Phosphatidylethanolamine and phosphatidylcholine are sources of diacylglycerol in ras-transformed NIH 3T3 fibroblasts

Metabolomic Evidence for Peroxisomal Dysfunction in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a chronic and debilitating disease characterized by unexplained physical fatigue, cognitive and sensory dysfunction, sleeping disturbances, orthostatic intolerance, and gastrointestinal problems. People with ME/CFS often report a prodrome consistent with infections. Using regression, Bayesian and enrichment analyses, we conducted targeted and untargeted metabolomic analysis of plasma from 106 ME/CFS cases and 91 frequency-matched healthy controls. Subjects in the ME/CFS group had significantly decreased levels of plasmalogens and phospholipid ethers (p < 0.001), phosphatidylcholines (p < 0.001) and sphingomyelins (p < 0.001), and elevated levels of dicarboxylic acids (p = 0.013). Using machine learning algorithms, we were able to differentiate ME/CFS or subgroups of ME/CFS from controls with area under the receiver operating characteristic curve (AUC) values up to 0.873. Our findings provide the first metabolomic evidence of peroxisomal dysfunction, and are consistent with dysregulation of lipid remodeling and the tricarboxylic acid cycle. These findings, if validated in other cohorts, could provide new insights into the pathogenesis of ME/CFS and highlight the potential use of the plasma metabolome as a source of biomarkers for the disease.

Evidence for Peroxisomal Dysfunction and Dysregulation of the CDP-Choline Pathway in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Background

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a chronic and debilitating disease that is characterized by unexplained physical fatigue unrelieved by rest. Symptoms also include cognitive and sensory dysfunction, sleeping disturbances, orthostatic intolerance, and gastrointestinal problems. A syndrome clinically similar to ME/CFS has been reported following well-documented infections with the coronaviruses SARS-CoV and MERS-CoV. At least 10% of COVID-19 survivors develop post acute sequelae of SARS-CoV-2 infection (PASC). Although many individuals with PASC have evidence of structural organ damage, a subset have symptoms consistent with ME/CFS including fatigue, post exertional malaise, cognitive dysfunction, gastrointestinal disturbances, and postural orthostatic intolerance. These common features in ME/CFS and PASC suggest that insights into the pathogenesis of either may enrich our understanding of both syndromes, and could expedite the development of strategies for identifying those at risk and interventions that prevent or mitigate disease.

Methods

Using regression, Bayesian and enrichment analyses, we conducted targeted and untargeted metabolomic analysis of 888 metabolic analytes in plasma samples of 106 ME/CFS cases and 91 frequency-matched healthy controls.

Results

In ME/CFS cases, regression, Bayesian and enrichment analyses revealed evidence of peroxisomal dysfunction with decreased levels of plasmalogens. Other findings included decreased levels of several membrane lipids, including phosphatidylcholines and sphingomyelins, that may indicate dysregulation of the cytidine-5’-diphosphocholine pathway. Enrichment analyses revealed decreased levels of choline, ceramides and carnitines, and increased levels of long chain triglycerides (TG) and hydroxy-eicosapentaenoic acid. Elevated levels of dicarboxylic acids were consistent with abnormalities in the tricarboxylic acid cycle. Using machine learning algorithms with selected metabolites as predictors, we were able to differentiate female ME/CFS cases from female controls (highest AUC=0.794) and ME/CFS cases without self-reported irritable bowel syndrome (sr-IBS) from controls without sr-IBS (highest AUC=0.873).

Conclusion

Our findings are consistent with earlier ME/CFS work indicating compromised energy metabolism and redox imbalance, and highlight new abnormalities that may provide insights into the pathogenesis of ME/CFS.

Plasma levels of plasmalogens are decreased in patients with myalgic encephalomyelitis/chronic fatigue syndrome suggesting peroxisome dysfunction.

