Biochemical studies on cell fusion. I. Lipid composition of fusion-resistant cells

Lipid-mediated muscle insulin resistance: different fat, different pathways?

Increased dietary fat intake and lipolysis result in excessive lipid availability, which relates to impaired insulin sensitivity. Over the last years, several mechanisms possibly underlying lipid-mediated insulin resistance evolved. Lipid intermediates such as diacylglycerols (DAG) associate with changes in insulin sensitivity in many models. DAG activate novel protein kinase C (PKC) isoforms followed by inhibitory serine phosphorylation of insulin receptor substrate 1 (IRS1). Activation of Toll-like receptor 4 (TLR4) raises another lipid class, ceramides (CER), which induce pro-inflammatory pathways and lead to inhibition of Akt phosphorylation. Inhibition of glucosylceramide and ganglioside synthesis results in improved insulin sensitivity and increased activatory tyrosine phosphorylation of IRS1 in the muscle. Incomplete fat oxidation can increase acylcarnitines (ACC), which in turn stimulate pro-inflammatory pathways. This review analyzed the effects of lipid metabolites on insulin action in skeletal muscle of humans and rodents. Despite the evidence for the association of both DAG and CER with insulin resistance, its causal relevance may differ depending on the subcellular localization and the tested cohorts, e.g., athletes. Nevertheless, recent data indicate that individual lipid species and their degree of fatty acid saturation, particularly membrane and cytosolic C18:2 DAG, specifically activate PKCθ and induce both acute lipid-induced and chronic insulin resistance in humans.

Exploitation of the interaction of measles virus fusogenic envelope proteins with the surface receptor CD46 on human cells for microcell-mediated chromosome transfer

Background

Microcell-mediated chromosome transfer (MMCT) is a technique by which a chromosome(s) is moved from donor to recipient cells by microcell fusion. Polyethylene glycol (PEG) has conventionally been used as a fusogen, and has been very successful in various genetic studies. However, PEG is not applicable for all types of recipient cells, because of its cell type-dependent toxicity. The cytotoxicity of PEG limits the yield of microcell hybrids to low level (10^-6 to 10^-5 per recipient cells). To harness the full potential of MMCT, a less toxic and more efficient fusion protocol that can be easily manipulated needs to be developed.

Results

Microcell donor CHO cells carrying a human artificial chromosome (HAC) were transfected with genes encoding hemagglutinin (H) and fusion (F) proteins of an attenuated Measles Virus (MV) Edmonston strain. Mixed culture of the CHO transfectants and MV infection-competent human fibrosarcoma cells (HT1080) formed multinucleated syncytia, suggesting the functional expression of the MV-H/F in the CHO cells. Microcells were prepared and applied to HT1080 cells, human immortalized mesenchymal stem cells (hiMSC), and primary fibroblasts. Drug-resistant cells appeared after selection in culture with Blasticidin targeted against the tagged selection marker gene on the HAC. The fusion efficiency was determined by counting the total number of stable clones obtained in each experiment. Retention of the HAC in the microcell hybrids was confirmed by FISH analyses. The three recipient cell lines displayed distinct fusion efficiencies that depended on the cell-surface expression level of CD46, which acts as a receptor for MV. In HT1080 and hiMSC, the maximum efficiency observed was 50 and 100 times greater than that using conventional PEG fusion, respectively. However, the low efficiency of PEG-induced fusion with HFL1 was not improved by the MV fusogen.

Conclusions

Ectopic expression of MV envelope proteins provides an efficient recipient cell-oriented MMCT protocol, facilitating extensive applications for studies of gene function and genetic corrections.

Nuclear envelope formation: mind the gaps

During mitosis in metazoans, the nuclear envelope (NE) breaks down at prophase and reassembles at telophase. The regulation of NE assembly is essential to correct cell functioning. The complex issue of the regulation of NE formation remains to be solved. It is still uncertain that a single mechanism depicts NE formation during mitosis. The aim of this review is to address some of the cytological, biophysical, and molecular aspects of models of NE formation. Our emphasis is on the role of lipids and their modifying enzymes in envelope assembly. We consider how the NE can be used as a model in characterizing membrane dynamics during membrane fusion. Fusion mechanisms that give insight into the formation of the double membrane of the envelope are summarized. We speculate on the possible roles of phosphoinositides in membrane fusion and NE formation.

