Gö 6976 is a potent inhibitor of neurotrophin-receptor intrinsic tyrosine kinase

Serine biosynthesis as a novel therapeutic target for dilated cardiomyopathy

AIMS

Genetic dilated cardiomyopathy (DCM) is a leading cause of heart failure. Despite significant progress in understanding the genetic aetiologies of DCM, the molecular mechanisms underlying the pathogenesis of familial DCM remain unknown, translating to a lack of disease-specific therapies. The discovery of novel targets for the treatment of DCM was sought using phenotypic sceening assays in induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) that recapitulate the disease phenotypes in vitro.

METHODS AND RESULTS

Using patient-specific iPSCs carrying a pathogenic TNNT2 gene mutation (p.R183W) and CRISPR-based genome editing, a faithful DCM model in vitro was developed. An unbiased phenotypic screening in TNNT2 mutant iPSC-derived cardiomyocytes (iPSC-CMs) with small molecule kinase inhibitors (SMKIs) was performed to identify novel therapeutic targets. Two SMKIs, Gö 6976 and SB 203580, were discovered whose combinatorial treatment rescued contractile dysfunction in DCM iPSC-CMs carrying gene mutations of various ontologies (TNNT2, TTN, LMNA, PLN, TPM1, LAMA2). The combinatorial SMKI treatment upregulated the expression of genes that encode serine, glycine, and one-carbon metabolism enzymes and significantly increased the intracellular levels of glucose-derived serine and glycine in DCM iPSC-CMs. Furthermore, the treatment rescued the mitochondrial respiration defects and increased the levels of the tricarboxylic acid cycle metabolites and ATP in DCM iPSC-CMs. Finally, the rescue of the DCM phenotypes was mediated by the activating transcription factor 4 (ATF4) and its downstream effector genes, phosphoglycerate dehydrogenase (PHGDH), which encodes a critical enzyme of the serine biosynthesis pathway, and Tribbles 3 (TRIB3), a pseudokinase with pleiotropic cellular functions.

CONCLUSIONS

A phenotypic screening platform using DCM iPSC-CMs was established for therapeutic target discovery. A combination of SMKIs ameliorated contractile and metabolic dysfunction in DCM iPSC-CMs mediated via the ATF4-dependent serine biosynthesis pathway. Together, these findings suggest that modulation of serine biosynthesis signalling may represent a novel genotype-agnostic therapeutic strategy for genetic DCM.

Vibrio cholerae Cholix Toxin-Induced HepG2 Cell Death is Enhanced by Tumor Necrosis Factor-Alpha Through ROS and Intracellular Signal-Regulated Kinases

Cholix toxin (Cholix) from Vibrio cholerae is a potent virulence factor exhibiting ADP-ribosyltransferase activity on eukaryotic elongation factor 2 (eEF2) of host cells, resulting in the inhibition of protein synthesis. Administration of Cholix or its homologue Pseudomonas exotoxin A (PEA) to mice causes lethal hepatocyte damage. In this study, we demonstrate cytotoxicity of Cholix on human hepatocytes in the presence of tumor necrosis factor α (TNF-α), which has been reported to play a fatal role in PEA administered to mice. Compared with incubating HepG2 cells with Cholix alone, co-treatment with TNF-α and Cholix (TNF-α/Cholix) significantly enhanced the activation of caspases, cytochrome c release from mitochondria into cytoplasm, and poly-ADP-ribose polymerase (PARP) cleavage, while incubation with TNF-α alone or co-treatment with TNF-α/catalytically inactive Cholix did not. In the early stage of cell death, Cholix increased phosphorylation of mitogen-activated protein kinases (e.g., p38, ERK, JNK) and Akt, which was not affected by TNF-α alone. MAPK inhibitors (SP600125, SB20852, and U0126) suppressed PARP cleavage induced by TNF-α/Cholix. Protein kinase inhibitor Go6976 suppressed JNK phosphorylation and PARP cleavage by TNF-α/Cholix. In contrast, PKC activator PMA in the absence of TNF-α promoted Cholix-induced PARP cleavage. Reactive oxygen species (ROS) inhibitor, N-acetyl cysteine (NAC), suppressed TNF-α/Cholix-induced JNK and ERK phosphorylation, resulting in inhibition of PARP cleavage. These data suggest that ROS and JNK pathways are important mediators of TNF-α/Cholix-induced HepG2 cell death.

