Human natural killer cells express VLA-4 and VLA-5, which mediate their adhesion to fibronectin.

Very late Ag (VLA)-3, VLA-4, and VLA-5, belonging to the beta-1 subfamily of integrins, have been recently identified as receptors for different binding regions of fibronectin (FN). We have detected VLA-4 and VLA-5, but not VLA-3, on fresh CD3-, CD16+, CD56+ human NK cells by flow cytometry and immunochemical analyses using mAb directed against beta-1, alpha-3, alpha-4, and alpha-5 subunits. Binding assays, performed on FN-coated plates, showed that NK cells specifically adhere to FN and their binding capacity is increased by MgCl2 but not by CaCl2. Using as inhibitory probes a polyclonal antibody against the beta-1 chain of the human FN receptor, the synthetic peptide GRGDSP, which is able to inhibit cellular adhesion mediated by VLA-5, the CS1 fragment, which contains the principal adhesion site in the IIICS domain recognized by VLA-4, and functional mAb directed against alpha-4 or alpha-5 subunits, we show that both VLA-4 and VLA-5 mediate the adhesion of human NK cells to FN. The expression of these integrin receptors may be relevant for NK interaction with extracellular matrix components and other cell types.     

Cytokine production by cholesterol-loaded human peripheral monocyte-macrophages: the effect on fibrinogen mRNA levels in a hepatoma cell-line (HepG2)

Conditioned medium from human monocyte-macrophages incubated under various conditions was tested for its ability to stimulate fibrinogen mRNA levels in the hepatoma cell line HepG2. Recombinant human interleukin-6 (IL-6) stimulated fibrinogen mRNA levels 4.4-fold over control levels; this response was blocked by an anti-IL-6 antibody. Conditioned medium from 3-day-cultured monocyte-macrophages produced a slight stimulation of fibrinogen synthesis in HepG2 cells which was enhanced when the monocyte-macrophages had been treated with lipopolysaccharide (LPS). This stimulation was blocked by the anti IL-6 antibody. The cytokines, interleukin-1 (IL-1) and tumour necrosis factor (TNF) were also detected in the conditioned medium from the 3-day-cultured monocyte-macrophages. Monocyte-macrophages were cultured for 17 days and then incubated with acetylated low density lipoprotein (AcLDL) for 48 h. Such cells were 'foamy' in appearance and showed a 4-fold increase in apoE mRNA and a 10 to 50-fold increase in apoE secretion. This increase in apoE production was suppressed by almost a third when cells were coincubated with AcLDL and LPS. Conditioned medium from these 17-day-cultured AcLDL-treated human monocyte-macrophages did not stimulate fibrinogen mRNA synthesis in HepG2 cells, nor did the conditioned medium contain detectable levels of cytokines. These results suggest that cytokine production from foam cells in the atherosclerotic lesion is unlikely to be a major contributing factor in determining the elevated fibrinogen levels seen in the plasma of patients with IHD.     

Variation at the apolipoprotein (apo) AI-CIII-AIV gene cluster and apo B gene loci is associated with lipoprotein and apolipoprotein levels in Italian children.

We have used RFLPs of the apolipoprotein (apo) B gene and apo AI-CIII-AIV gene cluster to estimate the genetic contribution of variation at these loci to the variability of plasmid lipid, lipoprotein, and apolipoprotein levels in 209 children from Sezze in central Italy. The sample was randomly divided into group I (107 children) and group II (102 children). Four site polymorphisms (PvuII, XbaI, MspI, and EcoRI) of the apo B gene and five site polymorphisms (XmnI, PstI, SstI, PvuII-CIII, and PvuII-AIV) of the apo AI-CIII-AIV gene cluster were examined in group I children. After adjustment for gender, age, and body-mass index, polymorphisms at both gene loci (PvuII-B, PvuII-CIII, and PvuII-AIV) were associated with significant effects on the levels of plasma apo AI, apo B, or high-density lipoprotein-cholesterol. RFLPs that showed significant effects in group I were genotyped in group II. All three polymorphisms were associated with similar effects on apolipoprotein levels, though for all RFLPs the magnitude of the effects was smaller in the group II children and only statistically significant for the effect of the PvuII-B genotype on apo AI levels. In the total sample of 209 children 7.4% of the sample variance in apo AI levels was explained by variation associated with the apo B PvuII-B RFLP. In addition, the PvuII-B RFLP was associated with significant effects on plasma apo B levels and explained 5.7% of the sample variance. The PvuII-CIII and PvuII-AIV polymorphisms were both associated with differences in apo AI levels, explaining 3.7%-5.7% of the sample variance. Taken together, the three PvuII polymorphisms explained 17.7% of the phenotypic variance in apo AI levels. There was significant evidence for an effect of nonlinearity of the PvuII-CIII genotypes on apo AI levels, with the individuals heterozygous for the polymorphism having the highest apo AI levels. No evidence of interaction between genotype and gender, age, and body-mass index was shown by covariance analysis. The molecular explanation of this effect is unclear. Our data show that variation at both the apo AI-CIII-AIV and apo B loci are associated with lipoprotein and apolipoprotein levels in this sample of Italian children.     

