A specific inhibitor of protein kinase C induces differentiation of neuroblastoma cells

Evidence for the interaction of protein kinase C and melanocortin 3-receptor signaling pathways

The melanocortin-3 receptor, MC3-R, is abundant in the brain and is activated by gamma-2-melanocyte stimulating hormone (gamma-2-MSH). We have previously reported the translocation of protein kinase C (PKC) in spontaneous hypertensive rat (SHR) brain synaptosomes treated with gamma-2-MSH. In this study, the expression of PKA and the related PKB in SHR brain synaptosomes was analyzed. PKA was detected in total synaptosomal fractions but not in particulate fractions, whereas PKB was not detected in either fraction. We next tested the hypothesis that the PKC pathway is involved in MC3-R signaling in a neuronal, CAD, cell line. Mobilization of intracellular Ca2+ was analyzed by dual fluorescence imaging of Fura-2AM loaded MC3-R transfected cells. An increase in intracellular Ca2+ was observed upon treatment with gamma-2-MSH. A MC3-R-green fluorescent protein (GFP) fusion protein was expressed and shown to localize mainly to the plasma membrane in the soma and to neurites in differentiated CAD cells. Treatment with gamma-2-MSH led to a punctate appearance and co-immunoprecipitation of the receptor fusion protein with protein kinase C-gamma (PKC-gamma). Differentiation of some neuronal cells has been shown to be associated with changes in the expression levels of protein kinase C isoenzymes. Induction of CAD cell differentiation was associated with down-regulation of the atypical PKC-zeta and protein kinase B (PKB/Akt1), that was less pronounced in MC3-R transfected cells. However, the levels of classical PKC isozymes, PKC-alpha, PKC-gamma, and PKC-beta were unchanged. These studies therefore indicate a role for PKC isozymes in gamma-2-MSH/MC3-R receptor signaling and in neuronal cell differentiation.

Free PKC catalytic subunits (PKM) phosphorylate tau via a pathway distinct from that utilized by intact PKC

Protein kinase C (PKC) is reversibly activated at the plasma membrane by the generation of diacylglycerol (DAG) coupled with the release of Ca2+ from intracellular stores. PKC is also irreversibly activated by calpain-mediated PKC cleavage of the regulatory and catalytic subunits; resultant free PKC catalytic subunits are termed "PKM". Unlike PKC, PKM is co-factor-independent, remains active following diffusion away from the membrane, and can theoretically phosphorylate targets inaccessible to, and inappropriate for, PKC. We examined the downstream consequences of PKC activation by the phorbol ester TPA and by ionophore A23187-mediated calcium influx (which experimentally correspond to DAG-mediated and calpain-mediated activation, respectively) on phosphorylation of the microtubule-associated protein tau. Both methods increased phospho-tau immunoreactivity, and neither was inhibited by lithium or olomoucin (inhibitors of tau kinases GSK-3 beta and cdk5, respectively). The TPA-mediated increase, and not the ionophore-mediated increase, was blocked by co-treatment with the mitogen-activated protein (MAP) kinase kinase inhibitor PD98059. These findings indicate that PKC phosphorylates tau via the MAP kinase pathway, but that PKM can bypass this requirement, therefore demonstrating that distinct intracellular pathways can be mediated by PKC and PKM. PKM generation may therefore trigger one or more additional pathways contributing to tau phosphorylation following inappropriate calcium influx.

Somatostatin enhances neurite outgrowth in PC12 cells

The rat pheochromocytoma cell line PC12 forms neurites in response to nerve growth factor (NGF), and it was also reported to extend processes in the presence of somatostatin (somatotropin release-inhibiting factor, SRIF), a neuroactive peptide that seems to act as a morphogenetic factor in the developing nervous system. In the present study, we re-evaluated the effects of SRIF on PC12 cell differentiation. Our results indicate that SRIF alone is ineffective in promoting neurite outgrowth. Instead, SRIF or its analogue, octreotide (a SRIF agonist on the receptor subtypes 2, 3 and 5), potentiates neurite extension induced by NGF. These results suggest that SRIF enhances neurite formation in PC12 cells without directly promoting neurite outgrowth. SRIF potentiation of NGF-induced neurite outgrowth persists at least in part in the presence of pertussis toxin (PTX), suggesting the involvement of PTX-insensitive G-proteins. In addition, protein kinase-dependent pathways are likely to mediate SRIF effects on NGF-induced differentiation.

Studies on the teratogen pharmacophore of valproic acid analogues: evidence of interactions at a hydrophobic centre

Propyl-4-yn-valproic acid (2-propyl-4-pentynoic acid), an analogue of valproic acid with a triple bond in one alkyl side chain, potently induces exencephaly in mice. Given that propyl-4-yn-valproic acid is a branched chain carboxylic acid, we synthesized a series of analogues with n-alkyl side chains of increasing length and correlated their potential to induce neural tube defects and to inhibit proliferation and induce differentiation in cells of neural origin, the latter being crucial to the orderly structuring of the embryo. All analogues significantly increased the incidence of neural tube defects in the embryos of dams exposed to a single dose of 1.25 mmol/kg on day 8 of gestation. This effect occurred in a dose-dependent manner and the rate of exencephaly increased with the progressive increase in n-alkyl side chain length. Moreover, increasing chain length resulted in a dose-dependent inhibition of C6 glioma proliferation rate over a concentration range of 0-3 mM and this was independent of the cell type employed and mode of estimating proliferative rate. The antiproliferative action of these analogues was associated with profound shape change in neuro-2A neuroblastoma involving extensive neuritogenesis and an associated increase in neural cell adhesion molecule (NCAM) prevalence at points of cell-cell contact, the latter exhibiting a dose-dependent increase when the n-alkyl chain was extended to five carbon units. These results suggest an interaction with a specific site in which the n-alkyl side is proposed to serve as an 'anchor' within a hydrophobic pocket to facilitate the ionic and/or H-bonding of the carboxylic acid and high electron density of the carbon-carbon triple bond.

