K-252b, c and d, potent inhibitors of protein kinase C from microbial origin

A self-restricted CD38-connexin 43 cross-talk affects NAD+ and cyclic ADP-ribose metabolism and regulates intracellular calcium in 3T3 fibroblasts

Connexin 43 (Cx43) hexameric hemichannels, recently demonstrated to mediate NAD(+) transport, functionally interact in the plasma membrane of several cells with the ectoenzyme CD38 that converts NAD(+) to the universal calcium mobilizer cyclic ADP-ribose (cADPR). Here we demonstrate that functional uncoupling between CD38 and Cx43 in CD38-transfected 3T3 murine fibroblasts is paralleled by decreased [Ca(2+)](i) levels as a result of reduced intracellular conversion of NAD(+) to cADPR. A sharp inverse correlation emerged between [Ca(2+)](i) levels and NAD(+) transport (measured as influx into cells and as efflux therefrom), both in the CD38(+) cells (high [Ca(2+)](i), low transport) and in the CD38(-) fibroblasts (low [Ca(2+)](i), high transport). These differences were correlated with distinctive extents of Cx43 phosphorylation in the two cell populations, a lower phosphorylation with high NAD(+) transport (CD38(-) cells) and vice versa (CD38(+) cells). Conversion of NAD(+)-permeable Cx43 to the phosphorylated, NAD(+)-impermeable form occurs via Ca(2+)-stimulated protein kinase C (PKC). Thus, a self-regulatory loop emerged in CD38(+) fibroblasts whereby high [Ca(2+)](i) restricts further Ca(2+) mobilization by cADPR via PKC-mediated disruption of the Cx43-CD38 cross-talk. This mechanism may avoid: (i) leakage of NAD(+) from cells; (ii) depletion of intracellular NAD(+) by CD38; (iii) overproduction of intracellular cADPR resulting in potentially cytotoxic [Ca(2+)](i).

Efficient syntheses of novel C2'-alkylated (+/-)-K252a analogues

Recent efforts in our laboratories have resulted in a synthetic approach toward C2'-alkylated K252a analogues via extension of a K252a cyclofuranosylation strategy. The bis-indole-N-glycosidic coupling of 6-N-(3,4-dimethoxybenzyl)-staurosporinone (21) with a number of highly functionalized carbohydrates has given access to previously unattainable, biologically relevant analogues.

Chemical inhibitors of cyclin-dependent kinases: insights into design from X-ray crystallographic studies

Cyclin-dependent kinases (CDKs) are a family of protein kinases that regulate progression through the eukaryotic cell cycle. Aberrant CDK activity or function is a common defect in human tumours, resulting in unrestrained cellular proliferation. X-ray crystallographic analysis of monomeric CDK2 and CDK2 complexes has revealed how phosphorylation and cyclin binding mediate enzyme activation and how this activity can be regulated by further protein association. Current research aims to improve the selectivity and/or potency of small molecule CDK inhibitors, both to develop specific probes to study the roles of the different CDK family members in coordinating cell cycle progression, and as lead molecules for the design of therapeutically useful drugs. This design process has been assisted by the availability of a number of CDK2/inhibitor structures determined using X-ray crystallography. These structures have shown that molecules related to ATP can be accommodated in the ATP-binding site in a number of orientations, utilising interactions observed between CDK2 and its natural ligand, as well as novel interactions with CDK2 residues that lie both within and outside the active site cleft. This site can also bind inhibitors that are structurally unrelated to ATP. These results suggest that it may be possible to design pharmacologically and pharmaceutically important ATP-binding site-directed ligands that act as specific and potent inhibitors of CDK activity.

