Choline/ethanolamine kinase from mammalian tissues

Ether-Linked Glycerophospholipids Are Potential Chemo-Desensitisers and Are Associated With Overall Survival in Carcinoma Patients

Lipid reprogramming in carcinoma is reported to have a role in carcinogenesis, prognosis and therapy response. The lipid reprogramming could be contributed by either autonomous or nonautonomous resources. Since the nonautonomous lipid resources contributed by lipoproteins and their receptors have been reported in epithelial ovarian cancer (EOC), the impact of autonomous lipid metabolites was unknown. This report revealed a unique lipid class, ether-linked phosphatidyl-ethanolamine (PE O-), which enhances chemo-insensitivity and progression in EOC and potentially cross carcinomas. Analysis of CCLEC/GDSCC database and in-house cell line lipidomes identified PE O- as the major lipid associated with cisplatin/paclitaxel sensitivity. In the testing of PE O- effect on cancer phenotypes, it enhanced cell growth, migratory activities and promoted cisplatin/paclitaxel insensitivity. In addition, treating AGPS inhibitor-sensitised chemo-cytotoxic upon cisplatin/paclitaxel treatments. Treating PE O- could reverse AGPS inhibitor chemosensitisation effect on EOC cells. At last, using TCGA-EOC transcriptome database, the PE O- related gene expressions were positive correlated with patient prognosis in general, or in whom were treated with platin- or taxel-based chemotherapies. The expressions of genes for the synthesis of PE O- aggravates therapy response in EOC patients. PE O- facilitates human carcinoma cell line growth, mobility and chemo-insensitivity.

Correlation between choline kinase alpha expression and 11C-choline accumulation in breast cancer using positron emission tomography/computed tomography: a retrospective study

Choline kinase (CK) is reportedly overexpressed in various malignancies. Among its isoforms, CKα overexpression is presumably related to oncogenic change. Choline positron emission tomography (PET) is reportedly useful for detecting and evaluating therapy outcomes in malignancies. In this study, we investigated the correlation between CKα expression and 11C-choline accumulation in breast cancer cells. We also compared the CKα expression level with other pathological findings for investigating tumour activity. Fifty-six patients with breast cancer (mean age: 51 years) who underwent their first medical examination between May 2007 and December 2008 were enrolled. All the patients underwent 11C-choline PET/computed tomography imaging prior to surgery. The maximum standardised uptake value was recorded for evaluating 11C-choline accumulation. The intensity of CKα expression was classified using immunostaining. A significant correlation was observed between CKα expression and 11C-choline accumulation (P < 0.0001). A comparison of breast cancer mortality demonstrated that strong CKα expression was associated with a shorter survival time (P < 0.0001). 11C-choline accumulation was also negatively correlated with survival time (P < 0.0001). Tumours with strong CKα expression are reportedly highly active in breast cancer. A correlation was observed between CKα expression and 11C-choline accumulation, suggesting their role as prognostic indicators of breast cancer.

Digital Cascade Assays for ADP- or ATP-Producing Enzymes Using a Femtoliter Reactor Array Device

Digital enzyme assays are emerging biosensing methods for highly sensitive quantitative analysis of biomolecules with single-molecule detection sensitivity. However, current digital enzyme assays require a fluorogenic substrate for detection, which limits the applicability of this method to certain enzymes. ATPases and kinases are representative enzymes for which fluorogenic substrates are not available; however, these enzymes form large domains and play a central role in biology. In this study, we implemented a fluorogenic cascade reaction in a femtoliter reactor array device to develop a digital bioassay platform for ATPases and kinases. The digital cascade assay enabled quantitative measurement of the single-molecule activity of F1-ATPase, the catalytic portion of ATP synthase. We also demonstrated a digital assay for human choline kinase α. Furthermore, we developed a digital cascade assay for ATP-synthesizing enzymes and demonstrated a digital assay for pyruvate kinase. These results show the high versatility of this assay platform. Thus, the digital cascade assay has great potential for the highly sensitive detection and accurate characterization of various ADP- and ATP-producing enzymes, such as kinases, which may serve as disease biomarkers.

Mechanism of action and therapeutic route for a muscular dystrophy caused by a genetic defect in lipid metabolism

CHKB encodes one of two mammalian choline kinase enzymes that catalyze the first step in the synthesis of the membrane phospholipid phosphatidylcholine. In humans and mice, inactivation of the CHKB gene (Chkb in mice) causes a recessive rostral-to-caudal muscular dystrophy. Using Chkb knockout mice, we reveal that at no stage of the disease is phosphatidylcholine level significantly altered. We observe that in affected muscle a temporal change in lipid metabolism occurs with an initial inability to utilize fatty acids for energy via mitochondrial β-oxidation resulting in shunting of fatty acids into triacyglycerol as the disease progresses. There is a decrease in peroxisome proliferator-activated receptors and target gene expression specific to Chkb^−/− affected muscle. Treatment of Chkb^−/− myocytes with peroxisome proliferator-activated receptor agonists enables fatty acids to be used for β-oxidation and prevents triacyglyerol accumulation, while simultaneously increasing expression of the compensatory choline kinase alpha (Chka) isoform, preventing muscle cell injury.

Mutations in the CHKB gene cause muscular dystrophy. Here, the authors show that in mouse models of the disease changes in lipid metabolism are associated with decreased PPAR signaling, and show PPAR agonists can rescue expression of injury markers in myocytes in vitro.

Blood Metabolomic Phenotyping of Dry Cows Could Predict the High Milk Somatic Cells in Early Lactation—Preliminary Results

Subclinical mastitis (SCM) is a very common disease of dairy cows. Currently, somatic cell count (SCC) is used for SCM diagnoses. There are no prognostic tests to detect which cows may develop SCM during the dry-off period. Therefore, the objectives of this study were to identify metabolic alterations in the serum of pre-SCM cows during the dry-off period, at −8 and −4 weeks before calving, through a targeted mass spectrometry (MS) assay. Fifteen cows, free of any disease, and 10 cows affected only by SCM postpartum served as controls (CON) and the SCM group, respectively. Results showed 59 and 47 metabolites that differentiated (p ≤ 0.05) CON and pre-SCM cows at –8 and −4 weeks prior to the expected date of parturition, respectively. Regression analysis indicated that a panel of four serum metabolites (AUC = 0.92, p < 0.001) at −8 weeks and another four metabolites (AUC = 0.92, p < 0.01) at −4 weeks prior to parturition might serve as predictive biomarkers for SCM. Early identification of susceptible cows can enable development of better preventive measurements ahead of disease occurrence.

Imaging and Tissue Biomarkers of Choline Metabolism in Diffuse Adult Glioma: 18F-Fluoromethylcholine PET/CT, Magnetic Resonance Spectroscopy, and Choline Kinase α

The cellular and molecular basis of choline uptake on PET imaging and MRS-visible choline-containing compounds is not well understood. Choline kinase alpha (ChoKα) is an enzyme that phosphorylates choline, an essential step in membrane synthesis. We investigate choline metabolism through 18F-fluoromethylcholine (18F-FMC) PET, MRS, and tissue ChoKα in human glioma. Fourteen patients with a suspected diffuse glioma underwent multimodal 3T MRI and dynamic 18F-FMC PET/CT prior to surgery. Co-registered PET and MRI data were used to target biopsies to regions of high and low choline signal, and immunohistochemistry for ChoKα expression was performed. The 18F-FMC/PET differentiated WHO (World Health Organization) grade IV from grade II and III tumours, whereas MRS differentiated grade III/IV from grade II tumours. Tumoural 18F-FMC/PET uptake was higher than in normal-appearing white matter across all grades and markedly elevated within regions of contrast enhancement. The 18F-FMC/PET correlated weakly with MRS Cho ratios. ChoKα expression on IHC was negative or weak in all but one glioblastoma sample, and did not correlate with tumour grade or imaging choline markers. MRS and 18F-FMC/PET provide complimentary information on glioma choline metabolism. Tracer uptake is, however, potentially confounded by blood–brain barrier permeability. ChoKα overexpression does not appear to be a common feature in diffuse glioma.