Use of explant cultures of peripheral nerves of adult vertebrates to study axonal regeneration in vitro

Explanted preparations of peripheral nerves with attached dorsal root ganglia of adult mammals and amphibia survive for several days in serum-free medium and can be used to study axonal regeneration in vitro. This review outlines the methods which we routinely use and how they may be applied to study different aspects of axonal regeneration. When the peripheral nerves are crushed in vitro, axons regenerate through the crush site into the distal stump within 1 day (mouse) or 3 days (frog). The outgrowth distance of the leading sensory axons can be determined with the use of a simple method based on axonal transport of labelled proteins. A compartmentalised system permits selective application of drugs and other agents to either ganglia or peripheral nerve containing the regenerating axons and has been used to study selected aspects of regeneration including influence of non-neuronal cells, retrograde signalling, axonal release of proteins during regeneration and the role of phospholipase A2 activity. Explanted preparations may also be cultured in a layer of extracellular matrix material (matrigel), in which spontaneous outgrowth of a large number of naked axons from the cut ends of nerves starts within 1 day and continues for several days. This provides an opportunity to study the direct effects of different agents on axonal elongation. Preparations cultured in collagen gels show sparse spontaneous axonal growth, but this can be increased by addition of certain growth factors. The phenotype of the regenerating axons can be studied using immunohistochemical methods.

Selective activation by bryostatin-1 demonstrates unique roles for PKC epsilon in neurite extension and tau phosphorylation

Phorbol esters such as 12-O-tetradeonyl phorbol-13 acetate (TPA) induce a time-dependent biphasic effect on protein kinase C (PKC)-mediated events by fostering translocation of cytosolic (latent) PKC to the plasma membrane (where it is activated). Continued treatment, however, depletes the cell's entire PKC complement and induces a functional stake of PKC inhibition. Previous studies from several laboratories have demonstrated that long-term TPA treatment, like treatment with PKC inhibitors, induces neuronal differentiation. Bryostatin-1 also induces translocation and overall downregulation of PKC following long-term treatment, yet, unlike TPA or PKC inhibitors, does not induce neuronal differentiation, promoting controversy regarding the role of PKC inhibition in neuronal differentiation. We demonstrate herein that, despite overall downregulation in human neuroblastoma cells, membrane-associated levels of one PKC isoform (PKC epsilon) are actually increased following long-term bryostatin-1 treatment. Since previous studies have implicated this PKC isoform in phosphorylation of the microtubule-associated protein tau and in neuritogenesis, we examined the consequences of long-term bryostatin treatment on these phenomena. Treatment with 25 n-100 M bryostatin-1 for 72 h increased tau phosphorylation and inhibited neuritogenesis. By contrast, treatment with either TPA or the PKC inhibitor staurosporine did not induce tau phosphorylation and induced neurite elaboration. Bryostatin-1 antagonized neurite induction by staurosporine. These findings provide additional evidence for a unique role of PKC epsilon in the regulation of tau phosphorylation and neuronal differentiation, and demonstrate that bryostatin-1 can function under certain conditions as a selective PKC epsilon activator even following long-term treatment.

Modulation of neurite branching by protein phosphorylation in cultured rat hippocampal neurons

The control of branching of axons and dendrites is poorly understood. It has been hypothesized that branching may be produced by changes in the cytoskeleton [F.J. Diez-Guerra, J. Avila, MAP2 phosphorylation parallels dendrite arborization in hippocampal neurones in culture, NeuroReport 4 (1993) 412-419; P. Friedrich, A. Aszodi, MAP2: a sensitive cross-linker and adjustable spacer in dendritic architecture, FEBS Lett. 295 (1991) 5-9]. The assembly and stability of microtubules, which are prominent cytoskeletal elements in both axons and dendrites, are regulated by microtubule-associated proteins, including tau (predominantly found in axons) and MAP2 (predominantly found in dendrites). The phosphorylation state of tau and MAP2 modulates their interactions with microtubules. In their low-phosphorylation states, tau and MAP2 bind to microtubules and increase microtubule assembly and/or stability. Increased phosphorylation decreases these effects. Diez-Guerra and Avila [F.J. Diez-Guerra, J. Avila, MAP2 phosphorylation parallels dendrite arborization in hippocampal neurones in culture, NeuroReport 4 (1993) 412-419] found that protein phosphorylation correlates with neurite branching in cultured rat hippocampal neurons, and hypothesized that increased protein phosphorylation stimulates neurite branching. To test this hypothesis, we cultured rat hippocampal neurons in the presence of specific modulators of serine-threonine protein kinases and phosphatases. Inhibitors of several protein kinases, which would be expected to decrease protein phosphorylation, reduced branching. KT5720, an inhibitor of cyclic AMP-dependent protein kinase, and KN62, an inhibitor of Ca(2+)-calmodulin-dependent protein kinases, inhibited branching of both axons and dendrites. Calphostin C and chelerythrine, inhibitors of protein kinase C, inhibited branching of axons but not dendrites. Treatments that would be expected to increase protein phosphorylation, including inhibitors of protein phosphatases (okadaic acid, cyclosporin A and FK506) and stimulators of PKA (SP-cAMPS) or PKC (phorbol 12-myristate 13-acetate), increased dendrite branching. Only FK506 and phorbol 12-myristate 13-acetate stimulated axon branching. A subset of these agents was tested to confirm their effects on protein phosphorylation in this preparation. Okadaic acid, FK506 and SP-cAMPS all increased protein phosphorylation; KT5720 and KN62 decreased protein phosphorylation. On Western blots, the position of MAP2c extracted from cultures exposed to okadaic acid was slightly shifted toward higher molecular weight, suggesting greater phosphorylation, while the position of MAP2c from cultures exposed to KT5720 and KN62 was slightly shifted toward lower molecular weight, suggesting less phosphorylation. We conclude that protein phosphorylation modulates both dendrite branching and axon branching, but with differences in sensitivity to phosphorylation and/or dephosphorylation by specific kinases and phosphatases.

