Abstract
Neuroblastoma cell lines are commonly used as models to study neuronal differentiation, as they retain the capacity to differentiate into a neuronal‐like phenotype. Receptor tyrosine kinase (RTK) signaling is essential for neuronal differentiation during development, and cholesterol‐containing lipid‐rafts are important for RTK signaling. Hydroxymethylglutaryl–coenzyme A reductase inhibitors of the statin family impair cholesterol biosynthesis and are in widespread clinical use for the treatment of cardiovascular diseases. It is of great clinical interest that statin treatment also correlates with a lower incidence of malignancies. We found that mevastatin triggered neurite outgrowth of neuroblastoma cells and examined the responsible signaling pathways. Treatment of Neuro2a cells with mevastatin for 24 hr induced neurite outgrowth associated with up‐regulation of the neuronal marker protein NeuN. Interestingly, we found that mevastatin triggered phosphorylation of the key kinases epidermal growth factor receptor (EGFR), ERK1/2, and Akt/protein kinase B. Inhibition of EGFR, PI3K, and the mitogen‐activated protein kinase cascade blocked mevastatin‐induced neurite outgrowth. Moreover, add‐back experiments of cell‐permeable cholesterol precursors indicated that farnesylated and geranylgeranylated proteins play a major role in statin‐induced neurite outgrowth. Taken together, our results provide the first mechanistic insight into statin‐triggered signaling pathways that lead to neurite outgrowth in neuroblastoma cells. Surprisingly, we revealed that mevastatin triggered the phosphorylation of the EGFR and that this was because of the inhibition of farnesylated and geranylgeranylated proteins. We propose that members of the large family of farnesylated or geranylgeranylated small GTPases (such as Rabs or Rap1) regulating the trafficking and signaling of EGFR might be responsible for the statin‐induced effects on EGFR signaling. © 2009 Wiley‐Liss, Inc.