EB-3D a novel choline kinase inhibitor induces deregulation of the AMPK-mTOR pathway and apoptosis in leukemia T-cells

Choline kinase alpha 1 (ChoKα1) has recently become an interesting therapeutic target since its overexpression has been associated to tumorigenesis in many cancers. Nevertheless, little is known regarding hematological malignancies. In this manuscript, we investigated the effect of a novel and selective ChoKα inhibitor EB-3D in T acute lymphoblastic leukemia (T-ALL). The effect of EB-3D was evaluated in a panel of T-leukemia cell lines and ex-vivo primary cultures derived from pediatric T-ALL patients. We also evaluated in detail, using Reverse Phase Protein Array (RPPA), protein phosphorylation level changes in T-ALL cells upon treatment. The drug exhibits a potent antiproliferative activity in a panel of T-leukemia cell lines and primary cultures of pediatric patients. Moreover, the drug strongly induces apoptosis and more importantly it enhanced T-leukemia cell sensitivity to chemotherapeutic agents, such as dexamethasone and l-asparaginase. In addition, the compound induces an early activation of AMPK, the main regulator of cellular energy homeostasis, by its phosphorylation at residue T712 of catalytic subunit α, and thus repressing mTORC1 pathway, as shown by mTOR S2448 dephosphorylation. The inhibition of mTOR in turn affects the activity of several known downstream targets, such as 4E-BP1, p70S6K, S6 Ribosomal Protein and GSK3 that ultimately may lead to a reduction of protein synthesis and cell death. Taken together, our findings suggest that targeting ChoKα may be an interesting option for treating T-ALL and that EB-3D could represent a valuable therapeutic tool.

Mutant IDH1 gliomas downregulate phosphocholine and phosphoethanolamine synthesis in a 2-hydroxyglutarate-dependent manner

BACKGROUND

Magnetic resonance spectroscopy (MRS) studies have identified elevated levels of the phospholipid precursor phosphocholine (PC) and phosphoethanolamine (PE) as metabolic hallmarks of cancer. Unusually, however, PC and PE levels are reduced in mutant isocitrate dehydrogenase 1 (IDHmut) gliomas that produce the oncometabolite 2-hydroxyglutarate (2-HG) relative to wild-type IDH1 (IDHwt) gliomas. The goal of this study was to determine the molecular mechanism underlying this unusual metabolic reprogramming in IDHmut gliomas.

METHODS

Steady-state PC and PE were quantified using 31P-MRS. To quantify de novo PC and PE synthesis, we used 13C-MRS and measured flux to 13C-PC and 13C-PE in cells incubated with [1,2-13C]-choline and [1,2-13C]-ethanolamine. The activities of choline kinase (CK) and ethanolamine kinase (EK), the enzymes responsible for PC and PE synthesis, were quantified using 31P-MR-based assays. To interrogate the role of 2-HG, we examined IDHwt cells incubated with 2-HG and, conversely, IDHmut cells treated with the IDHmut inhibitor AGI-5198. To examine the role of hypoxia-inducible factor 1-α (HIF-1α), we silenced HIF-1α using RNA interference. To confirm our findings in vivo and in the clinic, we studied IDHwt and IDHmut orthotopic tumor xenografts and glioma patient biopsies.

RESULTS

De novo synthesis of PC and PE was reduced in IDHmut cells relative to IDHwt. Concomitantly, CK activity and EK activity were reduced in IDHmut cells. Pharmacological manipulation of 2-HG levels established that 2-HG was responsible for reduced CK activity, EK activity, PC and PE. 2-HG has previously been reported to stabilize levels of HIF-1α, a known regulator of CK activity. Silencing HIF-1α in IDHmut cells restored CK activity, EK activity, PC and PE to IDHwt levels. Our findings were recapitulated in IDHmut orthotopic tumor xenografts and, most importantly, in IDHmut patient biopsies, validating our findings in vivo and in the clinic.

CONCLUSIONS

This study identifies, to our knowledge for the first time, a direct role for 2-HG in the downregulation of CK and EK activity, and thereby, PC and PE synthesis in IDHmut gliomas. These results highlight the unusual reprogramming of phospholipid metabolism in IDHmut gliomas and have implications for the identification of MRS-detectable metabolic biomarkers associated with 2-HG status.

PET Imaging of Prostate Cancer Using Radiolabeled Choline

Although PET using fludeoxyglucose F 18 (FDG) is a promising modality for metabolic imaging of different tumors, the results in prostate cancer have been somewhat inconsistent. Low FDG avidity of most prostate cancer cells and urinary activity are suggested as the main limitations of FDG PET for the evaluation of prostate cancer. Prostate cancer exhibits increased choline metabolism, which is the rationale for using radiolabeled choline for PET. This article describes the basic concepts of radiolabeled choline regarding pharmacokinetics, radiation dosimetry, synthesis, and biodistribution, in addition to advances concerning clinical PET using 11C- and 18F-choline in primary staging and restaging of prostate cancer patients.

Design, synthesis, crystallization and biological evaluation of new symmetrical biscationic compounds as selective inhibitors of human Choline Kinase α1 (ChoKα1)

A novel family of compounds derivative of 1,1′-(((ethane-1,2-diylbis(oxy))bis(4,1-phenylene))bis(methylene))-bispyridinium or –bisquinolinium bromide (10a-l) containing a pair of oxygen atoms in the spacer of the linker between the biscationic moieties, were synthesized and evaluated as inhibitors of choline kinase against a panel of cancer-cell lines. The most promising compounds in this series were 1,1′-(((ethane-1,2-diylbis(oxy))bis(4,1-phenylene))bis(methylene))bis(4-(dimethylamino)pyridinium) bromide (10a) and 1,1′-(((ethane-1,2-diylbis(oxy))bis(4,1-phenylene))bis(methylene))-bis(7-chloro-4-(pyrrolidin-1-yl)quinolinium) bromide (10l), which inhibit human choline kinase (ChoKα1) with IC₅₀ of 1.0 and 0.92 μM, respectively, in a range similar to that of the previously reported biscationic compounds MN58b and RSM932A. Our compounds show greater antiproliferative activities than do the reference compounds, with unprecedented values of GI₅₀ in the nanomolar range for several of the cancer-cell lines assayed, and more importantly they present low toxicity in non-tumoral cell lines, suggesting a cancer-cell-selective antiproliferative activity. Docking studies predict that the compounds interact with the choline-binding site in agreement with the binding mode of most previously reported biscationic compounds. Moreover, the crystal structure of ChoKα1 with compound 10a reveals that this compound binds to the choline-binding site and mimics HC-3 binding mode as never before.

Choline kinase β mutant mice exhibit reduced phosphocholine, elevated osteoclast activity, and low bone mass

The maintenance of bone homeostasis requires tight coupling between bone-forming osteoblasts and bone-resorbing osteoclasts. However, the precise molecular mechanism(s) underlying the differentiation and activities of these specialized cells are still largely unknown. Here, we identify choline kinase β (CHKB), a kinase involved in the biosynthesis of phosphatidylcholine, as a novel regulator of bone homeostasis. Choline kinase β mutant mice (flp/flp) exhibit a systemic low bone mass phenotype. Consistently, osteoclast numbers and activity are elevated in flp/flp mice. Interestingly, osteoclasts derived from flp/flp mice exhibit reduced sensitivity to excessive levels of extracellular calcium, which could account for the increased bone resorption. Conversely, supplementation of cytidine 5'-diphosphocholine in vivo and in vitro, a regimen that bypasses CHKB deficiency, restores osteoclast numbers to physiological levels. Finally, we demonstrate that, in addition to modulating osteoclast formation and function, loss of CHKB corresponds with a reduction in bone formation by osteoblasts. Taken together, these data posit CHKB as a new modulator of bone homeostasis.

Correlation of metabolic tumor volume and 11C-choline uptake with the pathology of prostate cancer: evaluation by use of simultaneously recorded MR and PET images

PURPOSE

This study was conducted to assess the relationship between (11)C-choline uptake and pathologic findings obtained by combined use of magnetic resonance (MR) and positron emission tomography (PET) imaging of patients with prostate cancer.

