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.