Involvement of a ceramide activated protein phosphatase in the differentiation of neuroblastoma Neuro2a cells

The possible involvement of protein phosphatase in ceramide-mediated neural cell differentiation was investigated. Neuroblastoma Neuro2a cell differentiation induced by retinoic acid, or conditions causing an increase in cellular ceramide, was significantly inhibited by the serine/threonine phosphatase inhibitor okadaic acid, at concentrations as low as 2.5 nM. A crude cytosolic preparation from Neuro2a cells was found to have a cation-independent protein phosphatase activity that was stimulated by ceramide in a dose-dependent manner. Short- and long-chain ceramides, but not sphingosine and related dihydro-derivatives, were active. Ceramide-activated protein phosphatase activity from Neuro2a cells was inhibited by 5 nM okadaic acid. The data indicate that a type 2A protein phosphatase is involved in ceramide-mediated differentiation of Neuro2a cells.

Overexpression of alpha and beta isoforms of Ca2+/calmodulin-dependent protein kinase II in neuroblastoma cells -- H-7 promotes neurite outgrowth

Since the alpha and beta isoforms of CaM kinase II are known to be expressed almost exclusively in the brain, we compared the effect of overexpression of the beta isoform of CaM kinase II with that of the alpha isoform. The subcellular distribution of the alpha isoform was different from that of the beta isoform, although the catalytic properties of the alpha and beta isoforms expressed in transfected cells were similar to those of brain CaM kinase II. The alpha isoform was found in the soluble fraction more than in the particulate fraction, whereas most of the beta isoform bound to subcellular structures. In the cell overexpressing alpha and beta isoforms of CaM kinase II, neurite extension was promoted when compared with the morphology of neo transfectants. Neurite outgrowth of cells overexpressing CaM kinase II was further stimulated by the treatment of 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7), a selective but not absolutely specific inhibitor of protein kinase C. The morphological change was rapid and observed within 1 h followed by H-7 treatment. Morphological changes, such as the number of cells with neurites and length of neurites were greater in the beta cells than in the alpha cells. Chelerythrine, a specific inhibitor of protein kinase C, also stimulated the neurite outgrowth of these cells. Some substrates of CaM kinase II related to neurite outgrowth were detected in cells overexpressing CaM kinase II stimulated with H-7. These results suggest that CaM kinase H and protein kinase C play an important role in the control of cell change, and that the subcellular distribution of CaM kinase II is important for regulating cellular functions efficiently.

1-(5-Isoquinolinesulfonyl)-2-methylpiperazine induces apoptosis in human neuroblastoma cells, SH-SY5Y, through a p53-dependent pathway

We have studied the effect of 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7), a protein kinase inhibitor, on the regulation of apoptosis in the human neuroblastoma cell line, SH-SY5Y. H-7 (20-100 microM) induced apoptosis in these cells characterized by DNA fragmentation and chromatin condensation. Immunoblot analyses were performed with specific antibody against BCL-2, BCL-XS/L, BAX, JUNB, c-JUN, ICH-1L, c-FOS, RB, CDK-2, and p53. H-7 treatment did not significantly alter the level of these proteins with the exception of p53. H-7, but not staurosporine, caused a dramatic nuclear accumulation of p53. The kinetics of nuclear accumulation of p53 correlates well with the kinetics of induction of apoptosis. The effect of H-7 was further assessed in a group of human cell lines. Only cell lines harboring the wild-type p53 gene were responsive to the stimulatory effect of H-7 on nuclear accumulation of p53. Furthermore, cell lines carrying a mutated p53 gene were resistant to the cytotoxic effect of H-7. The ability of H-7 in mediating apoptosis in the SH-SY5Y line expressing a dominant negative mutant of p53 was significantly diminished. Taken together, these data strongly suggest that a p53-dependent mechanism contributes to the cytotoxicity of H-7 in human neuroblastoma cells.

H7, an inhibitor of protein kinase C, prevents serum-induced phosphorylation of Raf and MAP kinase in neuroblastoma cells

We have previously shown that 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7), an inhibitor of protein kinase C, inhibits proliferation of neuroblastoma cells in culture. We have now tested whether the effect of H7 is mediated by MAP kinase and Raf. It is shown that, in Neuro 2a cells, activation of protein kinase C by addition of 4 beta-phorbol-12 beta-myristate-13 alpha-acetate (PMA), leads to phosphorylation of Raf and Mitogen-activated protein kinase (MAP kinase). PMA-induced phosphorylation of these proteins is prevented by H7. When quiescent Neuro 2a were stimulated to proliferate by addition of serum, Raf and MAP kinase were rapidly phosphorylated. Serum-induced phosphorylation of Raf and MAP kinase is prevented by H7. These results suggest that, in Neuro 2a cells, the control of proliferation by protein kinase C could be mediated by phosphorylation (and concomitant activation) of Raf and MAP kinase.

Protein kinase C and mouse sciatic nerve regeneration

We have studied the role of protein kinase C (PKC) in peripheral nerve regeneration by using the cultured adult mouse sciatic nerve, which displays regrowth of sensory axons under serum-free conditions. By the use of immunohistochemistry we show that one of the isoforms of PKC, PKC beta, is present in the nerve cell bodies of normal nerves and is upregulated after injury. In spite of this, the specific PKC inhibitor chelerythrine at 5 microM, a concentration well above its IC50 value for PKC, failed to reduce the outgrowth distance of new axons. This was not due to impermeability of the drug, since the same concentration caused a clear reduction of the injury-induced proliferation of Schwann cells in the crush region. Likewise, HA-1004, an inhibitor of cyclic nucleotide-dependent protein kinases, also lacked effect on outgrowth when used on its own, even at very high concentrations (100 microM). In contrast, outgrowth was significantly reduced when 5 microM chelerythrine and 5 microM HA-1004 were used in combination. In conclusion, the present results suggest that PKC-activity is important but not indispensable for the regeneration process. Successful completion of the latter could be achieved by several, perhaps redundant, phosphorylation systems.