MATERIALS AND METHODS

We retrospectively evaluated 69 patients with prostate cancer who underwent (11)C-choline PET-CT and magnetic resonance imaging before radical prostatectomy. Combined MR-PET images were acquired to obtain precise anatomic information. The maximum standardized uptake value (SUVmax) and metabolic tumor volume (MTV) were compared with pathologic findings from resected specimens as the reference standard.

RESULTS

The mean and standard deviation of tumor SUVmax and MTV were 3.9 ± 1.8 and 12.9 ± 16.4, respectively. Tumors with high MTV (≧8.2) were more likely to be admixed with prostatic intraepithelial neoplasia (PIN) (p < 0.0001) or hyperplasia (p < 0.0001) in the background than those without these findings. Multiple regression analysis also revealed that the presence of hyperplasia (OR; 4.25, 95% CI 1.25-14.4, p = 0.02) and PIN (OR; 9.22, 95% CI 2.60-32.7, p = 0.001) were associated with tumors with high MTV.

CONCLUSION

We have demonstrated, by pathologic evaluation of patients with prostate cancer, that (11)C-choline uptake volume is greater for prostate cancer admixed with PIN and hyperplasia than that without.

Choline kinase-alpha by regulating cell aggressiveness and drug sensitivity is a potential druggable target for ovarian cancer

Background:

Aberrant choline metabolism has been proposed as a novel cancer hallmark. We recently showed that epithelial ovarian cancer (EOC) possesses an altered MRS-choline profile, characterised by increased phosphocholine (PCho) content to which mainly contribute over-expression and activation of choline kinase-alpha (ChoK-alpha).

Methods:

To assess its biological relevance, ChoK-alpha expression was downmodulated by transient RNA interference in EOC in vitro models. Gene expression profiling by microarray analysis and functional analysis was performed to identify the pathway/functions perturbed in ChoK-alpha-silenced cells, then validated by in vitro experiments.

Results:

In silenced cells, compared with control, we observed: (I) a significant reduction of both CHKA transcript and ChoK-alpha protein expression; (II) a dramatic, proportional drop in PCho content ranging from 60 to 71%, as revealed by ¹H-magnetic spectroscopy analysis; (III) a 35–36% of cell growth inhibition, with no evidences of apoptosis or modification of the main cellular survival signalling pathways; (IV) 476 differentially expressed genes, including genes related to lipid metabolism. Ingenuity pathway analysis identified cellular functions related to cell death and cellular proliferation and movement as the most perturbed. Accordingly, CHKA-silenced cells displayed a significant delay in wound repair, a reduced migration and invasion capability were also observed. Furthermore, although CHKA silencing did not directly induce cell death, a significant increase of sensitivity to platinum, paclitaxel and doxorubicin was observed even in a drug-resistant context.

Conclusion:

We showed for the first time in EOC that CHKA downregulation significantly decreased the aggressive EOC cell behaviour also affecting cells' sensitivity to drug treatment. These observations open the way to further analysis for ChoK-alpha validation as a new EOC therapeutic target to be used alone or in combination with conventional drugs.

Lipids of mitochondria

A unique organelle for studying membrane biochemistry is the mitochondrion whose functionality depends on a coordinated supply of proteins and lipids. Mitochondria are capable of synthesizing several lipids autonomously such as phosphatidylglycerol, cardiolipin and in part phosphatidylethanolamine, phosphatidic acid and CDP-diacylglycerol. Other mitochondrial membrane lipids such as phosphatidylcholine, phosphatidylserine, phosphatidylinositol, sterols and sphingolipids have to be imported. The mitochondrial lipid composition, the biosynthesis and the import of mitochondrial lipids as well as the regulation of these processes will be main issues of this review article. Furthermore, interactions of lipids and mitochondrial proteins which are highly important for various mitochondrial processes will be discussed. Malfunction or loss of enzymes involved in mitochondrial phospholipid biosynthesis lead to dysfunction of cell respiration, affect the assembly and stability of the mitochondrial protein import machinery and cause abnormal mitochondrial morphology or even lethality. Molecular aspects of these processes as well as diseases related to defects in the formation of mitochondrial membranes will be described.

Comparative study of the value of dual tracer PET/CT in evaluating breast cancer

The present study was conducted to assess the relationship between tumor uptake and pathologic findings using dual-tracer PET/computed tomography (CT) in patients with breast cancer. Seventy-four patients with breast cancer (mean age 54 years) who underwent (11)C-choline and 2-[(18)F]fluoro-2-deoxy-d-glucose ((18)F-FDG) PET/CT prior to surgery on the same day were enrolled in the present study. Images were reviewed by a board-certified radiologist and two nuclear medicine specialists who were unaware of any clinical information and a consensus was reached. Uptake patterns and measurements of dual tracers were compared with the pathologic findings of resected specimens as the reference standard. Mean (±SD) tumor size was 5.9 ± 3.2 cm. All primary tumors were identified on (18)F-FDG PET/CT and (11)C-choline PET/CT. However, (18)F-FDG PET/CT demonstrated focal uptake of the primary tumor with (n = 38; 51%) or without (n = 36; 49%) diffuse background breast uptake. Of the pathologic findings, multiple logistic regression analysis revealed an independent association between fibrocystic change and diffuse background breast uptake (odds ratio [OR] 8.57; 95% confidence interval [CI] 2.86-25.66; P < 0.0001). Tumors with higher histologic grade, nuclear grade, structural grade, nuclear atypia, and mitosis had significantly higher maximum standardized uptake values (SUV(max)) and tumor-to-background ratios (TBR) for both tracers. Multiple logistic regression analysis revealed that only the degree of mitosis was independently associated with a high SUV(max) (OR 7.45; 95%CI 2.21-25.11; P = 0.001) and a high TBR (OR 5.41; 95%CI 1.13-25.96; P = 0.035) of (11)C-choline PET/CT. In conclusion, (11)C-choline may improve tumor delineation and reflect tumor aggressiveness on PET/CT in patients with breast cancer.

Regulation of phospholipid synthesis in the yeast Saccharomyces cerevisiae

The yeast Saccharomyces cerevisiae, with its full complement of organelles, synthesizes membrane phospholipids by pathways that are generally common to those found in higher eukaryotes. Phospholipid synthesis in yeast is regulated in response to a variety of growth conditions (e.g., inositol supplementation, zinc depletion, and growth stage) by a coordination of genetic (e.g., transcriptional activation and repression) and biochemical (e.g., activity modulation and localization) mechanisms. Phosphatidate (PA), whose cellular levels are controlled by the activities of key phospholipid synthesis enzymes, plays a central role in the transcriptional regulation of phospholipid synthesis genes. In addition to the regulation of gene expression, phosphorylation of key phospholipid synthesis catalytic and regulatory proteins controls the metabolism of phospholipid precursors and products.

Transport and metabolism of radiolabeled choline in hepatocellular carcinoma

Altered choline (Cho) metabolism in cancerous cells can be used as a basis for molecular imaging with PET using radiolabeled Cho. In this study, the metabolism of tracer Cho was investigated in a woodchuck hepatocellular carcinoma (HCC) cell line (WCH17) and in freshly derived rat hepatocytes. The transporter responsible for [(11)C]-Cho uptake in HCC was also characterized in WCH17 cells. The study helped to define the specific mechanisms responsible for radio-Cho uptake seen on the PET images of primary liver cancer such as HCC. Cells were pulsed with [(14)C]-Cho for 5 min and chased for varying durations in cold media to simulate the rapid circulation and clearance of [(11)C]-Cho. Radioactive metabolites were extracted and analyzed by radio-HPLC and radio-TLC. The Cho transporter (ChoT) was characterized in WCH17 cells. WCH17 cells showed higher (14)C uptake than rat primary hepatocytes. [(14)C]-Phosphocholine (PC) was the major metabolite in WCH17. In contrast, the intracellular Cho in primary hepatocytes was found to be oxidized to betaine (partially released into media) and, to a lesser degree, phosphorylated to PC. [(14)C]-Cho uptake by WCH17 cells was found to have both facilitative transport and nonfacilitative diffusion components. The facilitative transport was characterized by Na(+) dependence and low affinity (K(m) = 28.59 ± 6.75 μM) with partial energy dependence. In contrast, ChoT in primary hepatocytes is Na(+) independent and low affinity. Our data suggest that transport and phosphorylation of Cho are responsible for the tracer accumulation during [(11)C]-Cho PET imaging of HCC. WCH17 cells incorporate [(14)C]-Cho preferentially into PC. Conversion of [(14)C]-PC into phosphatidylcholine occurred slowly in vitro. Basal oxidation and phosphorylation activities in surrounding hepatic tissue contribute to the background seen in [(11)C]-Cho PET images.

