Mapping choline metabolites in normal and transformed cells

Irena Roci,Jeramie D Watrous,Mohit Jain,Roland Nilsson,Kim A Lagerborg

doi:10.1007/s11306-020-01749-0

Irena Roci, Jeramie D Watrous + Show 3 more

Open Access

https://doi.org/10.1007/s11306-020-01749-0

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Abstract

IntroductionCholine is an essential human nutrient that is particular important for proliferating cells, and altered choline metabolism has been associated with cancer transformation. Yet, the various metabolic fates of choline in proliferating cells have not been investigated systematically.ObjectivesThis study aims to map the metabolic products of choline in normal and cancerous proliferating cells.MethodsWe performed 13C-choline tracing followed by liquid chromatography-high resolution mass spectrometry (LC-HRMS) analysis of metabolic products in normal and in vitro-transformed (tumor-forming) epithelial cells, and also in tumor-derived cancer cell lines. Selected metabolites were quantified by internal standards.ResultsUntargeted analysis revealed 121 LCMS peaks that were 13C-labeled from choline, including various phospholipid species, but also previously unknown products such as monomethyl- and dimethyl-ethanolamines. Interestingly, we observed formation of betaine from choline specifically in tumor-derived cells. Expression of choline dehydrogenase (CHDH), which catalyzes the first step of betaine synthesis, correlated with betaine synthesis across the cell lines studied. RNAi silencing of CHDH did not affect cell proliferation, although we observed an increased fraction of G2M phase cells with some RNAi sequences, suggesting that CHDH and its product betaine may play a role in cell cycle progression. Betaine cell concentration was around 10 µM, arguing against an osmotic function, and was not used as a methyl donor. The function of betaine in these tumor-derived cells is presently unknown.ConclusionThis study identifies novel metabolites of choline in cancer and normal cell lines, and reveals altered choline metabolism in cancer cells.

Highlights

Choline is an essential human nutrient that is particular important for proliferating cells, and altered choline metabolism has been associated with cancer transformation
We chose to study a normal, telomerase-immortalized human mammary epithelial cell (HMEC-Tert) and two derived cell lines that were stepwise transformed with the SV40 early region proteins (HMEC-SV40) followed by a mutant Ras protein (HMECRAS), where the latter is tumorigenic in vivo (Elenbaas et al 2001); and the tumor-derived cell lines MCF7, HCT116 and HeLa
To identify the fate of choline in these cells, we performed isotope tracing with a 13C3-choline tracer with 13C methyl groups (Fig. 1a, 1b)

Summary

Introduction

Choline is an essential human nutrient that is particular important for proliferating cells, and altered choline metabolism has been associated with cancer transformation. Conclusion This study identifies novel metabolites of choline in cancer and normal cell lines, and reveals altered choline metabolism in cancer cells. Choline can be synthesized from ethanolamine, this occurs mainly in the liver (Vance and Ridgway 1988), and for most proliferating cell types, choline is considered essential. It is present in virtually all cell culture media at substantial concentrations, usually around 10–100 μM, which is comparable to most amino acids.

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