The protein kinase inhibitor staurosporine, like phorbol esters, induces the association of protein kinase C with membranes

The effect of putative protein kinase C inhibitors, K252a and staurosporine, on the human neutrophil respiratory burst activated by both receptor stimulation and post-receptor mechanisms

1. Two compounds, reported to be potent inhibitors of protein kinase C (PKC), K252a and staurosporine, have been examined in order to gain further information as to the possible role played by PKC in the signal transduction sequence of the neutrophil respiratory burst as determined by superoxide (O2-) production. 2. A number of stimuli were used in the study, some acting at receptors i.e. fMet-Leu-Phe (fMLP), opsonized zymosan and heat-aggregated IgG (HAGG), one acting on a G-protein, fluoride, and two direct PKC activators, dioctanoylglycerol (diC8) and phorbol myristate acetate (PMA). 3. K252a and staurosporine inhibited the respiratory burst with all the stimuli but the order of agonist sensitivity was very different with the two inhibitors. 4. For K252a-induced inhibition of O2- release, the order of potency was fluoride greater than fMLP, HAGG greater than opsonized zymosan greater than PMA, DiC8. For staurosporine-induced inhibition of O2- release, the order of potency changed to fluoride greater than DiC8, PMA greater than HAGG, fMLP greater than opsonized zymosan. The significance of this unexpected difference in relative rank order of potency is discussed with reference to the reported mechanism of action of the two inhibitors and the events involved in the oxidative burst. 5. Staurosporine at low concentrations increased the fMLP-stimulated O2- response by 100%, the maximum effect occurring at 35 nM. 6. To the extent that the compounds used are specific inhibitors of PKC, these findings support a role for the enzyme PKC in stimulus-activation coupling in O2- generation with all the stimuli used in this study.

Evidence for a relationship between B-50 (GAP-43) and [3H]noradrenaline release in rat brain synaptosomes

Phosphorylation of the neuron-specific substrate of protein kinase C (PKC), B-50 (GAP-43), was studied parallel with noradrenaline release in rat brain synaptosomes. Both could be evoked by treating the synaptosomes with high K+ or veratridine. Phorbol 12,13-dibutyrate enhanced depolarization-induced B-50 phosphorylation and noradrenaline release. To investigate the involvement of PKC-mediated B-50 phosphorylation in noradrenaline release, we applied a variety of kinase inhibitors. Prior to measuring the effects of these inhibitors in intact synaptosomes, we determined their effectivity and specificity in a membrane phosphorylation assay. H-7 most specifically inhibited PKC-dependent phosphorylation, whereas calmidazolium inhibited calmodulin-dependent phosphorylation. Polymyxin B affected both protein kinase systems. Only polymyxin B effectively inhibited noradrenaline release in the intact synaptosomes. We conclude that PKC as well as calmodulin-dependent processes are important for the release event. Data are discussed in view of the presumed function of B-50 as a calmodulin-binding protein.

Mechanism of action of gonadotropin releasing hormone upon gonadotropin secretion: involvement of protein kinase C as revealed by staurosporine inhibition and enzyme depletion

The role of protein kinase C (PKC) in the mechanism of action of gonadotropin-releasing hormone (GnRH) upon gonadotropin secretion is controversial and therefore was investigated in primary cultures of rat anterior pituitary cells. A relatively selective PKC inhibitor, staurosporine, inhibited both GnRH- and 12-O-tetradecanoylphorbol 13-acetate (TPA)-induced luteinizing hormone (LH) release with half-maximal inhibition (IC50) of about 80 nM. Inhibition of GnRH action was not complete suggesting also a PKC-insensitive component in GnRH-induced gonadotropin release. Staurosporine had no effect on basal LH release, or on cellular LH content, neither did the drug interfere with the binding of [125I]iodo-[D-Ser(t-Bu)6]des-Gly10-GnRH N-ethylamide to its receptor in pituitary cells. When cultured pituitary cells were incubated with TPA (1 microM) for 24-48 h no measurable cellular PKC activity could be detected. The decrease in total PKC activity was accompanied by an increase in Ca2+, phosphatidylserine (PS), diacylglycerol (DG)-insensitive activity suggesting the release of a portion of the catalytic domain of PKC (M-kinase) by the phorbol ester treatment. TPA-induced LH release was nearly abolished in PKC-depleted cells and the response to GnRH was markedly reduced (40%). The stimulatory effect of the Ca2+ ionophore, ionomycin, was not impaired in PKC-depleted cells. Impaired responses to GnRH in PKC-depleted cells were only noticed at a later phase (2-4 h) of the exocytotic response of the neurohormone. The data strongly suggest a role for PKC during the second phase of GnRH-induced gonadotropin secretion.

Inhibition of protein kinase C by H-7 potentiates the release of oleic, linoleic and arachidonic acids in A23187-stimulated human neutrophils

This present report describes the effect of H-7, a protein kinase C inhibitor, on the release of oleic, linoleic and arachidonic acids in A23187-stimulated neutrophils. Surprisingly, the inhibitor potentiated the release of all three unsaturated fatty acids in neutrophils stimulated with A23187 alone. In contrast, released oleic acid, linoleic acid and arachidonic acid in phorbol 12-myristate 13-acetate-primed neutrophils were attenuated by 35, 47 and 33%, respectively, in the presence of H-7 (300 microM). Phorbol 12-myristate 13-acetate (PMA) had no effect on A23187-stimulated release of saturated fatty acids. Both PMA and H-7 when used alone had no effect on the release of saturated or unsaturated fatty acids. We, therefore, conclude that H-7 may have effects other than inhibiting PMA-primed responses including superoxide generation, degranulation and arachidonic acid release in human neutrophils.

