Balance of human choline kinase isoforms is critical for cell cycle regulation

Abstract

The enzyme choline kinase (CK), which catalyzes the phosphorylation of choline to phosphorylcholine in the presence of ATP, has an essential role in the biosynthesis of phosphatidylcholine, the major constituent of all mammalian cell membranes. CK is encoded by two separate genes expressing the three isoforms CKα1, CKα2 and CKβ that are active as homodimeric or heterodimeric species. Metabolic changes observed in various cancer cell lines and tumors have been associated with differential and marked up‐regulation of the CKα genes, and specific inhibition of CKα activity has been proposed as a potential anti‐cancer strategy. As a result, less attention has been given to CKβ and its interaction with CKα. With the aim of profiling the intracellular roles of CKα and CKβ, we used RNA interference (RNAi) as a molecular approach to down‐regulate the expression of CK in HeLa cells. Individual and simultaneous RNAi‐based silencing of the CK α and β isoforms was achieved using different combinations of knockdown strategies. Efficient knockdown was confirmed by immunodetection using our isoform‐specific antibodies and by quantitative real‐time PCR. Our analyses of the phenotypic consequences of CK depletion showed the expected lethal effect of CKα knockdown. However, CKβ‐ and CKα + CKβ‐silenced cells had no aberrant phenotype. Therefore, our results support the hypothesis that the balance of the α and β isoforms is critical for cancer cell survival. The suppression of the cancer cell killing effect of CKα silencing by simultaneous knockdown of both isoforms implies that a more effective CK‐based anti‐cancer strategy can be achieved by reducing cross‐reactivity with CKβ.

The novel choline kinase inhibitor ICL-CCIC-0019 reprograms cellular metabolism and inhibits cancer cell growth

“…The protein is overexpressed in several cancers through amplification or mRNA upregulation. In cancer cells, overexpression of CHKA is associated with transformation of normal cells to cancer [18], and conversely, depletion of CHKA by RNAi can reduce cell survival and tumor growth (Supplementary Figure S1C and[8, 20, 36]). To date, attention in the field of cancer has focused on the requirement of choline together with channeling of fatty acids into PC synthesis to support the increased need for membrane synthesis; however, this mechanism alone does not explain the effects of chemical inhibitors.…”

“…CHK exists in at least three isoforms: CHKA1, CHKA2 and CHKB encoded by two separate genes, of which the A, but not the B isoforms, have been implicated in cancer [6]. While under normal physiological conditions, CCT is the rate-limiting step of the pathway, CHKA is anticipated to be a major regulator in cancer [7, 8]. …”

Overexpression of CHKA contributes to tumor progression and metastasis and predicts poor prognosis in colorectal carcinoma

“…Among the multiple enzymes involved in the biosynthesis of phosphatidylcholine, the major structural component of eukaryotic cell membranes, choline kinase is the first enzyme of the Kennedy pathway responsible for catalyzing the phosphorylation of free choline to form phosphocholine [5, 6]. In mammalian cells, choline kinase is encoded by two separate genes, choline kinase alpha (CHKA) and beta (CHKB), of which only CHKA has a central role in sustaining the biosynthesis of phosphatidylcholine [7, 8]. To date, Increased expression and enzymatic activity of CHKA has been identified in a variety of human malignancies including breast, lung, colorectal, bladder, prostate, ovarian, endometrial carcinomas, osteosarcoma, and T-cell lymphoma [9–18].…”

Determination of Potential Scaffolds for Human Choline Kinase α1 by Chemical Deconvolution Studies

“…[3] A recent manuscript has clearly shown that a potent anticancer effect inducing maximum apoptosis is only achieved when CHOKa expression is specifically diminished without CHOKb levels being affected. [4] Compounds that are selective and potent against CHOKa are therefore proposed as valuable tools for treatment of cancer. We have previously described a new series of unsymmetrical monocationic compounds that showed moderate potency against CHOK in HepG2 cells.…”