Cell cycle regulation of membrane phospholipid metabolism

Cell cycle dependent changes in membrane stored curvature elastic energy: evidence from lipidomic studies

One of the most developed theories of phospholipid homeostasis is the intrinsic curvature hypothesis, which, in broad terms, postulates that cells regulate their lipid composition so as to keep constant the membrane stored curvature elastic energy. The implication of this hypothesis is that lipid composition is determined by a ratio control function consisting of the weighted sum of concentrations of type II lipids in the numerator and the weighted sum of concentrations of Type 0 lipids in the denominator. In previous work we used a data-driven approach, based on lipidomic data from asynchronous cell cultures, to determine a criterion that allows the different lipid species to be assigned to the set of type 0 or of type II lipids, and hence construct a ratio control function that serves as a proxy for the lipid contribution to total membrane stored curvature elastic energy in vivo. Here we apply the curvature elastic energy proxy to the analysis of lipid composition data from synchronous HeLa cells as they traverse the cell cycle. Our analysis suggests HeLa cells modify their membrane stored elastic energy through the cell cycle. In S-phase type 0 lipids are the most abundant, whilst in G2 type II lipids are most abundant. Changes in our proxy for membrane stored elastic energy correlate with membrane curvature dependent processes in the HeLa cell around division, providing some insights into the interplay between the individual lipid and protein contributions to membrane free energy.

Impaired coenzyme A synthesis in fission yeast causes defective mitosis, quiescence-exit failure, histone hypoacetylation and fragile DNA

Biosynthesis of coenzyme A (CoA) requires a five-step process using pantothenate and cysteine in the fission yeast Schizosaccharomyces pombe. CoA contains a thiol (SH) group, which reacts with carboxylic acid to form thioesters, giving rise to acyl-activated CoAs such as acetyl-CoA. Acetyl-CoA is essential for energy metabolism and protein acetylation, and, in higher eukaryotes, for the production of neurotransmitters. We isolated a novel S. pombe temperature-sensitive strain ppc1-537 mutated in the catalytic region of phosphopantothenoylcysteine synthetase (designated Ppc1), which is essential for CoA synthesis. The mutant becomes auxotrophic to pantothenate at permissive temperature, displaying greatly decreased levels of CoA, acetyl-CoA and histone acetylation. Moreover, ppc1-537 mutant cells failed to restore proliferation from quiescence. Ppc1 is thus the product of a super-housekeeping gene. The ppc1-537 mutant showed combined synthetic lethal defects with five of six histone deacetylase mutants, whereas sir2 deletion exceptionally rescued the ppc1-537 phenotype. In synchronous cultures, ppc1-537 cells can proceed to the S phase, but lose viability during mitosis failing in sister centromere/kinetochore segregation and nuclear division. Additionally, double-strand break repair is defective in the ppc1-537 mutant, producing fragile broken DNA, probably owing to diminished histone acetylation. The CoA-supported metabolism thus controls the state of chromosome DNA.

The role of phosphatidylcholine and choline metabolites to cell proliferation and survival

The reorganization of metabolic pathways in cancer facilitates the flux of carbon and reducing equivalents into anabolic pathways at the expense of oxidative phosphorylation. This provides rapidly dividing cells with the necessary precursors for membrane, protein and nucleic acid synthesis. A fundamental metabolic perturbation in cancer is the enhanced synthesis of fatty acids by channeling glucose and/or glutamine into cytosolic acetyl-CoA and upregulation of key biosynthetic genes. This lipogenic phenotype also extends to the production of complex lipids involved in membrane synthesis and lipid-based signaling. Cancer cells display sensitivity to ablation of fatty acid synthesis possibly as a result of diminished capacity to synthesize complex lipids involved in signaling or growth pathways. Evidence has accrued that phosphatidylcholine, the major phospholipid component of eukaryotic membranes, as well as choline metabolites derived from its synthesis and catabolism, contribute to both proliferative growth and programmed cell death. This review will detail our current understanding of how coordinated changes in substrate availability, gene expression and enzyme activity lead to altered phosphatidylcholine synthesis in cancer, and how these changes contribute directly or indirectly to malignant growth. Conversely, apoptosis targets key steps in phosphatidylcholine synthesis and degradation that are linked to disruption of cell cycle regulation, reinforcing the central role that phosphatidylcholine and its metabolites in determining cell fate.

The role of phospholipids in the biological activity and structure of the endoplasmic reticulum

The endoplasmic reticulum (ER) is an interconnected network of tubular and planar membranes that supports the synthesis and export of proteins, carbohydrates and lipids. Phospholipids, in particular phosphatidylcholine (PC), are synthesized in the ER where they have essential functions including provision of membranes required for protein synthesis and export, cholesterol homeostasis, and triacylglycerol storage and secretion. Coordination of these biological processes is essential, as highlighted by findings that link phospholipid metabolism in the ER with perturbations in lipid storage/secretion and stress responses, ultimately contributing to obesity/diabetes, atherosclerosis and neurological disorders. Phospholipid synthesis is not uniformly distributed in the ER but is localized at membrane interfaces or contact zones with other organelles, and in dynamic, proliferating ER membranes. The topology of phospholipid synthesis is an important consideration when establishing the etiology of diseases that arise from ER dysfunction. This review will highlight our current understanding of the contribution of phospholipid synthesis to proper ER function, and how alterations contribute to aberrant stress responses and disease. This article is part of a Special Issue entitled: Functional and structural diversity of endoplasmic reticulum.

Daily rhythms of glycerophospholipid synthesis in fibroblast cultures involve differential enzyme contributions

Circadian clocks regulate the temporal organization of several biochemical processes, including lipid metabolism, and their disruption leads to severe metabolic disorders. Immortalized cell lines acting as circadian clocks display daily variations in [(32)P]phospholipid labeling; however, the regulation of glycerophospholipid (GPL) synthesis by internal clocks remains unknown. Here we found that arrested NIH 3T3 cells synchronized with a 2 h-serum shock exhibited temporal oscillations in a) the labeling of total [(3)H] GPLs, with lowest levels around 28 and 56 h, and b) the activity of GPL-synthesizing and GPL-remodeling enzymes, such as phosphatidate phosphohydrolase 1 (PAP-1) and lysophospholipid acyltransferases (LPLAT), respectively, with antiphase profiles. In addition, we investigated the temporal regulation of phosphatidylcholine (PC) biosynthesis. PC is mainly synthesized through the Kennedy pathway with choline kinase (ChoK) and CTP:phosphocholine cytidylyltranferase (CCT) as key regulatory enzymes. We observed that the PC labeling exhibited daily changes, with the lowest levels every ~28 h, that were accompanied by brief increases in CCT activity and the oscillation in ChoK mRNA expression and activity. Results demonstrate that the metabolisms of GPLs and particularly of PC in synchronized fibroblasts are subject to a complex temporal control involving concerted changes in the expression and/or activities of specific synthesizing enzymes.

