Enhanced Expression and Activation of CTP:Phosphocholine Cytidylyltransferase β2 during Neurite Outgrowth

Abstract

During differentiation neurons increase phospholipid biosynthesis to provide new membrane for neurite growth. We studied the regulation of phosphatidylcholine (PC) biosynthesis during differentiation of two neuronal cell lines: PC12 cells and Neuro2a cells. We hypothesized that in PC12 cells nerve growth factor (NGF) would up-regulate the activity and expression of the rate-limiting enzyme in PC biosynthesis, CTP:phosphocholine cytidylyltransferase (CT). During neurite out-growth, NGF doubled the amount of cellular PC and CT activity. CT∪2 mRNA increased within 1 day of NGF application, prior to the formation of visible neurites, and continued to increase during neurite growth. When neurites retracted in response to NGF withdrawal, CTβ2 mRNA, protein, and CT activity decreased. NGF specif. ically activated CTβ2 by promoting its translocation from cytosol to membranes. In contrast, NGF did not alter CTα expression or translocation. The increase in both CTβ2 mRNA and CT activity was inhibited by U0126, an inhibitor of mitogen-activated kinase/extracellular signal-regulated kinase kinase 1/2 (MEK1/2). In Neuro2a cells, retinoic acid significantly increased CT activity (by 54%) and increased CTβ2 protein, coincident with neurite outgrowth but did not change CTα expres. sion. Together, these data suggest that the CTβ2 isoform of CT is specifically up-regulated and activated during neuronal differentiation to increase PC biosynthesis for growing neurites.