The effects of acyl chain length and saturation of diacylglycerols and phosphatidylcholines on membrane monolayer curvature

The second messenger, diacylglycerol (DAG), introduces negative curvature in phospholipid monolayers and strongly induces the lamellar (L(alpha)) to reverse hexagonal (H(II)) phase transition. The chain lengths and degree of unsaturation of symmetric DAGs influence this effect. Within dioleoylphosphatidylcholine (DOPC) monolayers, the apparent spontaneous radius of curvature (R(0)) of the short, saturated dicaprylglycerol (C10-DCG) itself was determined to be -13.3 A, compared with an R(0) value of -10.1 A for the long, di-monounsaturated dioleoylglycerol (C18-DOG). Such increased length and unsaturation of the DAG acyl chains produces this small change. Di-saturated phosphatidylcholines (PCs) with equal length chains (from C10-C18) with 25 mol % DOG do not form the H(II) phase, even under the unstressed conditions of excess water and alkane. Di-unsaturated PCs with equal chain length (from C14-C18) with 25 mol % DOG do form the H(II) phase. Asymmetric chained PCs (position 1 saturated with varying lengths, position 2 differentially unsaturated with varying lengths) all form the H(II) phase in the presence of 25 mol % DOG. As a general rule for PCs, their unsaturation is critical for the induction of the H(II) phase by DOG. The degree of curvature stress induced by the second messenger DOG in membranes, and any protein that might be affected by it, would appear to depend on chain unsaturation of neighboring PCs.

A single mutation in the E2 glycoprotein important for neurovirulence influences binding of sindbis virus to neuroblastoma cells

The amino acid at position 55 of the E2 glycoprotein (E2(55)) of Sindbis virus (SV) is a critical determinant of SV neurovirulence in mice. Recombinant virus strain TE (E2(55) = histidine) differs only at this position from virus strain 633 (E2(55)= glutamine), yet TE is considerably more neurovirulent than 633. TE replicates better than 633 in a neuroblastoma cell line (N18), but similarly in BHK cells. Immunofluorescence staining showed that most N18 cells were infected by TE at a multiplicity of infection (MOI) of 50 to 500 and by 633 only at an MOI of 5,000, while both viruses infected essentially 100% of BHK cells at an MOI of 5. When exposed to pH 5, TE and 633 viruses fused to similar extents with liposomes derived from BHK or N18 cell lipids, but fusion with N18-derived liposomes was less extensive (15 to 20%) than fusion with BHK-derived liposomes ( approximately 50%). Binding of TE and 633 to N18, but not BHK, cells was dependent on the medium used for virus binding. Differences between TE and 633 binding to N18 cells were evident in Dulbecco's modified Eagle medium (DMEM), but not in RPMI. In DMEM, the binding efficiency of 633 decreased significantly as the pH was raised from 6.5 to 8.0, while that of TE did not change. The same pattern was observed with RPMI when the ionic strength of RPMI was increased to that of DMEM. TE bound better to heparin-Sepharose than 633, but this difference was not pH dependent. Growth of N18 and BHK cells in sodium chlorate to eliminate all sulfation decreased virus-cell binding, suggesting the involvement of sulfated molecules on the cell surface. Taken together, the presence of glutamine at E2(55) impairs SV binding to neural cells under conditions characteristic of interstitial fluid. We conclude that mutation to histidine participates in or stabilizes the interaction between the virus and the surface of neural cells, contributing to greater neurovirulence.

A single mutation in the E2 glycoprotein important for neurovirulence influences binding of sindbis virus to neuroblastoma cells

The amino acid at position 55 of the E2 glycoprotein (E2(55)) of Sindbis virus (SV) is a critical determinant of SV neurovirulence in mice. Recombinant virus strain TE (E2(55) = histidine) differs only at this position from virus strain 633 (E2(55)= glutamine), yet TE is considerably more neurovirulent than 633. TE replicates better than 633 in a neuroblastoma cell line (N18), but similarly in BHK cells. Immunofluorescence staining showed that most N18 cells were infected by TE at a multiplicity of infection (MOI) of 50 to 500 and by 633 only at an MOI of 5,000, while both viruses infected essentially 100% of BHK cells at an MOI of 5. When exposed to pH 5, TE and 633 viruses fused to similar extents with liposomes derived from BHK or N18 cell lipids, but fusion with N18-derived liposomes was less extensive (15 to 20%) than fusion with BHK-derived liposomes ( approximately 50%). Binding of TE and 633 to N18, but not BHK, cells was dependent on the medium used for virus binding. Differences between TE and 633 binding to N18 cells were evident in Dulbecco's modified Eagle medium (DMEM), but not in RPMI. In DMEM, the binding efficiency of 633 decreased significantly as the pH was raised from 6.5 to 8.0, while that of TE did not change. The same pattern was observed with RPMI when the ionic strength of RPMI was increased to that of DMEM. TE bound better to heparin-Sepharose than 633, but this difference was not pH dependent. Growth of N18 and BHK cells in sodium chlorate to eliminate all sulfation decreased virus-cell binding, suggesting the involvement of sulfated molecules on the cell surface. Taken together, the presence of glutamine at E2(55) impairs SV binding to neural cells under conditions characteristic of interstitial fluid. We conclude that mutation to histidine participates in or stabilizes the interaction between the virus and the surface of neural cells, contributing to greater neurovirulence.