Unique pharmacological interactions of taurine and chelerythrine in the retina

The effects of taurine and chelerythrine (CHT) on ATP-dependent calcium uptake and the phosphorylation of the approximately 20 kDa phosphoprotein in the retina were compared. In the absence of the CHT, taurine stimulated ATP-dependent calcium uptake and attenuated the phosphorylation of the approximately 20 kDa phosphoprotein. On the other hand, CHT produced the opposite results in the absence of taurine. When the two agents were used simultaneously, it was found that CHT non-competitively inhibited the action of taurine to stimulate calcium uptake, while taurine non-competitively inhibited the action of CHT to stimulate the phosphorylation of the approximately 20 kDa phosphoprotein. The data present an unusual pharmacological mechanism for controlling the signal transduction pathway involving the two distinct cellular processes being studied. Given the unique data, a control system is proposed in which the function of the approximately 20 kDa phosphoprotein is linked to the stimulation of ATP-dependent calcium uptake.

Effect of taurine on chelerythrine inhibition of calcium uptake and ATPase activity in the rat retina

Taurine potentiates calcium uptake in whole retinal homogenates as well as in rod outer segments and mitochondrial fractions. The aim of this study was to correlate taurine potentiation of calcium uptake with its effects on other cellular processes through the use of chelerythrine (CHT), a modulator of protein kinase C (PKC), ATPase activity, and, as recently shown, of retinal protein phosphorylation. CHT inhibited calcium uptake only when ATP was present, and inhibition increased significantly in conditions of ATP excess. Taurine potentiated ATP-dependent calcium uptake but decreased the potency of ATP to induce uptake activity. CHT inhibition of calcium uptake exhibited similar potencies in the presence and absence of taurine, and this inhibition seemed to be independent of PKC inhibition. Because of the ATP-dependence of the observed effect, total ATPase activity was studied using similar treatments. In the absence of taurine, CHT inhibited ATPase activity with the same potency (IC50 approximately 59.3 microM) as with calcium uptake inhibition (IC50 approximately 87.9 microM), presenting a possible mechanism of action of CHT. In the presence of taurine, no such correlation was observed, suggesting an ATPase-independent mechanism of action. In fact, taurine did not potentiate ATPase activity, but rather it decreased the potency of CHT inhibition of ATPase, effects incongruent with the effects of taurine on calcium uptake and on CHT inhibition of calcium uptake. Enzyme kinetic experiments provided more supporting data. Taurine was found to cause an increase in the affinity of the ATP substrate for the ATPase enzyme, contradicting the aforementioned effect of taurine to decrease the potency of ATP to induce calcium uptake. Thus, taurine seems to increase calcium uptake through a hitherto unreported mechanism distinct from its modulation of ATPase activity.

Practical Preparation of K-252a from a Fermentation Solution

We developed a practical preparation procedure for K-252a by methylating K-252b on an industrial scale. The water-insoluble K-252a, which was present in the cell mass, was converted to the water-soluble K-252b Na salt in an alkaline solution. The obtained K-252b was methylated with dimethylsulfate in the presence of potassium carbonate in dimethylacetamide. We have already used this method to manufacture 90 kg of K-252b from the fermentation broth, and regenerated 65 kg of K-252a from K-252b.

CEP-751 inhibits TRK receptor tyrosine kinase activity in vitro exhibits anti-tumor activity

The present report describes the in vitro and in vivo profile of CEP-751, a novel receptor tyrosine kinase inhibitor. CEP-751 at 100 nM inhibits the receptor tyrosine kinase activity of the neurotrophin receptors trkA, trkB and trkC. CEP-751 has no effect on activity of receptors for EGF, IGF-I, insulin or on erbB2; inhibition of receptors for PDGF and bFGF was observed but occurred with lesser potency than inhibition of trk. CEP-751 exhibited anti-tumor efficacy against tumors derived from NIH3T3 cells transfected with trkA. Inhibition of trk phosphorylation could also be measured in these tumors, suggesting that anti-tumor efficacy of CEP-751 is related to inhibition of trk receptor tyrosine kinase activity. CEP-751 was found to be without effect when administered to nude mice bearing SK-OV-3 tumors, which overexpress erbB2 receptors, providing further evidence that inhibition of tumor growth may be related to inhibition of trk receptor tyrosine kinase activity. Our data indicate that CEP-751 is a potent trk inhibitor which possesses anti-tumor activity.

