Differential Role of Human Choline Kinase α and β Enzymes in Lipid Metabolism: Implications in Cancer Onset and Treatment

Abstract

BackgroundThe Kennedy pathway generates phosphocoline and phosphoethanolamine through its two branches. Choline Kinase (ChoK) is the first enzyme of the Kennedy branch of synthesis of phosphocholine, the major component of the plasma membrane. ChoK family of proteins is composed by ChoKα and ChoKβ isoforms, the first one with two different variants of splicing. Recently ChoKα has been implicated in the carcinogenic process, since it is over-expressed in a variety of human cancers. However, no evidence for a role of ChoKβ in carcinogenesis has been reported.Methodology/Principal FindingsHere we compare the in vitro and in vivo properties of ChoKα1 and ChoKβ in lipid metabolism, and their potential role in carcinogenesis. Both ChoKα1 and ChoKβ showed choline and ethanolamine kinase activities when assayed in cell extracts, though with different affinity for their substrates. However, they behave differentially when overexpressed in whole cells. Whereas ChoKβ display an ethanolamine kinase role, ChoKα1 present a dual choline/ethanolamine kinase role, suggesting the involvement of each ChoK isoform in distinct biochemical pathways under in vivo conditions. In addition, while overexpression of ChoKα1 is oncogenic when overexpressed in HEK293T or MDCK cells, ChoKβ overexpression is not sufficient to induce in vitro cell transformation nor in vivo tumor growth. Furthermore, a significant upregulation of ChoKα1 mRNA levels in a panel of breast and lung cancer cell lines was found, but no changes in ChoKβ mRNA levels were observed. Finally, MN58b, a previously described potent inhibitor of ChoK with in vivo antitumoral activity, shows more than 20-fold higher efficiency towards ChoKα1 than ChoKβ.Conclusion/SignificanceThis study represents the first evidence of the distinct metabolic role of ChoKα and ChoKβ isoforms, suggesting different physiological roles and implications in human carcinogenesis. These findings constitute a step forward in the design of an antitumoral strategy based on ChoK inhibition.

Alterations of Choline Phospholipid Metabolism in Endometrial Cancer Are Caused by Choline Kinase Alpha Overexpression and a Hyperactivated Deacylation Pathway

“…Although our approach illustrates tissue heterogeneity, the use of microdissection techniques and larger samples size may reduce the variation observed in the presented results. In a number of studies, CHKA has been shown to mediate cellular proliferation, transformation, and carcinogenesis, and mediation of this target using siRNA and smallmolecule inhibitors suggests inhibition of tumor growth (11,16,18,40,41). As indicated, we further observed in clinical samples and endometrial cancer cell lines, a significant increase in the mRNA expression of enzymes of the phosphatidylcholine deacylation pathway; GPCPD1, LYPLA1, and LYPLA2.…”

Evidence for Bidirectional Endocannabinoid Transport across Cell Membranes

“…AEA-generated (25), most of the studies on AEA uptake have been performed using cancer cell lines that have been shown to possess a high activity of the PL biosynthesis pathway due their rapid and unlimited proliferation rate (18). In fact, choline kinase has been reported to be overexpressed in many cancer types, where it promotes proliferation (79). In the present study, we show that the human U937 monocyte leukemia cells retain the vast majority of the AEA-derived [ 3 H]ethanolamine in PLs within 5 min due to the high rate of PL biosynthesis in this cell line (80).…”

A mechanism for suppression of the CDP-choline pathway during apoptosis

“…This suggests that the synthesis of phosphocholine is inhibited due to reduced choline transport and/or phosphorylation. CK ␣ is the major isoform expressed in MCF7 cells and is overexpressed in many types of cancer ( 48 ). However, total CK activity in the cytosolic fractions from control and camptothecin-treated MCF7 and MCF7-C3 cells was similar ( Fig.…”