Deletion of the cytoplasmic tail of the fusion protein of the paramyxovirus simian virus 5 affects fusion pore enlargement

The fusion (F) protein of the paramxyovirus simian parainfluenza virus 5 (SV5) promotes virus-cell and cell-cell membrane fusion. Previous work had indicated that removal of the SV5 F protein cytoplasmic tail (F Tail- or FDelta19) caused a block in fusion promotion at the hemifusion stage. Further examination has shown that although the F Tail- mutant is severely debilitated in promotion of fusion as measured by using two reporter gene assays and is debilitated in the formation of syncytia relative to the wild-type F protein, the F Tail- mutant is capable of promoting the transfer of small aqueous dyes. These data indicate that F Tail- is fully capable of promoting formation of small fusion pores. However, enlargement of fusion pores is debilitated, suggesting that either the cytoplasmic tail of the F protein plays a direct role in pore expansion or that it interacts with other components which control pore growth.

Vesicular stomatitis virus G protein acquires pH-independent fusion activity during transport in a polarized endometrial cell line

Entry of vesicular stomatitis virus (VSV), the prototype member of the rhabdovirus family, occurs by receptor-mediated endocytosis. Subsequently, during traversal through the endosomal compartments, the VSV G protein acquires a low-pH-induced fusion-competent form, allowing for fusion of the viral membrane with endosomal and lysosomal membranes. This fusion event releases genomic RNA into the cytoplasm of the cell. Here we provide evidence that the VSV G protein acquires a fusion-competent form during exocytosis in a polarized endometrial cell line, HEC-1A. VSV infection of HEC-1A cells results in high viral yields and giant cell formation. Syncytium formation is blocked in a concentration-dependent manner by treatment with the lysosomotropic weak base ammonium chloride, which raises intravesicular pH. Virus release is somewhat delayed by treatment with ammonium chloride, but virus yields gradually reach those of control cells. In addition, inhibition of vacuolar H(+)-ATPases by treatment with bafilomycin A1 also inhibited cell to cell fusion without altering virus yields. Virions released from infected HEC cells were themselves not fusion competent, since viral entry required an active H(+)-ATPase and a low-pH-induced conformational change in the viral G protein. Thus, the conformation change leading to fusion competence during exocytotic transport is reversible and reverts during or after release of the virion from the infected cell.

Effects of N-6 essential fatty acids on glioma invasion and growth: experimental studies with glioma spheroids in collagen gels

OBJECT

Intracranial infusions of gamma-linolenic acid (GLA), an essential fatty acid, have been used as an adjuvant therapy following malignant glioma resection; however, little is known about the dose response of glioma cells to this therapy. In this in vitro study the authors address this important pharmacological question.

METHODS

Glioma spheroids derived from U87, U373, MOG-G-CCM, and C6 cell lines were grown in collagen gel and exposed to a range of GLA concentrations (0-1 mM) for 5 days. The diameter of glioma spheroids was measured, the apoptotic index was assessed using both the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling technique and cell morphological testing, and the levels of proliferating cell nuclear antigen were also measured.

CONCLUSIONS

The dose-response patterns were similar for all four glioma spheroids. Low concentrations of GLA (<100 microM) increased both apoptosis and proliferation with a net increase in tumor growth and invasion, whereas high-dose GLA (>100 microM) significantly impaired spheroid cell growth. The proliferative effects of low-dose GLA could be a hazard in the clinical treatment of malignant glioma; however, because of the low toxicity of GLA against normal cells, local delivery of millimolar doses of GLA could significantly reduce tumor size.

Non-bilayer lipids and biological fusion intermediates

Disparate biological fusion reactions and fusion of purely lipid bilayers are similarly influenced by 'non-bilayer' lipids (lipids which do not form lipid bilayers in water by themselves). Lipid composition of membranes affects biological fusion at a stage downstream of activation of fusion proteins and prior to fusion pore formation. These data suggest that actual merger of membrane lipid bilayers in different fusion reactions proceeds via the same pathway. The effects of non-bilayer lipids specifically correlate with their ability to bend lipid monolayers in different directions, and appear to be consistent with the specific hypothesis of membrane fusion suggesting that fusion proceeds through highly bent intermediates--stalks, local connections between contacting monolayers of fusing membranes.

Poly(ethylene glycol)-induced and temperature-dependent phase separation in fluid binary phospholipid membranes

