More Than a Building Block

Science Signaling  17 Aug 2010:
Vol. 3, Issue 135, pp. ec249
DOI: 10.1126/scisignal.3135ec249

The growth of neurites during the process of neuronal differentiation is associated with an increase in surface area that requires substantial membrane biosynthesis. Phosphatidylcholine (PtdCho), the major membrane phospholipid, can be synthesized from choline through a pathway in which choline is phosphorylated by choline kinase (CK), phosphocholine is converted to cytidine diphosphocholine (CDP-Cho) by CTP:phosphocholine cytidylyltransferase (CCT), and CDP-Cho is converted into PtdCho by CPT (CDP-choline:1,2-diacylglycerol cholinephosphotransferase). Marcucci et al. used radiolabeled choline together with lipid extraction to evaluate changes in the abundance of choline metabolites in Neuro-2a mouse neuroblastoma cells undergoing retinoic acid (RA)–induced neuronal differentiation. They found an initial increase in the abundance of CDP-Cho and PtdCho and only later (after 24 hours) saw an increase in the amounts of choline and phosphocholine. A combination of microarray analysis, real-time RT-qPCR, promoter-reporter assays, and analyses of the effects of inhibitors of RNA or protein synthesis indicated that the early increase in PtdCho production likely resulted from an increase in the activity of CCTα. This was followed by an increase in the stability of the mRNA encoding CKα and then by the transcriptional activation of the genes encoding both CKα and CCTα. Clonal cell lines with stable expression of constitutively active CKα or CCTα showed increased PtdCho production in the absence of RA along with an increase in neurite formation. Moreover, they showed an increase in the abundance of βIII-tubulin, a neurite marker, and in the expression of various neuronal genes. RA stimulated the phosphorylation of extracellular signal–regulated kinase (ERK), whereas pharmacological inhibition of the ERK signaling pathway blocked the RA-dependent transcriptional activation of the genes encoding CKα and CCTα, the increase in PtdCho biosynthesis, and the stimulation of neurite outgrowth. ERK phosphorylation was also increased in the cell lines expressing constitutively active CKα or CCTα. The authors conclude that enhanced PtdCho biosynthesis, which is stimulated by RA, can itself promote neurite formation and neuronal differentiation.

H. Marcucci, L. Paoletti, S. Jackowski, C. Banchio, Phosphatidylcholine biosynthesis during neuronal differentiation and its role in cell fate determination. J. Biol. Chem. 285, 25382–25393 (2010). [Abstract] [Full Text]