. Only the highest dose of PI3-K inhibitors that significantly reduce PI3-K kinase activity induces apoptosis in neuroblasts but to a lower degree than lovastatin. In summary, this work shows that treatment of brain neuroblasts with lovastatin leads to an inhibition of the main pathway that controls cell growth and survival, PI3-K/PKB and the subsequent blockade of downstream proteins implicated in the regulation of protein synthesis. This work suggests that inactivation of the antiapoptotic PI3-K appears insufficient to induce the degree of neuroblasts apoptosis provoked by lovastatin, which must necessarily involve other intracellular pathways. These findings might contribute to elucidate the molecular mechanisms of some statins effects in the central nervous system. Keywords: apoptosis, lovastatin, neuroblasts, phosphoinositide 3-kinase, phosphorylation, protein kinase B/Akt. It is well established that mevalonate pathway, which yields different isoprenoid compounds and cholesterol, plays an important role in cell growth and survival (Goldstein and Brown 1990). Mevalonate is intracellularly synthesized from 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA), and this process is catalyzed by HMG-CoA reductase, the ratelimiting enzyme in this pathway (Goldstein and Brown 1990). Several studies show that competitive inhibitors of HMG-CoA reductase (statins), such as lovastatin, simvastatin and pravastatin, not only block the biosynthesis of mevalonate but, in addition, inhibit the growth and proliferation of both normal and tumour cells (Falke et al. 1989;Jones et al. 1994;Raiteri et al. 1997). Furthermore, inhibition of HMG-CoA reductase is also known to induce cell death by apoptosis in different non-neuronal cell types (Jones et al. 1994;Perez-Sala and Mollinedo 1994;Padayatty et al. 1997;Guijarro et al. 1998).This metabolic pathway is essential during late fetal and early neonatal life to ensure normal growth and development of the brain (Cavender et al. 1995;Spady and Dietschy 1983). Several studies suggest that HMG-CoA reductase inhibitors could seriously affect cholesterol Received April 13, 2005; accepted April 27, 2005. Address correspondence and reprint requests to Maria Julia Bragado, Departamento de Bioquímica, Biología Molecular y Genética, Fa...

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