Characterization of breast cancers and therapy response by MRS and quantitative gene expression profiling in the choline pathway

Tumor choline metabolites have potential for use as diagnostic indicators of breast cancer phenotype and can be non-invasively monitored in vivo by MRS. Extract studies have determined that the principle diagnostic component of these peaks is phosphocholine (PCho), the biosynthetic precursor to the membrane phospholipid, phosphatidylcholine (PtdCho). The ability to resolve and quantify PCho in vivo would improve the accuracy of this putative diagnostic tool. In addition, determining the biochemical mechanisms underlying these metabolic perturbations will improve the understanding of breast cancer and may suggest potential molecular targets for drug development. Reported herein is the in vivo resolution and quantification of PCho and glycerophosphocholine (GPC) in breast cancer xenografts in SCID mice via image-guided 31P MRS, localized to a single voxel. Tumor metabolites are also detected using ex vivo extracts and high-resolution NMR spectroscopy and are quantified in the metastatic tumor line, MDA-mb-231. Also reported is the quantification of cytosolic and lipid metabolites in breast cells of differing cancer phenotype, and the identification of metabolites that differ among these cell lines. In cell extracts, PCho and the PtdCho breakdown products, lysophosphatidylcholine, GPC and glycerol 3-phosphate, are all raised in breast cancer lines relative to an immortalized non-malignant line. These metabolic differences are in direct agreement with differences in expression of genes encoding enzymes in the choline metabolic pathway. Results of this study are consistent with previous studies, which have concluded that increased choline uptake, increased choline kinase activity, and increased phosholipase-mediated turnover of PtdCho contribute to the observed increase in PCho in breast cancer. In addition, this study presents evidence suggesting a specific role for phospholipase A2-mediated PtdCho catabolism. Gene expression changes following taxane therapy are also reported and are consistent with previously reported changes in choline metabolites after the same therapy in the same tumor model.

Alternative splicing of CTP:phosphoethanolamine cytidylyltransferase produces two isoforms that differ in catalytic properties

CTP:phosphoethanolamine cytidylyltransferase (Pcyt2) catalyzes the rate-controlling reaction of the CDP-ethanolamine (Kennedy) pathway. We have previously established that Pcyt2 is encoded by a single gene that can be alternatively spliced from an internal exon into two transcripts, designated Pcyt2alpha and Pcyt2beta. Little is currently known about the regulation of Pcyt2. Here, we functionally express both murine Pcyt2 (mPcyt2) transcripts and investigate the roles of the two proteins in the regulation of mPcyt2 activity. We demonstrate that the tagged and purified alpha and beta proteins differ significantly in their kinetic properties. The K(m) of mPcyt2alpha for phosphoethanolamine was 318.4 microM, compared with 140.3 microM for mPcyt2beta. The maximal velocities of the alpha and beta isoforms at saturating conditions for both substrates were 138.0 and 114.4 nmol/min/mumol enzyme, respectively. When phosphoethanolamine was used at a fixed concentration of 1 mM, the K(m) of mPcyt2alpha for CTP was 102.0 microM and that of mPcyt2beta was 84.09 microM. Using a combination of nondenaturing PAGE, gel filtration chromatography, and immunoprecipitation, we provide evidence that mPcyt2alpha and mPcyt2beta proteins can form both homodimeric and heterodimeric complexes. We show that alternative splicing of the mPcyt2 transcript is ubiquitous but could also be regulated in a tissue-specific manner, producing a variable ratio of mPcyt2alpha/mPcyt2beta mRNAs. The expression of two distinct protein isoforms maybe an important mechanism by which Pcyt2 activity is regulated.

CHKA and PCYT1A gene polymorphisms, choline intake and spina bifida risk in a California population

BACKGROUND

Neural tube defects (NTDs) are among the most common of all human congenital defects. Over the last two decades, accumulating evidence has made it clear that periconceptional intake of folic acid can significantly reduce the risk of NTD affected pregnancies. This beneficial effect may be related to the ability of folates to donate methyl groups for critical physiological reactions. Choline is an essential nutrient and it is also a methyl donor critical for the maintenance of cell membrane integrity and methyl metabolism. Perturbations in choline metabolism in vitro have been shown to induce NTDs in mouse embryos.

METHODS

This study investigated whether single nucleotide polymorphisms (SNPs) in human choline kinase A (CHKA) gene and CTP:phosphocholine cytidylytransferase (PCYT1A) gene were risk factors for spina bifida. Fluorescence-based allelic discrimination analysis was performed for the two CHKA intronic SNPs hCV1562388 (rs7928739) and hCV1562393, and PCYT1A SNP rs939883 and rs3772109. The study population consisted of 103 infants with spina bifida and 338 non-malformed control infants who were born in selected California counties in the period 1989-1991.

RESULTS

The CHKA SNP hCV1562388 genotypes with at least one C allele were associated with a reduced risk of spina bifida (odds ratio = 0.60, 95%CI = 0.38-0.94). The PCYT1A SNP rs939883 genotype AA was associated with a twofold increased risk of spina bifida (odds ratio = 1.89, 95% CI = 0.97-3.67). These gene-only effects were not substantially modified by analytic consideration to maternal periconceptional choline intake.

CONCLUSION

Our analyses showed genotype effects of CHKA and PCYT1A genes on spina bifida risk, but did not show evidence of gene-nutrient interactions. The underlying mechanisms are yet to be resolved.

Elucidation of human choline kinase crystal structures in complex with the products ADP or phosphocholine

Choline kinase, responsible for the phosphorylation of choline to phosphocholine as the first step of the CDP-choline pathway for the biosynthesis of phosphatidylcholine, has been recognized as a new target for anticancer therapy. Crystal structures of human choline kinase in its apo, ADP and phosphocholine-bound complexes, respectively, reveal the molecular details of the substrate binding sites. ATP binds in a cavity where residues from both the N and C-terminal lobes contribute to form a cleft, while the choline-binding site constitutes a deep hydrophobic groove in the C-terminal domain with a rim composed of negatively charged residues. Upon binding of choline, the enzyme undergoes conformational changes independently affecting the N-terminal domain and the ATP-binding loop. From this structural analysis and comparison with other kinases, and from mutagenesis data on the homologous Caenorhabditis elegans choline kinase, a model of the ternary ADP.phosphocholine complex was built that reveals the molecular basis for the phosphoryl transfer activity of this enzyme.

Staging performance of carbon-11 choline positron emission tomography/computed tomography in patients with bone and soft tissue sarcoma: comparison with conventional imaging

The present study was conducted to compare the diagnostic accuracy between carbon-11 choline (11C-choline) positron emission tomography (PET)/computed tomography (CT) and conventional imaging for the staging of bone and soft tissue sarcomas. Sixteen patients who underwent 11C-choline PET/CT prior to treatment were evaluated retrospectively for staging accuracy. Conventional imaging methods consisted of 99,mTc-hydroxymethylene diphosphonate bone scintigraphy, chest CT and magnetic resonance imaging of the primary site. The images were reviewed and a consensus was reached by two board-certified radiologists who were unaware of any clinical or radiological information using hard-copy films and multimodality computer platform. Tumor stage was confirmed by histological examination and/or by an obvious progression in number and/or size of the lesions on follow-up examinations. Reviewers examining both 11C-choline PET/CT and conventional imaging classified T stage in all patients. Interpretation based on 11C-choline PET/CT, the Node (N) stage was correctly diagnosed in all patients, whereas the accuracy of conventional imaging in N stage was 63%. Tumor Node Metastasis (TNM) stage was assessed correctly with 11C-choline PET/CT in 15 of 16 patients (94%) and with conventional imaging in eight of 16 patients (50%). The overall TNM staging and N staging accuracy of 11C-choline PET/CT were significantly higher than that of conventional imaging (P < 0.05). 11C-choline PET/CT is more accurate than conventional imaging regarding clinical staging of patients with bone and soft tissue sarcomas. A whole body 11C-choline PET/CT might be acceptable for imaging studies of tumor staging prior to treatment.