Exclusion of the strongly hygroscopic polymer, poly(ethylene glycol) (PEG), from the surface of phosphatidylcholine liposomes results in an osmotic imbalance between the hydration layer of the liposome surface and the bulk polymer solution, thus causing a partial dehydration of the phospholipid polar headgroups. PEG (average molecular weight of 6000 and in concentrations ranging from 5 to 20%, w/w) was added to the outside of large unilamellar liposomes (LUVs). This leads to, in addition to the dehydration of the outer monolayer, an osmotically driven water outflow and shrinkage of liposomes. Under these conditions phase separation of the fluorescent lipid 1-palmitoyl-2[6-(pyren-1-yl)]decanoyl-sn-glycero-3-phosphocholine (PPDPC) embedded in various phosphatidylcholine matrices was observed, evident as an increase in the excimer-to-monomer fluorescence intensity ratio (IE/IM). Enhanced segregation of the fluorescent lipid was seen upon increasing and equal concentrations of PEG both inside and outside of the LUVs, revealing that osmotic gradient across the membrane is not required, and phase separation results from the dehydration of the lipid. Importantly, phase separation of PPDPC could be induced by PEG also in binary mixtures with 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC), and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), for which temperature-induced phase segregation of the fluorescent lipid below Tm was otherwise not achieved. In the different lipid matrices the segregation of PPDPC caused by PEG was abolished above characteristic temperatures T0 well above their respective main phase transition temperatures Tm. For 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), DMPC, SOPC, and POPC, T0 was observed at approximately 50, 32, 24, and 20 degrees C, respectively. Notably, the observed phase separation of PPDPC cannot be accounted for the 1 degree C increase in Tm for DMPC or for the increase by 0.5 degrees C for DPPC observed in the presence of 20% (w/w) PEG. At a given PEG concentration maximal increase in IE/IM (correlating to the extent of segregation of PPDPC in the different lipid matrices) decreased in the sequence 1,2-dihexadecyl-sn-glycero-3-phosphocholine (DHPC) > DPPC > DMPC > SOPC > POPC, whereas no evidence for phase separation in 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) LUV was observed (Lehtonen and Kinnunen, 1994, Biophys. J. 66: 1981-1990). Our results indicate that PEG-induced dehydration of liposomal membranes provides the driving force for the segregation of the pyrene lipid. In brief, phase separation of PPDPC from the matrix lipid could be attributed to the diminishing effective size of the phosphatidylcholine polar headgroup resulting from its partial dehydration by PEG. This in turn would allow for enhanced van der Waals interactions between the acyl chains of the matrix lipid, which then caused the exclusion of PPDPC due to the perturbing bulky pyrene moiety. Phase separation in DMPC/PPDPC liposomes was abolished by the inclusion of 25 mol % cholesterol and to a lesser extent by epicholesterol.

Squalamine: an aminosterol antibiotic from the shark

In recent years, a variety of low molecular weight antibiotics have been isolated from diverse animal species. These agents, which include peptides, lipids, and alkaloids, exhibit antibiotic activity against environmental microbes and are thought to play a role in innate immunity. We report here the discovery of a broad-spectrum steroidal antibiotic isolated from tissues of the dogfish shark Squalus acanthias. This water-soluble antibiotic, which we have named squalamine, exhibits potent bactericidal activity against both Gram-negative and Gram-positive bacteria. In addition, squalamine is fungicidal and induces osmotic lysis of protozoa. The chemical structure of the antibiotic 3 beta-N-1-(N-[3-(4-aminobutyl)]- 1,3-diaminopropane)-7 alpha,24 zeta-dihydroxy-5 alpha-cholestane 24-sulfate has been determined by fast atom bombardment mass spectroscopy and NMR. Squalamine is a cationic steroid characterized by a condensation of an anionic bile salt intermediate with spermidine. The discovery of squalamine in the shark implicates a steroid as a potential host-defense agent in vertebrates and provides insights into the chemical design of a family of broad-spectrum antibiotics.

Microscopic analysis of interactions between HIV particles and living leukocytes

Video-enhanced/-intensified optical microscopy has been used to study the interaction of non-infectious HIV8E5 particles with living cells. The purified particles retained gp120 antigenic sites. Fluorescent lipids were intercalated into the particles' envelopes. When incubated with CD4+ cell lines, roughly 90% of the cells bound HIV8E5 particles. The extent of fusion and endocytosis varied among the cell lines tested. CD4- control cells did not significantly bind, fuse, or internalize particles. To control for non-specific exchange of the fluorescent label, HIV8E5 were bound to CD4- murine WEHI cells using concanavalin A; no apparent fusion or internalization took place. We suggest that both fusion and internalization are important mechanisms of virion-cell interaction. Adherent human peripheral blood mononuclear cells were much less efficient in binding HIV8E5 than non-adherent mononuclear cells. Both endocytosis and apparent fusion were observed for lymphocytes. Our results indicate that cells interact with HIV8E5 by multiple pathways and that these pathways are strongly affected by cell type (lymphocyte or monocyte) and origin (normal or transformed). These methods may be useful in characterizing viral entry and in anti-viral drug screening.

Studies on the immunological effects of fatty alcohols--I. Effects of n-hexacosanol on murine macrophages in culture

n-Hexacosanol (hexa), a long chain fatty alcohol extracted from Hygrophila erecta, has proved to possess neurotrophic activities on cultured neurons, and to attenuate the degeneration of cholinergic neurons after injury. In the present study, we show that hexa has also interesting properties on macrophages, a cell type largely represented in the brain: when added to mice resident peritoneal macrophages, it provokes significant morphological changes, and increases their phagocytosis capacity. These results may indicate that some membrane properties involved in these different effects and in macrophage functions are affected by n-hexacosanol, but other sites of action could also be considered.

Effects of exogenous phospholipids on lipid composition and sporulation by three strains of Lagenidium giganteum

The California (LGCA) and Butte Sink (LGBS) strains of the sterol auxotrophic fungus Lagenidium giganteum (Oomycetes: Lagenidiales) enter the sexual cycle on media supplemented with sterols. A third isolate of this mosquito pathogen, the North Carolina strain (LGNC), requires sterols plus phospholipids to produce oospores in vitro. Enrichment of the polar and neutral lipid fractions of the LGCA and LGBS strains with unsaturated fatty acids promoted oospore induction, and increased oospore viability. With the exception of the LGCA strain, there was no consistent relationship between phospholipid supplementation in growth media and mycelial phospholipid content.

