Suppressive effect of aqueous humor from person with type 2 diabetes with or without retinopathy on reactive oxygen species generation

AIM

To evaluate the antioxidant capacity and concentrations of vascular endothelial growth factor (VEGF) and interleukin 6 (IL-6) in aqueous humor from patients with type 2 diabetes mellitus (T2DM) with or without retinopathy.

METHODS

Aqueous humor was obtained during elective cataract surgery from T2DM patients with or without retinopathy and from healthy subjects. Reducing response was evaluated by MTT dye reduction and the generation of reactive oxygen species (ROS) was determined by chemiluminescence assay. Granulocytes were treated with phorbol dibutyrate (PDB)-stimulated. Cytokines were quantified by ELISA.

RESULTS

Antioxidant capacity of aqueous humor from patients with retinopathy was greater (P<0.05) than that of healthy controls or persons with diabetes without retinopathy. ROS production in PDB (protein kinase C activator)-stimulated granulocytes from T2DM patients with or without retinopathy was inhibited by autologous aqueous humor. Concentrations of VEGF and IL-6 were similar in aqueous humor from healthy controls and from patients without retinopathy, but lower (P<0.05) than those from T2DM patients with retinopathy. Plasma levels of VEGF and IL-6 were similar (P>0.05) in healthy controls and in T2DM patients with and without retinopathy.

CONCLUSION

Aqueous humor from T2DM patients with retinopathy exhibits elevated antioxidant activity with significant suppressive effect on ROS production and enhanced levels of locally secreted VEGF and IL-6 in comparison with T2DM patients without retinopathy. These results suggest an inflammatory profile in the absence of typical oxidative stress for T2DM patients with retinopathy, possibly resulting from the compensatory antioxidant response detected in the aqueous humor improving the ocular redox state.

[Effect of a soluble Jagged 1/Fc chimera protein on the activation, proliferation and cell cycle of lymphocytes in mice]

AIM

To investigate effect of a soluble Jagged 1/Fc chimera protein (Jagged 1/Fc) on activation, proliferation and cell cycles of lymphocytes in BALB/c mice.

METHODS

A model to evaluate the lymphocyte proliferation stimulated with a polyclonal activator, concanavalin A (ConA), was established by a carboxy-fluorescein diacetate-succinimidyl ester (CFDA-SE)-labeling technique. Under an effective dose of 500 mug/L of Jagged 1/Fc, the effect of it on the lymphocyte proliferation was analyzed by flow cytometry. A propidium iodide-labeling technique was applied to estimate the influence of Jagged 1/Fc on the lymphocyte cell-cycle stimulated by phorbol 12,13-dibutyrate (PDB) plus Ionomycin (Ion). Expression levels of CD69 and CD25 molecules on surface of CD3(+) lymphocytes activated with ConA in the presence of Jagged 1/Fc were observed by a fluorescein-conjugated monoclonal antibody-labeling technique.

RESULTS

Jagged 1/Fc had no effect on the expression levels of CD69 and CD25 of the CD3(+) lymphocytes stimulated with or without ConA, and no effect on the proliferation index of the lymphocytes stimulated by ConA or PDB plus Ion. It led to the increase of sub-G0 phase cell proportion and the decrease of S phase cell proportion of the lymphocytes, but did not influence the changes of the lymphocyte cell-cycle induced by PDB plus Ion.

CONCLUSION

The results suggest that Jagged 1/Fc has no obvious effect on the activation and proliferation of lymphocytes in mice, but may promote the apoptosis of them, cause the G0/G1 phase arrest and block the S phase entry.

Munc18-1 phosphorylation by protein kinase C potentiates vesicle pool replenishment in bovine chromaffin cells

