Activation of Phosphatidylcholine Cycle Enzymes in Human Epithelial Ovarian Cancer Cells

Abstract

Altered phosphatidylcholine (PC) metabolism in epithelial ovarian cancer (EOC) could provide cholinebased imaging approaches as powerful tools to improve diagnosis and identify new therapeutic targets. The increase in the major choline-containing metabolite phosphocholine (PCho) in EOC compared with normal and nontumoral immortalized counterparts (EONT) may derive from (a) enhanced choline transport and choline kinase (ChoK)-mediated phosphorylation, (b) increased PC-specific phospholipase C (PC-plc) activity, and (c) increased intracellular choline production by PC deacylation plus glycerophosphocholine-phosphodiesterase (GPC-pd) or by phospholipase D (pld)-mediated PC catabolism followed by choline phosphorylation. Biochemical, protein, and mRNA expression analyses showed that the most relevant changes in EOC cells were (a) 12-fold to 25-fold ChoK activation, consistent with higher protein content and increased ChoKα (but not ChoKβ) mRNA expression levels; and (b) 5-fold to 17-fold PC-plc activation, consistent with higher, previously reported, protein expression. PC-plc inhibition by tricyclodecan-9-yl-potassium xanthate (D609) in OVCAR3 and SKOV3 cancer cells induced a 30% to 40% reduction of PCho content and blocked cell proliferation. More limited and variable sources of PCho could derive, in some EOC cells, from 2-fold to 4-fold activation of pld or GPC-pd. Phospholipase A 2 activity and isoform expression levels were lower or unchanged in EOC compared with EONT cells. Increased ChoKα mRNA, as well as ChoK and PC-plc protein expression, were also detected in surgical specimens isolated from patients with EOC. Overall, we showed that the elevated PCho pool detected in EOC cells primarily resulted from upregulation/activation of ChoK and PC-plc involved in PC byosinthesis and degradation, respectively. Cancer Res; 70(5); 2126-35. ©2010 AACR.

Microfluidic sampling system for tissue analytics

“…1,2 The measurement of the oxidation levels of lipids is an indicator of cell-stress and also a biomarker for the onset of cancerous growth. 3 An amount of different phospholipids has been studied as biomarkers for ovarian 4 and breast cancers. 5 The role of metabolites and lipids such as Phosphatidylcholines (PCs) and Phosphoethanolamines (PEs) as breast cancer biomarkers has been investigated by Eliyahu et al, 6 Hilvo et al, 7 and Butczies et al 8 Separation of breast cancer tissues from normal breast tissues was demonstrated to be feasible with high sensitivity and specificity.…”

Reproducibility of total choline/water ratios in mouse U87MG xenograft tumors by 1H‐MRS

“…These tumors have been identified to have significantly higher concentrations of PCho compared to their matched normal tissues. The elevation in PCho in tumor tissues is due to the oncogene activation and high expression of the enzyme choline kinase (ChoK) (5,7). ChoK catalyzes the ATP-dependent phosphorylation of choline to form PCho, the first step in the Kennedy pathway (cytidine diphospho [CDP]-choline pathway) for phosphatidylcholine biosynthesis (8,9).…”

“…Phosphatidylcholine is the major membrane phospholipid of eukaryotic cells and it is essential for cell growth and viability, and serves as a precursor to bioactive lipids that are important for numerous lipidmediated signal transduction pathways in cancer. Choline is also an essential nutrient and phosphorylation by ChoK allows cancer cells to accumulate this phospholipid precursor at high concentrations, providing them with a significant growth advantage over normal cells (6,7,10). Numerous in vitro and in vivo studies have also established that a reduction in PCho correlates with the inhibition of cellular proliferation.…”

“…MRS is an analytical method that has been widely used to noninvasively measure changes in cellular and tissue metabolites including the choline-containing metabolites PCho, choline, and glycerophosphocholine (GPCho) (1,7,16,17). Numerous studies have also demonstrated that 1 H-MRS can be used clinically to diagnose human cancers, monitor responses to therapy, and investigate tumor metabolism by measuring tumor choline metabolites (2)(3)(4)18).…”

“…Numerous studies have also demonstrated that 1 H-MRS can be used clinically to diagnose human cancers, monitor responses to therapy, and investigate tumor metabolism by measuring tumor choline metabolites (2)(3)(4)18). These studies have identified changes in tumor choline metabolites as being a key feature of human cancers that can be used to distinguish normal cells from cancer cells (1,7) as well as to assess responses to therapy. In order to have confidence in changes in tumor choline metabolites produced by pharmacologic and other treatments, it is important to establish the reproducibility of such measurements.…”