LPEATs Tailor Plant Phospholipid Composition through Adjusting Substrate Preferences to Temperature

Acyl-CoA:lysophosphatidylethanolamine acyltransferases (LPEATs) are known as enzymes utilizing acyl-CoAs and lysophospholipids to produce phosphatidylethanolamine. Recently, it has been discovered that they are also involved in the growth regulation of Arabidopsis thaliana. In our study we investigated expression of each Camelina sativa LPEAT isoform and their behavior in response to temperature changes. In order to conduct a more extensive biochemical evaluation we focused both on LPEAT enzymes present in microsomal fractions from C. sativa plant tissues, and on cloned CsLPEAT isoforms expressed in yeast system. Phylogenetic analyses revealed that CsLPEAT1c and CsLPEAT2c originated from Camelina hispida, whereas other isoforms originated from Camelina neglecta. The expression ratio of all CsLPEAT1 isoforms to all CsLPEAT2 isoforms was higher in seeds than in other tissues. The isoforms also displayed divergent substrate specificities in utilization of LPE; CsLPEAT1 preferred 18:1-LPE, whereas CsLPEAT2 preferred 18:2-LPE. Unlike CsLPEAT1, CsLPEAT2 isoforms were specific towards very-long-chain fatty acids. Above all, we discovered that temperature strongly regulates LPEATs activity and substrate specificity towards different acyl donors, making LPEATs sort of a sensor of external thermal changes. We observed the presented findings not only for LPEAT activity in plant-derived microsomal fractions, but also for yeast-expressed individual CsLPEAT isoforms.

Spatially resolved metabolomic characterization of muscle invasive bladder cancer by mass spectrometry imaging

INTRODUCTION

Muscle invasive bladder cancer (MIBC) is an advanced stage of bladder cancer which poses a severe threat to life. Cancer development is usually accompanied by remarkable alterations in cell metabolism, and hence deep insights into MIBC at the metabolomic level can facilitate the understanding of the biochemical mechanisms involved in the cancer development and progression.

METHODS

In this proof-of-concept study, the optimal cutting temperature (OCT)-embedded MIBC samples were first washed with pure water to remove the polymer compounds which could cause severe signal suppression during mass spectrometry. Further, the tissue sections were analyzed by infrared matrix-assisted laser desorption electrospray ionization mass spectrometry imaging (IR-MALDESI MSI), providing an overview on the spatially resolved metabolomic profiles.

RESULTS

The MSI data enabled the discrimination between not only the cancerous and normal tissues, but also the subregions within a tissue section associated with different disease states. Using t-Distributed Stochastic Neighbor Embedding (t-SNE), the hyperdimensional MSI data was mapped into a two-dimensional space to visualize the spectral similarity, providing evidence that metabolomic alterations might have occurred outside the histopathological tumor border. Least absolute shrinkage and selection operator (LASSO) was further employed to classify sample pathology in a pixel-wise manner, yielding excellent prediction sensitivity and specificity up to 96% based on the statistically characteristic spectral features.

CONCLUSION

The results demonstrate great promise of IR-MALDESI MSI to identify molecular changes derived from cancer and unveil tumor heterogeneity, which can potentially promote the discovery of clinically relevant biomarkers and allow for applications in precision medicine.

Lipid metabolic pathways converge in motor neuron degenerative diseases

Motor neuron diseases (MNDs) encompass an extensive and heterogeneous group of upper and/or lower motor neuron degenerative disorders, in which the particular clinical outcomes stem from the specific neuronal component involved in each condition. While mutations in a large number of molecules associated with lipid metabolism are known to be implicated in MNDs, there remains a lack of clarity regarding the key functional pathways involved, and their inter-relationships. This review highlights evidence that defines defects within two specific lipid (cholesterol/oxysterol and phosphatidylethanolamine) biosynthetic cascades as being centrally involved in MND, particularly hereditary spastic paraplegia. We also identify how other MND-associated molecules may impact these cascades, in particular through impaired organellar interfacing, to propose ‘subcellular lipidome imbalance’ as a likely common pathomolecular theme in MND. Further exploration of this mechanism has the potential to identify new therapeutic targets and management strategies for modulation of disease progression in hereditary spastic paraplegias and other MNDs.