Characterization of sodium-calcium exchange in rabbit renal arterioles

Experiments were performed to test the hypothesis that renal arterioles exhibit Na-Ca exchange capability and that this process is regulated by protein kinase C (PKC). Glomeruli with attached arterioles were dissected from rabbit kidney and loaded with fura-2 for measurement of intracellular calcium concentration ([Ca2+]i) using microscope-based photometry. In tissue bathed in Ringer's solution containing 150 mM Na+ and 1.5 mM Ca2+, afferent and efferent arteriolar [Ca2+]i averaged 136 +/- 6 and 154 +/- 7 nM, respectively. Removal of extracellular Na+ increased afferent arteriolar [Ca2+]i by 70 +/- 7 mM, while efferent arteriolar [Ca2+]i only increased by 39 +/- 5 nM (P < 0.01 vs. afferent arteriole). These responses were inhibited by 6 nM Ni2+ and required extracellular Ca2+, but were unaffected by 10 microM diltiazem. After incubation in 500 microM ouabain, 5 microM monensin, and 5 microM nigericin, [Ca2+]i responses to removal of extracellular Na+ were exaggerated significantly, averaging 174 +/- 50 nM in afferent arterioles and 222 +/- 82 nM in efferent arterioles (NS vs. afferent arterioles). Moreover, responses to removal of extracellular Na+ were enhanced by 100 nM phorbol 12-myristate 13-acetate, an affect which was blocked by PKC inhibition (25 nM K252b). These data indicate that both afferent and efferent arterioles express the Na-Ca exchanger, and that PKC activity impacts on exchange capacity in these vessels.

Nicotine prolongs neutrophil survival by suppressing apoptosis

Neutrophil accumulation in the lung is implicated in the pathogenesis of pulmonary emphysema and chronic bronchitis associated with cigarette smoking. To determine whether nicotine contributes to this accumulation through the prolongation of neutrophil survival, we examined the survival rates of isolated neutrophils cultured with or without nicotine. We found that nicotine prolonged neutrophil survival in a dose-dependent fashion, with a maximum effect at 10(-6) mol/L. The survival rate at 72 hours was 35.6% +/- 1.2% in medium with 10(-6) mol/L nicotine, compared with 15.5% +/- 0.5% in control medium (mean +/- SEM; p < 0.01), as determined by trypan blue dye exclusion. This prolongation was brought about by suppression of apoptosis, as evidenced by both transmission electron and fluorescence microscopy, and was associated with the preservation of neutrophil functions such as chemotaxis and O2- generation. The prolongation of survival caused by nicotine was abrogated by the addition of Pro-Lys-Arg-NH2, a competitive inhibitor of the specific binding of nicotine to noncholinergic receptors on neutrophils. However, the prolongation of survival caused by nicotine was not suppressed in the presence of K-252b, an inhibitor of protein kinase C. These findings suggest that nicotine prolongs neutrophil survival through noncholinergic nicotine receptors and new protein synthesis, without activation of protein kinase C.

Neurotrophin-induced modulation of synaptic transmission in the adult hippocampus

