The effects of the protein kinase C inhibitors staurosporine and H7 on the IgE dependent mediator release from RBL 2H3 cells

Novel sulfhydryl-reactive compounds orazipone and OR-1958 inhibit cytokine production and histamine release in rat and human mast cells

Orazipone (OR-1384) and OR-1958 are novel anti-inflammatory sulfhydryl reactive compounds with potential applications in the treatment of chronic obstructive lung disease and colitis. Mast cells are potent immune system cells which can be found in abundant numbers in mucosa of lung and gut. We have studied whether the anti-inflammatory effect of these compounds could be mediated through inhibition of the function of mast cells and compared their effects with the glucocorticoid budesonide. Human mast cell line (HMC-1) cells were activated using a combination of a calcium ionophore and a phorbol ester and the production of cytokines was measured using ELISA assay. Tumour necrosis factor-alpha mRNA levels were assessed using a semiquantitative reverse transcriptase polymerase chain reaction assay. Histamine release was studied in rat peritoneal mast cells. Orazipone, OR-1958 and budesonide inhibited significantly and dose dependently tumour necrosis factor-alpha production in HMC-1 cells with IC50-values of 20, 10, and 0.25 microM, respectively. Polymerase chain reaction studies showed that OR-1958 attenuated the activation-induced increase of tumour necrosis factor-alpha mRNA in HMC-1 cells. OR-1958 and, to a lesser extent, orazipone inhibited dose dependently compound 48/80-induced histamine release from rat peritoneal mast cells in a reversible manner. In contrast, budesonide did not appreciably affect the histamine release. Both orazipone and OR-1958 inhibit efficiently mast cell functions and therefore could prove useful in the treatment of diseases associated with inappropriate mast cell activation.

Staurosporine inhibits the anaphylactic reaction of the isolated guinea-pig heart

Isolated hearts from ovalbumin sensitized guinea-pigs were perfused according to Langendorff. Ovalbumin injection decreased coronary flow. Left ventricular pressure amplitude and heart rate increased initially and decreased thereafter. Concomitantly, the liberation of histamine, prostaglandin F2 alpha, as well as the sum of leukotrienes C4/D4/E4/F4, measured in the perfusate by radioimmunoassay, was augmented. Staurosporine (1 microM), an inhibitor of protein kinases, did not influence the liberation of mediators in response to antigen challenge, but inhibited all mechanical responses. Infusion of phorbol myristate acetate, an activator of protein kinase C, into non-sensitized hearts decreased coronary flow and left ventricular pressure amplitude, but did not liberate mediators. Staurosporine (1 microM) abolished these mechanical responses. The results indicate that staurosporine suppresses cardiac anaphylaxis by blockage of mediator effects rather than by inhibition of liberation or formation of mediators.

Transforming growth factor-beta 1 stimulates macrophage urokinase expression and release of matrix-bound basic fibroblast growth factor

Macrophage expression of urokinase-type plasminogen activator (uPA) appears to play a role in their release of matrix-bound basic fibroblast growth factor (bFGF) and transforming growth factor-beta (TGF-beta). In experiments reported here, we have examined the potential regulatory effects of bFGF and TGF-beta 1 on macrophage uPA expression. TGF-beta 1 stimulated in a dose- and time-dependent manner the expression of secreted membrane and intracellular uPA activities by a macrophage cell line (RAW264.7). When examined at similar concentrations, bFGF had little effect, and interleukin-1 alpha, tumor necrosis factor-alpha, and monocyte colony stimulating factor had no effect on macrophage uPA expression. Exposure of macrophages to TGF-beta 1 led to a rapid and sustained increase in the steady-state levels of uPA mRNA that was independent of de novo protein synthesis and was completely inhibited by actinomycin D. However, the TGF-beta 1-induced increase in uPA mRNA was largely unaffected by subsequent incubation of cells with actinomycin D. The protein kinase C inhibitor H7 markedly reduced the ability of TGF-beta 1 to stimulate expression of uPA activity. Likewise, okadaic acid and microcystin, inhibitors of serine/threonine phosphatases, potentiated the ability of TGF-beta 1 to upregulate macrophage uPA expression. TGF-beta 1 primed cells converted nearly all added plasminogen to plasmin and expressed sixfold more membrane-bound plasmin than control cells. Preincubation of TGF-beta 1 with either serum or methylamine-modified alpha 2-macroglobulin did not affect its ability to induce macrophage uPA expression. When control and TGF-beta 1-primed macrophages were cultured on matrices containing bound 125I-bFGF, their release of 125I-bFGF was increased five and tenfold, respectively, in the presence of plasminogen. The ability of TGF-beta to induce macrophage uPA expression and the plasmin-dependent release of matrix-bound bFGF may provide an indirect mechanism by which TGF-beta stimulates angiogenesis.

Phosphatidylcholine-specific phospholipase D-derived 1,2-diacylglycerol does not initiate protein kinase C activation in the RBL 2H3 mast-cell line

We examined the role of phosphatidylcholine-specific phospholipase D (PC-PLD) in the IgE-dependent activation of protein kinase C (PKC) in RBL 2H3 cells (a model for mast-cell function). Cells were sensitized with mouse monoclonal anti-trinitrophenol (TNP) IgE (0.5 micrograms/ml) and were then triggered with an optimal concentration (10 ng/ml) of TNP-ovalbumin conjugate (TNP-OVA). This resulted in an immediate biphasic increase in the production of 1,2-diacylglycerol (DAG) and activation of PKC. The initial increase in DAG production reached a peak within 30 s, and the second phase reached a plateau within 5 min after stimulation. TNP-OVA-induced PC-PLD activation followed the initial increase in DAG formation in response to IgE-receptor cross-bridging, but coincided with the second peak. Phosphatidic acid (PA), derived from the PC-PLD pathway, is metabolized to DAG by the action of PA phosphohydrolase (PAPase). Propranolol (0.3 mM), which inhibits PAPase, blocked the IgE-dependent increase in DAG, activation of PKC, and subsequently degranulation. The PKC inhibitor staurosporine (0.1 microM) inhibited the second, but not first, peak of DAG accumulation, reversed PKC translocation after 10 min and inhibited subsequent mediator release. Taken together, these results demonstrate that PC-PLD does not initiate, but may play a latent role in, IgE-dependent DAG production, PKC activation and mediator release from RBL 2H3 cells.