Simulated microgravity significantly altered metabolism in epidermal stem cells

Simulated microgravity can significantly affect various cell types and multiple systems of the human body, such as cardiovascular system, skeletal muscle system, and immune system, and is known to cause anemia and loss of electrolyte and fluids. Epidermal stem cells (EpSCs) were cultured in a rotary cell culture system (RCCS) bioreactor to simulate microgravity. The metabolites of EpSCs were identified by liquid chromatography-mass spectrometry (LC-MS). Compared with normal gravity (NG) group, a total of 57 different metabolites of EpSCs were identified (P < 0.05, VIP > 1), including lipids and lipid-like molecules (51 molecules), amino acids (5 molecules), nucleosides, nucleotides, and analogues (1 molecule). According to the partial least squares discriminant analysis (PLS-DA) score plot, a VIP > 1 and P < 0.05 were obtained for the 57 different metabolites, of which 23 molecules were significantly downregulated and 34 were significantly upregulated in simulated microgravity (SMG) group. These results showed that SMG has a significant impact on different pathways, and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis indicated that multiple pathways were involved, mainly the amino acid metabolism pathway, lipid metabolism pathway, membrane transport pathway, and cell growth and death pathways. Thus, the metabolic profile of EpSCs was changed under SMG. Exploring the metabolic profile of EpSCs would be helpful to further understand the growth characteristics of EpSCs under SMG, which will provide a new approach to explore the metabolomics mechanism of stress injury and repair trauma under SMG.

The Effect of Dexamethasone, Adrenergic and Cholinergic Receptor Agonists on Phospholipid Metabolism in Human Osteoarthritic Synoviocytes

Phospholipids (PLs) possess the unique ability to contribute to synovial joint lubrication. The aim of our study was to determine for the first time the effect of dexamethasone and some adrenergic and cholinergic agonists on the biosynthesis and release of PLs from human fibroblast-like synoviocytes (FLS). Osteoarthritic human knee FLS were treated with dexamethasone, terbutaline, epinephrine, carbachol, and pilocarpine, or the glucocorticoid receptor antagonist RU 486. Simultaneously PL biosynthesis was determined through the incorporation of stable isotope-labeled precursors into PLs. Radioactive isotope-labeled precursors were used to radiolabel PLs for the subsequent quantification of their release into nutrient media. Lipids were extracted and quantified using electrospray ionization tandem mass spectrometry or liquid scintillation counting. Dexamethasone significantly decreased the biosynthesis of phosphatidylcholine, phosphatidylethanolamine (PE), PE-based plasmalogen, and sphingomyelin. The addition of RU 486 abolished these effects. A release of PLs from FLS into nutrient media was not recognized by any of the tested agents. None of the adrenergic or cholinergic receptor agonists modulated the PL biosynthesis. We demonstrate for the first time an inhibitory effect of dexamethasone on the PL biosynthesis of FLS from human knees. Moreover, our study indicates that the PL metabolism of synovial joints and lungs are differently regulated.

A mutation of EPT1 (SELENOI) underlies a new disorder of Kennedy pathway phospholipid biosynthesis