Protein kinase C isoforms and cell proliferation in neuroblastoma cells

The expression of protein kinase C isoforms in the neuroblastoma cell line Neuro 2a has been studied. It is shown that Neuro 2a cells express alpha, delta, epsilon and zeta PKCs. Inhibition of cell proliferation by using protein kinase C inhibitors (H7 or calphostin C) or medium without glutamine affects markedly the pattern of PKC isoforms. All treatments reduced significantly (50-70%) the content of PKC alpha. None of the treatments altered PKC zeta or epsilon. The content of PKC delta was increased (88-120%) in cells treated with PKC inhibitors but was slightly reduced in cells incubated in medium without glutamine. However, none of the treatments affected the content of the corresponding mRNAs. Long-term treatment of synchronized cells with the phorbol ester PMA depletes PKC alpha but not PKC delta or zeta and only partially PKC epsilon. This treatment with PMA did not affect DNA synthesis, indicating that PKC alpha does not play a significant role in the control of proliferation of these cells.

Antioxidants in peripheral nerve

Oxidative stress and antioxidants have been related in a wide variety of ways with nervous tissue. This review attempts to gather the most relevant information related to a) the antioxidant status in non pathologic nervous tissue; b) the hypothesis and evidence for oxidative stress (considered as the disequilibrium between prooxidants and antioxidants in the cell) as the responsible mechanism of diverse neurological diseases; and c) the correlation between antioxidant alterations and neural function, in different experimental neuropathies. Decreased antioxidant availability has been observed in different neurological disorders in the central nervous system, for example, Parkinson's disease, Alzheimer's disease, epilepsy, amyotrophic lateral sclerosis, cerebral ischaemia, etc. Moreover, the experimental manipulation of the antioxidant defense has led in some cases to interesting experimental models in which electrophysiological alterations are associated with the metabolic modifications induced. In view of the electrophysiological and biochemical effects of some protein kinase C inhibitors on different neural experimental models, special attention is dedicated to the role of this kinase in peripheral nervous tissue. The nervous tissue, central as well as peripheral, has two main special features that are certainly related to its antioxidant metabolism: the lipid-enriched membrane and myelin sheaths, and cellular excitability. The former explains the importance of the glutathione (GSH)-conjugating activity towards 4-hydroxy-nonenal, a biologically active product of lipid peroxidation, present in nervous tissue and in charge of its inactivation. The impairment of the latter by oxidative damage or experimental manipulation of antioxidant metabolism is discussed. Work on different experimental neuropathies from author's laboratory has been primarily used to provide information about the involvement of free radical damage and antioxidants in peripheral nerve metabolic and functional impairment.

Interleukin-1 beta induction of tissue inhibitor of metalloproteinase (TIMP-1) is functionally antagonized by prostaglandin E2 in human synovial fibroblasts

Elevated levels of tissue inhibitor of metalloproteases-1 (TIMP-1) have been demonstrated in inflamed synovial membranes, and it is believed that the inhibitor may play a critical role in the regulation of connective tissue degradation. The present study was undertaken to define the cellular mechanism of action of the inflammatory mediators, interleukin-1 beta (IL-1 beta) and prostaglandin E2 (PGE2), in the control of TIMP-1 synthesis and expression in human synovial fibroblasts. Recombinant human IL-1 beta induced a time- and dose-dependent saturable response in terms of TIMP-1 mRNA expression (effective concentration for 50% maximal response, EC50 = 31.5 +/- 3.3 pg/ml) and protein synthesis (EC50 = 30 +/- 3.3 pg/ml). The protein kinase C (PKC) inhibitors, H-7, staurosporine, and calphostin C, reversed the rhIL-1 beta induction of TIMP-1 mRNA. PGE2 also inhibited rhIL-1 beta-stimulated TIMP-1 mRNA expression and protein secretion in a dose-dependent fashion. The concentration of PGE2 necessary to block 50% of rhIL-1 beta-stimulated TIMP-1 secretion, IC50, was 1.93 ng/ml (4.89 nM). Forskolin, and other stable derivatives of cAMP, mimicked, to a large extent, the effects of PGE2. The phorbol ester, PMA, up-regulated considerably the mRNA expression of TIMP-1 but had no effect on protein production. Calphostin C substantially reduced PMA-activated TIMP-1 expression. Staurosporine, calphostin C, H-7, and substances that elevate cellular levels of cAMP, like PGE2, also reduced basal expression and synthesis of TIMP-1. Taken together, the data suggest that PKA and C may mediate opposing effects in terms of TIMP-1 expression and secretion in human synovial fibroblasts.

Protein kinase C inhibitors, H7 and calphostin C, inhibit induction of DNA synthesis by cytosolic extracts of exponentially growing neuroblastoma cells in isolated nuclei

Cytoplasmic extracts from proliferating Neuro-2a cells contain a protein factor, ADR (activator of DNA replication) that induces DNA synthesis in isolated quiescent nuclei. Cytoplasmic extracts derived from quiescent-made Neuro-2a cells contain none or very little ADR activity, but this activity can be generated after a brief exposure of cytosolic extracts to a membrane-enriched fraction derived from exponentially growing Neuro-2a cells. ADR activity appears at the beginning of the S phase of the cell cycle. Moreover it appears to be a protease, because aprotinin inhibits ADR activity. ADR activity can be also inhibited by the protein kinase C inhibitors, 1-(5-isoquinoline-sulfonyl)-2- methylpiperazine (H7) and calphostin C.