Independent expression of avian sarcoma virus in doubly infected chicken embryo fibroblasts.

Infection of a chicken cell with avian sarcoma virus requires division of the infected cell before synthesis of infectious progeny is initiated. This requirement for a cell division for the complete expression of avian sarcoma virus has been examined further with chicken embryo fibroblasts infected with two distinct viruses. Chicken cells infected with and producing a mutant of Rous sarcoma virus temperature sensitive for transformation (tsLA24PR-A) were arrested in G0 by depletion of serum factors from growth medium. These stationary cells continued to produce infectious progeny in the absence of further cell division. Superinfection of the stationary cells with the wild-type Prague strain of Rous sarcoma virus (PR-RSV-C) produced a stable double infection in these cells. Progeny of the superinfecting PR-RSV-C, however, were not detected until these cells underwent division after stimulation with fresh serum-containing medium. The addition of colchicine to these serum-stimulated cells, although not affecting production of the tsLA24PR-A, inhibited the appearance of progeny of the superinfecting PR-RSV-C. These experiments indicate that each avian sarcoma virus infection of a chicken embryo fibroblast requires division of the infected cell for production of that virus regardless of whether or not the cell is already producing a similar virus. The results suggest, therefore, that the requirement for a cell division represents a requirement for an event that controls virus expression in a "cis-acting" fashion specific for the provirus.     

A covalently bound photoisomerizable agonist. Comparison with reversibly bound agonists at electrophorus electroplaques

After disulphide bonds are reduced with dithiothreitol, trans-3- (α-bromomethyl)-3’-[α- (trimethylammonium)methyl]azobenzene (trans-QBr) alkylates a sulfhydryl group on receptors. The membrane conductance induced by this “tethered agonist” shares many properties with that induced by reversible agonists. Equilibrium conductance increases as the membrane potential is made more negative; the voltage sensitivity resembles that seen with 50 [mu]M carbachol. Voltage- jump relaxations follow an exponential time-course; the rate constants are about twice as large as those seen with 50 μM carbachol and have the same voltage and temperature sensitivity. With reversible agonists, the rate of channel opening increases with the frequency of agonist-receptor collisions: with tethered trans-Qbr, this rate depends only on intramolecular events. In comparison to the conductance induced by reversible agonists, the QBr-induced conductance is at least 10-fold less sensitive to competitive blockade by tubocurarine and roughly as sensitive to “open-channel blockade” bu QX-222. Light-flash experiments with tethered QBr resemble those with the reversible photoisomerizable agonist, 3,3’,bis-[α-(trimethylammonium)methyl]azobenzene (Bis-Q): the conductance is increased by cis {arrow} trans photoisomerizations and decreased by trans {arrow} cis photoisomerizations. As with Bis-Q, ligh-flash relaxations have the same rate constant as voltage-jump relaxations. Receptors with tethered trans isomer. By comparing the agonist-induced conductance with the cis/tans ratio, we conclude that each channel’s activation is determined by the configuration of a single tethered QBr molecule. The QBr-induced conductance shows slow decreases (time constant, several hundred milliseconds), which can be partially reversed by flashes. The similarities suggest that the same rate-limiting step governs the opening and closing of channels for both reversible and tethered agonists. Therefore, this step is probably not the initial encounter between agonist and receptor molecules.     