Activation of protein kinase C (PKC) after robust stimulation is necessary for vesicle pool replenishment in secretory cells. Here we studied the contribution of a prominent downstream PKC target, Munc18-1, to this process in bovine chromaffin cells. In these cells, both activation of endogenous PKC and overexpressing of Munc18-1 promote vesicle pool replenishment after an extensive stimulation. In order to study the physiological relevance of PKC-dependent Munc18-1 phosphorylation, we generated two Munc18-1 phospho-mutants; one that mimics a constitutively PKC-phosphorylated Munc18-1 (i.e. a phosphomimetic mutant; Munc18-1(S313D)) and a second that cannot be PKC-phosphorylated (Munc18-1(3A)). Overexpression of Munc18-1(3A) caused a significant decrease in vesicle pool replenishment following a depleting stimulation, while Munc18-1(S313D) caused a significant increase in vesicle pool replenishment. These findings suggested that the phosphorylation of Munc18-1 by PKC potentiates vesicle pool replenishment. This hypothesis was further strengthened by the finding that overexpression of wild type Munc18-1 in the presence of a PKC inhibitor caused a significant reduction in vesicle pool replenishment, similar to that observed with Munc18-1(3A). Moreover, overexpression of Munc18-1(S313D) in the presence of the PKC inhibitor partly alleviated this attenuation, elucidating Munc18-1's unique contribution to vesicle pool replenishment. Finally, we demonstrate that Munc18-1 promotes vesicle docking in a phosphorylation-independent manner. This is deduced from the findings that both the wild type and the two Munc18-1 phospho-mutants enhanced docking to the same extent in bovine chromaffin cells. We conclude that Munc18-1 facilitates docking in a PKC phosphorylation-independent manner, and that its phosphorylation by PKC potentiates vesicle pool replenishment following a depleting stimulation, at a post-docking stage.

Parathyroid hormone stimulates phosphatidylethanolamine hydrolysis by phospholipase D in osteoblastic cells

Parathyroid hormone (PTH) and phorbol-12,13-dibutyrate (PDBu) stimulate phospholipase D (PLD) activity and PC hydrolysis in UMR-106 osteoblastic cells {Singh, A.T., Kunnel, J.G., Strieleman, P.J., and Stern, P.H. (1999) Parathyroid Hormone (PTH)-(1-34), [Nle8,18,Tyr34]PTH-(3-34) Amide, PTH-(1-31) Amide, and PTH-Related Peptide-(1-34) Stimulate Phosphatidylcholine Hydrolysis in UMR-106 Osteoblastic Cells: Comparison with Effects of Phorbol 12,13-Dibutyrate, Endocrinology 140, 131-137}. The current studies were designed to determine whether ethanolamine-containing phospholipids, and specifically PE, could also be substrates. In cells labeled with 14C-ethanolamine, PTH and PDBu treatment decreased 14C-PE. In cells co-labeled with 3H-choline and 14C-ethanolamine, PTH and PDBu treatment increased both 3H-choline and 14C-ethanolamine release from the cells. Choline and ethanolamine phospholipid hydrolysis was increased within 5 min, and responses were sustained for at least 60 min. Maximal effects were obtained with 10 nM PTH and 50 nM PDBu. Dominant negative PLD1 and PLD2 constructs inhibited the effects of PTH on the phospholipid hydrolysis. The results suggest that both PC and PE are substrates for phospholipase D in UMR-106 osteoblastic cells and could therefore be sources of phospholipid hydrolysis products for downstream signaling in osteoblasts.

Induction of c-fos expression in the mouse brain associated with hyperalgesia induced by intrathecal injection of protein kinase C activator

Here, we found that a single intrathecal (i.t.) administration of a protein kinase C (PKC) activator, phorbol 12,13-dibutyrate (PDBu), induced pain-like behaviors in mice. Furthermore, i.t.-administered PDBu caused the increased c-fos-like immunoreactivity in the parafascicular nuclei (PF), amygdala and cingulate cortex (CG), but not hippocampus. These findings suggest that the stimulation of spinal PKC results in an enhancement of neuronal activity in the PF, amygdala and CG associated with hyperalgesia.

5-acyloxy-5-hydroxymethyltetrahydro-2-furancarboxylate as a novel template for protein kinase C (PKC) binding

A series of alkyl tetrahydrofuran-2-carboxylates (1-4) bearing a new set of three pharmacophoric groups were tested as protein kinase C (PKC) ligands. The compounds were synthesized from commercially available glycidyl 4-methoxyphenyl ether. The correlation between their binding affinities for PKC-alpha and a conformational fit to phorbol ester indicates they mimic a pharmacophore model comprising the C20-OH, C3-C=O and C9-OH rather than that including the C13-C=O moiety.