H7, an inhibitor of protein kinase C, inhibits tumour cell division in mice bearing ascitic Ehrlich's carcinoma

We have previously shown that H7, an inhibitor of protein kinase C (PKC), inhibits proliferation of several cell lines as well as of primary cultured cells from human tumours. The aim of this work was to assess whether H7 is able to prevent the division of tumour cells in mice bearing Ehrlich's ascitic carcinoma. The LD50 of H7 injected intravenously was 61 mg/kg and 94 mg/kg for starved and fed mice, respectively. Acute intraperitoneal injection of 100 mg/kg of H7 decreased the number of mitoses in tumoral cells from ascitic fluid of mice bearing the carcinoma. The reduction was maximal (approximately 50%) after 90 min and then the number of mitosis rose due to a decrease in H7. Continuous delivery of H7 from mini-osmotic pumps implanted on the backs of the mice reduced the number of mitoses by approximately 65%, and the effect was maintained for approximately 24 h. The effect cannot be maintained for longer because H7 is unstable at body temperature. These results indicate that inhibition of PKC can block division of tumour cells in carcinoma-bearing animals, and support the idea that inhibitors of PKC could be useful for the clinical control of proliferation of certain tumours.

Involvement of protein kinase C in the interleukin 1 alpha-induced gene expression of matrix metalloproteinases and tissue inhibitor-1 of metalloproteinases (TIMP-1) in human uterine cervical fibroblasts

The role of protein kinase C in the interleukin 1 (IL-1)-mediated production of pro-matrix metalloproteinases (proMMPs) and tissue inhibitor-1 of metalloproteinases (TIMP-1) in human uterine cervical fibro-blasts has been investigated. IL-1 and a protein kinase C activator, 12-O-tetradecanoylphorbol 13-acetate (TPA) augmented the production of proMMP-1 (interstitial procollagenase), proMMP-3 (prostromelysin-1) and TIMP-1, but their effects were inhibited by the protein kinase C inhibitors 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7) and staurosporine in a dose-dependent manner. The suppressive effect of H-7 and staurosporine on the IL-1-induced production of proMMPs-1 and -3 and TIMP-1 resulted from the decrease in the steady-state levels of their mRNAs. When protein kinase C was down-regulated by treating the cells with a high level of TPA, the inductive effect of IL-1 upon proMMP-3 production was reduced considerably. These results indicate that protein kinase C mediates the IL-1-induced production of proMMPs-1 and -3 and TIMP-1 at the pretranslational level in human uterine cervical fibroblasts. On the other hand, neither IL-1 nor TPA modulated the production of proMMP-2 (progelatinase A). Both IL-1 and TPA also accelerated the production of prostaglandin E2 (PGE2) by cervical fibroblasts. However, the treatment of the cells with staurosporine in the presence of IL-1 or TPA further augmented PGE2 synthesis, suggesting that the increased synthesis of PGE2 by IL-1 treatment is mediated via signalling pathways distinct from those of proMMPs-1 and -3 and TIMP-1.

Effects of selective inhibition of protein kinase C, cyclic AMP-dependent protein kinase, and Ca(2+)-calmodulin-dependent protein kinase on neurite development in cultured rat hippocampal neurons

A variety of experimental evidence suggests that calmodulin and protein kinases, especially protein kinase C, may participate in regulating neurite development in cultured neurons, particularly neurite initiation. However, the results are somewhat contradictory. Further, the roles of calmodulin and protein kinases on many aspects of neurite development, such as branching or elongation of axons vs dendrites, have not been extensively studied. Cultured embryonic rat hippocampal pyramidal neurons develop readily identifiable axons and dendrites. We used this culture system and the new generation of highly specific protein kinase inhibitors to investigate the roles of protein kinases and calmodulin in neurite development. Neurons were cultured for 2 days in the continuous presence of calphostin C (a specific inhibitor of protein kinase C), KT5720 (inhibitor of cyclic AMP-dependent protein kinase), KN62 (inhibitor of Ca(2+)-calmodulin-dependent protein kinase II), or calmidazolium (inhibitor of calmodulin), each at concentrations from approximately 1 to 10 times the concentration reported in the literature to inhibit each kinase by 50%. The effects of phorbol 12-myristate 13-acetate (an activator of protein kinase C) and 4 alpha-phorbol 12,13-didecanoate (an inactive phorbol ester) were also tested. At concentrations that had no effect on neuronal viability, calphostin C reduced neurite initiation and axon branching without significantly affecting the number of dendrites per neuron, dendrite branching, dendrite length, or axon length. Phorbol 12-myristate 13-acetate increased axon branching and the number of dendrites per cell, compared to the inactive 4 alpha-phorbol 12,13-didecanoate. KT5720 inhibited only axon branching. KN62 reduced axon length, the number of dendrites per neuron, and both axon and dendrite branching. At low concentrations, calmidazolium had no effect on any aspect of neurite development, but at high concentrations, calmidazolium inhibited every parameter that was measured (including viability). These results suggest that these three protein kinases selectively modulate different aspects of neurite development. The university of effects caused by calmodulin inhibition make it impossible to determine if there are specific targets of calmodulin action involved in neurite development. Finally, our data indicate that some superficially similar characteristics of neuronal differentiation, such as neurite initiation and branching, may be controlled by quite different molecular mechanisms.

