BBA - Molecular and Cell Biology of Lipids (v.1581, #1-2)

A novel lipid compound, epolactaene, induces apoptosis: its action is modulated by its side chain structure by Junko Nakai; Kentaro Kawada; Seigo Nagata; Kouji Kuramochi; Hiromi Uchiro; Susumu Kobayashi; Masahiko Ikekita (1-10).
A novel lipid compound, epolactaene, was isolated from the culture supernatant of Penicillium sp. 1689-P and it has already been reported that it induced neurite outgrowth in a human neuroblastoma cell line. In this study, we first investigated the effects of epolactaene on a human leukemia B-cell line, BALL-1 cells, and clarified that epolactaene induces apoptosis in BALL-1 cells in a dose- and time-dependent manner. Furthermore, we focused on the side chain structure of epolactaene, and chemically synthesized epolactaene derivatives. One derivative, which has a straight long alkyl chain as its side chain, induced apoptosis more effectively than epolactaene. On the other hand, other derivatives with a short alkyl side chain had weaker apoptosis-inducing actions. A good correlation was found between the apoptosis-inducing action of these compounds and their octanol/water partition coefficients (log P). These results suggested that the apoptosis-inducing activities of epolactaene and its derivatives were related to the hydrophobicity of these compounds; so that side chain structure of epolactaene is very important for its apoptosis-inducing activities. These apoptosis-inducing actions of epolactaene and its derivatives were also observed in various blood tumor cell lines and normal lymphocytes.
Keywords: Epolactaene; Leukemia B cell line; Cell death; Apoptosis; Neurite outgrowth; Side chain structure;

Semi-fluorinated alkanes C n F2n+1C m H2m+1 (FnHm) can be co-dispersed with standard phospholipids to form ‘fluorinated’ vesicles, i.e. vesicles with an internal fluorinated film within their bilayer membrane. This paper reports the effect of the presence of such FnHm diblocks in phosphatidylserine (PS)-based small unilamellar vesicles (SUVs) on their kinetics of fusion. Fusion was induced by calcium ions and monitored by the terbium/dipicolinic acid assay. The diblocks were composed of a 10-carbon long linear hydrocarbon segment and of a linear fluorocarbon segment of four, six or eight carbon atoms. We found that the incorporation of FnHm in the PS membrane considerably modifies the kinetics of the process of fusion, with Ca2+ concentration having a much more limited effect on the fluorinated vesicles. Both the rates of fusion and the rates of release of the internal content, as evaluated by the release of 5,6-carboxyfluorescein, were much lower for the fluorinated SUVs than for those based on phosphatidylserine alone, the highest effect being obtained for F6H10 with a 10 times slower rate of fusion and a 40-fold reduction in the release of content. FnHm molecules are proposed to have a dual action: by hindering fusion and release by creating an inert, hydrophobic and lipophobic fluorinated film in the core of the membrane, and by stabilizing the membrane by increasing van der Waals interactions in the hydrocarbon region.
Keywords: Small unilamellar vesicle; Calcium; Fusion; Fluorinated bilayer; Semi-fluorinated alkane; Fluorinated surfactant;

Plastids greatly rely on the import of extraplastidial precursors for the synthesis of their own lipids, and several studies have shown that a lyso-PC acyltransferase located in the envelope may be involved in the import process. Because the presence of heavy metals in soil or in nutrient solutions induces changes in the lipid composition of plastid membranes (and therefore greatly reduces the photosynthetic capability of plants), we analysed the effect of several metal salts on plastidial lyso-PC acyltransferase activity. Among the 12 heavy metals studied, silver, copper, mercury and lead inhibited this activity. Metal bound to the enzyme was not – or only very slightly – released from the protein except when thiol-reducing agents (and not imidazole) were added. The results strongly suggest that the inhibitory effect is due to a formation of mercaptide between metal and cysteine(s). The relationship between the inhibition of the plastidial lyso-PC acyltransferase activity and the in vivo effects of metal salts on the plastid membranes is discussed.
Keywords: Plastids; Lyso-PC acyltransferase; Heavy metals; Inhibition; Cysteine;

β-D-Glucopyranosyl caldarchaetidylglycerol is the main lipid of the acidophilic, mesophilic, ferrous iron-oxidising archaeon Ferroplasma acidiphilum by Stanislav G Batrakov; Tatiana A Pivovarova; Stanislav E Esipov; Vladimir I Sheichenko; Grigory I Karavaiko (29-35).
Chloroform–methanol-extractable lipids account for about 5% by weight of dry cells of the acidophilic, autotrophic, mesophilic, ferrous compound-oxidising, cell wall-less archaeon Ferroplasma acidiphilum strain YT, about 90% of these being contributed by phospholipids and glycophospholipids. The most abundant constituent (about 55% of total lipids) was purified by DEAE cellulose and silica gel column chromatography. By means of matrix-assisted laser desorption ionisation mass spectrometry, infrared spectroscopy, 1H-nuclear magnetic resonance spectroscopy, and chemical degradation experiments it was established to be β-D-glucopyranosyl caldarchaetidylglycerol, the isopranyl chains of which have a cyclopentane ring each.
Keywords: Tetraether lipid; Glycophospholipid; Glycosyl caldarchaetidylglycerol; Archaeon; Ferroplasma acidiphilum;