Differences between the endogenous and exogenous DNA sequences of Rous-associated virus-O.

DNA sequences related to the endogenous retrovirus of chickens, Rous-associated virus-O (RAV-O), have been examined using site-specific DNA endonuclease analysis of cellular DNA derived from line 15 and line 100 chickens. Individual embryos from both inbred lines were used as a source of embryonic fibroblasts from which cellular DNA was isolated. Analysis of DNA containing either endogenous RAV-O sequences alone or both endogenous and exogenous RAV-O sequences produced identical patterns of RAV-O-specific DNA fragments after digestion with the endonucleases Eco RI, Hind III, BgI II, Bam HI or Xho I. Similar analysis with endonucleases Hinc II or Hha I, however, produced several RAV-O-specific DNA fragments which were derived from cellular DNA containing both endogenous and exogenous RAV-O sequences but not from cellular DNA containing only endogenous sequences. Although some differences exist between the DNA fragments specific for the endogenous viral sequences of line 15 and line 100 cellular DNA, the DNA fragments specific for the exogenous viral sequences were identical between the two inbred lines. Cleavage of an unintegrated linear RAV-O DNA molecule with Hinc II or Hha I produced DNA fragments identical to those specific for the exogenously acquired RAV-O provirus. This suggests that these characteristic fragments contain no cellular DNA. The potential DNA junction fragments containing both viral and cellular DNA, identified after analysis of DNA that contains both endogenous and exogenous viral sequences, were identical to those observed after analysis of DNA containing only endogenous viral sequences. These results support the following conclusions. First, exogenous proviral sequences are integrated into chicken cell DNA following an interaction between viral and cellular DNA that is specific with respect to the virus and nonspecific with respect to the cell. Second, both the free linear RAV-O DNA intermediate and the newly integrated exogenous provirus contain specific endonuclease sites that are not found in endogenous RAV-O DNA sequences. These results suggest that the formation of the exogenous DNA provirus involves specific alteration of the endogenous viral DNA sequences before reinsertion of the sequences as the exogenous RAV-O DNA provirus. It is possible that newly integrated exogenous RAV-O sequences are characterized by specific differences in the pattern of base methylation and a limited sequence arrangement.     

Membrane structure and the tenuously maintained resistance to staining with N epsilon-dansyl-L-lysine shown by many cells

The ability to resist staining by N epsilon-dansyl-L-lysine is tenuously maintained in the majority of live nucleated cells taken from tissues concerned with immune function. Resistance is lost under a variety of nonphysiological conditions known to, or likely to, cause protein denaturation or aggregation. In contrast to that of dansyl-gamma-aminobutyrate, the fluorescence intensity of N epsilon-dansyl-L-lysine is only weakly enhanced by native proteins. This is further reduced on denaturation or aggregation of the proteins. It is unlikely, therefore, that cellular uptake of, and staining by, N epsilon-dansyl-L-lysine is a direct consequence of membrane protein denaturation/aggregation but may result from a decrease in protein-phospholipid interactions leading to formation of phospholipid domains. Previous work has indicated that such features are stained by N epsilon-dansyl-L-lysine (Humphries, G.M.K., Lovejoy, J.P., 1983, Biophys. J. 42:307-310; Humphries, G.M.K., Lovejoy, J.R., 1983, Biochem. Biophys. Res. Commun. 111:768-774). Although it appears likely that passage through a dansyl-lysine-staining state is a common, if not universal, prelude to cell death (as monitored by uptake of trypan blue), not all cells that lose resistance to dansyl-lysine staining are moribund. Resistance to staining is also lost by macrophages on binding to solid substrates and multivalent ligands. The possible physiological significance of this is discussed.     

A simple method for separating cells of Microcystis aeruginosa for counting

Heat was used to break up the mucilage-bound colonies of the blue-green alga, Microcystis aeruginosa Kütz. emend. Elenkin, for cell counting. Samples were heated in a water bath at 80°C for 5–10 min, then agitated in a Vortex mixer for 30–60 s. The treatment separated cells completely and reaggregation of cells did not occur. There was no evidence that heating distintegrated the cells.