The NGF-family of neurotrophic factors including NGF, BDNF and NT-3,4/5 is known to be crucial for neuronal survival and differentiation during development. However, recent studies suggest that the neurotrophins are also widely expressed and play a dynamic role in the mature nervous system. One of the major sites of expression of the neurotrophins in the adult brain is the hippocampus which has been also popular as an important structure for the adult plasticity. Moreover, the level of expression of the neurotrophins in the hippocampus can be regulated by a variety of neuronal inputs, such as experimentally-induced seizures, injection of glutamate receptor agonists, and LTP-inducing stimulation. The possibility that the neurotrophins modulate synaptic transmission in the mature brain has been investigated at the Schaffer collateral-CA1 synapses in the adult rat hippocampus. We report that transient application of BDNF and NT-3, but not NGF induces a long-lasting increase of synaptic transmission, which is likely to be mediated by Trk family of receptor tyrosine kinases. Both BDNF and NT-3 decrease paired pulse facilitation, suggesting a possible presynaptic modification. Interestingly, previous potentiation of synaptic activity by the application of neurotrophic factors does not occlude the induction of long-term potentiation. These results suggest that the neurotrophins may locally regulate synaptic plasticity in the adult nervous system.

Staurosporine aglycone (K252-c) and arcyriaflavin A from the marine ascidian, Eudistoma sp

Staurosporine aglycone (K252-c) (compound 1) and arcyriaflavin A (2) were isolated from a specimen of the marine ascidian, Eudistoma sp., collected off the coast of West Africa. In addition to expressing micromolar and submicromolar inhibition of enzyme activity against seven protein kinase C isoenzymes and inhibition of proliferation of the human lung cancer A549 and P388 murine leukemia cell lines, 1 also inhibited cell adhesion of the EL-4.IL-2 cell line and expressed activity in the K562 bleb and neutrophil assays.

Staurosporine and K-252 compounds protect hippocampal neurons against amyloid beta-peptide toxicity and oxidative injury

Recent studies have shown that amyloid beta-peptide (A beta) can be directly neurotoxic by a mechanism related to secondary structure of the peptide, and mediated by free radical production and an increase in the concentration of intracellular free calcium ([Ca2+]i). We now report that staurosporine and K-252 compounds, low molecular weight alkaloids of bacterial origin, can protect cultured rat hippocampal neurons against the toxicity of A beta in a concentration-dependent manner. The alkaloids also protected neurons against iron-induced (free radical-mediated) injury. Measurements of [Ca2+]i using fura-2 imaging revealed that the elevation of [Ca2+]i that occurred in response to long-term exposure to A beta was attenuated in neurons treated with staurosporine and K-252 compounds. These findings indicate that staurosporine and K-252 compounds can interupt a neurodegenerative pathway relevant to the pathophysiology of Alzheimer's disease.

Staurosporine, K-252a, and K-252b stabilize calcium homeostasis and promote survival of CNS neurons in the absence of glucose

Staurosporine, K-252a, and the 9-carboxylic related compound K-252b are low-molecular-weight alkaloids from microbial origin that at high concentrations are kinase inhibitors and can antagonize the effects of neuronal growth factors. Paradoxically, we have found that very low concentrations of these agents (10 fM-10 nM) prolong the survival of hippocampal, septal, and cortical neurons deprived of glucose. These agents did not prevent the depletion of ATP caused by glucose deprivation. The large elevation of intracellular calcium levels that normally mediates glucose deprivation-induced damage was attenuated by staurosporine, K-252a, and K-252b. Western blot analysis using antiphosphotyrosine antibody showed that staurosporine and the K-252 compounds (10-100 pM) stimulated tyrosine phosphorylation of several different proteins. The tyrosine kinase inhibitor genistein significantly reduced the protective effect of staurosporine and the K-252 compounds, indicating that tyrosine phosphorylation was required for neuroprotection by these compounds. Taken together, the data demonstrate that low concentrations of staurosporine and the K-252 compounds can stabilize calcium homeostasis, possibly by a mechanism involving activation of receptor tyrosine kinase transduction pathways.