Signal-transduction mechanisms of ATP-stimulated phosphatidylcholine secretion in rat type II pneumocytes: interactions between ATP and other surfactant secretagogues

ATP stimulates phosphatidylcholine secretion in type II cells, an effect that is mediated by both adenosine A2 receptors coupled to adenylate cyclase and P2 receptors coupled to phosphoinositide-specific phospholipase C. Activation of these effector enzymes leads to formation of cAMP, diacylglycerols and inositol trisphosphate (IP3). cAMP in turn activates cAMP-dependent protein kinase, diacylglycerols activate protein kinase C and IP3 promotes Ca2+ mobilization. To further investigate the signal-transduction mechanisms mediating the ATP effect, we examined its action in combination with that of other surfactant secretagogues: 5'(N-ethylcarboxyamido)adenosine (NECA), a A2 agonist that activates adenylate cyclase; TPA (12-O-tetradecanoylphorbol-13-acetate), a direct activator of protein kinase C; and ionomycin, an ionophore that increases intracellular Ca2+. The effects of NECA, TPA and ionomycin were additive and thus consistent with independent signaling mechanisms. However, the effects of all combinations of three or four secretagogues that contained ATP were 10-20% less than additive. This suggested that ATP and other secretagogues act via common mechanisms. Calmodulin antagonists decreased the effects of ionomycin and ATP by approx. 60% and 30%, respectively, but did not decrease the effects of NECA, terbutaline or TPA. Complete inhibition of the effect of ATP was achieved with a combination of a calmodulin antagonist, an A2 antagonist and a protein kinase C inhibitor. These and previous data suggest that the stimulatory effect of ATP on phosphatidylcholine secretion in type II cells is mediated by three signal-transduction mechanisms: activation of cAMP-dependent protein kinase; activation of protein kinase C; and a calmodulin-dependent mechanism.

Serum depletion increases the neurofilament protein mRNA levels in a neuroblastoma cell line, GOTO

A human neuroblastoma cell line, GOTO, extends neurite-like processes upon withdrawal of serum from culture medium. This morphological change was accompanied by a 5-fold increase in the neurofilament (NF)-L and a 10-fold increase in the NF-M mRNA levels after 24 h. The addition of a protein kinase inhibitor, H-7 (1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride) also induced the extension of neurite-like processes; however, it did not increase the NF mRNA levels. Thrombin inhibited the extension of neurite-like processes in serum-free culture without affecting the increase in the NF mRNA levels. There was no difference in the number of cells progressing through the S phase between serum-containing and -free cultures at 24 h. This indicates that the increase in the NF mRNA levels upon withdrawal of serum was not preceded by the growth arrest. Treatment with actinomycin D and cycloheximide inhibited the increase in the NF mRNA levels. The half life of the NF gene transcripts was prolonged in the serum-free condition. These results indicate that the serum depletion-induced increase in the NF-L and -M mRNA levels was regulated by both transcriptional and post-transcriptional mechanisms, and the increase in the expression of the NF genes was not simply mediated by growth arrest but controlled by unknown regulator proteins.

Differential effects of the protein kinase C inhibitors H7 and calphostin C on the cell cycle of neuroblastoma cells

We have studied the effect of protein kinase C inhibitors 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7) and calphostin C on the cycle of Neuro-2a cells. Both compounds inhibited cell proliferation and DNA synthesis. Transition from G2 to M phase was not altered by these compounds. Calphostin C blocked the cells in G0/G1, while H7 did not at any specific point in the cell cycle. We also show that the antiproliferative effect induced by both inhibitors is reversible.

Prevention of the acute neurotoxic effects of phenytoin on rat peripheral nerve by H7, an inhibitor of protein kinase C

The neurotoxic effects of a single dose of phenytoin (150 mg/kg body weight) alone or 30 min after H7 (a protein kinase C inhibitor) injection (20 mg/kg body weight) were investigated in terms of peripheral neuromuscular function and Na+,K(+)-ATPase activity of the sciatic nerve. This intraperitoneal injection of phenytoin induced complete blockade of muscle action potentials in the dorsal segmental muscles of the rat tail evoked by electric stimulation of the caudal nerve and a 40% decrease in the Na+,K(+)-ATPase activity of the rat sciatic nerve when compared with control values, measured as the difference between total and ouabain-insensitive ATPase activity. Prior administration of H7 resulted in the complete prevention of both effects. Implications of protein kinase C inhibition in phenytoin neurotoxicity are discussed.

Opposing influences of protein kinase activities on neurite outgrowth in human neuroblastoma cells: initiation by kinase A and restriction by kinase C

The respective roles of cAMP-dependent protein kinase (protein kinase A [PKA]) and protein kinase C (PKC) in the early stages of neurite outgrowth were examined in SH-SY-5Y human neuroblastoma cells. Forskolin or dbcAMP, agents that increase intracellular cAMP levels, and intracellular delivery of PKA catalytic subunit induced neurite outgrowth. The PKA inhibitor, N-(2-guanidinoethyl)-5-isoquinolinesulfonamide (HA 1004), prevented the increases, and decreased further the percentage of cells possessing short, filopodia-like neurites in the absence of inducers. In contrast to effects on PKA activation, PKC activation by 12-0-tetradecanoylphorbol-13-acetate (TPA) reduced the percentage of filopodia-like neurites elaborated by otherwise untreated cells, and prevented neurite outgrowth induced by PKA activators. PKC inhibitors 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H7), staurosporine, and sphingosine induced neurite outgrowth. Neurites induced by PKA activation contained higher levels of tubulin immunoreactivity than those induced by PKC inhibition. Furthermore, PKA-induced neurites rapidly retracted in the presence of colchicine, while those elaborated following PKC inhibition were more resistant. These data suggest that neurites elaborated in response to PKA activation are dependent upon microtubule polymerization, and that neurite induction following PKC inhibition is mediated by a different mechanism. PKA activators and PKC inhibitors exerted additive effects on neurite outgrowth, suggesting that the distinct pathways regulated by these two kinases function cooperatively during neuritogenesis.