Identification of plasma metabolomic profiling for diagnosis of esophageal squamous-cell carcinoma using an UPLC/TOF/MS platform

Epidemiological studies indicated that esophageal squamous-cell carcinoma (ESCC) is still one of the most common causes of cancer incidence in the world. Searching for valuable markers including circulating endogenous metabolites associated with the risk of esophageal cancer, is extremely important A comparative metabolomics study was performed by using ultraperformance liquid chromatography-electrospray ionization-accurate mass time-of-flight mass spectrometry to analyze 53 pairs of plasma samples from ESCC patients and healthy controls recruited in Huaian, China. The result identified a metabolomic profiling of plasma including 25 upregulated metabolites and five downregulated metabolites, for early diagnosis of ESCC. With a database-based verification protocol, 11 molecules were identified, and six upregulated molecules of interest in ESCC were found to belong to phospholipids as follows: phosphatidylserine, phosphatidic acid, phosphatidyl choline, phosphatidylinositol, phosphatidyl ethanolamine, and sphinganine 1-phosphate. Clinical estimation of metabolic biomarkers through hierarchical cluster analysis in plasma samples from 17 ESCC patients and 29 healthy volunteers indicated that the present metabolite profile could distinguish ESCC patients from healthy individuals. The cluster of aberrant expression of these metabolites in ESCC indicates the critical role of phospholipid metabolism in the oncogenesis of ESCC and suggests its potential ability to assess the risk of ESCC development in addition to currently used risk factors.

Environmental hyperosmolality regulates phospholipid biosynthesis in the renal epithelial cell line MDCK

Hyperosmolality is a key signal for renal physiology. On the one hand, it contributes to the differentiation of renal medullary structures and to the development of the urinary concentrating mechanism. On the other, it is a stress factor. In both cases, hyperosmolality activates processes that require an adequate extension of cellular membranes. In the present work, we examined whether hyperosmolality regulates phospholipid biosynthesis, which is needed for the membrane biogenesis in the renal epithelial cell line Madin-Darby canine kidney (MDCK). Because phospholipids are the structural determinants of all cell membranes, we evaluated their content, synthesis, and regulation in MDCK cultures subjected to different hyperosmotic concentrations of NaCl, urea, or both. Hyperosmolality increased phospholipid content in a concentration-dependent manner. Such an effect was exclusively due to changes in NaCl concentration and occurred at the initial stage of hyperosmolar treatment concomitantly with the expression of the osmoprotective protein COX-2. The hypertonic upregulation of phosphatidylcholine (PC) synthesis, the main constituent of all cell membranes, involved the transcriptional activation of two main regulatory enzymes, choline kinase (CK) and cytidylyltransferase α (CCTα) and required ERK1/2 activation. Considering that physiologically, renal medullary cells are constantly exposed to high and variable NaCl, these findings could contribute to explaining how renal cells could maintain cellular integrity even in a nonfavorable environment.

Arachidonoyl-phosphatidylcholine oscillates during the cell cycle and counteracts proliferation by suppressing Akt membrane binding

The activity of protein kinase B (Akt)--a major kinase promoting cell proliferation and survival--oscillates during the cell cycle. To investigate whether membrane phospholipids may regulate Akt phosphorylation and thus activity, we monitored the lipid profile of nocodazole-synchronized mouse NIH 3T3 fibroblasts during the cell cycle by liquid chromatography electrospray ionization tandem mass spectrometry (LC-MS/MS). The proportion of sn-2-arachidonoyl-phosphatidylcholine (20:4-PC) inversely correlated with Akt activity. Increasing the cellular ratio of 20:4-PC by supplementation of 20:4-PC to the cell culture medium diminished Akt [serine (Ser)473] phosphorylation. Saturated and monounsaturated phosphatidylcholines, used as control had no effect; 20:4-PC reduced cell proliferation relative to controls, interfered with S-phase transition, and suppressed Akt downstream signaling and cyclin expression like LY294002, which is a specific inhibitor of the phosphatidylinositol-3-kinase/Akt pathway. Additive effects of 20:4-PC and LY294002 were not observed, underlining the critical role of Akt for 20:4-PC signaling; 20:4-PC suppressed Akt membrane translocation as shown by immunofluorescence microscopy but left the concentration of the anchor lipid phosphatidylinositol-3,4,5-trisphosphate unchanged. An in vitro binding assay suggests that 20:4-PC attenuates the interaction of Akt with its membrane binding site. We conclude that 20:4-PC oscillates during the cell cycle and delays cell cycle progression by inhibiting Akt membrane binding.

Lipid biomarkers of glioma cell growth arrest and cell death detected by 1 H magic angle spinning MRS

Biomarkers of early response to treatment have the potential to improve cancer therapy by allowing treatment to be tailored to the individual. Alterations in lipids detected by in vivo MRS have been suggested as noninvasive biomarkers of cell stress and early indicators of cell death. An improved understanding of the relationship between MRS lipids and cell stress in vitro would aid in the translation of this technique into clinical use. Rat BT4C glioma cells were treated with 50 µ m cis-dichlorodiammineplatinum II (cisplatin), a commonly used chemotherapeutic agent, and harvested at several time points up to 72 h. High-resolution magic angle spinning (1) H MRS of cells was then performed on a 600-MHz NMR spectrometer. The metabolites were quantified using a time domain fitting method, TARQUIN. Increases were detected in saturated and polyunsaturated fatty acid resonances early during the exposure to cisplatin. The fatty acid CH(2) /CH(3) ratio was unaltered by treatment after allowing for contributions of macromolecules. Polyunsaturated fatty acids increased on treatment, with the group -CH=CH-CH(2) -CH=CH- accounting for all the unsaturated fatty acid signals. Transmission electron microscopy, in addition to Nile red and 4',6-diamino-2-phenylindole co-staining, revealed that the lipid increase was associated with cytoplasmic neutral lipid droplets. Small numbers of apoptotic and necrotic cells were detected by trypan blue, annexin V-fluorescein isothiocyanate-labelled flow cytometry and DNA laddering after up to 48 h of cisplatin exposure. Propidium iodide flow cytometry revealed that cells accumulated in the G1 stage of the cell growth cycle. In conclusion, an increase in the size of the lipid droplets is detected in morphologically viable cells during cisplatin exposure. (1) H MRS can detect lipid alterations during cell cycle arrest and progression of cell death, and has the potential to provide a noninvasive biomarker of treatment efficacy in vivo.

Translational regulation of Arabidopsis XIPOTL1 is modulated by phosphocholine levels via the phylogenetically conserved upstream open reading frame 30

In Arabidopsis thaliana, XIPOTL1 encodes a phosphoethanolamine N-methyltransferase with a central role in phosphatidylcholine biosynthesis via the methylation pathway. To gain further insights into the mechanisms that regulate XIPOTL1 expression, the effect of upstream open reading frame 30 (uORF30) on the translation of the major ORF (mORF) in the presence or absence of endogenous choline (Cho) or phosphocholine (PCho) was analysed in Arabidopsis seedlings. Dose-response assays with Cho or PCho revealed that both metabolites at physiological concentrations are able to induce the translational repression of a mORF located downstream of the intact uORF30, without significantly altering its mRNA levels. PCho profiles showed a correlation between increased endogenous PCho levels and translation efficiency of a uORF30-containing mORF, while no correlation was detectable with Cho levels. Enhanced expression of a uORF30-containing mORF and decreased PCho levels were observed in the xipotl1 mutant background relative to wild type, suggesting that PCho is the true mediator of uORF30-driven translational repression. In Arabidopsis, endogenous PCho content increases during plant development and affects root meristem size, cell division, and cell elongation. Because XIPOTL1 is preferentially expressed in Arabidopsis root tips, higher PCho levels are found in roots than shoots, and there is a higher sensitivity of this tissue to translational uORF30-mediated control, it is proposed that root tips are the main site for PCho biosynthesis in Arabidopsis.