Endogenous neuroprotection factors and traumatic brain injury: mechanisms of action and implications for therapy

Throughout evolution the brain has acquired elegant strategies to protect itself against a variety of environmental insults. Prominent among these are signals released from injured cells that are capable of initiating a cascade of events in neurons and glia designed to prevent further damage. Recent research has identified a remarkably large number of neuroprotection factors (NPFs), whose expression is increased in response to brain injury. Examples include the neurotrophins (NGF, NT-3, NT-5, and BDNF), bFGF, IGFs, TGFs, TNFs and secreted forms of the beta-amyloid precursor protein. Animal and cell culture studies have shown that NPFs can attenuate neuronal injury initiated by insults believed to be relevant to the pathophysiology of traumatic brain injury (TBI) including excitotoxins, ischemia, and free radicals. Studies of the mechanism of action of these NPFs indicate that they enhance cellular systems involved in maintenance of Ca2+ homeostasis and free radical metabolism. Recent work has identified several low-molecular-weight lipophilic compounds that appear to mimic the action of NPFs by activating signal transduction cascades involving tyrosine phosphorylation. Such compounds, alone or in combination with antioxidants and calcium-stabilizing agents, have proved beneficial in animal studies of ischemic brain injury and provide opportunities for development of preventative/therapeutic approaches for TBI.

Indolocarbazole protein kinase C inhibitors from rebeccamycin

Structural modifications were carried out on rebeccamycin, an antitumour antibiotic, to obtain analogues. The inhibitory potencies of these analogues against protein kinase C are compared. The method described represents an alternative route to the staurosporine aglycone, a potent protein kinase C inhibitor.

Studies on protein kinase C inhibitors; structure-activity relationships in indolocarbazole and bis-indole series

To assess the role of the cyclic amide moiety in indolocarbazole and bis-indole protein kinase C inhibitors, five amides in these series were synthesized in which the amide group is acyclic. These new compounds have no inhibitory effect on protein kinase C, indicating that the rigid cyclic structure of the amide group is compulsory for biological activity.

Protein kinase C inhibitors; structure-activity relationships in K252c-related compounds

K252c-related compounds were synthesized with different framework flexibilities and different functions (imide, amide and amide-alcohol) on the non-indolic heterocycle. The inhibitory activities towards protein kinase C and protein kinase A are compared.

Peptidomimetics derived from natural products

Although much has been written in recent years about rational drug design, no drug has been designed de novo, that is, without using a natural substrate or inhibitor or screening lead as a starting point. Instead, as we have seen, medicinal chemists continue to depend upon serendipitous discovery of novel biological activities and novel chemical entities for structures on which to begin work. What rational drug design really means at present is rational drug discovery and rational optimization. These result from the application of modern structural and mechanistic biochemistry, and good synthetic chemistry, to obtain structures with the desired spectrum of biological activities. Traditionally, lead compounds were discovered in plant and animal extracts, and more recently in microorganisms and chemical libraries. These traditional approaches continue, but are augmented by advances in molecular biology, which now provide pure proteins in quantity for screening and structure determination, as well as for characterization by modern biophysical methods. Remarkably, x-ray and NMR methods can now provide the most important information needed to design new drugs, that is, the conformations of ligands bound to target proteins. Approaches to identifying possible ligands based only on the knowledge of the enzyme active site are being developed. Some of these, such as CAVEAT, have been recently reviewed. In spite of these impressive gains, de novo design of new drugs will not be achieved until we learn how to logically build specific inhibitors of a target enzyme knowing only the protein sequence of the enzyme or the amino acid sequence of the messenger substances. We have a long way to go, because by this very rigorous definition, even the successful design of a new nonpeptide drug beginning with enzyme-ligand NMR or x-ray structure constitutes rational optimization. However, as this article has illustrated, we have made great progress. Some of the current and futuristic approaches to drug design are shown in Fig. 8. Development of useful enzyme inhibitors, designed by knowing the enzyme catalytic mechanism or discovered by screening for natural inhibitors, is a very successful rational method. Discovery of receptor antagonists by screening protocols is also productive.(ABSTRACT TRUNCATED AT 400 WORDS)