Staurosporine inhibits the respiratory burst and induces exocytosis in human neutrophils

The protein kinase C inhibitor staurosporine influenced in different ways the functions of human neutrophils. Staurosporine prevented the enhanced protein phosphorylation in phorbol ester- and N-formylmethyionyl-leucylphenylalanine (fMLP)-stimulated cells, and was a powerful inhibitor of the respiratory burst induced by phorbol myristate acetate [IC50 (concentration causing 50% inhibition) 17 nM] and the chemotactic peptides fMLP and C5a (IC50 24 nM). It did not alter, however, the superoxide production by cell-free preparations of NADPH oxidase. Staurosporine had no effect on agonist-dependent changes in cytosolic free Ca2+ and exocytosis of specific and azurophil granules, and showed only a slight inhibition of the release of vitamin B12-binding protein induced by phorbol myristate acetate (decreased by 40% at 200 nM). On the other hand, staurosporine also exhibited neutrophil-activating properties: it induced the release of gelatinase (from secretory vesicles) and vitamin-B12-binding protein (from specific granules). These effects were protracted, concentration-dependent, insensitive to Ca2+ depletion, and strongly enhanced by cytochalasin B. Staurosporine, however, did not induce the release of beta-glucuronidase or elastase (from azurophil granules). Except for the sensitivity to cytochalasin B, these properties suggest a similarity between the exocytosis-inducing actions of staurosporine and PMA. The results obtained with staurosporine provide further evidence that different signal-transduction processes are involved in neutrophil activation, and suggest that protein phosphorylation is required for the induction of the respiratory burst, but not for exocytosis.

Oleate-induced translocation of protein kinase C to hepatic microsomal membranes

The incubation of rat liver homogenates in the presence of oleate induces the translocation of protein kinase C from the cytosol to the endoplasmic reticulum membranes. The half-maximal effect was obtained at 0.3 mM oleate. The redistribution of this enzyme induced by oleate was also obtained with purified protein kinase C and hepatic microsomal membranes. This effect seems to be mediated by long-chain fatty acids since translocation was not obtained with esterified derivatives.

1,2-Diacylglycerol accumulation in human neutrophils does not correlate with respiratory burst activation

Measurements of the level of 1,2-diacylglycerol (1,2-DG) during activation of the respiratory burst of human neutrophils by formyl-methionyl-leucyl-phenylalanine (fMLP) in the presence of platelet-activating factor (PAF) or by opsonized particles show that a correlation between accumulation of 1,2-DG and O2 consumption does not exist. Inhibition of protein kinase C activity with staurosporine before addition of opsonized particles demonstrates that the first phase of the respiratory burst is not inhibited, whereas the second phase, which is accompanied by a rise in the content of 1,2-DG, is strongly inhibited. This study indicates that accumulation of 1,2-DG cannot be the sole signal for the initiation of the respiratory burst in human neutrophils.

The DNA synthesis of leukemic (L2C) guinea pig B lymphocytes involves a permanent activation of protein kinase C without corresponding phosphoinositide hydrolysis

L2C B lymphocytes have a constant high DNA synthesis due to their continuous proliferative state. The addition of polymyxin B (PmB), a rather selective inhibitor of protein kinase C, stopped (3H)thymidine incorporation with an IC50 of 10 microM when added 18 h before measuring DNA synthesis. Interestingly, PmB inhibition of DNA synthesis was suppressed when 4 nM 12-O-tetradecanoylphorbol-13-acetate was added along with PmB, indicating that PmB may act through inhibition of protein kinase C. In the node and spleen lymphocytes of normal guinea pigs, protein kinase C activity was entirely cytosolic and was eluted at 0.12 M NaCl when adsorbed on DEAE-cellulose. In L2C leukemic lymphocytes, total protein kinase C activity was of the same order of magnitude, but 20% of it was associated with the membrane fraction. The lipid-dependent activity, eluted at 0.12 M NaCl from cytosolic and membrane fractions, was suppressed by staurosporine with an IC50 of 10-40 nM and by polymyxin B with an IC50 of 2-6 microM. Phosphoinositide metabolism was studied in the transformed cells. Incorporation of 32Pi into polyphosphoinositides was considerable, whereas much more time was required for a tiny incorporation of inositol. We detected no release of radioactive inositol triphosphate. Taken together, these results suggest that protein kinase C function is indispensible for triggering L2C leukemic lymphocyte proliferation. The causes of this permanent activation merit further investigation.

Inhibition of phorbol ester-caused induction of ornithine decarboxylase and tumor promotion in mouse skin by staurosporine, a potent inhibitor of protein kinase C

We found that staurosporine, a potent inhibitor of protein kinase C, inhibits induction of ornithine decarboxylase (ODC) and tumor promotion caused by 12-O-tetradecanoylphorbol-13-acetate (TPA) in CD-1 mouse skin. When applied 5 min either before or after treatment with TPA, 1 microgram of staurosporine cause about 56% inhibition of ODC-induction by 5 micrograms of TPA. However, staurosporine did not inhibit TPA-induced epidermal hyperplasia. In two-stage carcinogenesis, staurosporine at 1 microgram was applied 5 min before application of 5 micrograms of TPA to the initiated skin: number of tumors was suppressed by about 40% although the incidence was not affected. No tumors developed when staurosporine alone was applied to the initiated skin.