okadaic-acid and mezerein

Neutrophils contain a 21-kDa phosphoprotein that undergoes rapid dephosphorylation upon stimulation of these cells with the chemoattractant N-fMet-Leu-Phe (fMLP), activators of protein kinase C [e.g., 4 beta-phorbol 12-myristate 13-acetate (PMA)] or the calcium ionophore A23187. This phosphoprotein was identified as the non-muscle form of cofilin by peptide sequencing and immunoblotting with specific antibodies. Evidence is presented that in neutrophils cofilin is regulated by a continual cycle of phosphorylation and dephosphorylation, and that the phosphatase undergoes activation during cell stimulation. Experiments with a wide variety of antagonists further suggested that the protein kinase that participates in these reactions may be a novel enzyme. The kinetics of cofilin dephosphorylation in neutrophils stimulated with fMLP or PMA were very similar to those observed for superoxide (O2-) release. Immunofluorescent studies revealed that cofilin was present throughout the cytosol of resting neutrophils and underwent rapid translocation to the F-actin-rich, ruffled membranes of stimulated cells. Cytochemical analysis further revealed that the ruffled membranes also contained large amounts of hydrogen peroxide (H2O2), a product of the O2-/H2O2-generating activity of stimulated neutrophils (NADPH oxidase). Cofilin is therefore well placed to participate in the continual polymerization and depolymerization of F-actin that is thought to give rise to the oscillatory pattern of H2O2 production observed under certain conditions.

Topics: Actin Depolymerizing Factors; Actins; Amino Acid Sequence; Animals; Calcimycin; Cell Membrane; Diglycerides; Diterpenes; Guinea Pigs; Humans; Hydrogen Peroxide; Immunoblotting; Marine Toxins; Microfilament Proteins; Molecular Sequence Data; N-Formylmethionine Leucyl-Phenylalanine; NADPH Oxidases; Neutrophil Activation; Neutrophils; Okadaic Acid; Oxazoles; Oxides; Phosphorylation; Staurosporine; Terpenes; Tetradecanoylphorbol Acetate

Microglia, the resident macrophages of the brain, secrete a number of mediators involved in neural-immune function. The cytokines, IL-1 alpha and TNF alpha, are two such factors which are stored as inactive precursor molecules requiring post-translational proteolytic processing prior to release. From investigations of second messenger pathways involved in regulating the secretion of these cytokines, we have demonstrated that the PKC inhibitor, H-7, blocks the induction of TNF alpha secretion induced by LPS. In contrast, H-89 and HA-1077, inhibitors of cyclic nucleotide-dependent protein kinases (PKA and PKG), did not alter LPS-stimulation of TNF alpha release. Consistent with these observations, the weak PKC activator, mezerein, induced TNF alpha secretion in an H-7-reversible manner. In marked contrast, PKC activation did not induce IL-1 alpha secretion and H-7 potentiated IL-1 alpha release. In the case of the protein phosphatase inhibitor, okadaic acid, secretion of both cytokines was induced, indicating that protein phosphorylation is important for the induction of cytokine secretion but only in the case of TNF alpha is PKC involved. In the case of IL-1 alpha, a tonic inhibitory regulation involving PKC activation may be present. We therefore conclude that alterations in phosphorylation-dephosphorylation cycles may be important triggers in the switching of microglial cellular function from a resting to an activated state.

Topics: 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; Animals; Cell Line; Diterpenes; Ethers, Cyclic; Interleukin-1; Isoquinolines; Lipopolysaccharides; Mice; Microglia; Nerve Tissue Proteins; Okadaic Acid; Pentoxifylline; Phosphorylation; Piperazines; Terpenes; Tumor Necrosis Factor-alpha

Lymphocytes can be stimulated to proliferate in vitro by mitogens such as concanavalin A. The tumor-promoting phorbol ester 12-O-tetradecanoyl phorbol-13-acetate (TPA) can enhance this proliferation, partly because of an increase in interleukin 2 (IL-2) production. However, if lymphocytes are treated with TPA for 24 h before concanavalin A exposure, IL-2 production and proliferation are depressed. The target of the action of TPA is protein kinase C, which is activated after a short exposure but down-regulated after a longer one. This study was designed to determine if the modulation of IL-2 was separable from the modulation of protein kinase C. When phorbol esters phorbol 12-retinoate-13-acetate, phorbol 12,13-dibutyrate, 12-deoxyphorbol 13-phenylacetate, and 12-deoxyphorbol 13-phenylacetate-20-acetate, as well as nonphorbol tumor promoters mezerein, telocidin, and okadaic acid, were tested, all but okadaic acid reproduced the effects of TPA. However, 12-deoxyphorbol 13-phenylacetate and 12-deoxyphorbol 13-phenylacetate-20-acetate were required at nearly 100-fold higher concentrations than TPA to suppress IL-2 production, suppress mitogenesis, and cause down-regulation of protein kinase C. A comparison of structures indicated that an R group at the 12-position was less important for IL-2 production and mitogenesis than for down-regulation of protein kinase C and the suppression of mitogenesis. In no case was the modulation of protein kinase C separated from the effects on IL-2 production and proliferation.

Topics: Animals; Cattle; Cell Compartmentation; Concanavalin A; Diterpenes; Dose-Response Relationship, Drug; Down-Regulation; Ethers, Cyclic; In Vitro Techniques; Interleukin-2; Lymphocyte Activation; Lymphocytes; Lyngbya Toxins; Okadaic Acid; Phorbol Esters; Protein Kinase C; Terpenes