StearoylCoA desaturase-5: a novel regulator of neuronal cell proliferation and differentiation

Recent studies have demonstrated that human stearoylCoA desaturase-1 (SCD1), a Δ9-desaturase that converts saturated fatty acids (SFA) into monounsaturated fatty acids, controls the rate of lipogenesis, cell proliferation and tumorigenic capacity in cancer cells. However, the biological function of stearoylCoA desaturase-5 (SCD5), a second isoform of human SCD that is highly expressed in brain, as well as its potential role in human disease, remains unknown. In this study we report that the constitutive overexpression of human SCD5 in mouse Neuro2a cells, a widely used cell model of neuronal growth and differentiation, displayed a greater n-7 MUFA-to-SFA ratio in cell lipids compared to empty-vector transfected cells (controls). De novo synthesis of phosphatidylcholine and cholesterolesters was increased whereas phosphatidylethanolamine and triacylglycerol formation was reduced in SCD5-expressing cells with respect to their controls, suggesting a differential use of SCD5 products for lipogenic reactions. We also observed that SCD5 expression markedly accelerated the rate of cell proliferation and suppressed the induction of neurite outgrowth, a typical marker of neuronal differentiation, by retinoic acid indicating that the desaturase plays a key role in the mechanisms of cell division and differentiation. Critical signal transduction pathways that are known to modulate these processes, such epidermal growth factor receptor (EGFR)Akt/ERK and Wnt, were affected by SCD5 expression. Epidermal growth factor-induced phosphorylation of EGFR, Akt and ERK was markedly blunted in SCD5-expressing cells. Furthermore, the activity of canonical Wnt was reduced whereas the non-canonical Wnt was increased by the presence of SCD5 activity. Finally, SCD5 expression increased the secretion of recombinant Wnt5a, a non-canonical Wnt, whereas it reduced the cellular and secreted levels of canonical Wnt7b. Our data suggest that, by a coordinated modulation of key lipogenic pathways and transduction signaling cascades, SCD5 participates in the regulation of neuronal cell growth and differentiation.

Global Gene Expression Profiling in PPAR-γ Agonist-Treated Kidneys in an Orthologous Rat Model of Human Autosomal Recessive Polycystic Kidney Disease

Kidneys are enlarged by aberrant proliferation of tubule epithelial cells leading to the formation of numerous cysts, nephron loss, and interstitial fibrosis in polycystic kidney disease (PKD). Pioglitazone (PIO), a PPAR-γ agonist, decreased cell proliferation, interstitial fibrosis, and inflammation, and ameliorated PKD progression in PCK rats (Am. J. Physiol.-Renal, 2011). To explore genetic mechanisms involved, changes in global gene expression were analyzed. By Gene Set Enrichment Analysis of 30655 genes, 13 of the top 20 downregulated gene ontology biological process gene sets and six of the top 20 curated gene set canonical pathways identified to be downregulated by PIOtreatment were related to cell cycle and proliferation, including EGF, PDGF and JNK pathways. Their relevant pathways were identified using the Kyoto Encyclopedia of Gene and Genomes database. Stearoyl-coenzyme A desaturase 1 is a key enzyme in fatty acid metabolism found in the top 5 genes downregulated by PIO treatment. Immunohistochemical analysis revealed that the gene product of this enzyme was highly expressed in PCK kidneys and decreased by PIO. These data show that PIO alters the expression of genes involved in cell cycle progression, cell proliferation, and fatty acid metabolism.

Herpes simplex virus 1 induces de novo phospholipid synthesis

Herpes simplex virus type 1 capsids bud at nuclear membranes and Golgi membranes acquiring an envelope composed of phospholipids. Hence, we measured incorporation of phospholipid precursors into these membranes, and quantified changes in size of cellular compartments by morphometric analysis. Incorporation of [³H]-choline into both nuclear and cytoplasmic membranes was significantly enhanced upon infection. [³H]-choline was also part of isolated virions even grown in the presence of brefeldin A. Nuclei expanded early in infection. The Golgi complex and vacuoles increased substantially whereas the endoplasmic reticulum enlarged only temporarily. The data suggest that HSV-1 stimulates phospholipid synthesis, and that de novo synthesized phospholipids are inserted into nuclear and cytoplasmic membranes to i) maintain membrane integrity in the course of nuclear and cellular expansion, ii) to supply membrane constituents for envelopment of capsids by budding at nuclear membranes and Golgi membranes, and iii) to provide membranes for formation of transport vacuoles.

Comparison of NMR lipid profiles in mitotic arrest and apoptosis as indicators of paclitaxel resistance in cervical cell lines

This study aimed to characterize changes in lipid saturation using magnetic resonance spectroscopy of sensitive (HeLa) and resistant (C33A; Me180) cervical cancer cell lines following exposure to paclitaxel to explore lipid profiles as biomarkers of drug resistance. Spectra were acquired at 11.74 T. Flow cytometry, electron, and confocal microscopy assessed cellular morphology. Western blots assessed cytoplasmic phospholipase A(2) , fatty acid synthase, and acyl-CoA synthetase1 expression. After 24 h of paclitaxel exposure, >60% of cells showed mitotic arrest. At 48 h, HeLa cells showed apoptosis while C33A/Me180 cells showed normal morphology indicating resistance. MR-visible lipids increased significantly in all lines at 24 h with further increases at 48 h; resistant lines showed smaller increases than HeLa. Cytoplasmic phospholipase A(2) and fatty acid synthase levels were unchanged at 24 h and dropped at 48 h in HeLa; acyl-CoA synthetase1 was higher in Me180/C33A than in HeLa controls but did not increase significantly. The percentage of cells displaying lipid droplets increased significantly at 24 and 48 h in all lines; droplet size increased only in HeLa cells. Droplet number was >3-4× greater in apoptotic compared with mitotic-arrested cells. Apoptotic cells accumulate unsaturated fatty acids in large (relative to control) droplets; resistant lines accumulated smaller droplets with less triglycerides.

Modulation of melanoma cell phospholipid metabolism in response to heat shock protein 90 inhibition

Molecular chaperone heat shock protein 90 (Hsp90) inhibitors are promising targeted cancer therapeutic drugs, with the advantage that they deplete multiple oncogenic client proteins and modulate all the classical hallmarks of cancer. They are now in clinical trial and show potential for activity in melanoma and other malignancies. Here we explore the metabolic response to Hsp90 inhibition in human melanoma cells using magnetic resonance spectroscopy. We show that, concomitant with growth inhibition and re-differentiation, Hsp90 inhibition in human melanoma cells is associated with increased glycerophosphocholine content. This was seen with both the clinical geldanamycin-based Hsp90 drug 17-AAG and the structurally dissimilar Hsp90 inhibitor CCT018159. The effect was noted in both BRAF mutant SKMEL28 and BRAF wildtype CHL-1 melanoma cells. Elevated content of the -CH2+CH3 fatty acyl chains and cytoplasmic mobile lipid droplets was also observed in 17-AAG-treated SKMEL28 cells. Importantly, the phospholipase A2 inhibitor bromoenol lactone prevented the rise in glycerophosphocholine seen with 17-AAG, suggesting a role for phospholipase A2 activation in the Hsp90 inhibitor-induced metabolic response. Our findings provide a basis for using metabolic changes as non-invasive indicators of Hsp90 inhibition and potentially as biomarkers of anticancer activity with Hsp90 drugs in malignant melanoma and possibly in other cancers.