Influence of staurosporine, a more selective derivative CGP 41,251 and an inactive analogue CGP 42,700 on histamine release from isolated rat mast cells

The influence of staurosporine, a potent but nonselective inhibitor of protein kinase C, on rat mast cell histamine release, was compared with that of two derivatives, CGP 41,251 with a high degree of selectivity for protein kinase C and the related CGP 42,700 which is without activity. Staurosporine was a more potent inhibitor of mast cell responses than CGP 41,251, in accordance with their reported potencies. CGP 42,700 was investigated in the same concentration range as CGP 41,251 and served as a control for unspecific effects. Antigen induced histamine release was more effectively inhibited by staurosporine than by CGP 41,251, and responses to compound 48/80 were only modestly affected by both drugs. Responses to the ionophore A23187 were unaffected by staurosporine whereas CGP 41,251 was an effective inhibitor at suboptimal ionophore concentrations. In contrast, responses to combinations of the phorbol ester TPA and subthreshold concentrations of the ionophore could be potently inhibited by staurosporine but were under certain conditions moderately enhanced by lower concentrations of the drug, whereas CGP 41,251 was only inhibitory. Except for a slight inhibition of ionophore responses CGP 42,700 was without effect. The results demonstrate that the actions of staurosporine cannot be ascribed solely to inhibition of protein kinase C, whereas the influence of CGP 41,251 appears to be consistent with an inhibition of this kinase.

Lysophosphatidylcholine induces mast cell secretion and protein kinase C activation

Lysophosphatidylcholine (lyso-PC), a natural product of phospholipase A2 activity, induced the secretion of both granule-associated beta-hexosaminidase and newly generated leukotriene C4 from mouse bone marrow-derived mast cells. Micromolar concentrations of lyso-PC potentiated the release of beta-hexosaminidase induced by specific antigen but not the calcium ionophore, A23187. Exogenous adenosine was relatively ineffective in enhancing beta-hexosaminidase release from cells challenged with lyso PC. Lyso-PC caused a marked increase in intracellular free-calcium levels and induced the activation of protein kinase C (PKC). These effects could not be abrogated by a prolonged preincubation with pertussis toxin. Staurosporine, an inhibitor of PKC, partially inhibited the abilities of antigen and A23187 to induce beta-hexosaminidase release but was ineffective when lyso-PC was the secretagogue. Lyso-PC appears to activate mast cell PKC, but its ability to stimulate mast cell mediator release appears to be related to its ability to elevate intracellular free calcium concentrations.

Differential effects of propranolol on the IgE-dependent, or calcium ionophore-stimulated, phosphoinositide hydrolysis and calcium mobilization in a mast (RBL 2H3) cell line

Our previous studies demonstrated that propranolol, an inhibitor of phosphatidic acid phosphohydrolase (PAPase) (EC 3.1.3.4) blocks the IgE-dependent mediator release from a rat mast (RBL 2H3) cell line. To continue these studies, we examined the ability of propranolol to inhibit the IgE-dependent or ionomycin-mediated phosphoinositide hydrolysis and calcium mobilization in RBL 2H3 cells. RBL 2H3 cells, sensitized with mouse monoclonal anti-trinitrophenol IgE (anti-TNP IgE), were stimulated to release both histamine and peptidoleukotrienes (LT) in response to a suboptimal concentration of trinitrophenol-ovalbumin conjugate (TNP-OVA) or ionomycin. Preincubation of the cells with d,l-propranolol (300 microM) significantly (P less than 0.05) inhibited the effects of both TNP-OVA and ionomycin on histamine and LT release. There was no difference in potency for the different isomers of propranolol, indicating that these effects were not a consequence of an effect on beta 2-adrenergic receptors. TNP-OVA produced a rapid hydrolysis of phosphoinositides resulting in a time-dependent increase in mono- (IP1), di- (IP2), tri- (IP3), and total inositol phosphate production. Ionomycin also produced a rapid increase in total inositol phosphate production; however, this largely reflected an accumulation of IP1. Both secretagogues produced a rapid elevation in cytosolic free calcium ([Ca2+]i); however, the effect of ionomycin maximized within a much shorter time frame than the effect of TNP-OVA. The effects of TNP-OVA on phosphoinositide hydrolysis and increase in [Ca2+]i were inhibited by propranolol over exactly the same concentration range as the effects of this compound on TNP-OVA-stimulated mediator release. In contrast, propranolol had no effect on the increase in [Ca2+]i and phosphoinositide hydrolysis in response to ionomycin. Taken together, these results suggest that PAPase/phospholipase D (PLD) (EC 3.1.4.4) activation may be a prerequisite for both IgE-dependent and ionomycin-stimulated mediator release from RBL 2H3 cells. Although other explanations are possible, the data further suggest that receptor-mediated, but not ionophore-stimulated, phosphoinositide hydrolysis and [Ca2+]i in RBL 2H3 cells may be regulated by a propranolol-sensitive pathway involving possible activation of PAPase.