Distant Metastasis of Prostate Cancer: Early Detection of Recurrent Tumor with Dual-Phase Carbon-11 Choline Positron Emission Tomography/Computed Tomography in Two Cases

Several types of recurrence may be detected by radiologic assessment after treatment in patients with prostate cancer. However, early detection of distant metastasis using positron emission tomography has so far never been published. We report two patients who underwent hormone therapy or surgical resection for prostate cancer. They developed distant metastases which were detected on whole body [C-11] choline positron emission tomography/computed tomography with significant elevation of serum PSA level. In one patient, recurrent tumor of the supraclavicular node (6 mm) diminished in size after subsequent hormone therapy. Surgical resection of recurrent tumor of the lung (12 mm) was performed in the other patient, the pathology of which confirmed the metastatic adenocarcinoma derived from the prostate. The recurrent tumor can be correctly detected by dual-phase whole body [C-11] choline positron emission tomography/computed tomography.

Completing the cycles; the dynamics of endonuclear lipidomics

Signal transductions via periodic generation and mobilisation of lipid second messengers within the nuclear matrix of eukaryotic cells have focused renewed attention on their precursor phospholipids' location, structure, form and function. The nuclear matrix contains and supports dynamic pools of phosphatidylcholine and phosphatidylinositol which serve as parent molecules of lipid second messengers but also of other phospholipids requiring cyclical replacement as cells proliferate. Applications of new, highly sensitive and specific analytical methodologies based on tandem electrospray ionisation mass spectrometry and the use of stable isotopes have allowed both static and dynamic lipidomic profiling of these endonuclear phospholipid pools. Together with more conventional enzymatic analyses and evaluation of the effect of specific "knock-out" of phospholipid transfer capacity, a number of important principles have been established. Specifically, a compartmental capacity to synthesise and remodel highly saturated phosphatidylcholine exists alongside transport mechanisms that facilitate the nuclear import of phosphatidylinositol and other phospholipids synthesised elsewhere within the cell. Subnuclear fractionation and the use of newly emerging techniques for sensitive lipidomic profiling of polyphosphoinositides, diacylglycerols and phosphatidate molecular species offer the potential for further significant advances in the near future.

A Rostrocaudal Muscular Dystrophy Caused by a Defect in Choline Kinase Beta, the First Enzyme in Phosphatidylcholine Biosynthesis

Muscular dystrophies include a diverse group of genetically heterogeneous disorders that together affect 1 in 2000 births worldwide. The diseases are characterized by progressive muscle weakness and wasting that lead to severe disability and often premature death. Rostrocaudal muscular dystrophy (rmd) is a new recessive mouse mutation that causes a rapidly progressive muscular dystrophy and a neonatal forelimb bone deformity. The rmd mutation is a 1.6-kb intragenic deletion within the choline kinase beta (Chkb) gene, resulting in a complete loss of CHKB protein and enzymatic activity. CHKB is one of two mammalian choline kinase (CHK) enzymes (alpha and beta) that catalyze the phosphorylation of choline to phosphocholine in the biosynthesis of the major membrane phospholipid phosphatidylcholine. While mutant rmd mice show a dramatic decrease of CHK activity in all tissues, the dystrophy is only evident in skeletal muscle tissues in an unusual rostral-to-caudal gradient. Minor membrane disruption similar to dysferlinopathies suggest that membrane fusion defects may underlie this dystrophy, because severe membrane disruptions are not evident as determined by creatine kinase levels, Evans Blue infiltration, and unaltered levels of proteins in the dystrophin-glycoprotein complex. The rmd mutant mouse offers the first demonstration of a defect in a phospholipid biosynthetic enzyme causing muscular dystrophy, representing a unique model for understanding mechanisms of muscle degeneration.

Phosphorylation of the yeast choline kinase by protein kinase C. Identification of Ser25 and Ser30 as major sites of phosphorylation

The Saccharomyces cerevisiae CKI1-encoded choline kinase catalyzes the committed step in phosphatidylcholine synthesis via the Kennedy pathway. The enzyme is phosphorylated on multiple serine residues, and some of this phosphorylation is mediated by protein kinase A. In this work we examined the hypothesis that choline kinase is also phosphorylated by protein kinase C. Using choline kinase as a substrate, protein kinase C activity was dose- and time-dependent and dependent on the concentrations of choline kinase (K(m) = 27 microg/ml) and ATP (K(m) = 15 microM). This phosphorylation, which occurred on a serine residue, was accompanied by a 1.6-fold stimulation of choline kinase activity. The synthetic peptide SRSSSQRRHS (V5max/K(m) = 17.5 mm(-1) micromol min(-1) mg(-1)) that contains the protein kinase C motif for Ser25 was a substrate for protein kinase C. A Ser25 to Ala (S25A) mutation in choline kinase resulted in a 60% decrease in protein kinase C phosphorylation of the enzyme. Phosphopeptide mapping analysis of the S25A mutant enzyme confirmed that Ser25 was a protein kinase C target site. In vivo the S25A mutation correlated with a decrease (55%) in phosphatidylcholine synthesis via the Kennedy pathway, whereas an S25D phosphorylation site mimic correlated with an increase (44%) in phosphatidylcholine synthesis. Although the S25A (protein kinase C site) mutation did not affect the phosphorylation of choline kinase by protein kinase A, the S30A (protein kinase A site) mutation caused a 46% reduction in enzyme phosphorylation by protein kinase C. A choline kinase synthetic peptide (SQRRHSLTRQ) containing Ser30 was a substrate (V(max)/K(m) = 3.0 mm(-1) micromol min(-1) mg(-1)) for protein kinase C. Comparison of phosphopeptide maps of the wild type and S30A mutant choline kinase enzymes phosphorylated by protein kinase C confirmed that Ser30 was also a target site for protein kinase C.

[Identification of muscle-type carnitine palmitoyltransferase I and characterization of its gene structure]

To characterize energy metabolism in brown adipose tissue (BAT), differential screening of a cDNA library of rat BAT with a cDNA probe of rat white adipose tissue was carried out. We isolated one novel cDNA clone encoding a protein of 88.2 kDa consisting of 772 amino acids. The deduced amino acid sequence showed the highest homology (62.6%) with that of rat liver carnitine palmitoyltransferase I (CPTI). The transcript corresponding to this cDNA was abundantly expressed not only in BAT but also in the heart and skeletal muscle. CPTI is a protein necessary for the beta-oxidation of long-chain fatty acids in mammalian mitochondria, and it has been suggested that at least two isoforms, the liver type and muscle (M-CPTI) type, exist. Based on these observations, we concluded that the novel cDNA clone isolated from rat BAT encodes M-CPTI. Isolation and characterization of a genomic DNA clone revealed that the gene for human M-CPTI consists of two 5'-noncoding exons, 18 coding exons, and one 3'-noncoding exon spanning approximately 10 kbp, and a gene encoding choline/ethanolamine kinase-beta (CK/EK-beta) was located about 300 bp upstream from the M-CPTI gene with the same strand direction. Furthermore, we found atypical transcripts containing exons of both CK/EK-beta and M-CPTI genes in humans and rodents. The physiologic role(s) of these transcripts is still unknown. However, it is interesting that such transcripts are produced from two tightly arranged and functionally unrelated genes in mammalian tissues.