K-252 compounds: modulators of neurotrophin signal transduction

K-252 compounds, which share a common polyaromatic aglycon structure, are rather general and potent inhibitors of various protein kinases, including protein kinase C and tyrosine-specific protein kinases, and possibly act by interfering at or near the ATP binding site. However, chemical modifications in their sugar moiety can result in high specificity of the inhibitory action and, furthermore, can induce other stimulatory and inhibitory effects on nerve cells. These compounds are of particular interest because, in intact cells, they inhibit the actions of NGF and other neurotrophins without diminishing comparable actions of other growth factors. This effect seems to reflect a direct inhibitory action on trk neurotrophin receptor proteins. At concentrations lower than those necessary to inhibit neurotrophin actions, K-252a and K-252b have been shown to potentiate the stimulatory effects of NT-3 on different neurons in culture and on PC12 cells. The structural requirements for this effect seem to be different from those for the inhibition of neurotrophin actions. These findings raise the possibility of development of compounds of high selectivity, able to inhibit or potentiate the transduction mechanisms of individual neurotrophins, and identify K-252a and K-252b as lead compounds for the development of such selective molecules. Specific inhibitors and stimulators of neurotrophins would be valuable tools to investigate biological functions of the neurotrophins in vitro and in vivo. Furthermore, it is possible that, in the future, highly selective drugs with agonistic or antagonistic actions on neurotrophin mechanisms could become therapeutically useful in the treatment of neurological disease and injury.

A novel glycosignaling system: GQ1b-dependent neuritogenesis of human neuroblastoma cell line, GOTO, is closely associated with GQ1b-dependent ecto-type protein phosphorylation

Previously, we reported that ganglioside GQ1b specifically promoted neuritogenesis of human neuroblastoma cells (GOTO), and also that is specifically stimulated the phosphorylation of several cell surface proteins on the same cells. To disclose the relationship between the two events, we examined them using a novel protein kinase inhibitor, K-252b, which is a derivative of K-252a and cannot pass through cell membrane. K-252b inhibited the GQ1b-dependent neuritogenesis as well as the GQ1b-stimulated phosphorylation. This suggests the direct coupling between the two cell events and the occurrence of a new biosignal transduction system.

Neuroprotective effect of protein kinase C inhibitors on oxygen/glucose free-induced decreases in 2-deoxyglucose uptake and CA1 field potentials in rat hippocampal slices

Staurosporine, a protein kinase C inhibitor, was found to produce a neuroprotective effect against an ischemic insult in both gerbils and rats in vivo. We have demonstrated that rat hippocampal slices exposed to oxygen/glucose-free medium showed decreases in 2-deoxyglucose (2-DG) uptake and CA1 field potentials elicited by the stimulation of Schaffer collaterals. Therefore we examined the effect of protein kinase C inhibitors on oxygen/glucose free-induced impairments of 2-DG uptake and CA1 field potentials. Pretreatment with staurosporine, K252a and H-7 attenuated decreases in 2-DG uptake and CA1 field potentials. Treatment with phorbol ester, a protein kinase C activator, for a long period (90 min) was found to induce a down-regulation of protein kinase C activity. Therefore we examined the effect of pretreatment with phorbol ester for 90 min on oxygen/glucose free-induced decreases in 2-DG uptake and CA1 field potentials. These decrements were not attenuated by 5-min treatment with phorbol ester but were attenuated by 90-min treatment. The present results suggest that the treatment which decreases protein kinase C activity shows a neuroprotective action against oxygen/glucose free-induced deficits of metabolic and synaptic activity in hippocampal slices.

Block of synapse formation between cerebral cortical neurons by a protein kinase inhibitor

Synchronized Ca2+ transients in cultured hippocampal neurons reflect the pattern of underlying electrical activity. Here we demonstrate a similar synchronization of cerebral cortical neurons in culture, and show that this functional coupling is correlated to the appearance of morphologically identified synapses using electron microscopy. During screening of a series of drugs for inhibition of in vitro synaptogenesis, the continuous presence of a protein kinase inhibitor (K-252b) in the culture medium was found to block the synchronous firing and to decrease significantly the number of morphologically identifiable synapses. Since K-252b does not permeate the cell membrane, the results strongly suggest that phosphorylation of cell surface protein(s) by a K-252b sensitive-protein kinase is an essential process in synapse formation.

