Phospholipase A2 sensitivity of uterine smooth muscle membrane phospholipids and adenylate cyclase activity. Effect of temperature on the action of phospholipase present in excess

Low temperatures and hypertonicity do not block cytokine-induced stimulation of the sphingomyelin pathway but inhibit nuclear factor-kappa B activation

In order to better understand the significance of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta)-receptor internalization in the sphingomyelin pathway signal transduction, we investigated receptor signaling under conditions in which receptor internalization is blocked. We demonstrate that human recombinant TNF-alpha and IL-1 beta both induced sphingomyelin and phosphatidylcholine hydrolysis at either 4, 14, or 37 degrees C in human skin fibroblasts and U937 monocytic cells. Cytokine-induced sphingomyelin degradation also occurred when endocytosis was inhibited by incubating the cells in hypertonic medium. While internalization was not required for the production of ceramide, activation of the transcription factor NF-kappa B was strongly reduced when cells were stimulated with TNF at low temperature or in hypertonic medium. Under these conditions, activation of NF-kappa B by the cell-permeant C2- ceramide (N-acetylsphingosine), by exogenous sphingomyelinase or by phorbol myristate acetate was also inhibited. These results suggest that low temperature and hypertonicity, two inhibitors of receptor internalization: (i) do not affect the TNF-alpha- or IL-1 beta-induced sphingomyelin hydrolysis, but (ii) do inhibit a step distal to ceramide of the intracellular signaling pathway leading to NF-kappa B activation.

Lipid changes in HL-60 cells on differentiation into macrophages by treatment with a phorbol ester

We studied changes in lipid composition of human promyelocytic leukemia cells (HL-60) on differentiation to the macrophage/monocytic lineage by treatment with the phorbol ester, 12-O-tetradecanoyl-phorbol-13-acetate. Differentiation was accompanied by: (i) a decrease in the level of phospholipids; (ii) a greater amount of triacylglycerols; (iii) an increase in 1-alk-1'-enyl-2-acyl- and 1-alkyl-2-acyl-sn-glycero-3-phosphoethanolamine and a decrease in 1-alkyl-2-acyl-sn-glycero-3-phosphocholine; and (iv) an increase in the level of arachidonic acid in ethanolamine phospholipids. The increased levels of ether-linked lipids and of arachidonic acid in ethanolamine phospholipids are consistent with an enhanced biosynthesis of platelet-activating factor and eicosanoids, which are particularly important in the macrophage function.

Effect of phosphatidylcholine structure on the adenylate cyclase activity of a murine fibroblast cell line

To determine which structural characteristics of membrane phospholipids influence adenylate cyclase activity, we measured basal and sodium fluoride-or forskolin-stimulated activity in a murine fibroblast cell line, i.e., Balb/c3T3 cells grown in media supplemented with fetal calf serum (FCS), lipid-depleted FCS (LD-FCS) or LD-FCS complexed with different phosphatidylcholine (PC) molecular species. Cells grown in the presence of LD-FCS showed a substantial decrease in their basal and NaF-stimulated adenylate cyclase activities; however, their forskolin-stimulated activity was not altered, suggesting that the enzyme's catalytic site is not affected by changes in membrane lipids. Media supplemented with different LD-FCS/PC complexes were shown to prevent the LD-FCS-mediated reduction of basal and NaF-stimulated adenylate cyclase activity to different extents. Addition of cis-9-16:1, cis-9-18:1/cis-9-18:1 or cis-9-18:1/cis-9,12-18:2 sn-glycerophosphocholine (GPC) completely restored adenylate cyclase activity, while cis-11-18:1/cis-11-18:1 GPC was not effective and only a partial recovery was observed with 16:0/16:0, 16:0/cis-9-18:1 and trans-9-18:1 GPC. Considering the structural features of these seven PC molecular species, the findings suggest that an optimal lipid environment is conferred to the enzyme by the presence of two cis double bonds, each located in delta 9 position of the PC acyl chains. The limited effect of cis-9-16:1/cis-9-18:1 GPC and cis-9-18:1/cis-9-16:1 GPC suggests that an equal length of the terminal hydrocarbon chains extending beyond the delta 9 double bonds is also important.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of neutrophils and phospholipase A2 on transvascular albumin flux in isolated rabbit lungs

In this study, addition of phospholipase A2 (PLA2) to salt-perfused isolated rabbit lungs containing rabbit polymorphonuclear leukocytes leads to an increase in pulmonary capillary permeability. We add 1.5 X 10(8) polymorphonuclear leukocytes to the perfusate. Next, indomethacin is added to the perfusate and 40 units of PLA2 are infused into the pulmonary arterial inflow of the lungs. At the end of the study, a lung sample is removed for measurement of transvascular albumin flux using I125-albumin as a measure of the permeability-surface area product. Control studies demonstrate no increase in transvascular albumin flux. Addition of a dual cyclooxygenase and lipoxygenase inhibitor, BW755C, to the perfusate prevents the increase in transvascular albumin flux. We conclude that PLA2 interacts with polymorphonuclear leukocytes to increase protein permeability. Since PLA2 can release endogenous arachidonic acid and platelet-activating factor from cells, this suggests that release of such products may contribute to an increase in pulmonary capillary permeability from polymorphonuclear leukocytes. The ability of BW755C to prevent the increase suggests the possibility that lipoxygenase products contribute.