Protein kinase C in platelets of depressed patients

BACKGROUND

We studied the role of protein kinase C (PKC), a major regulatory enzyme and an important component of the phosphoinositide signaling system, in depression.

METHODS

PKC was determined using [3H]phorbol dibutyrate (PDBu) as the radioligand in the membranal and cytosolic fractions of platelets obtained from hospitalized drug-free depressed patients during a baseline period and from drug-free normal control subjects.

RESULTS

We observed that the [3H]PDBu binding was significantly higher in the cytosolic fraction obtained from platelets of depressed patients compared to normal control subjects.

CONCLUSIONS

Our studies indicate increased formation of PKC in platelets of depressed patients. The significance and mechanisms involved in increased PKC in the cytosolic fraction of platelets are unclear, but they suggest that increased PKC may be associated with the pathophysiology of depressive illness.

Beta-adrenergic regulation of renin expression in differentiated U-937 monocytic cells

Previous studies from our laboratories demonstrated that human decidual macrophages and peripheral mononuclear cells express renin. In the present study, we found that U-937 monocytes, induced to differentiate into macrophage-like cells by treatment with phorbol dibutyrate (PDBU), express renin mRNA and release renin (95%, of which is in the form of prorenin). Treatment of these PDBU-exposed cells with dibutyryl-cAMP (1 mM) caused a 20-fold increase in renin mRNA and a 10-fold increase in prorenin release. Forskolin (10 microM), an activator of adenylyl cyclase, and terbutaline (100 microM), a beta2-adrenergic agonist known to increase cAMP levels, also increased renin mRNA and prorenin release. The secretory response to terbutaline was potentiated by the type IV cyclic AMP-phosphodiesterase (PDE) inhibitor Ro 20-1724 (50 microM). Angiotensin II agonist inhibited the stimulatory effect of terbutaline on renin secretion as did the cytokines tumor necrosis factor-alpha and lipopolysaccharide plus interferon-gamma. Since other studies have shown that U-937 cells possess beta2-adrenergic receptors and express mainly the type IV PDE, the present findings strongly suggest that beta-adrenergic receptors in mononuclear cells are coupled to renin expression via the cAMP transduction pathway. The results support a possible role for the renin-angiotensin system in macrophage function and suggest potential autocrine regulatory mechanisms in prorenin expression.

Postnatal development of inositol 1,4,5-trisphosphate receptors: a disparity with protein kinase C

Ligand-stimulated phosphoinositide hydrolysis activates a bifurcating second messenger system, releasing inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DG), which activates protein kinase C (PKC). Yet, in developing cat visual cortex and hippocampus, high levels of [3H]PDBu binding (labelling PKC) appear much earlier than do [3H]IP3 labelled sites. Binding distributions for the two ligands also appear to be complimentary in both brain regions. Moreover, early surgical removal of input to the visual cortex increases [3H]PDBu binding without affecting that of [3H]IP3. Our results suggest that, (1) at certain developmental stages, IP3 and PKC may act individually or complimentarily rather than synergistically in the visual cortex and hippocampus; (2) in neonatal cortex, IP3 metabolites rather than IP3 itself may act as second messengers; (3) although both IP3 receptors and PKC are localized in intracortical cells, their expression is regulated by different mechanisms during development.

Effects of thyrotropin-releasing hormone on rat motoneurons are mediated by G proteins

Numerous transmitter receptors are linked via GTP-binding proteins (G proteins) to membrane phosphoinositide metabolism by phospholipase C (PLC) and generation of second messengers such as activated protein kinase C (PKC), inositol trisphosphate (IP3) and/or elevations in intracellular calcium. In many cases, these same receptors also inhibit a resting ('leak') potassium current (IK(L)), thereby depolarizing neurons. It is unclear if activation of this PLC pathway mediates inhibition of IK(L) by neurotransmitter receptors. Therefore, we tested the contribution of this pathway to the TRH-induced inhibition of IK(L) in rat hypoglossal motoneurons (HMs) using conventional intracellular recording in brainstem slices. When HMs were recorded with electrodes containing 3 M KCl or 30 mM GTP (in KCl), TRH induced a depolarization that recovered quickly (within 8-10 min) and could be repeated with only modest tachyphylaxis (< 20%). However, with electrodes containing the non-hydrolyzable G protein activator, GTP gamma S (10 mM), the TRH-induced depolarization was long lasting (up to 1 h); with electrodes containing the G protein inhibitor, GDP beta S (20 mM) the tachyphylaxis with repeated TRH application was exaggerated (approximately 60%). Activation of PKC by phorbol dibutyrate (10 microM in perfusate) neither mimicked nor occluded the effects of TRH. There were no effects on membrane potential, input resistance (RN) or the response to TRH in HMs during long recordings with electrodes containing high concentrations of IP3 (60 mM).(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of resting and phorbol ester or concanavalin A activated bovine lymph node cells with leukocyte specific monoclonal antibodies