Mutations in genes involved in lipid metabolism have increasingly been associated with various subtypes of hereditary spastic paraplegia, a highly heterogeneous group of neurodegenerative motor neuron disorders characterized by spastic paraparesis. Here, we report an unusual autosomal recessive neurodegenerative condition, best classified as a complicated form of hereditary spastic paraplegia, associated with mutation in the ethanolaminephosphotransferase 1 (EPT1) gene (now known as SELENOI), responsible for the final step in Kennedy pathway forming phosphatidylethanolamine from CDP-ethanolamine. Phosphatidylethanolamine is a glycerophospholipid that, together with phosphatidylcholine, constitutes more than half of the total phospholipids in eukaryotic cell membranes. We determined that the mutation defined dramatically reduces the enzymatic activity of EPT1, thereby hindering the final step in phosphatidylethanolamine synthesis. Additionally, due to central nervous system inaccessibility we undertook quantification of phosphatidylethanolamine levels and species in patient and control blood samples as an indication of liver phosphatidylethanolamine biosynthesis. Although this revealed alteration to levels of specific phosphatidylethanolamine fatty acyl species in patients, overall phosphatidylethanolamine levels were broadly unaffected indicating that in blood EPT1 inactivity may be compensated for, in part, via alternate biochemical pathways. These studies define the first human disorder arising due to defective CDP-ethanolamine biosynthesis and provide new insight into the role of Kennedy pathway components in human neurological function.

Application of imaging mass spectrometry for the molecular diagnosis of human breast tumors

Distinguishing breast invasive ductal carcinoma (IDC) and breast ductal carcinoma in situ (DCIS) is a key step in breast surgery, especially to determine whether DCIS is associated with tumor cell micro-invasion. However, there is currently no reliable method to obtain molecular information for breast tumor analysis during surgery. Here, we present a novel air flow-assisted ionization (AFAI) mass spectrometry imaging method that can be used in ambient environments to differentiate breast cancer by analyzing lipids. In this study, we demonstrate that various subtypes and histological grades of IDC and DCIS can be discriminated using AFAI-MSI: phospholipids were more abundant in IDC than in DCIS, whereas fatty acids were more abundant in DCIS than in IDC. The classification of specimens in the subtype and grade validation sets showed 100% and 78.6% agreement with the histopathological diagnosis, respectively. Our work shows the rapid classification of breast cancer utilizing AFAI-MSI. This work suggests that this method could be developed to provide surgeons with nearly real-time information to guide surgical resections.

Regulation of sphingomyelin metabolism

Sphingolipids (SFs) represent a large class of lipids playing diverse functions in a vast number of physiological and pathological processes. Sphingomyelin (SM) is the most abundant SF in the cell, with ubiquitous distribution within mammalian tissues, and particularly high levels in the Central Nervous System (CNS). SM is an essential element of plasma membrane (PM) and its levels are crucial for the cell function. SM content in a cell is strictly regulated by the enzymes of SM metabolic pathways, which activities create a balance between SM synthesis and degradation. The de novo synthesis via SM synthases (SMSs) in the last step of the multi-stage process is the most important pathway of SM formation in a cell. The SM hydrolysis by sphingomyelinases (SMases) increases the concentration of ceramide (Cer), a bioactive molecule, which is involved in cellular proliferation, growth and apoptosis. By controlling the levels of SM and Cer, SMSs and SMases maintain cellular homeostasis. Enzymes of SM cycle exhibit unique properties and diverse tissue distribution. Disturbances in their activities were observed in many CNS pathologies. This review characterizes the physiological roles of SM and enzymes controlling SM levels as well as their involvement in selected pathologies of the Central Nervous System, such as ischemia/hypoxia, Alzheimer disease (AD), Parkinson disease (PD), depression, schizophrenia and Niemann Pick disease (NPD).

The Kennedy pathway--De novo synthesis of phosphatidylethanolamine and phosphatidylcholine

The glycerophospholipids phosphatidylcholine (PC) and phosphatidylethanolamine (PE) account for greater than 50% of the total phospholipid species in eukaryotic membranes and thus play major roles in the structure and function of those membranes. In most eukaryotic cells, PC and PE are synthesized by an aminoalcoholphosphotransferase reaction, which uses sn-1,2-diradylglycerol and either CDP-choline or CDP-ethanolamine, respectively. This is the last step in a biosynthetic pathway known as the Kennedy pathway, so named after Eugene Kennedy who elucidated it over 50 years ago. This review will cover various aspects of the Kennedy pathway including: each of the biosynthetic steps, the functions and roles of the phospholipid products PC and PE, and how the Kennedy pathway has the potential of being a chemotherapeutic target against cancer and various infectious diseases.