Phospholipid biosynthesis in mammalian cells

Identification of the genes and gene products involved in the biosynthesis of phosphatidylcholine, phosphatidylethanolamine, and phosphatidylserine has lagged behind that in many other fields because of difficulties encountered in purifying the respective proteins. Nevertheless, most of these genes have now been identified. In this review article, we have highlighted important new findings on the individual enzymes and the corresponding genes of phosphatidylcholine synthesis via its two major biosynthetic pathways: the CDP-choline pathway and the methylation pathway. We also review recent studies on phosphatidylethanolamine biosynthesis by two pathways: the CDP-ethanolamine pathway, which is active in the endoplasmic reticulum, and the phosphatidylserine decarboxylase pathway, which operates in mitochondria. Finally, the two base-exchange enzymes, phosphatidylserine synthase-1 and phosphatidylserine synthase-2, that synthesize phosphatidylserine in mammalian cells are also discussed.

Membrane lipid biosynthesis in Chlamydomonas reinhardtii: ethanolaminephosphotransferase is capable of synthesizing both phosphatidylcholine and phosphatidylethanolamine

Phosphatidylethanolamine, but not phosphatidylcholine, is found in Chlamydomonas reinhardtii. A cDNA coding for diacylglycerol: CDP-ethanolamine ethanolaminephosphotransferase (EPT) was cloned from C. reinhardtii. The C. reinhardtii EPT appears phylogenetically more similar to mammalian aminoalcoholphosphotransferases than to those of yeast and the least close to those of plants. Similar membrane topography was found between the C. reinhardtii EPT and the aminoalcoholphosphotransferases from mammals, yeast, and plants. A yeast mutant deficient in both cholinephosphotransferase and ethanolaminephosphotransferase was complemented by the C. reinhardtii EPT gene. Enzymatic assays of C. reinhardtii EPT from the complemented yeast microsomes demonstrated that the C. reinhardtii EPT synthesized both PC and PE in the transformed yeast. The addition of either unlabeled CDP-ethanolamine or CDP-choline to reactions reduced incorporation of radiolabeled CDP-choline and radiolabeled CDP-ethanolamine into phosphatidylcholine and phosphatidylethanolamine. EPT activity from the transformed yeast or C. reinhardtii cells was inhibited nearly identically by unlabeled CDP-choline, CDP-ethanolamine, and CMP when [14C]CDP-choline was used as the primary substrate, but differentially by unlabeled CDP-choline and CDP-ethanolamine when [14C]CDP-ethanolamine was the primary substrate. The Km value of the enzyme for CDP-choline was smaller than that for CDP-ethanolamine. This provides evidence that C. reinhardtii EPT, similar to plant aminoalcoholphosphotransferase, is capable of catalyzing the final step of phosphatidylcholine biosynthesis, as well as that of phosphatidylethanolamine in the Kennedy pathway.

Regulation of phosphatidylcholine biosynthesis under salt stress involves choline kinases in Arabidopsis thaliana

Increasing evidence suggests a major role for phosphatidylcholine (PC) in plant stress adaptation. The present work investigated the regulation of choline, PC and interconnected phosphatidylethanolamine biosynthesis in Arabidopsis thaliana L. as a function of cold- and salt- or mannitol-mediated hyperosmotic stresses. While PC synthesis is accelerated in both salt- and cold-treated plants, the choline kinase (CK) and phosphocholine cytidylyltransferase genes are oppositely regulated with respect to these abiotic treatments. Salt stress also stimulates CK activity in vitro. A possible regulatory role of CK in stimulating PC biosynthesis rate in salt-stressed plants is discussed.

Family-based association study of schizophrenia with 444 markers and analysis of a new susceptibility locus mapped to 11q13.3

Family-based linkage disequilibrium (LD) mapping has been suggested as a powerful and practical alternative to linkage analysis. We have performed a genome-wide LD survey of susceptibility loci for schizophrenia in a Japanese population. We first typed 119 schizophrenic pedigrees (357 individuals) using 444 microsatellite markers, and analyzed the data using the pedigree disequilibrium test. This analysis revealed 14 markers demonstrating significant transmission distortion. To corroborate these findings, the statistical methods were changed to the extended transmission disequilibrium test (ETDT), using 80 independent complete trios (schizophrenic proband and both parents), with 68 derived from initial pedigrees and 12 newly recruited trios. ETDT supported two markers for continued association, D11S987 on 11q13.3 (P = 0.00009) and D16S423 on 16p13.3 (P = 0.002). We scrutinized the most significant genomic locus on 11q11-13 by adding 26 new markers for analysis. Results of three-marker haplotype analysis in the region showed evidence of association with schizophrenia (most significant haplotype P = 0.0005, global P = 0.022). Although the present study may have missed other potential genomic intervals because of the sparse mapping density, we hope that it has identified promising anchor points for further studies to identify risk-conferring genes for schizophrenia in the Japanese population. In addition, we provide useful information on genomic LD structures in Japanese populations, which can be used for LD mapping of complex diseases.

Structure and function of choline kinase isoforms in mammalian cells

Choline kinase (CK) catalyzes the first phosphorylation reaction in the CDP-choline pathway for the biosynthesis of phosphatidylcholine (PC), yielding phosphocholine (P-Cho) from choline and ATP in the presence of Mg(2+). This enzyme exists in mammalian cells as at least three isoforms that are encoded by two separate genes termed ck-alpha and ck-beta. Each isoform is not active in its monomeric form. The active enzyme consists of either their homo- or hetero-dimeric (or oligomeric) forms. In recent years, the roles of CK in cell growth and cell stress/defense mechanisms have been intensely investigated. These functions of CK do not seem to be directly related to the net PC biosynthesis but predict another important role of this enzyme in certain cell physiology. This review summarizes briefly the recent progress of mammalian CK study which will include the gene structure of each isoform and its possible transcriptional regulation, the active configuration of the enzyme, induction of the particular isoform in chemically induced cell stress, and the possible role of this enzyme as well as of its reaction product, P-Cho, in cell growth and other cellular physiology.

Identification of critical residues of choline kinase A2 from Caenorhabditis elegans

Choline kinase catalyzes the phosphorylation of choline by ATP, the first committed step in the CDP-choline pathway for phosphatidylcholine biosynthesis. To begin to elucidate the mechanism of catalysis by this enzyme, choline kinase A-2 from Caenorhabditis elegans was analyzed by systematic mutagenesis of highly conserved residues followed by analysis of kinetic and structural parameters. Specifically, mutants were analyzed with respect to K(m) and k(cat) values for each substrate and Mg(2+), inhibitory constants for Mg(2+) and Ca(2+), secondary structure as monitored by circular dichroism, and sensitivity to unfolding in guanidinium hydrochloride. The most severe impairment of catalysis occurred with the modification of Asp-255 and Asn-260, which are located in the conserved Brenner's phosphotransferase motif, and Asp-301 and Glu-303, in the signature choline kinase motif. For example, mutation of Asp-255 or Asp-301 to Ala eliminated detectable catalytic activity, and mutation of Asn-260 and Glu-303 to Ala decreased k(cat) by 300- and 10-fold, respectively. Additionally, the K(m) for Mg(2+) for mutants N260A and E303A was approximately 30-fold higher than that of wild type. Several other residues (Ser-86, Arg-111, Glu-125, and Trp-387) were identified as being important: Catalytic efficiencies (k(cat)/K(m)) for the enzymes in which these residues were mutated to Ala were reduced to 2-25% of wild type. The high degree of structural similarity among choline kinase A-2, aminoglycoside phosphotransferases, and protein kinases, together with the results from this mutational analysis, indicates it is likely that these conserved residues are located at the catalytic core of choline kinase.