Characterization of fusion from without induced by herpes simplex virus

The process of fusion from without (FFWO) induced by herpes simplex virus (HSV) was analyzed by using various inhibitors and compared to fusion from within (FFWI). The fate of certain elements of the cytoskeleton after FFWO was also investigated. Our experiments demonstrate FFWO as a very suitable system for study of early virus-cell interactions. Zn++ ions proved inhibitory for penetration whilst pretreatment of cells with Ca++ ions before infection enhanced FFWO activity. Dissociation of penetration from the fusion process itself was possible by use of Zn++ ions, low pH-treatment and antiserum on the one hand and N-ethylmaleimide and cytochalasin D on the other. Penetration itself needs only 6 min or less to proceed. FFWO is independent of inhibitors of glycosylation (tunicamycin) and intracellular vesicular traffic (monensin), protein-synthesis (cycloheximide) and energy-delivery (2.4 dinitrophenol and Na-azide). Analyzed strains of HSV-1 and -2 producing FFWI could be subgrouped into three categories: Strain ANG with high, strain HFEM and Lux with low and strains IES, Len, MP, US with no FFWO activity. The results of these experiments indicate that the property of FFWO is not purely a consequence of the number of PFU but depends on certain inherent properties of the virus particles. Addition of heparin as well as treatment of cells with heparitinase effectively prevented FFWO, indicating identical virus receptors for entrance of virus into cells and FFWO. During our studies several calf sera were found to inhibit FFWO-activity. Inhibition of FFWO by a glycoconjugate (ferritin coupled with oleic acid) indicates specific stereochemical hindrance of FFWO by this compound. Shortly after FFWO the actin filaments rearrange to form long fibres and surface fibronectin is being lost from the cell membrane.

Control of virus-induced cell fusion by host cell lipid composition

Virus-induced cell fusion has been examined in a series of stable cell lines which were originally selected for resistance to the fusogenic effects of polyethylene glycol (PEG). For a wide variety of viruses, including murine hepatitis virus (a coronavirus), vesicular stomatitis virus (a rhabdovirus), and two paramyxoviruses (Sendai virus and SV5), susceptibility to virus-induced fusion was found to be inversely correlated with susceptibility to PEG-induced fusion. This phenomenon was observed both for cell fusion occurring in the course of viral infection and for fusion induced "from without" by the addition of high titers of noninfectious or inactivated virus. The fusion-altered cell lines (fusible by virus but not by PEG) are characterized by their unusual lipid composition, including marked elevation of saturated fatty acids and the presence of an unusual ether-linked neutral lipid. To test the association between lipid composition and fusion, acyl chain saturation was manipulated by supplementing the culture medium with exogenous fatty acids. In such experiments, it was possible to control the responses of these cells to both viral and chemical fusogens. Increasing the cellular content of saturated fatty acyl chains increased the susceptibility of cells to viral fusion and decreased susceptibility to PEG-induced fusion, whereas lowering fatty acid saturation had the opposite effect. Thus, parallel cultures of cells can be either driven toward the PEG-fusible/virus-fusion-resistant phenotype of the parental cells or rendered susceptible to viral fusion but resistant to PEG-induced fusion, solely by the alteration of cellular lipids. The ability of cellular lipid composition to regulate virus-induced membrane fusion suggests a possible role for lipids in viral infection and pathogenesis.

Uncoupler-resistant mutants of bacteria

The chemiosmotic model of energy transduction offers a satisfying and widely confirmed understanding of the action of uncouplers on such processes as oxidative phosphorylation; the uncoupler, by facilitating the transmembrane movement of protons or other compensatory ions, reduces the electrochemical proton gradient that is posited as the energy intermediate for many kinds of bioenergetic work. In connection with this formulation, uncoupler-resistant mutants of bacteria that neither exclude nor inactivate these agents represent a bioenergetic puzzle. Uncoupler-resistant mutants of aerobic Bacillus species are, in fact, membrane lipid mutants with bioenergetic properties that are indeed challenging in connection with the chemiosmotic model. By contrast, uncoupler-resistant mutants of Escherichia coli probably exclude uncouplers, sometimes only under rather specific conditions. Related phenomena in eucaryotic and procaryotic systems, as well as various observations on uncouplers, decouplers, and certain other membrane-active agents, are also briefly considered.