Assessment of 31P-NMR analysis of phospholipid profiles for potential differential diagnosis of human cerebral tumors

We describe a novel protocol for the non-histological diagnosis of human brain tumors in vitro combining high-resolution (31)P magnetic resonance spectroscopy ((31)P-MRS) of their phospholipid profile and statistical multivariate analysis. Chloroform/methanol extracts from 40 biopsies of human intracranial tumors obtained during neurosurgical procedures were prepared and analyzed by high-resolution (31)P-MRS. The samples were grouped in the following seven major classes: normal brain (n = 3), low-grade astrocytomas (n = 4), high-grade astrocytomas (n = 7), meningiomas (n = 9), schwannomas (n = 3), pituitary adenomas (n = 4), and metastatic tumors (n = 4). The phospholipid profile of every biopsy was determined by (31)P-NMR analysis of its chloroform/methanol extract and characterized by 19 variables including 10 individual phospholipid contributions and 9 phospholipid ratios. Most tumors depicted a decrease in phosphatidylethanolamine (PtdEtn) and phosphatidylserine (PtdSer), the former mainly in neuroepithelial neoplasms and the latter in metastases. An increase in phosphatidylcholine (PtdCho) and phosphatidylinositol (PtdIns) appeared predominantly in primary non-neuroepithelial tumors. Linear discriminant analysis (LDA) revealed the optimal combination of variables that could classify each biopsy between every pair of classes. The resultant discriminant functions were used to calculate the probability of correct classifications for each individual biopsy within the seven classes considered. Multilateral analysis classified correctly 100% of the normal brain samples, 89% of the meningiomas, 75% of the metastases, and 57% of the high-grade astrocytomas. The use of phospholipid profiles may complement appropriately previously proposed methods of intelligent diagnosis of human cerebral tumors.

Alterations of the composition and metabolism of pulmonary surfactant phospholipids induced by experimental peritonitis in rats

Pulmonary complications often accompany the development of acute peritonitis. In this study, we analyzed the alterations of alveolar surfactant phospholipids in rats with experimentally induced peritonitis. The results showed a reduction of almost all phospholipid fractions in pulmonary surfactant of experimental animals. The most abundant alveolar phospholipids-phosphatidylcholine and phosphatidylglycerol were reduced significantly in surfactant of rats with experimental peritonitis. In addition, analysis of the fatty acid composition of these two phospholipids revealed marked differences between experimental and control animals. The activity of phospholipase A2, which is localized in the hydrophyllic phase of alveolar surfactant, was higher in rats with experimental peritonitis compared to sham-operated ones. Also, a weak acyl-CoA:lysophospholipid acyltransferase activity was detected in alveolar surfactant of rats with experimental peritonitis, whereas in control animals this activity was not detectable. The lipid-transfer activity was quite similar in pulmonary surfactant of control and experimental rats. The total number of cells and the percentage of neutrophils were strongly increased in broncho-alveolar lavage fluid from rats with peritonitis. Thus, our results showed that the development of peritonitis was accompanied by pulmonary pathophysiological processes that involved alterations of the phospholipid and fatty acid composition of alveolar surfactant. We suggest that the increased populations of inflammatory cells, which basically participate in internalization and secretion of surfactant components, contributed to the observed alterations of alveolar phospholipids. These studies would be useful for clarification of the pathogenic mechanisms underlying the occurrence of pulmonary disorders that accompany acute inflammatory conditions, such as peritonitis and sepsis.