[11C]choline uptake in regenerating liver after partial hepatectomy or CCl4-administration

To characterize [methyl-(11)C]choline ([(11)C]choline) as an oncologic PET radiopharmaceutical, [(11)C]choline uptake in regenerating livers after partial hepatectomy as a model of typical proliferating tissue and after CCl(4) insult as that of proliferating tissue with inflammation, was studied in rats. [(11)C]Choline, [(18)F]2-fluoro-2-deoxy-D-glucose ([(18)F]FDG) and [2-(14)C]thymidine ([(14)C]TdR) uptake was studied in regenerating rat liver after 70% partial hepatectomy or CCl(4)-administration. [(11)C]Choline uptake in regenerating liver after partial hepatectomy was significantly increased with [(14)C]TdR uptake as a marker of DNA synthesis at 18 hours after surgery. On the other hand, the uptake was not accelerated by CCl(4)-administration, though it significantly increased [(14)C]TdR uptake. There were no differences of [(11)C]choline uptake acceleration following partial hepatectomy among the three parts of the regenerating liver. [(18)F]FDG uptake was accelerated in the regenerating liver on either partial hepatectomy or CCl(4)-administration. The magnitude of the increase in [(18)F]FDG uptake in the regenerating liver induced by partial hepatectomy was greater than that for [(11)C]choline. [(11)C]Choline uptake in the liver was accelerated by partial hepatectomy, but not by CCl(4)-administration. This might be expected given that the differentiation between proliferating tissues such as tumor and inflammatory tissue was possible by [(11)C]choline-PET.

Molecular and cell biology of phosphatidylserine and phosphatidylethanolamine metabolism

In this review, the pathways for phosphatidylserine (PS) and phosphatidylethanolamine (PE) biosynthesis, as well as the genes and proteins involved in these pathways, are described in mammalian cells, yeast, and prokaryotes. In mammalian cells, PS is synthesized by a base-exchange reaction in which phosphatidylcholine or PE is substrate for PS synthase-1 or PS synthase-2, respectively. Isolation of Chinese hamster ovary cell mutants led to the cloning of cDNAs and genes encoding these two PS synthases. In yeast and prokaryotes PS is produced by a biosynthetic pathway completely different from that in mammals: from a reaction between CDP-diacylglycerol and serine. The major route for PE synthesis in cultured cells is from the mitochondrial decarboxylation of PS. Alternatively, PE can be synthesized in the endoplasmic reticulum (ER) from the CDP-ethanolamine pathway. Genes and/or cDNAs encoding all the enzymes in these two pathways for PE synthesis have been isolated and characterized. In mammalian cells, PS is synthesized on the ER and/or mitochondria-associated membranes (MAM). PS synthase-1 and -2 are highly enriched in MAM compared to the bulk of ER. Since MAM are a region of the ER that appears to be in close juxtaposition to the mitochondrial outer membrane, it has been proposed that MAM act as a conduit for the transfer of newly synthesized PS into mitochondria. A similar pathway appears to operate in yeast. The use of yeast mutants has led to identification of genes involved in the interorganelle transport of PS and PE in yeast, but so far none of the corresponding genes in mammalian cells has been identified. PS and PE do not act solely as structural components of membranes. Several specific functions have been ascribed to these two aminophospholipids. For example, cell-surface exposure of PS during apoptosis is thought to be the signal by which apoptotic cells are recognized and phagocytosed. Translocation of PS from the inner to outer leaflet of the plasma membrane of platelets initiates the blood-clotting cascade, and PS is an important activator of several enzymes, including protein kinase C. Recently, exposure of PE on the cell surface was identified as a regulator of cytokinesis. In addition, in Escherichia coli, PE appears to be involved in the correct folding of membrane proteins; and in Drosophila, PE regulates lipid homeostasis via the sterol response element-binding protein.

Role of gain of 12p in germ cell tumour development

Within the human testis, three entities of germ cell tumours are distinguished: the teratomas and yolk sac tumors of newborn and infants, the seminomas and nonseminomas of adolescents and young adults, referred to as testicular germ cell tumours (TGCT), and the spermatocytic seminomas. Characteristic chromosomal anomalies have been reported for each group, supporting their distinct pathogenesis. TGCT are the most common cancer in young adult men. The initiating pathogenetic event of these tumours occurs during embryonal development, affecting a primordial germ cell or gonocyte. Despite this intra-uterine initiation, the tumour will only be clinically manifest after puberty, with carcinoma in situ (IS) as the precursor. All invasive TGCT, both seminomas and nonseminomas, as well as CIS cells are aneuploid. The only consistent (structural) chromosomal abnormalities in invasive TGCT are gains of the short arm of chromosome 12, mostly due to isochromosome (i(12p)) formation. This suggests that an increase in copy number of a gene(s) on 12p is associated with the development of a clinically manifest TGCT. Despite the numerous (positional) candidate gene approaches that have been undertaken thus far, identification of a causative gene(s) has been hampered by the fact that most 12p gains involve rather large genomic intervals, containing unmanageable numbers of candidate genes. Several years ago, we initiated a search for 12p candidate genes using TGCT with a restricted 12p-amplification, cytogenetically identified as 12p11.2-p12.1. This approach is mainly based on identification of candidate genes mapped within the shortest region of overlap of amplification (SROA). In this review, data will be presented, which support the model that gain of 12p-sequences is associated with suppression of apoptosis and Sertoli cell-independence of CIS cells. So far, DAD-R is one of the most likely candidate genes involved in this process, possibly via N-glycosylation. Preliminary results on high through-put DNA- and cDNA array analyses of 12p-sequences will be presented.

Phosphatidylcholine and cell death

Phosphatidylcholine (PC) constitutes a major portion of cellular phospholipids and displays unique molecular species in different cell types and tissues. Inhibition of the CDP-choline pathway in most mammalian cells or overexpression of the hepatic phosphatidylethanolamine methylation pathway in hepatocytes leads to perturbation of PC homeostasis, growth arrest or even cell death. Although many agents that perturb PC homeostasis and induce cell death have been identified, the signaling pathways that mediate this cell death have not been well defined. This review summarizes recent progress in understanding the relationship between PC homeostasis and cell death.

Phosphorylation of Saccharomyces cerevisiae choline kinase on Ser30 and Ser85 by protein kinase A regulates phosphatidylcholine synthesis by the CDP-choline pathway

The Saccharomyces cerevisiae CKI-encoded choline kinase is phosphorylated on a serine residue and stimulated by protein kinase A. We examined the hypothesis that amino acids Ser(30) and Ser(85) contained in a protein kinase A sequence motif in choline kinase are target sites for protein kinase A. The synthetic peptides SQRRHSLTRQ (V(max)/K(m) = 10.8 microm(-1) nmol min(-1) mg(-1)) and GPRRASATDV (V(max)/K(m) = 0.15 microm(-1) nmol min(-1) mg(-1)) containing the protein kinase A motif for Ser(30) and Ser(85), respectively, within the choline kinase protein were substrates for protein kinase A. Choline kinase with Ser(30) to Ala (S30A) and Ser(85) to Ala (S85A) mutations were constructed alone and in combination by site-directed mutagenesis and expressed in a cki1Delta eki1Delta double mutant that lacks choline kinase activity. The mutant enzymes were expressed normally, but the specific activity of choline kinase in cells expressing the S30A, S85A, and S30A,S85A mutant enzymes was reduced by 44, 8, and 60%, respectively, when compared with the control. In vivo labeling experiments showed that the extent of phosphorylation of the S30A, S85A, and S30A,S85A mutant enzymes was reduced by 70, 17, and 83%, respectively. Phosphorylation of the S30A, S85A, and S30A,S85A mutant enzymes by protein kinase A in vitro was reduced by 60, 7, and 96%, respectively, and peptide mapping analysis of the mutant enzymes confirmed the phosphorylation sites in the enzyme. The incorporation of (3)H-labeled choline into phosphocholine and phosphatidylcholine in cells bearing the S30A, S85A, and S30A,S85A mutant enzymes was reduced by 56, 27, and 81%, respectively, and by 58, 33, and 84%, respectively, when compared with control cells. These data supported the conclusion that phosphorylation of choline kinase on Ser(30) and Ser(85) by protein kinase A regulates PC synthesis by the CDP-choline pathway.