Bovine lymph node cells (LNC) have been used as a model to study cell activation and proliferation. Because monoclonal antibodies to bovine lymphoid-specific surface antigens have only recently become available, these cells have not been previously characterized in regard to subpopulations. Furthermore, it was not known how expression of lymphoid differentiation antigens and subset proportionalities might change following different modes of activation of LNC. Therefore, the distribution of cell-surface differentiation antigens in unstimulated LNC as well as in LNC incubated with the mitogen concanavalin A (Con A) or the phorbol ester, phorbol dibutyrate (PDBU), was measured using a series of leukocyte-specific monoclonal antibodies and flow cytometry. Unstimulated LNC were found to have similar proportions of T cells, B cells (sIgM positive), and MHC Class II positive cells similar to bovine peripheral blood mononuclear leukocytes (reviewed by Baldwin et al., 1988a). Treatment of the LNC with PDBU or mitogenic doses of Con A induced changes in the expression of surface antigens consistent with the changes observed with human and mouse cells after similar activation. However, these two compounds did not cause identical effects. After treatment with PDBU, the percentage of cells expressing CD4 as well as the density of surface expression decreased. An increase in the percentage of cells expressing and/or density of surface expression of the pan T cell antigens CD2, CD5, CD6, MHC Class II and J5, a T cell activation antigen, also occurred. PDBU treatment also increased the percentage of CD8 positive cells. The change in CD6 following PDBU treatment has not been reported previously. Con A treatment led to a significant increase in the percentage of cells bearing CD8, CD6, MHC Class II and J5, but it had no effect on the percentages of cells positive for the other T cell markers CD5, CD4, or CD2. Because Con A is a complete mitogen and PDBU is not, the changes observed following Con A stimulation probably reflected an expansion of a particular subpopulation. In contrast, PDBU most likely modifies surface antigen expression directly. Neither treatment affected the B cell subpopulation.

Abnormal function of protein kinase C in cells having phosphatidylethanolamine-deficient and phosphatidylcholine-excess membranes

When rat mammary carcinoma 64-24 cells are grown in the absence of ethanolamine, their membrane phospholipid composition changes significantly, becoming phosphatidylethanolamine-deficient and phosphatidylcholine-excess due to a reduced de novo rate of phosphatidylethanolamine synthesis, and growth stops. We have assumed that this membrane phospholipid environment is not suitable for membrane-associated functions. We have previously demonstrated that functions normally stimulated by tumor-promoting phorbol ester, phorbol 12,13-dibutyrate, are not stimulated in ethanolamine-deprived cells, suggesting that function of protein kinase C may be abnormal under the altered membrane environment. In the present study, the behavior of protein kinase C in 64-24 cells grown in the presence and absence of ethanolamine (having normal and phosphatidylethanolamine-deficient/phosphatidylcholine-excess phospholipid) was compared by enzyme assay as well as Western blotting. The results show that the nature of association of protein kinase C to the membrane, which is induced by phorbol ester, is abnormal when cells have the altered membrane phospholipid, and thus argue that membrane phospholipid environment is important in the function of protein kinase C.