Hypoxia-mediated impaired differentiation by LLC-PK1 cells: evidence based on the protein kinase C profile

We recently reported that mild hypoxia in LLC-PK1 cells, grown in standard fashion under a still layer of overlying medium at 5% CO2/18% O2 environment, result in decreased oxidative metabolism and impaired differentiated functions in comparison to adequately oxygenated cultures maintained either under a higher oxygen (36% O2) environment or conditions of continuous rocking of the media fluid. In the present study, subcellular distribution of a regulatory enzyme protein kinase C (PKC) was examined between hypoxic still and normoxic rocked LLC-PK1 cells. Subconfluent cultures of hypoxic LLC-PK1 cells exhibited significantly lower and predominantly membrane-bound PKC activity in comparison to mostly cytosolic localization of this enzyme in normoxic rocked cells. One hour of exposure of adequately oxygenated-rocked LLC-PK1 cells with the phorbol ester TPA, a dedifferentiating agent that did not effect the cell ATP content, resulted in significant inhibition of dome formation and sodium-dependent glucose transport activity, a partial loss of pH-responsive ammoniagenesis, and almost complete translocation of protein kinase C activity from cytosol to the membrane pool; all of which resembles the behavior of hypoxic still cultured cells. In addition, acute re-oxygenation of hypoxic still cultures by rocking the media fluid for one hour resulted in an increase in cell ATP content to the cellular levels of ATP observed in normoxic rocked cells. However, all the parameters of differentiation were unaffected by re-oxygenation. These studies support the notion that hypoxia can act in some primary fashion, independent of its effects on energy metabolism, to impair cellular differentiation in LLC-PK1 cells. They also raise the possibility that activation of protein kinase C may act as an important mediator in this process.

Differentiation of Neuro-2a neuroblastoma cells by an antibody to GM3 ganglioside

A monoclonal antibody against GM3 ganglioside (GM3Ab) was found to trigger differentiation of Neuro-2a cells in culture. The differentiation of Neuro-2a cells by GM3Ab was accompanied by increased levels of intracellular serotonin and amino acid neurotransmitters viz. aspartate, glutamate, glutamine, glycine and taurine. Further study indicated that the increase in the serotonin level was not due to a higher rate of serotonin synthesis but rather to a higher rate of active transport of serotonin from the medium. Studies on the cell surface gangliosides revealed that unlike the proliferating cells, the GM3Ab-mediated differentiated cells contained higher gangliosides in addition to GM3 and GM2 gangliosides. Analysis of total cellular proteins indicated the appearance of a 25 kDa protein, pI 5.4, in the GM3Ab-treated cells--a small amount of this protein was observed in dibutyryl cAMP (Bt2cAMP)-treated cells, however, the protein was totally absent in the 5-bromo-2'-deoxyuridine (BrdU)-treated cells. Investigation of the mode of action of GM3Ab indicated that the cellular differentiation was due to increased cAMP accumulation resulting from an increase in the adenylate cyclase activity. Further studies with different agents affecting protein kinase C (PKC) activity and direct assay of PKC ruled out the possibility that GM3Ab mediated its effect via PKC. This GM3Ab-induced differentiation could be inhibited by protein kinase A (PKA) inhibitor, H8, but could not be inhibited by sphingosine, an inhibitor of PKC. Pertussis toxin could mimic the effect of GM3Ab, suggesting that GM3Ab caused the elevation in the adenylate cyclase activity by reducing the Gi-protein inhibition of the adenylate cyclase. The data suggests that GM3Ab, after interaction with cell surface GM3, elevated intracellular cAMP level by withdrawing the inhibitory effect of some undefined factor(s) present in culture medium which normally keeps adenylate cyclase activity low through activation of Gi-protein.

H7, a protein kinase C inhibitor, increases the glutathione content of neuroblastoma cells

It is shown that the intracellular glutathione (GSH) concentration of neuroblastoma-2a cells in culture increases with a maximum at 24 h after starting treatment with 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7), an inhibitor of protein kinase C (PKC). Other inhibitors of this and other protein kinases, e.g. sphingosine, staurosporine, and HA 1004, at the concentrations tested, had a less marked or negligible effect on intracellular GSH concentration. 12-O-Tetradecanoylphorbol-13-acetate (TPA) was also tested and showed no significant effect 24 h after addition.

Development and characterization of a protein kinase C beta-isozyme-deficient T-cell line

In the human T-cell lymphoma line, HuT 78, proliferation and phorbol ester-induced growth arrest and differentiation were inhibited by the protein kinase C (PKC) inhibitor, staurosporine. By contrast, an alternative PKC inhibitor, H-7, inhibited proliferation but not phorbol ester-induced growth arrest. The cell line was found to contain both alpha and beta isoforms of PKC by Western blot techniques. A cell line, K-4, was cloned from HuT 78 in the presence of H-7 and this clone was found to be positive for PKC-alpha only. PKC-beta did not return on cultivation in the absence of H-7. Proliferation of K-4 was insensitive to inhibition with both H-7 and staurosporine. However, phorbol ester-induced growth arrest remained staurosporine sensitive. Phorbol-stimulated IL-2 secretion was minimal in the PKC-beta-deficient cell line. These data suggest that PKC-beta may be a regulatory enzyme for proliferation and stimulated interleukin-2 secretion in HuT 78 cells. Heterogeneity of responses to PKC activation may reflect the use of different isozymes in different intracellular pathways. The K-4 cell line should provide a useful tool in the dissection of involvement of PKC isozymes in cellular function.

Inhibition of protein kinase C restores Na+,K(+)-ATPase activity in sciatic nerve of diabetic mice

We have tested if inhibition of protein kinase C is able to prevent and/or to restore the decrease of Na+,K(+)-ATPase activity in the sciatic nerve of alloxan-induced diabetic mice. Mice were made diabetic by subcutaneous injection of 200 mg of alloxan/kg of body weight. The activity of Na+,K(+)-ATPase decreased rapidly (43% after 3 days) and slightly thereafter (58% at 11 days). We show that intraperitoneal injection of 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7), an inhibitor of protein kinase C, prevents completely the loss of Na+,K(+)-ATPase activity produced by alloxan. Also, H7 injected into diabetic mice, 4-9 days after the injection of alloxan, restores the activity of the enzyme. The amount of activity recovered depends on the dose of H7 administered; complete recovery was reached with injection of 15 mg of H7/kg of body weight. The effect of H7 is transient, with a half-life of approximately 1 h.