Retrograde TrkAIII transport from ERGIC to ER: a re-localisation mechanism for oncogenic activity

In human SH-SY5Y neuroblastoma (NB) cells, nascent immature N-glycosylated 110kDa TrkA moves rapidly from the endoplasmic reticulum (ER) to the Golgi Network (GN), where it matures into the 140kDa receptor prior to being transported to the cell surface, creating GN and cell surface pools of inactive receptor maintained below the spontaneous activation threshold by a full compliment of inhibitory domains and endogenous PTPases. In contrast, the oncogenic alternative TrkAIII splice variant is not expressed at the cell surface but re-localises to intracellular membranes, within which it exhibits spontaneous ERGIC/COPI-associated activation and oncogenic Akt signalling. In this study, we characterise the mechanism responsible for TrkAIII re-localisation. Spontaneous TrkAIII activation, facilitated by D4 IG-like domain and N-glycosylation site omission, increases spontaneous activation potential by altering intracellular trafficking, inhibiting cell surface expression and eliminating an important inhibitory domain. TrkAIII, spontaneously activated within the permissive ERGIC/COPI compartment, rather than moving in an anterograde direction to the GN exhibits retrograde transport back to the ER, where it is inactivated. This sets-up self-perpetuating TrkAIII re-cycling between the ERGIC and ER, that ensures continual accumulation above the spontaneous activation threshold of the ERGIC/COPI compartment. This is reversed by TrkA tyrosine kinase inhibitors, which promote anterograde transport of inactivated TrkAIII to the GN, resulting in GN-associated TrkAIII maturation to a 120kDa species that is degraded at the proteasome.

NGF sensitizes TrkA SH-SY5Y neuroblastoma cells to TRAIL-induced apoptosis

We report a novel pro-apoptotic function for nerve growth factor (NGF) and its tropomyosin-related kinase A (TrkA) receptor in sensitizing TRAIL (TNF-related apoptotis-inducing ligand)-resistant SH-SY5Y neuroblastoma (NB) cells to TRAIL-induced apoptosis, resulting in the abrogation of anchorage-independent tumourigenic growth in vitro. We show that the TRAIL-resistant SH-SY5Y phenotype is cFLIP (cellular FLICE-like inhibitory protein) dependent and not due to low-level functional TRAIL receptor or caspase expression or an inhibitory equilibrium between functional and decoy TRAIL receptors or B-cell lymphoma 2 (Bcl-2) and BH3-only (Bcl-2 homology domain 3-only) family proteins. NGF sensitization of SH-SY5Y cells to TRAIL-induced apoptosis was dependent upon TrkA expression, activation and subsequent sequestration of cFLIP. This reduces cFLIP recruitment to TRAIL-activated death receptors and increases the recruitment of caspase-8, leading to TRAIL-induced, caspase-dependent, type II apoptosis via the intrinsic mitochondrial pathway. This effect was temporary, inhibited within 6 h by nuclear factor-κ binding (NF-κB)-mediated increase in myeloid cell leukaemia-1 (Mcl-1) expression, abrogated by transient cFLIP or B-cell lymphoma-extra large (Bcl-xL) overexpression and optimized by NF-κB and Mcl-1 inhibitors. This novel mechanism adds an important pro-apoptotic immunological dimension to NGF/TrkA interaction that may not only help to explain the association between TrkA expression, better prognosis and spontaneous remission in NB, but also provides a novel potential pro-apoptotic therapeutic use for NGF, TRAIL and inhibitors of NF-κB and/or Mcl-1 in favourable and unfavourable NBs that express TrkA and exhibit cFLIP-mediated TRAIL resistance.