Remarkable inhibitory effects of hybrid liposomes on growth of human colon cancer cells through induction of cell cycle arrest along with apoptosis

Background

Hybrid liposomes can be prepared by simply sonicating a mixture of vesicular and micellar molecules in buffer solutions. In this study, we investigated the effects of hybrid liposomes on the growth of human colon cancer cells in vitro.

Methods

Hybrid liposomes (HL-n, n = 21, 23, 25) composed of L-α-dimyristoylphosphatidylcholine (DMPC) and polyoxyethylene(n) dodecyl ethers (C₁₂(EO)_n, n = 21, 23, 25) were prepared by the sonication method and their inhibitory effects on growth of human colon cancer HCT116 cells were examined in vitro.

Results

Significant growth inhibition of HCT116 cells was observed in the presence of HL-n. The fifty percent inhibitory concentration (IC₅₀) of HL-n was less than half that of DMPC liposomes. Furthermore, fluorescence microscopic and flow cytometric analyses indicated that the markedly inhibitory effects of HL-n on the growth of HCT116 cells could be attained through the induction of cell cycle arrest at the G₀/G₁ phase along with apoptotic cell death.

Conclusion

It was found for the first time that HL-n can induce both cell cycle arrest and apoptosis in colon cancer cells. The findings in this study should contribute to novel chemotherapy for colon cancer.

Choline metabolism, proliferation, and angiogenesis in nonenhancing grades 2 and 3 astrocytoma

PURPOSE

To study choline metabolism in biopsies from nonenhancing Grade 2 (AS2) and Grade 3 (AS3) astrocytomas to determine whether (1) phosphocholine (PC) dominates in AS3, and (2) PC is associated with proliferation or angiogenesis. PC and glycerophosphocholine (GPC) are involved in phospholipid metabolism that accompanies mitosis. PC is the predominant peak in Grade 4 astrocytoma (GBM) while GPC dominates in AS2.

MATERIALS AND METHODS

We used high resolution magic angle spinning magnetic resonance spectroscopy to compare the concentrations of 10 metabolites in 41 biopsies (16 AS2 and 25 AS3) from 24 tumors. Immunohistochemistry was performed on paired biopsies to determine the cell density, Ki-67 proliferation index, and vascular endothelial growth factor (VEGF) angiogenic marker expression.

RESULTS

AS3 had higher PC than AS2; however, the PC:GPC was less than 1 in all cases irrespective of tumor grade. Within tumors, GPC increased with Ki-67 and PC and tCho increased with cell density. There was no association between any choline compound and VEGF.

CONCLUSION

These data suggest that PC:GPC less than 1 is not unique to low grade glioma. Furthermore, the PC concentration that is a marker of aggressive glial tumors is not tightly linked to cell proliferation or angiogenesis in nonenhancing astrocytomas.

Phospholipid synthesis participates in the regulation of diacylglycerol required for membrane trafficking at the Golgi complex

The lipid metabolite diacylglycerol (DAG) is required for transport carrier biogenesis at the Golgi, although how cells regulate its levels is not well understood. Phospholipid synthesis involves highly regulated pathways that consume DAG and can contribute to its regulation. Here we altered phosphatidylcholine (PC) and phosphatidylinositol synthesis for a short period of time in CHO cells to evaluate the changes in DAG and its effects in membrane trafficking at the Golgi. We found that cellular DAG rapidly increased when PC synthesis was inhibited at the non-permissive temperature for the rate-limiting step of PC synthesis in CHO-MT58 cells. DAG also increased when choline and inositol were not supplied. The major phospholipid classes and triacylglycerol remained unaltered for both experimental approaches. The analysis of Golgi ultrastructure and membrane trafficking showed that 1) the accumulation of the budding vesicular profiles induced by propanolol was prevented by inhibition of PC synthesis, 2) the density of KDEL receptor-containing punctated structures at the endoplasmic reticulum-Golgi interface correlated with the amount of DAG, and 3) the post-Golgi transport of the yellow fluorescent temperature-sensitive G protein of stomatitis virus and the secretion of a secretory form of HRP were both reduced when DAG was lowered. We confirmed that DAG-consuming reactions of lipid synthesis were present in Golgi-enriched fractions. We conclude that phospholipid synthesis pathways play a significant role to regulate the DAG required in Golgi-dependent membrane trafficking.

Roles of StearoylCoA Desaturase-1 in the Regulation of Cancer Cell Growth, Survival and Tumorigenesis

The development and maintenance of defining features of cancer, such as unremitting cell proliferation, evasion of programmed cell death, and the capacity for colonizing local tissues and distant organs, demand a massive production of structural, signaling and energy-storing lipid biomolecules of appropriate fatty acid composition. Due to constitutive activation of fatty acid biosynthesis, cancer cell lipids are enriched with saturated (SFA) and, in particular, monounsaturated fatty acids (MUFA), which are generated by StearoylCoA desaturase-1, the main enzyme that transforms SFA into MUFA. An increasing number of experimental and epidemiological studies suggest that high levels of SCD1 activity is a major factor in establishing the biochemical and metabolic perturbations that favors the oncogenic process. This review examines evidence that suggests the critical implication of SCD1 in the modulation of multiple biological mechanisms, specifically lipid biosynthesis and proliferation and survival signaling pathways that contribute to the development and progression of cancer.

Inhibition of stearoyl-CoA desaturase 1 expression induces CHOP-dependent cell death in human cancer cells

BACKGROUND

Cancer cells present a sustained de novo fatty acid synthesis with an increase of saturated and monounsaturated fatty acid (MUFA) production. This change in fatty acid metabolism is associated with overexpression of stearoyl-CoA desaturase 1 (Scd1), which catalyses the transformation of saturated fatty acids into monounsaturated fatty acids (e.g., oleic acid). Several reports demonstrated that inhibition of Scd1 led to the blocking of proliferation and induction of apoptosis in cancer cells. Nevertheless, mechanisms of cell death activation remain to be better understood.

PRINCIPAL FINDINGS

In this study, we demonstrated that Scd1 extinction by siRNA triggered abolition of de novo MUFA synthesis in cancer and non-cancer cells. Scd1 inhibition-activated cell death was only observed in cancer cells with induction of caspase 3 activity and PARP-cleavage. Exogenous supplementation with oleic acid did not reverse the Scd1 ablation-mediated cell death. In addition, Scd1 depletion induced unfolded protein response (UPR) hallmarks such as Xbp1 mRNA splicing, phosphorylation of eIF2α and increase of CHOP expression. However, the chaperone GRP78 expression, another UPR hallmark, was not affected by Scd1 knockdown in these cancer cells indicating a peculiar UPR activation. Finally, we showed that CHOP induction participated to cell death activation by Scd1 extinction. Indeed, overexpression of dominant negative CHOP construct and extinction of CHOP partially restored viability in Scd1-depleted cancer cells.

CONCLUSION

These results suggest that inhibition of de novo MUFA synthesis by Scd1 extinction could be a promising anti-cancer target by inducing cell death through UPR and CHOP activation.