Effects of protein kinase inhibitors on regeneration in vitro of adult frog sciatic sensory axons

The effects of protein kinase inhibitors on regeneration in vitro of adult frog sciatic sensory axons were tested. Regeneration of crush-injured nerves for 8 days in serum-free medium was inhibited by staurosporine (100 nM) and H-7 (100 microM), which are both known to inhibit protein kinase C. With the use of a compartmented culture system it could be shown that H-7 exerted both local (outgrowth region) and central (ganglia) effects, the latter being more pronounced. The local effects could be due to reduction of Schwann cell proliferation by H-7. Immunohistochemistry demonstrated the presence of protein kinase C in neuronal cell bodies but not in axonal processes. Proliferation of Schwann cells was accompanied by increased protein kinase C immunoreactivity at the site of injury. H-7 caused a selective inhibition in the incorporation of radioactive phosphate into one 74 kDa protein of both ganglia and nerve but also a more general decrease in protein labelling. The results show that protein phosphorylations, possibly mediated by protein kinase C, are involved in regeneration-related mechanisms operating at both local and central levels in the adult frog sciatic sensory axons.

Differential expression of PKC isoforms and PC12 cell differentiation

Recent reports indicate that the protein kinase inhibitor H7 is capable of inducing both morphological and functional differentiation of a number of neural cell types. This investigation demonstrates that H7 potentiates the neurogenic properties of nerve growth factor (NGF) in PC12 cells with a concomitant change in the accumulation of the beta II-protein kinase C (beta IIPKC) isoform protein without changes in either alpha or gamma. However, NGF alone stimulates a coordinate increase in all three isoforms. The assay of acetylcholine esterase as a functional marker of neuronal differentiation demonstrates that H7 alone is not capable of stimulating morphological or functional differentiation in PC12 cells. H7 synergizes with NGF through a PKC-dependent pathway and by differential expression of PKC subtypes. The expression of the PKC transcripts for alpha, beta II, and gamma all undergo simultaneous yet differential changes in their patterns of expression during treatment with H7 and/or NGF. These data suggest that isoform switching is regulated primarily at the protein level. Last, these findings suggest that expression of PKC isoforms is tightly coupled with neuronal differentiation and may play a role in the maintenance of the differentiated state.

Cellular distribution of gastric chief cell protein kinase C activity: differential effects of diacylglycerol, phorbol esters, carbachol, and cholecystokinin

Stimulation of chief cells with carbachol or cholecystokinin (CCK) results in the production of inositol trisphosphate (IP3) and diacylglycerol (DAG). Although IP3 increases cell calcium concentration, thereby stimulating pepsinogen secretion, the role of DAG and its target, protein kinase C (PKC), is less clear. To examine the relation between the cellular distribution of PKC activity and pepsinogen secretion, we determined PKC activity in cytosolic and membrane fractions from dispersed chief cells from guinea pig stomach. To validate our assay, we studied the actions of the phorbol ester PMA. PMA caused a rapid, dose-dependent, 6-fold increase in pepsinogen secretion and membrane-associated PKC activity. Similarly, dose-response curves for pepsinogen secretion and the increase in membrane-associated PKC activity induced by a membrane-permeant DAG (1-oleoyl-2-acetylglycerol) were superimposable. In contrast, CCK (0.1 nM to 1.0 microM) and carbachol (0.1 microM to 1.0 mM) caused a 4-fold increase in pepsinogen secretion, but did not alter the distribution of PKC activity. These results indicate that in gastric chief cells, PMA- and DAG-induced pepsinogen secretion is accompanied by increased membrane-associated PKC activity. However, the cellular distribution of PKC activity is not altered by CCK or carbachol.

Inhibition of protein kinase C arrests proliferation of human tumors

We have shown that inhibition of protein kinase C by 1-5-isoquinolinylsulfonyl-2-methylpiperazine, H7, induces differentiation and inhibits proliferation of Neuro 2a cells. We have now tested if H7 is able to inhibit proliferation of: 1) human tumor cell lines from tissues other than brain; and 2) primary cultured cells from several human brain tumors. H7 inhibits, in a dose-dependent manner, proliferation of all human tumor cell lines tested and of primary cultured cells from human brain tumors. These results indicate that inhibition of protein kinase C inhibits proliferation of tumoral cells, therefore, H7, and likely other inhibitors of protein kinase C, could be useful in the clinical treatment of brain (and probably other) tumors.

Actinomycin D decreases protein kinase C content and induces neuritogenesis in neuroblastoma cells

We have previously reported that inhibition of protein kinase C induces differentiation of neuroblastoma cells in culture. It is shown now that actinomycin D, a well known inhibitor of DNA synthesis, reduces selectively the content of protein kinase C and induces neuritogenesis in Neuro 2a cells in culture.

Staurosporine, a protein kinase inhibitor, attenuates basal forebrain-lesion-induced amnesia and cholinergic neuronal deficit

We have investigated whether administration of staurosporine, which has been reported to induce differentiation in the human neuroblastoma cell in vitro, attenuates amnesia induced by basal forebrain lesion in rats. Multiple dosage of staurosporine at the doses of 0.05 and 0.1 mg/kg (i.p.) attenuated the impaired performance of the water maze task. Moreover, staurosporine (0.1 mg/kg) reversed the decrease of choline acetyltransferase activity in the fronto-parietal cortex. These results suggest that staurosporine attenuates amnesia through reversal of deficits in cholinergic neurons induced by basal forebrain lesion, and that neurotrophic factor-like substances may open the way for novel therapeutic approaches to Alzheimer's disease.