The TrkAIII oncoprotein inhibits mitochondrial free radical ROS-induced death of SH-SY5Y neuroblastoma cells by augmenting SOD2 expression and activity at the mitochondria, within the context of a tumour stem cell-like phenotype

The developmental and stress-regulated alternative TrkAIII splice variant of the NGF receptor TrkA is expressed by advanced stage human neuroblastomas (NBs), correlates with worse outcome in high TrkA expressing unfavourable tumours and exhibits oncogenic activity in NB models. In the present study, we report that constitutive TrkAIII expression in human SH-SY5Y NB cells inhibits Rotenone, Paraquat and LY83583-induced mitochondrial free radical reactive oxygen species (ROS)-mediated death by stimulating SOD2 expression, increasing mitochondrial SOD2 activity and attenuating mitochondrial free radical ROS production, in association with increased mitochondrial capacity to produce H2O2, within the context of a more tumour stem cell-like phenotype. This effect can be reversed by the specific TrkA tyrosine kinase inhibitor GW441756, by the multi-kinase TrkA inhibitors K252a, CEP-701 and Gö6976, which inhibit SOD2 expression, and by siRNA knockdown of SOD2 expression, which restores the sensitivity of TrkAIII expressing SH-SY5Y cells to Rotenone, Paraquat and LY83583-induced mitochondrial free radical ROS production and ROS-mediated death. The data implicate the novel TrkAIII/SOD2 axis in promoting NB resistance to mitochondrial free radical-mediated death and staminality, and suggest that the combined use of TrkAIII and/or SOD2 inhibitors together with agents that induce mitochondrial free radical ROS-mediated death could provide a therapeutic advantage that may also target the stem cell niche in high TrkA expressing unfavourable NB.

Enhanced survival of wild-type and Lurcher Purkinje cells in vitro following inhibition of conventional PKCs or stress-activated MAP kinase pathways

Recent studies using both dissociated and organotypic cell cultures have shown that heterozygous Lurcher (Lc/+) Purkinje cells (PCs) grown in vitro share many of the same survival and morphological characteristics as Lc/+ PCs in vivo. We have used this established tissue culture system as a valuable model for studying cell death mechanisms in a relatively simple system where neurodegeneration is induced by a constitutive cation leak mediated by the Lurcher mutation in the δ2 glutamate receptor (GluRδ2). In this study, Ca(++) imaging and immunocytochemistry studies indicate that intracellular levels of Ca(++) are chronically increased in Lc/+ PCs and the concentration and/or distribution of the conventional PKCγ isoform is altered in degenerating Lc/+ PCs. To begin to characterize the molecular mechanisms that regulate Lc/+ PC death, the contributions of conventional PKC pathways and of two MAP kinase family members, JNK and p38, were examined in slice cultures from wild-type and Lc/+ mutant mouse cerebellum. Cerebellar slice cultures from P0 pups were treated with either a conventional PKC inhibitor, a JNK inhibitor, or a p38 inhibitor either from 0 to 14 or 7 to 14 DIV. Treatment with either of the three inhibitors from 0 DIV significantly increased wild type and Lc/+ PC survival through 14 DIV, but only Lc/+ PC survival was significantly increased following treatments from 7 to 14 DIV. The results suggest that multiple PC death pathways are induced by the physical trauma of making organotypic slice cultures, naturally-occurring postnatal cell death, and the GluRδ2 (Lc) mutation.

The indolocarbazole, Gö6976, inhibits guanylyl cyclase-A and -B

BACKGROUND AND PURPOSE

Atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) decrease vascular volume and pressure by activating guanylyl cyclase-A (GC-A). C-type natriuretic peptide (CNP) activation of guanylyl cyclase-B (GC-B) stimulates long bone growth. This study investigated the effects of the indolocarbazole, Gö6976, on the guanylyl cyclase activity of GC-A and GC-B as a first step towards developing small molecule regulators of these enzymes.

EXPERIMENTAL APPROACH

Whole cell cGMP concentrations or ³²P-cGMP accumulation in membrane preparations measured the effects of indolocarbazoles on the enzymatic activity GC-A and GC-B from transfected 293T or endogenously expressing 3T3-L1 cells.

KEY RESULTS

Gö6976 blocked cellular CNP-dependent cGMP elevations in 293T-GC-B cells. The t(½) for Gö6976 inhibition was 7 s and IC₅₀ was 380 nM. Gö6976 increased the EC₅₀ for CNP 4.5-fold, but increasing the CNP concentration did not overcome the inhibition. Half of the inhibition was lost 1 h after removal of Gö6976 from the medium. Cellular exposure to Gö6976 reduced basal and natriuretic peptide-dependent, but not detergent-dependent, GC-A and GC-B activity. Inhibition was also observed when Gö6976 was added directly to the cyclase assay. A constitutively phosphorylated form of GC-B was similarly inhibited.