Inhibition of stearoylCoA desaturase activity blocks cell cycle progression and induces programmed cell death in lung cancer cells

Lung cancer is the most frequent form of cancer. The survival rate for patients with metastatic lung cancer is approximately 5%, hence alternative therapeutic strategies to treat this disease are critically needed. Recent studies suggest that lipid biosynthetic pathways, particularly fatty acid synthesis and desaturation, are promising molecular targets for cancer therapy. We have previously reported that inhibition of stearoylCoA desaturase-1 (SCD1), the enzyme that produces monounsaturated fatty acids (MUFA), impairs lung cancer cell proliferation, survival and invasiveness, and dramatically reduces tumor formation in mice. In this report, we show that inhibition of SCD activity in human lung cancer cells with the small molecule SCD inhibitor CVT-11127 reduced lipid synthesis and impaired proliferation by blocking the progression of cell cycle through the G(1)/S boundary and by triggering programmed cell death. These alterations resulting from SCD blockade were fully reversed by either oleic (18:1n-9), palmitoleic acid (16:1n-7) or cis-vaccenic acid (18:1n-7) demonstrating that cis-MUFA are key molecules for cancer cell proliferation. Additionally, co-treatment of cells with CVT-11127 and CP-640186, a specific acetylCoA carboxylase (ACC) inhibitor, did not potentiate the growth inhibitory effect of these compounds, suggesting that inhibition of ACC or SCD1 affects a similar target critical for cell proliferation, likely MUFA, the common fatty acid product in the pathway. This hypothesis was further reinforced by the observation that exogenous oleic acid reverses the anti-growth effect of SCD and ACC inhibitors. Finally, exogenous oleic acid restored the globally decreased levels of cell lipids in cells undergoing a blockade of SCD activity, indicating that active lipid synthesis is required for the fatty acid-mediated restoration of proliferation in SCD1-inhibited cells. Altogether, these observations suggest that SCD1 controls cell cycle progression and apoptosis and, consequently, the overall rate of proliferation in cancer cells through MUFA-mediated activation of lipid synthesis.

13C-labelling studies indicate compartmentalized synthesis of triacylglycerols in C6 rat glioma cells

NMR-visible mobile lipid (ML) signals have been detected in (1)H-NMR spectra of tissues in vivo, ex vivo and in vitro, and have been shown to change in apparent intensity in association with pathology (necrosis in brain tumours) and normal processes (cell differentiation, cell growth arrest and apoptosis). Although it is widely accepted that ML signals originate mainly from fatty-acyl chains in triacylglycerols (TAG) contained in cytosolic lipid droplets (LD), the dynamics of TAG in LD is not yet fully understood. In order to better understand the synthesis of cellular TAG and its relationship to ML dynamics we carried out a set of labelling experiments with C6 rat glioma cells in culture. TAG and phospholipid metabolism was monitored by incubating C6 cells with [1-(13)C]-glucose at two time points during cell growth curve -24 h incubation starting at log-phase; 48 h incubation starting at saturation density- and by acquiring the 2D-HMQC NMR spectra of the respective total lipid extracts. The resulting TAG, diacylglycerol (DAG) and phospholipid labelling patterns can only be explained if TAG synthesis takes place in two different subcellular compartments. One compartment would be the endoplasmic reticulum, which is known to be involved in TAG metabolism, while the other compartment could be the plasma membrane and/or the LD. This possible role of LD is further supported by the recent description of diacylglycerolacyltranferase-activity associated with LD. Accordingly, we postulate the existence of a carbon-shuttling mechanism between plasma membrane phospholipids and endoplasmic reticulum by way of LD content. The results we have obtained with C6 cells may also apply to other cellular systems and should be taken into account when interpreting ML dynamics detected by NMR in vivo.

ATPase family AAA domain-containing 3A is a novel anti-apoptotic factor in lung adenocarcinoma cells

AAA domain-containing 3A (ATAD3A) is a member of the AAA-ATPase family. Three forms of ATAD3 have been identified: ATAD3A, ATAD3B and ATAD3C. In this study, we examined the type and expression of ATAD3 in lung adenocarcinoma (LADC). Expression of ATAD3A was detected by reverse transcription-polymerase chain reaction, immunoblotting, immunohistochemistry and confocal immunofluorescent microscopy. Our results show that ATAD3A is the major form expressed in LADC. Silencing of ATAD3A expression increased mitochondrial fragmentation and cisplatin sensitivity. Serum deprivation increased ATAD3A expression and drug resistance. These results suggest that ATAD3A could be an anti-apoptotic marker in LADC.

Specific interaction between E2F1 and Sp1 regulates the expression of murine CTP:phosphocholine cytidylyltransferase alpha during the S phase

CTP:phosphocholine cytidylyltransferase alpha (CCTalpha) is a key enzyme for phosphatidylcholine biosynthesis in mammalian cells. This enzyme plays an essential role in all processes that require membrane biosynthesis such as cell proliferation and viability. Thus, CCTalpha activity and expression fluctuate during the cell cycle to achieve PtdCho requirements. We demonstrated, for the first time, that CCTalpha is localized in the nucleus in cells transiting the S phase, whereas it is localized in the cytoplasm of G(0)-arrested cells, suggesting a specific role of nuclear CCTalpha during the S phase. We also investigated how E2F1 influences the regulation of the CCTalpha-promoter during the S phase; we demonstrated that E2F1 is necessary, but not sufficient, to activate CCTalpha expression when this factor is over-expressed. However, when E2F1 and Sp1 were over-expressed, the transcription from the CCTalpha-promoter reporter construct was super-activated. Transient transfection studies demonstrated that E2F1 could super-activate Sp1-dependent transcription in a promoter containing only the Sp1 binding sites "B" or "C", and that Sp1 could activate Sp1-dependent transcription in a promoter containing the E2F site, thus, further demonstrating a functional interaction of these factors. In conclusion, the present results allowed us to portray the clearest picture of the CCTalpha-gene expression in proliferating cells, and understand the mechanism by which cells coordinate cell cycle progression with the requirement for phosphatidylcholine.

Depletion of phosphatidylcholine affects endoplasmic reticulum morphology and protein traffic at the Golgi complex

The mutant Chinese hamster ovary cell line MT58 contains a thermosensitive mutation in CTP:phosphocholine cytidylyltransferase, the regulatory enzyme in the CDP-choline pathway. As a result, MT58 cells have a 50% decrease in their phosphatidylcholine (PC) level within 24 h when cultured at the nonpermissive temperature (40 degrees C). This is due to a relative rapid breakdown of PC that is not compensated for by the inhibition of de novo PC synthesis. Despite this drastic decrease in cellular PC content, cells are viable and can proliferate by addition of lysophosphatidylcholine. By [(3)H]oleate labeling, we found that the FA moiety of the degraded PC is recovered in triacylglycerol. In accordance with this finding, an accumulation of lipid droplets is seen in MT58 cells. Analysis of PC-depleted MT58 cells by electron and fluorescence microscopy revealed a partial dilation of the rough endoplasmic reticulum, resulting in spherical structures on both sites of the nucleus, whereas the morphology of the plasma membrane, mitochondria, and Golgi complex was unaffected. In contrast to these morphological observations, protein transport from the ER remains intact. Surprisingly, protein transport at the level of the Golgi complex is impaired. Our data suggest that the transport processes at the Golgi complex are regulated by distal changes in lipid metabolism.