Dexamethasone stimulates very low density lipoprotein (VLDL) receptor gene expression in differentiating 3T3-L1 cells by Katharina Ensler; Majid Mohammadieh; Anders Bröijersén; Bo Angelin; Mats Gåfvels (36-48).
To characterize endocrine mechanisms of very low density lipoprotein (VLDL) receptor regulation we studied mouse adipocytic 3T3-L1 cells. Lipid filled adipocyte-like cells are formed during a 5–7 day time course in the presence of insulin, dexamethasone and isobutylmethylxanthine (IBMX). The VLDL receptor protein, in the form of its ≈120 and ≈100 kDa type I and type II isoforms, as well as binding of 125I-β-VLDL, was induced several-fold during differentiation. Among the three different constituents added to the culture medium only dexamethasone (1 μM), but not insulin or IBMX, induced a time- and dose-dependent increase of VLDL receptor expression. Inclusion of RU-486 (10 μM) blocked the stimulatory effect of dexamethasone on VLDL receptor mRNA and protein levels. 3.6 kb of the 5′-untranslated region representing the VLDL receptor promoter were cloned and sequenced, and the transcriptional start site was determined by primer extension to be located 574 bases upstream from the initiating methionine. To investigate the functionality of the promoter, luciferase reporter gene constructs for the region −181 to −3726 bases were assembled and transfected into 3T3-L1 cells. An increased reporter gene activity was recorded when comparing preconfluent cells to fully differentiated cells. Between day 0 and day 2 (48 h after transfection) reporter gene activity was induced by dexamethasone, but not by insulin or IBMX. RU-486 inhibited this stimulatory effect for all constructs tested. No classical glucocorticoid receptor (GR) response element was found in the sequenced region of the VLDL receptor promoter. Thus, an indirect stimulatory effect mediated via GR on VLDL receptor gene transcription is the most likely mechanism of VLDL receptor gene activation in differentiating 3T3-L1 cells.
Keywords: Corticosteroid; Adipocytic 3T3-L1 cell; Very low density lipoprotein receptor promoter;

Overexpression of PEMT2 downregulates the PI3K/Akt signaling pathway in rat hepatoma cells by Wei Zou; Zhao-Yu Li; Ya-Li Li; Ke-Li Ma; Zhao-Chun Tsui (49-56).
Phosphatidylethanolamine N-methyltransferase 2 (PEMT2) is an isoform of PEMT that converts phosphatidylethanolamine to phosphatidylcholine in mammalian liver. Overexpression of PEMT2 led to inhibition of proliferation of hepatoma cells [J. Biol. Chem. 269 (1994) 24531]. The present study aims to unravel the molecular mechanism of the reduced proliferation, especially the signaling transducer proteins involved in this process. Thus, we chose PI3K/Akt pathway that is initiated by growth factors and leads to cell survival and proliferation. Rat hepatoma CBRH-7919 cells transfected with pemt2-cDNA showed that: (1) signaling proteins including c-Met, PDGF receptor, PI3K, Akt and Bcl-2 all had reduced expression as shown by Western blotting studies; (2) flow cytometric and DNA ladder assays showed that 22.9% of the pemt2-transfected cells were undergoing apoptosis; (3) the activity of Akt was decreased as shown by Western blotting using antibody directed against p-Akt (Thr308); (4) wortmannin and PD98059, inhibitors of PI3K and MEK, respectively, both inhibited Akt activity, indicating that PI3K and MAPK pathways were merging at Akt in CBRH-7919 cells. The above results suggest that overexpression of PEMT2 strongly downregulated the PI3K/Akt signaling pathway at multiple sites and induced apoptosis. This, at least partly, explains the molecular mechanism of impaired proliferation induced by pemt2 transfection.
Keywords: Apoptosis; Cell proliferation; Growth factor; Hepatoma; Phosphatidylethanolamine N-methyltransferase-2; PI3K/Akt signaling pathway;

Myeloperoxidase, in the presence of hydrogen peroxide and nitrite, promotes the lipid peroxidation of low density lipoprotein (LDL); the modified lipoprotein is then capable of being readily endocytosed by macrophages. Since acetaminophen has been shown to inhibit the leukocyte myeloperoxidase antimicrobial system and is, under certain experimental conditions, an antioxidant, the effect of acetaminophen on the myeloperoxidase–hydrogen peroxide–nitrite mediated oxidation of LDL was examined. The content of LDL lipid hydroperoxides after incubation with 50 nM myeloperoxidase, 100 μM nitrite and a hydrogen peroxide generating system for 6 h was reduced by approx. 80% in the presence of 25–250 μM acetaminophen. The production of thiobarbituric acid-reactive substances was also inhibited by acetaminophen to a similar extent. Acetylsalicylic acid (25–100 μM) did not inhibit LDL lipid peroxidation mediated by the myeloperoxidase enzyme system. LDL, treated with myeloperoxidase, hydrogen peroxide and nitrite for 14 h, was metabolized by macrophages to a much greater extent than native LDL. The presence of acetaminophen prevented the modification of LDL; the lipoprotein was metabolized by macrophages to the same extent as was native LDL. These results demonstrate that acetaminophen is a potent inhibitor of the myeloperoxidase–hydrogen peroxide–nitrite mediated modification of LDL.
Keywords: Acetaminophen; Paracetamol; Myeloperoxidase; Low density lipoprotein; Oxidation;