Increased Choline Kinase Activity and Elevated Phosphocholine Levels in Human Colon Cancer^†

Abstract

Nuclear magnetic resonance spectroscopy has detected elevated phosphocholine levels in human tumor tissues and cells, and in cells that were transformed with the activated Ha-ras gene and stimulated in vitro with growth-promoting factors such as platelet-derived growth factor, epidermal growth factor, and phorbol ester. However, the mechanism of the elevation and the function of the increased phosphocholine levels have not been clearly demonstrated. We studied phosphocholine levels enzymatically and analyzed the activity of choline kinase, which catalyzes the phosphorylation of choline to produce phosphocholine, in human colon cancer and adenoma. Both choline kinase activity and phosphocholine levels were increased in colon cancer and adenoma tissue. The activation of choline kinase and the increased levels of choline kinase α α α α were partly responsible for the elevated phosphocholine levels. This study suggests that choline kinase might play a role in growth promotion or signal transduction in carcinogenesis.Key words: Choline kinase -Phosphocholine -Human colon cancerCancer of the colon is one of the most common cancers in developed countries and its prevention is of great interest throughout the world. It is thought that the accumulation of certain mutated genes, including oncogenes, tumor suppressor genes, genes for DNA-repair enzymes, and invasion/metastasis-related genes, is necessary for the onset and progression of cancer. Mutation may cause further malignant changes in cellular proliferation, especially in enzymatic properties and activity.1-3) Some of the changes in enzymatic properties and activity with proliferation may be advantageous to the cancer cells. [4][5][6][7] Studying the cellular properties of cancer cells improves our understanding of the mechanism of cellular growth control and sheds further light on cancer prevention and treatment. 8) Choline kinase is the first enzyme in the cytidine 5′-diphosphate (CDP)-choline pathway for the synthesis of phosphatidylcholine, and phosphorylates choline to phosphocholine using adenosine 5′-triphosphate (ATP) as the phosphate donor. [9][10][11] In vitro studies of oncogenic ras proteins, and products and growth factors have shown that phosphocholine contributes to cellular growth regulation and intracellular signal transduction. Ras proteins play a pivotal role in cellular signal transduction, and help regulate cellular proliferation and terminal differentiation. [12][13][14] Microinjecting the oncogenic Ha-ras gene product p21 ras into Xenopus oocytes causes meiosis, 15) quickly activates choline kinase and elevates phosphocholine levels. 16)Transforming fibroblastic cells with oncogenic Ha-ras also activates choline kinase. [17][18][19] Growth factors essential for cellular growth also activate choline kinase, elevating the intracellular phosphocholine level. Prolactin is one such growth factor for Nb 2 rat node lymphoma cells.20) It has been suggested that platelet-derived growth factor might use a choline kinase-phosphocholine route to promote c...

Increased Choline Kinase Activity in 1,2‐Dimethylhydrazine‐induced Rat Colon Cancer

“…The elevated phosphocholine levels were due in part to the activation of choline kinase and the increased choline kinase α protein levels. 25) These results suggest that choline kinase and phosphocholine may play a role not only in phospholipid synthesis, but also in regulating cellular growth in cancer cells.This study is the first to analyze choline kinase in DMH-induced rat colon cancer. We further analyzed the mechanism of activation and found that the activation involved increases in both the protein and mRNA levels.…”

“…25,31) Western blot analysis The cytosolic proteins were separated by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis, 32) and transferred onto polyvinylidene difluoride (PVDF) membranes (Millipore Corp., Bedford, MA). Choline kinase α was detected with the affinitypurified anti-choline kinase α antibody and goat anti-rabbit IgG using the ECL reagent as reported previously.…”

PET for Therapy Response Assessment in Glioblastoma

“…Phosphorylation by choline kinase (CK) constitutes an important step in the incorporation of choline into phospholipids, which is an essential component of all cell membranes. In cancer, there is often an increase in the cellular transport and phosphorylation of choline, as well as an increase in the expression of CK, increasing the uptake of radiolabeled choline (87)(88)(89). Choline can be labeled with either 11 C or 18 F. As a tracer, 11 C-Cho is biochemically indistinguishable from natural choline; however, the short half-life of 11 C has led to the development of 18 F-labeled derivatives, such as 18 F-Fluoromethylcholine ( 18 F-FCho) (90,91).…”

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

“…THE PHOSPHOLIPID PRECURSOR phosphocholine (PCho) has been identified as being a well-validated metabolic biomarker of human cancers including breast, brain, ovarian, gastric, and prostate tumors (1)(2)(3)(4)(5)(6). These tumors have been identified to have significantly higher concentrations of PCho compared to their matched normal tissues.…”

“…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.…”