Content of endoplasmic reticulum and Golgi complex membranes positively correlates with the proliferative status of brain cells

Although the molecular and cellular basis of particular events that lead to the biogenesis of membranes in eukaryotic cells has been described in detail, understanding of the intrinsic complexity of the pleiotropic response by which a cell adjusts the overall activity of its endomembrane system to accomplish these requirements is limited. Here we carried out an immunocytochemical and biochemical examination of the content and quality of the endoplasmic reticulum (ER) and Golgi apparatus membranes in two in vivo situations characterized by a phase of active cell proliferation followed by a phase of declination in proliferation (rat brain tissue at early and late developmental stages) or by permanent active proliferation (gliomas and their most malignant manifestation, glioblastomas multiforme). It was found that, in highly proliferative phases of brain development (early embryo brain cells), the content of ER and Golgi apparatus membranes, measured as total lipid phosphorous content, is higher than in adult brain cells. In addition, the concentration of protein markers of ER and Golgi is also higher in early embryo brain cells and in human glioblastoma multiforme cells than in adult rat brain or in nonpathological human brain cells. Results suggest that the amount of endomembranes and the concentration of constituent functional proteins diminish as cells decline in their proliferative activity.

CTP:phosphocholine cytidylyltransferase alpha is required for B-cell proliferation and class switch recombination

CTP:phosphocholine cytidylyltransferase (CCT) is a key rate-controlling enzyme in the biosynthetic pathway leading to the principle membrane phospholipid, phosphatidylcholine. CCTalpha is the predominant isoform expressed in mammalian cells. To investigate the role of CCTalpha in the development and function of B-lymphocytes, mice with B-lymphocytes that selectively lacked CCTalpha were derived using the CD19-driven Cre/loxP system. When challenged with a T-cell-dependent antigen, the animals harboring CCTalpha-deficient B-cells exhibited a hyper-IgM secretion phenotype coupled with a lack of IgG production. The inability of CCTalpha-/- B-cells to undergo class switch recombination correlated with a proliferation defect in vivo and in vitro in response to antigenic and mitogenic stimuli. Lipopolysaccharide stimulation of CCTalpha-/- B-cells resulted in an early trigger of the unfolded protein response-mediated splicing of Xbp-1 mRNA, and this was accompanied by accelerated kinetics of IgM secretion and higher incidence of IgM-secreting cells. Thus, the inability of stimulated B-cells to produce enough phosphatidylcholine prevents proliferation and class switch recombination but leads to unfolded protein response activation and a hyper-IgM secretion phenotype.

Activation of cytosolic phospholipase A2-{alpha} as a novel mechanism regulating endothelial cell cycle progression and angiogenesis

Release of endothelial cells from contact-inhibition and cell cycle re-entry is required for the induction of new blood vessel formation by angiogenesis. Using a combination of chemical inhibition, loss of function, and gain of function approaches, we demonstrate that endothelial cell cycle re-entry, S phase progression, and subsequent angiogenic tubule formation are dependent upon the activity of cytosolic phospholipase A(2)-alpha (cPLA(2)alpha). Inhibition of cPLA(2)alpha activity and small interfering RNA (siRNA)-mediated knockdown of endogenous cPLA(2)alpha reduced endothelial cell proliferation. In the absence of cPLA(2)alpha activity, endothelial cells exhibited retarded progression from G(1) through S phase, displayed reduced cyclin A/cdk2 expression, and generated less arachidonic acid. In quiescent endothelial cells, cPLA(2)alpha is inactivated upon its sequestration at the Golgi apparatus. Upon the stimulation of endothelial cell proliferation, activation of cPLA(2)alpha by release from the Golgi apparatus was critical to the induction of cyclin A expression and efficient cell cycle progression. Consequently, inhibition of cPLA(2)alpha was sufficient to block angiogenic tubule formation in vitro. Furthermore, the siRNA-mediated retardation of endothelial cell cycle re-entry and proliferation was reversed upon overexpression of an siRNA-resistant form of cPLA(2)alpha. Thus, activation of cPLA(2)alpha acts as a novel mechanism for the regulation of endothelial cell cycle re-entry, cell cycle progression, and angiogenesis.

Mechanism of the elevation in cardiolipin during HeLa cell entry into the S-phase of the human cell cycle

CL (cardiolipin) is a key phospholipid involved in ATP generation. Since progression through the cell cycle requires ATP we examined regulation of CL synthesis during S-phase in human cells and investigated whether CL or CL synthesis was required to support nucleotide synthesis in S-phase. HeLa cells were made quiescent by serum depletion for 24 h. Serum addition resulted in substantial stimulation of [methyl-3H]thymidine incorporation into cells compared with serum-starved cells by 8 h, confirming entry into the S-phase. CL mass was unaltered at 8 h, but increased 2-fold by 16 h post-serum addition compared with serum-starved cells. The reason for the increase in CL mass upon entry into S-phase was an increase in activity and expression of CL de novo biosynthetic and remodelling enzymes and this paralleled the increase in mitochondrial mass. CL de novo biosynthesis from D-[U-14C]glucose was elevated, and from [1,3-3H]glycerol reduced, upon serum addition to quiescent cells compared with controls and this was a result of differences in the selection of precursor pools at the level of uptake. Triascin C treatment inhibited CL synthesis from [1-14C]oleate but did not affect [methyl-3H]thymidine incorporation into HeLa cells upon serum addition to serum-starved cells. Barth Syndrome lymphoblasts, which exhibit reduced CL, showed similar [methyl-3H]thymidine incorporation into cells upon serum addition to serum-starved cells compared with cells from normal aged-matched controls. The results indicate that CL de novo biosynthesis is up-regulated via elevated activity and expression of CL biosynthetic genes and this accounted for the doubling of CL seen during S-phase; however, normal de novo CL biosynthesis or CL itself is not essential to support nucleotide synthesis during entry into S-phase of the human cell cycle.

Testing the hypothesis that amphiphilic antineoplastic lipid analogues act through reduction of membrane curvature elastic stress

The alkyllysophospholipid (ALP) analogues Mitelfosine and Edelfosine are anticancer drugs whose mode of action is still the subject of debate. It is agreed that the primary interaction of these compounds is with cellular membranes. Furthermore, the membrane-associated protein CTP: phosphocholine cytidylyltransferase (CCT) has been proposed as the critical target. We present the evaluation of our hypothesis that ALP analogues disrupt membrane curvature elastic stress and inhibit membrane-associated protein activity (e.g. CCT), ultimately resulting in apoptosis. This hypothesis was tested by evaluating structure-activity relationships of ALPs from the literature. In addition we characterized the lipid typology, cytotoxicity and critical micelle concentration of novel ALP analogues that we synthesized. Overall we find the literature data and our experimental data provide excellent support for the hypothesis, which predicts that the most potent ALP analogues will be type I lipids.

Cell cycle regulation of the BRCA1/acetyl-CoA-carboxylase complex

Germ-line alterations in BRCA1 are associated with an increased susceptibility to breast and ovarian cancer. The BRCA1 protein has been implicated in multiple cellular functions. We have recently demonstrated that BRCA1 reduces acetyl-CoA-carboxylase alpha (ACCA) activity through its phospho-dependent binding to ACCA, and further established that the phosphorylation of the Ser1263 of ACCA is required for this interaction. Here, to gain more insight into the cellular conditions that trigger the BRCA1/ACCA interaction, we designed an anti-pSer1263 antibody and demonstrated that the Ser1263 of ACCA is phosphorylated in vivo, in a cell cycle-dependent manner. We further showed that the interaction between BRCA1 and ACCA is regulated during cell cycle progression. Taken together, our findings reveal a novel mechanism of regulation of ACCA distinct from the previously described phosphorylation of Ser79, and provide new insights into the control of lipogenesis through the cell cycle.