Phosphocholine as a biomarker of breast cancer: Molecular and biochemical studies

The discovery of metabolic and molecular markers that help improving the detection and diagnosis of breast cancer is an important goal to be achieved. A high composite-choline signal in magnetic resonance spectra of breast lesions has been demonstrated to improve the accuracy of breast cancer diagnosis. In the present study we revealed the principal molecular and biochemical steps associated with the induction of choline metabolism and phosphocholine accumulation in human breast cancer cell-lines in comparison with normal human mammary epithelial cells. We found upregulation of the expression levels of specific choline transporters: organic cation transporter-2 and choline high affinity transporter-1, as well as of the enzyme choline kinase alpha in the cancerous cells in comparison with that in the normal mammary epithelial cells. The expression levels of choline transporter like-1, organic cation transporter-1 and choline kinase beta were similar in normal and cancerous cells. We further showed that choline transport rates and choline kinase activity indeed increased by several fold in the cancer cells leading to the elevation of phosphocholine. The results strongly suggest that phosphocholine can serve as a biomarker of breast cancer reflecting upregulation of specific choline transporters and choline kinase genes.

The plasma membrane lipid composition affects fusion between cells and model membranes

Investigations were carried out on the effect of plasma membrane lipid modifications on the fusogenic capacity of control and ras-transformed fibroblasts. The plasma membrane lipid composition was modified by treatment of cells with exogenous phospholipases C and D, sphingomyelinase and cyclodextrin. The used enzymes hydrolyzed definite membrane lipids thus inducing specific modifications of the lipid composition while cyclodextrin treatment reduced significantly the level of cholesterol. The cells with modified membranes were used for assessment of their fusogenic capacity with model membranes with a constant lipid composition. Treatment with phospholipases C and D stimulated the fusogenic potential of both cell lines whereas the specific reduction of either sphingomyelin or cholesterol induced the opposite effect. The results showed that all modifications of the plasma membrane lipid composition affected the fusogenic capacity irrespective of the initial differences in the membrane lipid composition of the two cell lines. These results support the notion that the lipid composition plays a significant role in the processes of membrane-membrane fusion. This role could be either direct or through modulation of the activity of specific proteins which regulate membrane fusion.

Cholesterol distribution in plasma membranes of beta1 integrin-expressing and beta1 integrin-deficient fibroblasts

The effect of integrin receptors on the level and transmembrane localization of cholesterol molecules was investigated in beta1 integrin-expressing (beta1) and beta1 integrin-deficient (beta1 null) cells. We found that the content of specific raft components-cholesterol, sphingomyelin, and caveolin-was increased in integrin-expressing cells. Integrin presence affected as well the transmembrane distribution of cholesterol-a higher percent was found in the plasma membrane outer monolayer of beta1 compared to beta1 null cells. Sphingomyelin depletion reduced the presence of cholesterol in the outer membrane monolayer of both cell lines, but the differences in cholesterol asymmetry, observed between beta1 and beta1 null cells before sphingomyelinase treatment were preserved. These findings implied that integrin receptors affected the non-random transmembrane distribution of cholesterol. Finally, a higher percent of detergent-resistant membranes was obtained from beta1 integrin-expressing cells, suggesting that the presence of these receptors in the membranes influenced the formation and/or stabilization of lipid raft domains.

Phosphatidylcholine-specific phospholipase C in mitogen-stimulated fibroblasts

To investigate expression, subcellular localization and mechanisms of translocation of phosphatidylcholine-specific phospholipase C (PC-PLC) during the cell proliferative response, biochemical, immunoblotting, and immunofluorescence analyses were performed on quiescent and mitogen-stimulated NIH-3T3 fibroblasts. Platelet-derived growth factor (PDGF), insulin and 12-O-tetradecanoylphorbol-13-acetate induced, in 10-60 min, PC-PLC translocation from a perinuclear cytoplasmic area to the plasma membrane. Following cell exposure to PDGF (60 min), the overall PC-PLC expression increased up to 2-3x, while the enzyme activity increased 5x in total cell lysates, 2x in the plasma membrane, and 4x in the nucleus; moreover, confocal laser scanning microscopy showed a progressive externalization of PC-PLC on the outer plasma membrane surface and its accumulation in the nuclear matrix. Pre-incubation of cells with the PC-PLC inhibitor tricyclodecan-9-yl potassium xanthate (D609), before PDGF-stimulation, not only reduced the enzyme activity in total cell lysates as well as in plasma membrane and nuclear fractions, but also blocked the mechanisms of PC-PLC subcellular redistribution. These effects were associated with a D609-induced long-lasting cell cycle block in Go.