Assessment of protein kinase C isozymes by two-site enzyme immunoassay in human brains and changes in Alzheimer's disease

We assessed the amount of protein kinase C (PKC) in samples from postmortem normal human and Alzheimer's disease (AD) brains by a two-site enzyme immunoassay that quantitatively identified types alpha, beta, and gamma isozymes. In the normal human brain matter, type beta was the main type present, the majority of each isozyme of PKC being present in the membranous fraction of the brain tissues. In AD brains, the amount of type beta PKC was significantly reduced in the membranous fraction of the temporal cortical tissues. The amounts of types alpha and gamma in the membranous fraction and types alpha, beta, and gamma in the cytosolic fraction in AD brains were lower than in the control brains, but the difference was not significant. There was also a significant decrease in the levels of PKC in the membranous fraction of AD brains, as measured by radioactive phorbol ester binding. These results suggest that the type beta PKC isozyme is mainly present in the human temporal cortex and that reduced levels of type beta PKC in the membranous fraction may reflect a biochemical deficit related specifically to the pathogenesis of AD.

Activation of protein kinase C increases the extracellular release of the transmembrane amyloid protein precursor of Alzheimer's disease

The beta A4 peptide is the major constituent of the amyloid core of abundant senile plaques found in the cerebral cortex of patients with Alzheimer's disease. This amyloid peptide is synthesized as part of a large transmembrane amyloid protein precursor or APP. In addition to the highly expressed transmembrane APP isoforms, an mRNA encoding a secreted APP lacking the transmembrane domain has been identified. A cleavage of the transmembrane protein also yields an extracellular soluble APP fragment. The effect of phorbol esters on the release of the extracellular APP was studied in transfected Chinese hamster ovary cells which stably express either a transmembrane or a secreted APP isoform. The activation of protein kinase C by phorbol-12,13-dibutyrate increased the extracellular release of the transmembrane APP resulting from its proteolytic cleavage, while 4-beta-phorbol, which does not activate protein kinase C, did not significantly affect the recovery of the soluble APP. On the contrary, the recovery of APP secreted in the culture medium without proteolytic cleavage was not increased by protein kinase C-mediated phosphorylation.

Alteration of protein kinase C activity in the postischemic rat brain areas using in vitro [3H]phorbol 12,13-dibutyrate autoradiography

Chronological changes of protein kinase C (PKC) activity were measured using in vitro [3H]phorbol 12,13-dibutyrate (PDBu) autoradiography to investigate the postischemic alteration of this second messenger system in the rat brain. Transient ischemia was induced by the occlusion of the middle cerebral artery (MCA) for 90 min and such occlusion followed by various recirculation periods of up to 4 weeks. After 90 min of ischemia followed by 3 hours of recirculation, [3H]PDBu binding sites were found to be significantly decreased in the cerebral cortex and lateral segment of the caudate putamen, both supplied by the occluded MCA; thereafter, the binding sites decreased progressively in those ischemic foci. On the contrary, there was no alteration on day 1, but 3 days after ischemic insult, a significant decrease of [3H]PDBu binding sites was first detected in the ipsilateral thalamus and the substantia nigra, which both areas had not been directly affected by the original ischemic insult. This postischemic delayed phenomenon observed in the thalamus and the substantia nigra developed concurrently with 45Ca accumulation, which was detected there in our previous study. These results suggest that alteration of second messenger (PKC) pathways may be involved not only in the ischemic foci, but also in neuronal degeneration of the exo-focal remote areas in relation to the disruption of intracellular calcium homeostasis which plays a key role in the pathogenesis of postischemic neuronal damage and that marked alteration of intracellular signal transduction may precede the neuronal damage in the exo-focal postischemic brain areas.

[3,4-Diaminopyridine-evoked norepinephrine release and B-50 (GAP-43) phosphorylation]

3,4-Diaminopyridine (3,4-DAP 100 mumol.L-1) evoked [3H]norepinephrine ([3H]NE) release in rat hippocampal slices preincubated with [3H]NE and superfused with medium with or without Ca2+. Phorbolester 4 beta-phorbol 12, 13, dibutyrate 1 mumol.L-1) enhanced and polymyxin B (100 mumol.L-1) inhibited the release of [3H]NE under both conditions. The neuron-specific protein B-50 is a major presynaptic substrate of protein kinase C and involved in exocytosis. Using in situ protein phosphorylation analyzed by SDS-PAGE and autoradiography, we observed that B-50 phosphorylation was significantly decreased by 3,4-DAP in the presence of extracellular Ca2+ and completely inhibited by removal of extracellular Ca2+. It was suggested that B-50 phosphorylation was not involved in 3,4-DAP-evoked [3H]NE release.

