Protein kinase C in transmembrane signalling

Cloning and molecular characterization of the murine macrophage "68-kDa" protein kinase C substrate and its regulation by bacterial lipopolysaccharide

We have isolated and characterized a cDNA clone encoding the murine macrophage 68-kDa protein kinase C substrate, which is homologous to the 80- to 87-kDa protein identified by the acronym MARCKS (myristoylated alanine-rich C kinase substrate). The murine MARCKS cDNA clone encodes an acidic protein of 309 amino acids with a calculated molecular weight of 29,661. Transfection of the murine MARCKS gene into TK-L fibroblasts produced a myristoylated protein kinase C substrate that migrated on SDS/PAGE with an apparent molecular mass of 68 kDa. Peptide mapping studies indicated that MARCKS produced by the transfected gene was indistinguishable from the endogenous murine macrophage protein. Comparison of the murine macrophage sequence with the previously published chicken and bovine brain sequences revealed two conserved domains: an N-terminal membrane-binding domain and a phosphorylation domain that also contains calmodulin and actin binding sites. In murine peritoneal macrophages, bacterial lipopolysaccharide increased MARCKS mRNA levels by greater than 30-fold. Multiple MARCKS transcripts were observed and could be accounted for by differential polyadenylylation and incomplete processing. Genomic Southern blot analysis suggested a single MARCKS gene per haploid genome.

Photosensitizing action of furocoumarins on membrane components and consequent intracellular events

The photodamage induced in membrane components by furocoumarins is reviewed. The oxygen-dependent photoreactions between furocoumarins and cell membrane constituents lead mainly to lipid peroxidation and the formation of cross-linking in ghost proteins, whereas the oxygen-independent photoreactions lead essentially to a C4 cycloaddition between the furocoumarin and the unsaturated fatty acids. In the latter, cycloadducts are formed between the 3,4 double bond of the furocoumarin and the olefinic double bond of the unsaturated fatty acid. The stereochemical structures of these cycloadducts and the reaction mechanism of the cycloaddition are discussed. Finally, the modulation of several membrane systems by furocoumarins and the consequent intracellular events are reviewed.

Evidence for the regulation of the activity of protein kinase C through changes in membrane properties

We measured the effects of two branched-chain analogs of distearoyl-phosphatidylcholine, containing either a methyl or an n-butyl group at the 8 position, on the bilayer to hexagonal phase transition temperature of dielaidoylphosphatidylethanolamine. The former compound raised the bilayer to hexagonal phase transition temperature while the latter compound lowered it. The opposite effects of these amphiphiles on protein kinase C activity (inhibition and activation, respectively) correlated with their effects on lipid polymorphism. Because of the similarity of the structures of these two compounds, it seems likely that their opposite effects on the activity of protein kinase C is a result of their alteration of the lipid environment of the membrane rather than to binding to a specific site on the protein. We also compared the effects of hexachlorophene on lipid polymorphism and protein kinase C activity at high and at low calcium concentrations. We also found that the effect of hexachlorophene forming a complex with Ca2+ is to increase both the hexagonal phase forming propensity of the membrane as well as to increase the activity of protein kinase C, again demonstrating the correlation between lipid phase propensity and effects on protein kinase C activity.

Membrane depolarization was required to induce DNA synthesis in murine macrophage cell line PU5-1.8

The role of membrane potential (Em) on the initiation of DNA synthesis in murine macrophage cell line PU5-1.8 was investigated with fluorescent probes bis-oxonol and diS-C3-(5). Incubation of PU5-1.8 cells in high K(+)-HEPES buffer or with gramicidin at 37 degrees C for 1h that depolarized the membrane induced [3H]-thymidine incorporation and expression of early response gene such as c-myc and c-fos. When PU5-1.8 cells were treated with a number of agents including fetal calf serum (FCS), lipopolysaccharide (LPS), epidermal growth factor (EGF), N-formyl-methionyl-leucyl-phenylalanine (FMLP) and bradykinin (BK), only FCS caused DNA synthesis and membrane depolarization. Other agents had no effect on these events. The FCS-mediated DNA synthesis in PU5-1.8 cells was inhibited by clamping the membrane potential with valinomycin. Moreover, intracellular alkalinization induced by nigericin at pH 7.9, which is believed to be a permissive signal for mitogenesis, caused membrane depolarization. On the other hand, challenge of cells with phorbol 12-myristate 13 acetate (PMA) suppressed the K(+)-mediated DNA synthesis. However, the treatment of cells with PMA did not change the membrane potential but suppressed the gramicidin-mediated membrane depolarization. These observations suggest that there is a correlation between membrane depolarization and initiation of DNA synthesis in PU5-1.8 cells. PKC may be acting as a modulator in this transducing pathway.

Dual effect of arachidonic acid on protein kinase C isoenzymes isolated from rabbit thymus cells

Type II and type III isoenzymes of protein kinase C isolated from rabbit thymus cells were activated at relatively low concentrations but were inhibited at higher concentrations of arachidonic acid. Activation by cis-unsaturated fatty acids required Ca2+; the maximal activity was approached at about 10(-6) M Ca2+ concentration. The kinetics of activation and inhibition by arachidonic acid depended strongly on the nature of the substrate (synthetic oligopeptide or H1 histone), on the concentration of the protein substrate and on the stage of purification of the isoenzyme preparation investigated. Activation seemed to be favoured at high protein concentrations.

K-252a inhibits the response of tomato cells to fungal elicitors in vivo and their microsomal protein kinase in vitro

Two characteristic responses of plant cells to fungal elicitors, induction of phenylalanine ammonia-lyase activity and of ethylene biosynthesis, were studied in suspension-cultured tomato cells. Induction of both responses was completely blocked by 500 nM K-252a, a known inhibitor of mammalian protein kinases. About 100 nM K-252a caused half-maximal inhibition. In vitro, K-252a inhibited protein kinase activity in microsomal preparations from tomato cells. Inhibition was competitive with respect to ATP and had a Ki of about 15 nM. Thus, protein kinases sensitive to K-252a occur in plants and might be important for the plant's response to fungal elicitors.