Growth suppression of a tumorigenic rat liver cell line by the anticancer agent, ET-18-O-CH(3), is mediated by inhibition of cytokinesis

PURPOSE

This study was undertaken to elucidate the potential mechanism of the antitumor activity of ET-18-O-CH(3), a synthetic analogue of lysophosphatidyl choline, and a known antitumor agent and specific inhibitor of phosphoinositide phospholipase C (PI-PLC).

METHODS

A normal rat liver epithelial "oval" cell line (WB-F344) was neoplastically transformed by the H-ras oncogene (WB-ras2) and treated with a series of ET-18-O-CH(3) concentrates for a number of days. Cell growth, morphological "differentiation", cell cycle regulation, karyotypic changes, growth in soft agar (anchorage-independent growth) and the expression of cdk2, cdc2 and ERK genes were studied to determine the effect of ET-18-O-CH(3) on these neoplastic cells.

RESULTS

ET-18-O-CH(3) at 5 and 10 microg/ml was found to cause an increase in cell size, suppress cell growth, reduce the colony-forming efficiency and inhibit the anchorage-independent growth of the WB-ras2 cells. Significantly, flow-cytometric analysis revealed that while control cells and cells treated with concentrations of ET-18-O-CH(3) below 5 microg/ml were diploid, cell populations treated with 5 and 10 microg/ml ET-18-O-CH(3) comprised 33-37% diploid cells and over 60% tetraploid cells (4n-8n cycle cells). ET-18-O-CH(3) was found to induce aberrant cytokinesis as evidenced by the presence of a high frequency of enlarged cells, which were binucleated or multinucleated and mitotic cells with 4n and 8n numbers of chromosomes. ET-18-O-CH(3) was also capable of inhibiting both the expression of cdk2 and cdc2 and the activation of ERK1/2, while no effect was found on the expression of p21 ras.

CONCLUSIONS

The effect of ET-18-O-CH(3) on neoplastically transformed H-ras rat liver cells has been interpreted as the result of an altered phenotype characterized by an enlarged and flattened cell morphology with ploidy changes caused by inhibition of cytokinesis.

Stimulated nonspecific transport of phospholipids results in elevated external appearance of phosphatidylserine in ras-transformed fibroblasts

The content of phosphatidylserine (PS) was found to be increased three times in the plasma membrane outer leaflet of ras-transformed fibroblasts compared to their nontransformed counterparts. In an attempt to determine the mechanisms responsible for the enhanced external appearance of PS, we investigated the activities of aminophospholipid translocase and the nonspecific lipid scramblase. Both transport systems could separately or in combination contribute to PS accumulation in the extracellular leaflet. Aminophospholipid transfer was assessed by measuring the rate of NBD-PS internalization, and scramblase activity was estimated from the internalization of NBD-PC. The results showed that the aminophospholipid transport was inhibited and the nonspecific transport was stimulated in ras-transformed cells. To assess which of these two transport systems was related to elevation of PS external appearance, each of them was submitted to reversible alterations and the content of PS was measured simultaneously. Aminophospholipid translocase activity was inhibited by pyridyldithioethylamine treatment and reversed by reduction with dithiothreitol. Scramblase activity was modulated by a calcium repletion-depletion procedure. Calcium depletion was performed by cell incubation with BAPTA-AM and EGTA as Ca2+ intracellular and extracellular chelators. Restoration of the intracellular Ca2+ was achieved by cell incubation with Ca2+ and Ca2+-ionophore A23187. The results showed that the changes in PS outer appearance did not correlate with the uptake of NBD-PS but were closely related to NBD-PC internalization, suggesting that the nonspecific bidirectional lipid transfer was the major transport system translocating PS to the outer leaflet in ras-transformed cells.