Potent and preferential inhibition of Ca2+/calmodulin-dependent protein kinase II by K252a and its derivative, KT5926

Effects of protein kinase inhibitors, K252a and its derivative KT5926, on Ca2+/calmodulin-dependent protein kinase II were examined. Both compounds potently inhibited Ca2+/calmodulin-dependent protein kinase II. Kinetic analyses indicated that the inhibitory effect of K252a and KT5926 was competitive with respect to ATP (Ki: 1.8 and 4.4 nM, respectively) and noncompetitive with respect to the substrates. Taken together with a previous report (Nakanishi et al. Mol. Pharmacol. 37, 482, 1990) concerning the Ki values of these compounds for ATP with various protein kinases, the results suggest that K252a and KT5926 are potent and preferential inhibitors of Ca2+/calmodulin-dependent protein kinase II.

Inhibition of nerve growth factor-induced neurite outgrowth of PC12 cells by a protein kinase inhibitor which does not permeate the cell membrane

K-252a, a protein kinase inhibitor of microbial origin, has proven to be a specific inhibitor of nerve growth factor. In this study, the effects of K-252b, the 9-carboxylic acid derivative of K-252a, on nerve growth factor-induced neurite outgrowth in PC12 cells was examined. K-252b is hydrophilic and does not permeate the cell membrane of PC12 cells, whereas K-252a clearly does. K-252b is, however, as potent as K-252a itself in inhibiting the nerve growth factor-induced neurite outgrowth. These results can be interpreted to suggest that effects of K-252b may be through surface-bound/anchored K-252b-sensitive molecules on PC12 cells.

K-252b is a selective and nontoxic inhibitor of nerve growth factor action on cultured brain neurons

K-252b is a kinase inhibitor structurally related to K-252a, which is known to abolish selectively the effects of nerve growth factor (NGF) on PC12 cells and PNS neurons. We tested whether K-252b, K-252a, and staurosporine, another related compound, are effective and selective inhibitors of NGF actions on CNS neurons. All three compounds, at appropriate concentrations, completely and selectively prevented the NGF-mediated activity increase of the cholinergic marker enzyme choline acetyltransferase in cultures of rat basal forebrain cells. The stimulatory effects of basic fibroblast growth factor and insulin on choline acetyltransferase in these cultures and on dopamine uptake in cultures of dissociated ventral mesencephalon were not affected. No signs of toxicity were observed in cultures treated with K-252b. In contrast, K-252a and staurosporine, at concentrations required to block the NGF actions on cholinergic cells, were cytotoxic and produced cell loss. In addition, K-252a, at higher concentrations and in the absence of growth factors, increased cell numbers. Our study suggests that K-252b is a selective and nontoxic inhibitor of NGF actions in the brain and may become a useful tool to study these actions in vivo.

Identification of indolepyruvic acid as an intermediate of rebeccamycin biosynthesis

Experimental evidence is presented to demonstrate that indolepyruvic acid is an intermediate in the rebeccamycin biosynthetic pathway. [3-14C]Indolepyruvic acid was prepared and efficiently incorporated (8%) into rebeccamycin by Saccharothrix aerocolonigenes.