Comparison of the inhibitory effect of polyunsaturated fatty acids on prostaglandin synthesis. II. Fibroblasts

In a previous publication we reported that PUFAs of the n-6 and n-3 series caused significant inhibition of synthesis of both PGE2 (28.4-92.8%) and PGF2 alpha (24.4-84.0%) in the oral squamous carcinoma cell line SCC-25. In this report we describe the inhibitory effect of the same acids on PG synthesis in normal human gingival fibroblasts under the same experimental conditions. It was found that a combination of EPA + DCHA (6:4), DCHA and ALA caused significant reduction in synthesis of PGE2 (10.1-87.8%) and PGF2 alpha (14.0-54.6%) at the four dose levels studied. The rank order of potency of acids in reduction of PG synthesis was: EPA + DCHA greater than DCHA greater than EPA greater than ALA greater than LA greater than DGLA greater than GLA. The data suggest that although PUFAs are effective inhibitors of PG synthesis by gingival fibroblasts and SCC-25, the fibroblast is less susceptible to the inhibitory effect of fatty acids.

Rapid morphological fusion of severed myelinated axons by polyethylene glycol

We are able to morphologically fuse the severed halves of an invertebrate-myelinated axon by application of polyethylene glycol (PEG) to closely apposed cut ends. Morphological fusion of the medial giant axon (MGA) of the earthworm Lumbricus terrestris is defined as axoplasmic and axolemmal continuity in serial longitudinal sections of MGAs taken through the fusion site as viewed with light or electron microscopes. Morphological continuity is also shown by the transfer of Lucifer yellow dye between apposed MGA segments fused with PEG, but not between apposed MGA segments in normal or hypotonic saline without PEG application. PEG-induced MGA fusion rates can be as high as 80-100% with an appropriate choice of PEG concentration and molecular mass, tight apposition and careful alignment of the cut ends, and treatment with hypotonic salines containing reduced calcium and increased magnesium. A variant of this technique might produce rapid repair of severed mammalian-myelinated axons.

Reassessment of the role of phospholipids in sexual reproduction by sterol-auxotrophic fungi

Several genera of oomycete fungi which are incapable of de novo sterol synthesis do not require these compounds for vegetative growth. The requirement for an exogenous source of sterols for sexual reproduction by several members of the Pythiaceae has been questioned by reports of apparent induction and maturation of oospores on defined media supplemented with phospholipids in the absence of sterols. A more detailed examination of this phenomenon suggested that trace levels of sterols in the inoculum of some pythiaceous fungi act synergistically with phospholipid medium supplements containing unsaturated fatty acid moieties to induce oosporogenesis. Phospholipid analysis of one species, Pythium ultimum, suggested that only the fatty acid portion of the exogenous phospholipid is taken up by the fungus. Enrichment of the phospholipid fraction of total cell lipid of P. ultimum with unsaturated fatty acids promoted oospore induction, and enhanced levels of unsaturated fatty acids in the neutral lipid fraction increased oospore viability. For some pythiaceous fungi, the levels of sterols required for the maturation of oospores with appropriate phospholipid medium supplementation suggest that these compounds are necessary only for the sparking and critical domain roles previously described in other fungi.

Effect of phorbolmyristate acetate on fatty acid uptake and distribution in human promyelocytic leukemia (HL-60) cells in vitro

Human promyelocytic leukemia (HL-60) cells can be induced to differentiate to macrophages in vitro by phorbolmyristate acetate (PMA). HL-60 cells, unlike normal cells incorporated a major portion of linoleic acid (LA) and arachidonic acid (AA) in the ether lipid fraction. On exposure to PMA, similar to the normal cells tested, the fatty acids were incorporated mainly in the phospholipid fraction. Since, ether lipid pool is metabolically inert and considered as a storage pool where as the phospholipid fraction is a metabolically active pool this may explain, at least in part, the low metabolic rate of AA and the low phospholipase A2 activity in HL-60 cells.

Stable variant of LM fibroblast defective in fluid-phase but competent in receptor-mediated endocytosis

The F-40 cell line, a stable variant of LM fibroblasts selected for its resistance to polyethylene glycol (PEG)-induced fusion (Roos and Davidson: Somatic Cell and Molecular Genetics 6:381-391, 1980), has a decreased capacity to internalize fluid-phase markers and nonspecifically surface-bound macromolecules. It is not defective in exocytosis since, after a short sucrose pulse, it releases the same fraction of ingested sucrose into the medium as does the parental line. F40 cells have a normal capacity to carry out receptor-mediated endocytosis, as tested with 125I-alpha-2 macroglobulin (alpha-2 MG) and 125I-transferrin (Tf), and to recycle Tf receptor to the cell surface. These data demonstrate that receptor-mediated and non-receptor mediated endocytosis are distinct processes that can be altered independently. Of the many membrane fusions occurring in the course of endocytosis, the only one that appears associated with the defect in cell fusion characteristic of F40 cells is the formation of primary endocytotic vesicles engaged in non-receptor-mediated internalizations.