Cytokine secretion requires phosphatidylcholine synthesis

Choline cytidylyltransferase (CCT) is the rate-limiting enzyme in the phosphatidylcholine biosynthetic pathway. Here, we demonstrate that CCTα-mediated phosphatidylcholine synthesis is required to maintain normal Golgi structure and function as well as cytokine secretion from the Golgi complex. CCTα is localized to the trans-Golgi region and its expression is increased in lipopolysaccharide (LPS)-stimulated wild-type macrophages. Although LPS triggers transient reorganization of Golgi morphology in wild-type macrophages, similar structural alterations persist in CCTα-deficient cells. Pro–tumor necrosis factor α and interleukin-6 remain lodged in the secretory compartment of CCTα-deficient macrophages after LPS stimulation. However, the lysosomal-mediated secretion pathways for interleukin-1β secretion and constitutive apolipoprotein E secretion are unaltered. Exogenous lysophosphatidylcholine restores LPS-stimulated secretion from CCTα-deficient cells, and elevated diacylglycerol levels alone do not impede secretion of pro–tumor necrosis factor α or interleukin-6. These results identify CCTα as a key component in membrane biogenesis during LPS-stimulated cytokine secretion from the Golgi complex.

The increase of cell-membranous phosphatidylcholines containing polyunsaturated fatty acid residues induces phosphorylation of p53 through activation of ATR

The G1 phase of the cell cycle is marked by the rapid turnover of phospholipids. This turnover is regulated by CTP:phosphocholine-cytidylyltransferase (CCT) and group VIA Ca(2+)-independent-phospholipase A(2) (iPLA(2)). We previously reported that inhibition of iPLA(2) arrests cells in G1 phase of the cell cycle by activating the p53-p21 checkpoint. Here we further characterize the mechanism of p53 activation. We show that specific inhibition of iPLA(2) induces a time dependent phosphorylation of Ser15 in p53 in the absence of DNA damage. This phosphorylation requires the kinase ataxia-telangiectasia and Rad-3-related (ATR) but not the ataxia-telangiectasia-mutated (ATM) kinase. Moreover, we identify in cell membranes a significant increase of phosphatidylcholines (PCs) containing chains of polyunsaturated fatty acids and a decrease of PCs containing saturated fatty acids in response to inhibition of iPLA(2). The time course of phosphorylation of Ser15 in p53 correlates with increasing levels of PCs containing polyunsaturated fatty acids. We further demonstrate that the PCs with linoleic acid in their sn-2 position (18:2n6) induce phosphorylation of Ser15 in p53 in an ATR-dependent manner. Our findings establish that cells can regulate the levels of polyunsaturated fatty acids in phospholipids through iPLA(2)-mediated deacylation of PCs. Disruption of this regulation increases the proportions of PCs containing polyunsaturated fatty acids and activates the ATR-p53 signalling pathway.

Biophysical regulation of lipid biosynthesis in the plasma membrane

We present a cellular model of lipid biosynthesis in the plasma membrane that couples biochemical and biophysical features of the enzymatic network of the cell-wall-less Mycoplasma Acholeplasma laidlawii. In particular, we formulate how the stored elastic energy of the lipid bilayer can modify the activity of curvature-sensitive enzymes through the binding of amphipathic alpha-helices. As the binding depends on lipid composition, this results in a biophysical feedback mechanism for the regulation of the stored elastic energy. The model shows that the presence of feedback increases the robustness of the steady state of the system, in the sense that biologically inviable nonbilayer states are less likely. We also show that the biophysical and biochemical features of the network have implications as to which enzymes are most efficient at implementing the regulation. The network imposes restrictions on the steady-state balance between bilayer and nonbilayer lipids and on the concentrations of particular lipids. Finally, we consider the influence of the length of the amphipathic alpha-helix on the efficacy of the feedback and propose experimental measurements and extensions of the modeling framework.

Phosphatidylcholine catabolism in the MCF-7 cell cycle

The catabolism of phosphatidylcholine (PtdCho) appears to play a key role in regulating the net accumulation of the lipid in the cell cycle. Current protocols for measuring the degradation of PtdCho at specific cell-cycle phases require prolonged periods of incubation with radiolabelled choline. To measure the degradation of PtdCho at the S and G2 phases in the MCF-7 cell cycle, protocols were developed with radiolabelled lysophosphatidylcholine (lysoPtdCho), which reduces the labelling period and minimizes the recycling of labelled components. Although most of the incubated lysoPtdCho was hydrolyzed to glycerophosphocholine (GroPCho) in the medium, the kinetics of the incorporation of label into PtdCho suggests that the labelled GroPCho did not contribute significantly to cellular PtdCho formation. A protocol which involved exposing the cells twice to hydroxyurea, was also developed to produce highly synchronized MCF-7 cells with a profile of G1:S:G2/M of 90:5:5. An analysis of PtdCho catabolism in the synchronized cells following labelling with lysoPtdCho revealed that there was increased degradation of PtdCho in early to mid-S phase, which was attenuated in the G2/M phase. The results suggest that the net accumulation of PtdCho in MCF-7 cells may occur in the G2 phase of the cell cycle.

Crystal structure of uncleaved L-aspartate-alpha-decarboxylase from Mycobacterium tuberculosis

L-aspartate-alpha-decarboxylase (ADC) is a critical regulatory enzyme in the pantothenate biosynthetic pathway and belongs to a small class of self-cleaving and pyruvoyl-dependent amino acid decarboxylases. The expression level of ADC in Mycobacterium tuberculosis (Mtb) was confirmed by cDNA analysis, immunoblotting with an anti-ADC polyclonal antibody using whole cell lysate and immunoelectron microscopy. The recombinant ADC proenzyme from Mycobacterium tuberculosis (MtbADC) was overexpressed in E. coli and the protein structure was determined at 2.99 A resolution. The proteins fold into the double-psi beta-barrel structure. The subunits of the two tetramers (there are eight ADC molecules in the asymmetric unit) form pseudo fourfold rotational symmetry, similar to the E. coli ADC proenzyme structure. As pantothenate is synthesized in microorganisms, plants, and fungi but not in animals, structure elucidation of Mtb ADC is of substantial interest for structure-based drug development.

Golgi twins in late mitosis revealed by genetically encoded tags for live cell imaging and correlated electron microscopy

Combinations of molecular tags visible in light and electron microscopes become particularly advantageous in the analysis of dynamic cellular components like the Golgi apparatus. This organelle disassembles at the onset of mitosis and, after a sequence of poorly understood events, reassembles after cytokinesis. The precise location of Golgi membranes and resident proteins during mitosis remains unclear, partly due to limitations of molecular markers and the resolution of light microscopy. We generated a fusion consisting of the first 117 residues of alpha-mannosidase II tagged with a fluorescent protein and a tetracysteine motif. The mannosidase component guarantees docking into the Golgi membrane, with the tags exposed in the lumen. The fluorescent protein is optically visible without further treatment, whereas the tetracysteine tag can be reduced acutely with a membrane-permeant phosphine, labeled with ReAsH, monitored in the light microscope, and used to trigger the photoconversion of diaminobenzidine, allowing 4D optical recording on live cells and correlated ultrastructural analysis by electron microscopy. These methods reveal that Golgi reassembly is preceded by the formation of four colinear clusters at telophase, two per daughter cell. Within each daughter, the smaller cluster near the midbody gradually migrates to rejoin the major cluster on the far side of the nucleus and asymmetrically reconstitutes a single Golgi apparatus, first in one daughter cell and then in the other. Our studies provide previously undescribed insights into Golgi disassociation and reassembly during mitosis and offer a powerful approach to follow recombinant protein distribution in 4D imaging and correlated high-resolution analysis.