Interleukin-6 and 12-O-tetradecanoyl phorbol-13-acetate act synergistically in inducing cell-cell separation and migration of human breast carcinoma cells

Interleukin-6 (IL-6) causes an epithelial to fibroblastoid conversion and an increase in the motility of human ductal breast carcinoma cell lines ZR-75-1 and T-47D. Although IL-6 decreases DNA synthetic activity in these cell lines, the IL-6-induced alterations in cell shape and motility occur independently of inhibition of DNA synthesis per se. Whereas tumor necrosis factor alpha (TNF-alpha) inhibits DNA synthesis in T-47D cells, it does not cause an epithelial-fibroblastoid conversion or other major morphological changes and does not increase cell motility; TNF-alpha rapidly lyses a majority of ZR-75-1 cells. Furthermore, the DNA synthesis inhibitors 5-fluoro-2'-deoxyuridine (FUDR) and methotrexate (MTX) also do not cause effects mimicking the action of IL-6 on cell structure and motility. Transforming growth factors alpha and beta 1, acidic and basic fibroblast growth factors, epidermal growth factor, and insulin-like growth factor-1 (TGF-alpha, TGF-beta 1, aFGF, bFGF, EGF, and IGF-1) have little or no effect on breast cancer cell morphology, which serves to exclude the possibility that the IL-6-induced changes are a consequence of induction of these growth factors by IL-6. 12-O-tetradecanoyl phorbol-13-acetate (TPA) but not 8-bromoadenosine 3',5'-cyclic monophosphate (Br-cAMP) induces changes in the morphology and associative behavior of ZR-75-1 cells that are similar but not identical to those caused by IL-6. The TPA-induced alterations are not blocked by anti-IL-6 neutralizing antibodies; staurosporine inhibits the TPA-induced cell alterations but not those induced by IL-6. IL-6 and TPA used together have a phenotypic effect that greatly exceeds that of either agent alone and results in extensive cell scattering in less than 1 day. These findings are consistent with the hypothesis that IL-6 and TPA induce similar morphological changes and cell scattering via independent pathways.

Differential inhibition of histamine release from mast cells by protein kinase C inhibitors: staurosporine and K-252a

Pretreatment of rat peritoneal mast cells with either staurosporine or an analog K-252a [(8R*,9S*,11S*)-(-)-9-hydroxyl-9-methoxycarbonyl-8-methyl-2,3, 9,10-tetrahydro-8,11-epoxy-1H,8H,11H-2,7b,11-atrizadibenzo- [a,g]cycloocta[cde]trinden-1-one] led to a concentration-related inhibition of histamine release when the cells were stimulated with anti-IgE (IC50: staurosporine = 110 nM; K-252a = 100 nM). In contrast, the two protein kinase C (PKC) inhibitors (1-1000 nM) partially (less than 15%) inhibited histamine release induced by compound 48/80 (0.5 to 1 micrograms/mL). Furthermore, prostaglandin E2 (PGE2) synthesis mediated by anti-IgE from rat peritoneal mast cells was also inhibited by staurosporine and K-252a (IC50 = 100 nM). Exposure of anti-arsenate IgE (anti-Ars-IgE) sensitized mouse bone marrow derived mast cells to arsenate-bovine serum albumin (Ars-BSA) led to the release of both histamine (510 +/- 12.6 ng/10(6) cells) and immunoreactive leukotriene C4 (LTC4) (27.0 +/- 2.6 ng/10(6) cells). Both histamine and LTC4 release was inhibited by staurosporine and K-252a with an IC50 of 50 nM for both compounds. We also characterized a 45K molecular weight protein which is phosphorylated by PKC after Ars-BSA or phorbol, 12-myristate, 13-acetate (PMA) stimulation. This protein is phosphorylated in a broken cell preparation in which PKC is activated by phosphatidylserine/Diolein and Ca2+. Peptide mapping by V8 protease of the phosphorylated 45K protein revealed that the 45K protein phosphorylation patterns induced by IgE or PMA or in the broken cell preparation are identical. Pretreatment of 32P-labeled mouse bone marrow derived mast cells with either staurosporine or K-252a led to a concentration-related inhibition of 45K protein phosphorylation induced by PMA or Ars-BSA. This inhibition of protein phosphorylation correlated well with the inhibition of histamine and leukotriene release in bone marrow derived mast cells.