Changes of phorbol ester binding sites in rat brain following intracerebroventricular administration of thyrotropin-releasing hormone (TRH): an in vitro macroautoradiographic investigation

We examined the influence of the intracerebroventricular (icv) administration of thyrotropin-releasing hormone (TRH) on protein kinase C (PKC) activities in various rat forebrain regions in order to cast light on the mechanism of extra-pituitary non-endocrine physiological actions of TRH in the central nervous system. An in vitro macroautoradiographic method, with [3H]phorbol 12, 13-dibutyrate (PDBu) as the radioactive ligand, was used to investigate quantitative alterations of PKC activities. The optical densities for PDBu binding sites in the striatum and hippocampal formation were significantly increased after the icv administration of TRH, while those in the frontal cortex and septum were unchanged. These findings suggest that TRH may exert some of its non-endocrine functions through striatal and hippocampal neurons which used PKC in their second messenger systems.

Alteration of second messenger systems after transient cerebral ischemia in gerbils: protective effect of pentobarbital and an autoradiographic analysis

The postischemic alteration of second messenger systems in the gerbil brain was analyzed by receptor autoradiography using [3H]phorbol 12,13-dibutyrate (PDBu) and [3H]inositol 1,4,5-trisphosphate (IP3). The alteration of the [3H]PDBu binding in striatum and hippocampus was milder than that of the [3H]IP3 binding 5 h and 7 days after 10-min ischemia. The administration of pentobarbital prevented a decrease in the [3H]IP3 binding sites in all areas 5 h and 7 days after ischemia. These results suggest that the disruption of intracellular calcium homeostasis may play an important factor in ischemic brain damage.

Differential effects of protein kinase C activation on catecholamine secretions evoked by stimulations of various receptors in the rat adrenal medulla

Catecholamine secretions during continuous receptor stimulations by histamine, muscarine and bradykinin in the rat adrenal medulla commonly consisted of two phases, a transient initial secretion followed by a sustained secretion. On activating protein kinase C (PKC) by phorbol dibutyrate (PDBu), both phases of histamine-evoked secretion were inhibited whereas the initial phase alone was inhibited with muscarine. In contrast, bradykinin-evoked secretion as a whole was potentiated. Similar modes of modulations were exhibited when the secretions with these agonists were elicited in muscarine- or bradykinin-pretreated medullae in which PKC had been activated by endogenous processes. It is suggested that PKC may selectively affect the receptors or/and GTP-binding proteins to cause the differential effects on the secretory response in the rat adrenal medulla.

Inhibition of mouse skin protein kinase C by benzoyl peroxide

Benzoyl peroxide (BP), used widely in dermatologic therapy and by the food industry, is considered a tumor promoter in chemically induced skin. Tumor promoters of both the phorbol and non-phorbol type interact with protein kinase C (PKC). This enzyme, therefore, is regarded as the intracellular receptor for a number of tumor promoters. BP bears some structural resemblance to diacylglycerol (DAG) and thus may exert its action through the PKC system. Based on these observations, we have investigated the effect of BP on PKC from mouse skin. Our data show that unlike phorbol esters, which stimulate PKC (in vivo and in vitro), BP inhibits PKC. Concentration-dependent inhibition by BP is observed when PKC is stimulated by phorbol esters, diacylglycerol, phosphatidyl serine (PS), or a combination of the latter two. BP also inhibits PKC stimulated by (-) Indolactam V, a nonphorbol compound resembling the teleocidins. 3H-phorbol ester binding experiments reveal that inhibition by BP may be due to its interference with the phorbol ester binding site and consequently diacylglycerol binding. The binding data and the inability of BP to inhibit either cyclic AMP-dependent protein kinase I or II imply that BP interacts with PKC, and not with the histone substrate. Results presented here clearly indicate that unlike phorbol and certain non-phorbol type of tumor promoters BP does not stimulate PKC in vitro.