Expression and characterization of the active molecular forms of choline/ethanolamine kinase-alpha and -beta in mouse tissues, including carbon tetrachloride-induced liver

Choline/ethanolamine kinase (ChoK/EtnK) exists as at least three isoforms (alpha1, alpha2 and beta) in mammalian cells. The physiological significance for the existence of more than one form of the enzyme, however, remains to be determined. In the present study, we examined the expression and distribution of the isoforms in mouse tissues using isoform-specific cDNA probes and polyclonal antibodies raised against each N-terminal peptide sequence. Both Northern- and Western-blot analyses indicated that either the alpha (alpha1 plus alpha2) or the beta isoform appeared to be the ubiquitously expressed enzyme. The mRNA abundance for the alpha isoform was highest in testis, whereas that for the beta isoform was relatively high in heart and liver. While the native form of each isoform was reported to consist of either homodimers or homotetramers, our immunotitration studies clearly indicated that a considerable part of the active form of the enzyme consists of alpha/beta hetero-oligomers, with relatively small parts of activity expressed by alpha/alpha and beta/beta homo-oligomers. This is the first experimental evidence for the presence of heteromeric ChoK/EtnK in any source. Thus our results strongly suggested that the activity of ChoK/EtnK in the cell is controlled not only by the level of each isoform but also by their combination to form the active oligomer complex. Carbon tetrachloride (CCl(4)) was shown to induce ChoK activity 2-4-fold in murine liver. Our analysis for the mechanism involved in this induction revealed that the responsible isoform for CCl(4) was alpha, not beta. The level of alpha mRNA was strongly induced in mouse liver, which resulted in a sustained increase in the amount of the alpha isoform. Consequently, the composition of alpha/alpha homo-oligomers came to represent up to 80% of the total active molecular form of ChoK in CCl(4)-induced liver, whereas it was less than 20% in normal uninduced liver.

Differential routing of choline in implanted breast cancer and normal organs

Choline is an essential nutrient participating as the initial substrate in major metabolic pathways. The differential metabolic routing of choline was investigated in MCF7 human breast cancer implanted in nude mice and in the kidney, liver, and brain of these mice. The distribution of metabolites following infusion of [1,2-(13)C]-choline was monitored by (13)C magnetic resonance spectroscopy. This infusion led to an 18-fold increase in plasma choline and to concomitant changes in the content and distribution of choline metabolites. In vivo kinetic studies of the tumor during the infusion demonstrated accumulation of choline in the interstitium and intracellular synthesis of phosphocholine. The amount of unlabeled choline metabolites was 7.1, 4.1, 3.5, and 1.4 micromol/g in the kidney, liver, tumor, and brain, respectively. The variations in the labeled metabolites were more pronounced with high amounts in the kidney and liver (8.0 and 4.3 micromol/g, respectively) and very low amounts in the tumor and brain (0.33 and 0.12 micromol/g, respectively). In the kidney and liver, betaine (unlabeled and labeled) was the predominant choline metabolite. The dominant unlabeled metabolite in breast cancer was phosphocholine and in the brain glycerophosphocholine. Magn Reson Med 46:31-38, 2001.

A new expression cloning strategy for isolation of substrate-specific kinases by using phosphorylation site-specific antibody

Signal transduction from cell surface receptors to the nucleus is regulated in most part by protein phosphorylation. For the purpose of identification of kinases which play an important role at a particular phosphorylation step in a series of signal transduction pathways, we have developed a new expression-screening method using a phosphorylation site specific antibody and a vector encoding substrate polypeptide. We have applied this method for screening kinases which phosphorylate STAT3 at serine(727). In this screening, antibody (PS727 antibody) specifically recognizing STAT3 in which serine(727) is phosphorylated was first prepared. Escherichia coli, bacteria expressing a serine(727)-containing fragment of STAT3 which was fused to glutathione-S-transferase (GST) (GST-STAT3-WT) were infected by lambda phage cDNA expression libraries. Phosphorylation of GST-STAT3-WT was effectively performed in E. coli as expected, and clones positive for PS727 antibody immunoreactivity were selected. Isolated 53 clones encode four serine/threonine kinases; extracellular signal regulated kinase 1 (ERK1/p44-MAPK), dual specificity Yak1 related kinase (DYRK), dual specificity Yak1 related kinase 2 (DYRK2) and homeodomain interacting protein kinase 2 (HIPK2). These kinases have a potential to phosphorylate serine(727) in STAT3 protein also in mammalian cells. The present method is considered to be applicable in general to isolate kinases.

Regulation of mammalian cell membrane biosynthesis

This review explores current information on the interrelationship between phospholipid biochemistry and cell biology. Phosphatidylcholine is the most abundant phospholipid and it biosynthesis has been studied extensively. The choline cytidylyltransferase regulates phosphatidylcholine production, and recent advances in our understanding of the mechanisms that govern cytidylyltransferase include the discovery of multiple isoforms and a more complete understanding of the lipid regulation of enzyme activity. Similarities between phosphatidylcholine formation and the phosphatidylethanolamine and phosphatidylinositol biosynthetic pathways are discussed, together with current insight into control mechanisms. Membrane phospholipid doubling during cell cycle progression is a function of periodic biosynthesis and degradation. Membrane homeostasis is maintained by a phospholipase A-mediated degradation of excess phospholipid, whereas insufficient phosphatidylcholine triggers apoptosis in cells.

Phosphatidylcholine metabolism in nuclei of phorbol ester-activated LA-N-1 neuroblastoma cells

The agonist stimulation of a variety of cells results in the induction of specific lipid metabolism in nuclear membranes, supporting the hypothesis of an important role of the lipids in nuclear signal transduction. While the existence of a phosphatidylinositol cycle has been reported in cellular nuclei, little attention has been given to the metabolism of phosphatidylcholine in nuclear signaling. In the present study the metabolism of phosphatidylcholine in the nuclei of neuroblastoma cells LA-N-1 was investigated. The incubation of LA-N-1 nuclei with radioactive choline, phosphocholine or CDP-choline led to the production of labelled phosphatidylcholine. The incorporation of choline and phosphocholine but not CDP-choline was enhanced in nuclei of TPA treated cells. Moreover the presence of choline kinase, phosphocholine cytidylyltransferase and phosphocholine transferase activities were detected in the nuclei and the TPA treatment of the cells stimulated the activity of the phosphocholine cytidylyltransferase. When cells prelabelled with [3H]palmitic acid were stimulated with TPA in the presence of ethanol, an increase of labelled diacylglycerol and phosphatidylethanol in the nuclei was observed. Similarly, an increase of labelled diacylglycerol and phosphatidic acid but not of phosphatidylethanol occurred in [3H]palmitic acid prelabelled nuclei stimulated with TPA in the presence of ethanol. However the production of phosphatidylethanol was observed when the nuclei were treated with TPA in the presence of ATP and GTPgammaS. The stimulation of [3H]choline prelabelled nuclei with TPA also generated the release of free choline and phosphocholine. The results indicate the presence of PLD and probably PLC activities in LA-N-1 nuclei and the involvement of phosphatidylcholine in the production of nuclear lipid second messengers upon TPA stimulation of LA-N-1 cells. The correlation of the disappearance of phosphatidylcholine, the production of diacylglycerol and phosphatidic acid with the stimulation of phosphatidylcholine synthesis in nuclei of TPA treated LA-N-1 suggests the existence of a phosphatidylcholine cycle in these nuclei.

Glycerophospholipids in brain: their metabolism, incorporation into membranes, functions, and involvement in neurological disorders

Neural membranes contain several classes of glycerophospholipids which turnover at different rates with respect to their structure and localization in different cells and membranes. The glycerophospholipid composition of neural membranes greatly alters their functional efficacy. The length of glycerophospholipid acyl chain and the degree of saturation are important determinants of many membrane characteristics including the formation of lateral domains that are rich in polyunsaturated fatty acids. Receptor-mediated degradation of glycerophospholipids by phospholipases A(l), A(2), C, and D results in generation of second messengers such as arachidonic acid, eicosanoids, platelet activating factor and diacylglycerol. Thus, neural membrane phospholipids are a reservoir for second messengers. They are also involved in apoptosis, modulation of activities of transporters, and membrane-bound enzymes. Marked alterations in neural membrane glycerophospholipid composition have been reported to occur in neurological disorders. These alterations result in changes in membrane fluidity and permeability. These processes along with the accumulation of lipid peroxides and compromised energy metabolism may be responsible for the neurodegeneration observed in neurological disorders.