Fusion of lipid vesicles with ascites tumor cells and their lipid-depleted variants. Studies with radioactive- and fluorescent-labeled vesicles

Cultured ascites tumor cells and their lipid-depleted variants, which contained 35-40% less membrane phospholipid and cholesterol, were used for fusion experiments with unilamellar lipid vesicles which were between 300 and 600 nm in diameter. Vesicle-cell interaction was followed by tracer studies using vesicles double-labeled in the lipid moiety, by vesicle-encapsulated [3H] dextran, and by measurements of energy transfer between N-(10-[1-pyrene]decanoyl)sphingomyelin-labeled vesicles and alpha-parinaric acid-labeled cells in the presence of poly(ethylene glycol) (PEG) as fusogen. The reaction rates measured with the radiolabeled vesicles were found to follow patterns similar to those obtained with the resonance energy transfer assay. This latter method revealed a vesicle-cell membrane fusion reaction, which was substantiated by radiolabeling the internal cellular compartment after treatment of the cells with [3H]dextran-encapsulated vesicles as shown by electron microscopic autoradiography on semi-thin sections. Endocytosis as a reaction mechanism can be excluded, since no energy transfer was observed at 25 degrees C in the absence of PEG. Investigations of vesicle bilayer order and fluidity on vesicle-cell interaction revealed optimal reactivity, with intermediate fluidity corresponding to cholesterol/phospholipid ratios between 0.7 and 1.0 and fluorescence depolarization (P) values of 0.18 and 0.21. Lipid depletion decreased the reaction velocity between cells and vesicles by about 20%, exhibiting V values of 33.2 mumol/min, as compared to the control of 41.4 mumol/min determined for 10(7) cells. The affinity constants for vesicle lipid were affected only slightly with Km values of 0.195 mM (0.210 mM). The activation energies for the reaction were calculated to give values of EA = 22.44 kJ/mol for the control and of EA = 20.4 kJ/mol for the modified cells. These data indicate that the decrease in membrane lipid content apparently has no major influence on the extent of the interaction.

Characteristics of ether-linked glycerophospholipids in Friend erythroleukaemia cells differentiated by dimethyl sulphoxide or hexamethylenebisacetamide and in non-inducible clones treated with the inducers

The present study deals with changes in ether-linked glycerophospholids which accompany differentiation of Friend erythroleukaemia (FEL) cells by dimethyl sulphoxide (DMSO) and hexamethylenebisacetamide (HMBA). We also tested clones of FEL cells non-inducible by DMSO or HMBA for ether-linked lipid changes not related to the differentiation process. FEL cells contained appreciable proportions of alkenylacyl and alkylacyl subfractions in phosphatidylethanolamine (PE) and phosphatidylcholine (PC). Compared with FEL cells, clones non-inducible by DMSO or HMBA had a greater amount of alkenylacyl PE associated with a lack of alkenylacyl PC. The differentiation of FEL cells by DMSO or HMBA was accompanied by a reduction of alkylacyl PE and PC. DMSO- and HMBA-differentiated FEL cells showed changes in alkenyl- and alkyl-chain profiles, some of which were also observed in non-inducible FEL cells treated with DMSO or HMBA.

Calcium is essential in the fusion of mouse alveolar macrophages induced by 1 alpha,25-dihydroxyvitamin D3

We have reported that the active form of vitamin D3, 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25(OH)2D3], directly induces activation and fusion of mouse alveolar macrophages (Abe et al., 1983, 1984). The activated state appeared to be a prerequisite to the fusion of macrophages. Macrophages began to fuse 36 hr after adding 1 alpha,25(OH)2D3; the fusion rate attained a maximum of 70-80% at 72 hr. During the course of further investigating the mechanisms of fusion induced by the vitamin, we found that the calcium ion is closely involved in the fusion process of macrophages induced by 1 alpha,25(OH)2D3. When alveolar macrophages were cultured with 1 alpha,25(OH)2D3 in medium with graded concentrations (0.13-1.85 mM) of calcium, the fusion rate went down in parallel with the decrease of medium calcium. Neither calcium ionophore A23187 nor 12-O-tetradecanoylphorbol-13-acetate (TPA) induced fusion of freshly isolated macrophages, but the two compounds greatly promoted fusion of the macrophages pretreated for 18 hr with 1 alpha,25(OH)2D3. The vitamin effect for the first 18 hr was similar, irrespective of the medium calcium concentration. In contrast, millimolar amounts of calcium were essential in the subsequent period of incubation(18-72 hr) for inducing fusion. The activation of macrophages measured by the induction of cytotoxicity and the enhancement of glucose consumption by 1 alpha,25(OH)2D3 occurred similarly, irrespective of the medium calcium concentration. These results clearly indicate that the fusion process of alveolar macrophages induced by 1 alpha,25(OH)2D3 can be divided into two phases: 1) the calcium-independent priming phase (0-18 hr) and 2) the calcium-dependent progression phase (18-72 hr). 1 alpha,25(OH)2D3 is necessary only in the priming phase; A23187 and TPA can be substituted for 1 alpha,25(OH)2D3 in the progression phase.

Effects of polyunsaturated fatty acids and of their oxidation products on cell survival

The stimulatory, cytostatic and cytotoxic effects of polyunsaturated fatty acids, prostaglandins, thromboxanes, hydroperoxy fatty acids, hydroxy fatty acids and leukotrienes on normal and tumor cells are described. Their effects are related to the ability of the cells to undergo lipid peroxidation. The significance of controlled peroxidation of selected polyunsaturated fatty acids in the control of tumor development is examined. It is suggested that selected polyunsaturated fatty acids if used at appropriate concentrations may have a protective role against cancer development by inducing and/or mediating cytotoxic reactions in malignant cells directly or indirectly through the intermediacy of immune cells.