An automated filtration assay for protein kinase C ligands

[3H]Phorbol dibutyrate ([3H]PDBu) binding to soluble mouse brain protein kinase C (PKC) was established in a 96-well microtiter plate assay. [3H]PDBu-PKC receptor complexes were rapidly aspirated from wells, filtered, and washed onto glass fiber filter mats using an automated cell harvester. Results were compared to a modification of a previously described assay in which components were incubated in tubes, and manually delivered and washed onto filters with a manifold filtration apparatus. Both 96-well plate and tube assays gave qualitatively and quantitatively similar results since: (i) [3H]PDBu binding to PKC was phosphatidylserine (PS) dependent and calcium stimulatable; (ii) the amounts of [3H]PDBu bound by filters with each technique at receptors excess were similar, 3.2 +/- 0.3 and 3.1 +/- 0.4 pmol respectively; and (iii) the affinities of [3H]PDBu for PKC were comparable; Kd's were 1.95 +/- 0.3 and 2.2 +/- 0.55 nM, respectively. The 96-well plate assay was more accurate and rapid than the tube assay. The microtiter plate assay was adapted for use with [N,N-dimethyl-3H]N,N-dimethylstaurosporine ([3H]DMS). With [3H]PDBu and [3H]DMS as ligands, the 96-well plate method was used for the rapid discrimination of agents which bound selectively at the regulatory and/or catalytic domains of PKC.

Phorbol ester receptors in cerebral cortex of cats with GM1 gangliosidosis

The pathogenesis of neuronal dysfunction in the gangliosidoses is poorly understood. Studies of the feline gangliosidoses and in vitro experiments implicate ganglioside inhibition of protein kinase C (PKC) in the pathogenesis of these neurological diseases. Therefore, in the present study, the binding of [3H]phorbol-12, 13 dibutyrate was measured to determine the levels of PKC in cerebral cortex of cats with GM1 gangliosidosis (mutant) and age matched normal siblings. This binding of ([3H]PDB) to cerebral cortex homogenates in both normal and mutant cats was highly specific. The specificity of receptors was ascertained also from displacement studies using nonradioactive phorbol ester analogues to displace [3H]PDB bound to its receptors. In both mutant and normal cat brain, phorbol 12,13-dibutyrate (PDB), 4-beta-phorbol 12,13-didecanoate (beta-PDD) and 4-beta-phorbol 12,13-dibenzoate (beta-PDBz) were highly potent (approximately to same degree) and effective in displacing [3H]PDB. On the other hand, 4-beta phorbol 12,13-diacetate (beta-PDA) was a weak displacer and 4-alpha-phorbol did not displace the bound [3H]PDB in either normal or mutant brain. Scatchard analysis of the binding data indicated a homogenous single class of binding sites in normal and mutant brain (Normal: Kd = 1.42 x 10(-7) M, Bmax = 8.40 pmoles/mg protein. Mutant: Kd = 1.60 x 10(-7) M, Bmax = 10.00 pmoles/mg protein). Sphingosine inhibited the binding to approximately the same extent in normal and mutant cortex. These studies demonstrate the presence of highly specific, homogenous, single type phorbol ester receptors in cerebral cortex of cats with GM1 gangliosidosis which are qualitatively and quantitatively similar to normal cat brain.

Involvement of lipid peroxidation and inhibitory mechanisms on ischemic neuronal damage in gerbil hippocampus: quantitative autoradiographic studies on second messenger and neurotransmitter systems