Phospholipids are synthesized in the G2/M phase of the cell cycle

Very little is known about the metabolism of phospholipids in the G2 and M phases of the cell cycle, but limited studies have led to the postulation that phospholipid synthesis ceases during this period. To investigate whether phospholipids are synthesized in the G2/M phase of the cell cycle, protocols were developed to produce synchronized MCF-7 cell populations with greater than 80% of the cells in G1/S or G2/M phases that moved in synchrony following removal of the blocking agent. Analysis of the activities of key phosphatidylcholine and phosphatidylethanolamine biosynthetic enzymes in subcellular fractions obtained from MCF-7 cells at different cell cycle phases revealed that there was robust activity of key enzymes in the fractions prepared from MCF-7 cells in G2/M phase. Radiolabeled choline and ethanolamine were rapidly incorporated into cells maintained at G2/M phase with nocodazole, and the rates of incorporation were similar to those obtained in cells allowed to progress into the G1 phase. Furthermore, radiolabeled glycerol was incorporated into phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine and phosphatidic acid in MCF-7 cells maintained at G2/M phase with nocodazole. Similar results were obtained in CHO cells. These results demonstrate that glycerophospholipid synthesis is very active in the G2/M phase of these cells. Therefore, the postulated cessation of phospholipid synthesis in G2/M phases is not applicable to all cell types.

Unique molecular signatures of glycerophospholipid species in different rat tissues analyzed by tandem mass spectrometry

Glycerophospholipids (GPL) in animal tissues are composed of a large array of molecular species that mainly differ in the fatty acyl composition. In order to further understand the roles of GPL at the molecular level, it is necessary to have comprehensive, accurate accounts of the molecular makeup for these molecules in animal tissues. However, this task was difficult simply because the conventional technologies of profiling GPL species depended heavily on technical skill for accuracy and reliability and were extremely labor-intensive. In recent years, tandem mass spectrometry (MS/MS) proved to be a highly reliable and sensitive technology for profiling small molecules, including GPL, in biological samples. In this study, we used this technology to perform simultaneous comparative analyses for phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS) and phosphatidylinositol (PI) in the same lipid preparations of liver, lung, kidney, heart, pancreas, stomach, small intestine, spleen, skeleton muscle and brain of an adult rat. We produced molecular profiles of these 4 GPL classes in these 10 different tissues that are highly reproducible between different scans of the same sample and between samples from different animals. It is intriguing that each tissue was found to possess a unique signature of GPL profile that may be used to identify unknown tissues. More importantly, these profiles may also set reference points for studying changes of GPL metabolism in different physiological and pathological conditions.

Host resistance to Candida albicans infection of mice with collagen-induced arthritis treated with leflunomide

The dehydro-orotate dehydrogenase inhibitor leflunomide is used for the treatment of rheumatoid arthritis. In the present study, its influence on host resistance to Candida albicans infection in mice with collagen-induced arthritis (CIA) was investigated. Leflunomide administered at a dose of 5 mg/kg for 5 consecutive days in mice with CIA inhibited collagen-specific cellular and humoral responses. The drug did not change the severity of primary C. albicans infection evaluated by kidney and liver colonization. At the early stage of infection leflunomide inhibited IFN-gamma production and enhanced IL-4 secretion. The effect of the drug on IL-4 production was less pronounced at the late phase of infection. Leflunomide enhanced anti-Candida IgM antibody production and diminished anti-Candida IgG antibody synthesis. This correlated with impaired resistance to reinfection. Results demonstrate that leflunomide administration to mice with collagen-induced arthritis might affect mechanisms of the late immune response to C. albicans infection.

Maternal dietary (n-3) fatty acid deficiency alters neurogenesis in the embryonic rat brain

Docosahexaenoic acid [22:6(n-3)] is enriched in brain membrane phospholipids and essential for brain function. Neurogenesis during embryonic and fetal development requires synthesis of large amounts of membrane phospholipid. We determined whether dietary (n-3) fatty acid deficiency during gestation alters neurogenesis in the embryonic rat brain. Female rats were fed diets with 1.3% energy [(n-3) control] or 0.02% energy [(n-3) deficient], from alpha-linolenic acid [18:3(n-3)], beginning 2 wk before gestation. Morphometric analyses were performed on embryonic day 19 to measure the mean thickness of the neuroepithelial proliferative zones corresponding to the cerebral cortex (ventricular and subventricular zones) and dentate gyrus (primary dentate neuroepithelium), and the thickness of the cortical plate and sectional area of the dentate gyrus. Phospholipids and fatty acids were determined by HPLC and GLC. Docosahexaenoic acid was 55-65% lower and (n-6) docosapentaenoic acid [22:5(n-6)] was 150-225% higher in brain phospholipids at embryonic day 19 in the (n-3) deficient (n = 6 litters) than in the control (n = 5 litters) group. The mean thickness of the cortical plate and mean sectional area of the primordial dentate gyrus were 26 and 48% lower, respectively, and the mean thicknesses of the cortical ventricular zone and the primary dentate neuroepithelium were 110 and 70% higher, respectively, in the (n-3) deficient than in the control embryonic day 19 embryos. These studies demonstrate that (n-3) fatty acid deficiency alters neurogenesis in the embryonic rat brain, which could be explained by delay or inhibition of normal development.

Differential Targets and Subcellular Localization of Antitumor Alkyl-lysophospholipid in Leukemic Versus Solid Tumor Cells

Synthetic alkyl-lysophospholipids represent a family of promising anticancer drugs that induce apoptosis in a variety of tumor cells. Here we have found a differential subcellular distribution of the alkyl-lysophospholipid edelfosine in leukemic and solid tumor cells that leads to distinct anticancer responses. Edelfosine induced rapid apoptosis in human leukemic cells, including acute T-cell leukemia Jurkat and Peer cells, but promoted a late apoptotic response, preceded by G(2)/M arrest, in human solid tumor cells such as cervix epitheloid carcinoma HeLa cells and lung carcinoma A549 cells. c-Jun amino-terminal kinase (JNK) and caspase-3 were accordingly activated at earlier times in edelfosine-treated Jurkat cells as compared with drug-treated HeLa cells. Both leukemic and solid tumor cells took up this alkyl-lysophospholipid and expressed the two putative edelfosine targets, namely cell surface Fas death receptor (also known as APO-1 or CD95) and endoplasmic reticulum CTP: phosphocholine cytidylyltransferase. However, edelfosine was mainly located to plasma membrane lipid rafts in Jurkat and Peer leukemic cells and to endoplasmic reticulum in solid tumor HeLa and A549 cells. Edelfosine induced translocation of Fas, Fas-associated death domain-containing protein, and JNK into membrane rafts in Jurkat cells, but not in HeLa cells. In contrast, edelfosine inhibited phosphatidylcholine biosynthesis in both HeLa and A549 cells, but not in Jurkat or Peer leukemic cells, before the triggering of apoptosis. These data indicate that edelfosine targets two different subcellular structures in a cell type-dependent manner, namely cell surface lipid rafts in leukemic cells and endoplasmic reticulum in solid tumor cells.