Biosynthesis and biotransformation of ether lipids

Some naturally occurring as well as synthetic ether lipids are biologically active. In certain cases, the effects of these substances are enhanced, in others, they are inhibited by compounds that were isolated from natural sources or prepared by chemical synthesis. The biotransformation of natural or "unnatural" ether lipids in microorganisms, plant or animal tissue also can lead to substances that elicit biological effects. The production of such compounds through various biotechnological techniques is a field wide open for future exploration. In addition to animal cell cultures, plant cell cultures may become useful tools in biomedical studies concerned with ether lipids.

Uptake and distribution of cis-unsaturated fatty acids and their effect on free radical generation in normal and tumor cells in vitro

We have previously shown that cis-unsaturated fatty acids (c-UFAs) possess a selective tumoricidal action that can be blocked by antioxidants. This property of c-UFAs might be due to various factors, including increased uptake, unusual distribution, or an ability to alter free radical generation in tumor but not normal cells. 14C-labelled linoleic acid (LA) uptake was almost the same in normal and tumor cells, whereas that of 14C-labelled arachidonic acid (AA) and 14C-labelled eicosapentaenoic acid (EPA) in tumor cells was substantially less than in normal cells. Tumor cells incorporate major portions of the fatty acids in the ether lipid and phospholipid fractions, whereas normal cells incorporate the fatty acids primarily in the phospholipid fraction. LA, AA, and EPA augmented nitroblue tetrazolium reduction, an indication of free radical generation, selectively in the tumor cells. These results suggest that there are significant differences between normal and tumor cells in fatty acid uptake and distribution, and in the ability of fatty acids to generate free radicals.

Calpain-calpastatin and fusion. Fusibility of erythrocytes is determined by a protease-protease inhibitor [calpain-calpastatin] balance

Rat erythrocytes fuse when treated with the membrane mobility agent, 2-(2-methoxyethoxy)ethyl-cis-8-(2-octylcyclopropyl)octanoate (A2C) and Ca2+, whereas human cells do not. Membrane proteolysis promoted by calpain is required for rat cell fusion [(1986) Eur. J. Biochem., in press]. Human calpain induced a selective proteolysis in both the human and rat erythrocyte ghosts (mainly band 4.1 in the human, band 4.1 and band 3 in the rat cell) and rendered them fusible. Calpastatin (calpain inhibitor) prevented A2C-induced fusion in both ghosts, via inhibition of proteolysis. The human erythrocyte has excess calpastatin and resists A2C-promoted fusion. A regulatory role of calpastatin in membrane fusion is thus indicated.

Fusion of rat erythrocytes by membrane-mobility agent A2C depends on membrane proteolysis by a cytoplasmic calpain

The membrane-mobility agent 2-(2-methoxyethoxy)ethyl-cis-8-(2-octylcyclopropyl)octanoate (A2C) promotes fusion of rat, but not of human, erythrocytes. The difference in fusibility was shown to be correlated with membrane proteolysis, a process induced by Ca2+ in the rat erythrocytes or hemolysate-loaded ghosts, but not in the human cell. Membrane proteolysis is necessary but not sufficient for fusion. Fusion requires both Ca2+ and A2C [Kosower, N. S., Glaser, T. and Kosower, E. M. (1983) Proc. Natl Acad. Sci USA 80, 7542-7546]. Membrane proteolysis (Ca2+-dependent) and fusion (Ca2+ and A2C-dependent) requires a Ca2+-activated cytoplasmic thiol protease, as shown by the following observations. In intact rat erythrocytes, proteolysis and fusion are prevented by thiol alkylation and by inhibitors of Ca2+-dependent thiol proteases. Inhibitors to other proteases have no effect. Erythrocyte ghosts undergo proteolysis and fusion only when loaded with non-inhibited hemolysate, irrespective of membrane status (native or alkylated membrane). A partially purified cytosolic enzyme, identified as calpain I, promotes proteolysis in rat erythrocyte ghosts. A2C induces fusion only in such calpain-treated ghosts.

Free radicals as possible mediators of the actions of interferon

Interferons (IFNs), in addition to their antiviral action, have been shown to inhibit cell proliferation, induce differentiation of some tumor cells, activate NK cells and macrophages, and modulate phagocytosis. The exact mechanism(s) by which IFN can bring about these pleiotropic actions is not known. Recent studies, including our own (presented here), showed that IFN can augment free radical generation in the cells. Free radicals can stimulate lymphocytes mitogenically and activate macrophages and NK cells. It is also known that activated machophages and polymorphs produce oxidative metabolites, such as hydrogen peroxide, which is responsible for sterilizing action against microorganisms and cytotoxic activity against tumor cells. Free radicals are also known to inhibit cell division. Since IFN can augment free radical generation, it is suggested that free radicals mediate some of the actions of IFN.