We investigated, to examine the involvement of lipid peroxidation and inhibitory mechanisms, a novel lipid peroxidation inhibitor (KB-5666) and a GABAA receptor-effector (pentobarbital) on ischemic neuronal damage and the alterations in the second messenger and neurotransmitter systems in Mongolian gerbils by means of morphology and in vitro receptor autoradiography. Quantitative receptor autoradiography visualized binding sites for [3H]inositol 1,4,5-trisphosphate, [3H]forskolin, [3H]phorbol 12,13-dibutyrate, [3H]isradipine (PN200-110), [3H]N6-cyclohexyl-adenosine, and [3H]quinuclidinyl benzilate indicating binding sites for inositol 1,4,5-trisphosphate, forskolin, protein kinase C, L-type calcium channels (or dihydropyridine binding sites), adenosine A1, and muscarinic cholinergic receptors, respectively. In the morphological study, KB-5666, 10 and 50 mg/kg, i.v., 5 min before ischemia, protected against ischemic neuronal damage to the hippocampal CA1 subfield following 5 min of bilateral carotid artery occlusion in a dose-dependent manner. Pentobarbital, 30 mg/kg, i.v., 5 min before ischemia, also had a protective effect. In receptor autoradiographic studies, all receptor bindings decreased significantly in the CA1 subfield seven days after ischemia. In particular, [3H]inositol 1,4,5-trisphosphate binding in the CA1 subfield was completely lost after ischemia. [3H]Inositol 1,4,5-trisphosphate and [3H]forskolin binding decreased as early as 6 h after ischemia. In the CA3 subfield, [3H]inositol 1,4,5-trisphosphate, [3H]PN200-110, and [3H]N6-cyclohexyladenosine bindings decreased seven days after ischemia. In the dentate gyrus, [3H]inositol 1,4,5-trisphosphate binding decreased seven days after ischemia. KB-5666 and pentobarbital prevented reductions in these receptor bindings in the CA1 subfield at 6 h and seven days after ischemia. These results indicate that KB-5666 and pentobarbital protect the brain from both structural and functional damage after ischemia, and that lipid peroxidation and inhibitory mechanisms may play a pivotal role in the neuronal damage of the hippocampal CA1 subfield after ischemia.

Cross-talk between B cell surface immunoglobulin and interleukin 4 receptors: the role of protein kinase C and Ca2(+)-mediated signals

A well-known property of IL4 is its capacity to synergize with low concentrations of anti-immunoglobulin (Ig) antibodies to induce B cells to synthesize DNA. Cross-linking of surface Ig receptors stimulates phosphoinositide hydrolysis, with consequent production of two signals: the elevation of intracellular Ca2+ levels and activation of protein kinase C (PKC). Little is known about the second messengers utilized by interleukin (IL)4 receptors. In this study we have investigated the relative contributions of the two signals emanating from the ligation of surface Ig receptors to the synergistic activation of B cells by IL4. We show that IL4 plus carefully titrated concentrations of PKC-activating phorbol esters [such as phorbol 12,13-dibutyrate (PBu2)] induce cell cycle entry of virtually all murine B cells and substantial levels of DNA synthesis. Ca2+ ionophores, in contrast do not act as co-mitogens with IL4. However, a critical concentration of ionomycin further enhanced DNA synthesis induced by PBu2 plus IL4. Taken together, these results suggest that PKC activation alone is sufficient to synergize with IL4 in inducing B cells to enter cell cycle. However, the co-mitogenic effects of anti-Ig and IL4 are evidently also dependent on Ca2+ signals. This interpretation is supported by the findings that cyclosporin, which abrogates the activation of lymphocytes by Ca2(+)-dependent stimuli, inhibits B cell proliferation induced by anti-Ig plus IL4, but not the response to PBu2 plus IL4.

Protein kinase C-independent activation of nuclear factor kappa B by tumor necrosis factor

Tumor necrosis factor (TNF) is one of the few physiological inducers of the pleiotropic transcription factor NF kappa B. NF kappa B may play a central role in mediating TNF's gene regulatory action; however, the molecular mechanisms of TNF-induced NF kappa B activation are poorly understood. In this study, we demonstrate with two human leukemic cell lines, K562 and Jurkat, that TNF induces rapid and transient activation and translocation of protein kinase C (PK-C) from the cytosol to the membranes, which is followed by the emergence of kappa B-binding activity. In order to investigate whether TNF-mediated PK-C activation can be linked to induction of NF kappa B, we tried to block TNF action by use of various protein kinase C inhibitors as well as down-regulation of PK-C. Preincubation of Jurkat cells with protein kinase inhibitor H7 or staurosporine blocked PK-C activation by either TNF or phorbol 12-myristate 12-acetate (PMA). This pretreatment regimen completely inhibited NF kappa B activation by PMA. In contrast, TNF's ability to induce NF kappa B remained unaffected. In addition, NF kappa B was TNF-inducible in Jurkat cells depleted for PK-C by long-term exposure to high dose phorbol ester. The data indicate that PK-C is not required for NF kappa B activation by TNF and imply a novel, PK-C-independent mechanism of physiological NF kappa B activation.