CONCLUSIONS AND IMPLICATIONS

These data demonstrate that Gö6976 potently, rapidly and reversibly inhibited GC-A and GC-B via a process that did not require intact cells, known phosphorylation sites or inactivation of all catalytic sites. This is the first report of an intracellular inhibitor of a transmembrane guanylyl cyclase and the first report of a non-kinase target for Gö6976.

Neurotrophin-mediated dendrite-to-nucleus signaling revealed by microfluidic compartmentalization of dendrites

Signaling from dendritic synapses to the nucleus regulates important aspects of neuronal function, including synaptic plasticity. The neurotrophin brain-derived neurotrophic factor (BDNF) can induce long-lasting strengthening of synapses in vivo and this effect is dependent on transcription. However, the mechanism of signaling to the nucleus is not well understood. Here we describe a microfluidic culture device to investigate dendrite-to-nucleus signaling. Using these microfluidic devices, we demonstrate that BDNF can act directly on dendrites to elicit an anterograde signal that induces transcription of the immediate early genes, Arc and c-Fos. Induction of Arc is dependent on dendrite- and cell body-derived calcium, whereas induction of c-Fos is calcium-independent. In contrast to retrograde neurotrophin-mediated axon-to-nucleus signaling, which is MEK5-dependent, BDNF-mediated anterograde dendrite-to-nucleus signaling is dependent on MEK1/2. Intriguingly, the activity of TrkB, the BDNF receptor, is required in the cell body for the induction of Arc and c-Fos mediated by dendritically applied BDNF. These results are consistent with the involvement of a signaling endosome-like pathway that conveys BDNF signals from the dendrite to the nucleus.

A novel protein kinase D inhibitor attenuates early events of experimental pancreatitis in isolated rat acini

Novel protein kinase C isoforms (PKC δ and ε) mediate early events in acute pancreatitis. Protein kinase D (PKD/PKD1) is a convergent point of PKC δ and ε in the signaling pathways triggered through CCK or cholinergic receptors and has been shown to activate the transcription factor NF-κB in acute pancreatitis. For the present study we hypothesized that a newly developed PKD/PKD1 inhibitor, CRT0066101, would prevent the initial events leading to pancreatitis. We pretreated isolated rat pancreatic acinar cells with CRT0066101 and a commercially available inhibitor Gö6976 (10 μM). This was followed by stimulation for 60 min with high concentrations of cholecystokinin (CCK, 0.1 μM), carbachol (CCh, 1 mM), or bombesin (10 μM) to induce initial events of pancreatitis. PKD/PKD1 phosphorylation and activity were measured as well as zymogen activation, amylase secretion, cell injury and NF-κB activation. CRT0066101 dose dependently inhibited secretagogue-induced PKD/PKD1 activation and autophosphorylation at Ser-916 with an IC(50) ∼3.75-5 μM but had no effect on PKC-dependent phosphorylation of the PKD/PKD1 activation loop (Ser-744/748). Furthermore, CRT0066101 reduced secretagogue-induced zymogen activation and amylase secretion. Gö6976 reduced zymogen activation but not amylase secretion. Neither inhibitor affected basal zymogen activation or secretion. CRT0066101 did not affect secretagogue-induced cell injury or changes in cell morphology, but it reduced NF-κB activation by 75% of maximal for CCK- and CCh-stimulated acinar cells. In conclusion, CRT0066101 is a potent and specific PKD family inhibitor. Furthermore, PKD/PKD1 is a potential mediator of zymogen activation, amylase secretion, and NF-κB activation induced by a range of secretagogues in pancreatic acinar cells.

PKC and cAMP positively modulate alkaline-induced exocytosis in the human mast cell line HMC-1

We study in HMC-1 the activation process, measured as histamine release. We know that ammonium chloride (NH(4)Cl) and ionomycin release histamine, and the modulatory role of drugs targeting protein kinase C (PKC), adenosine 3',5'-cyclic monophosphate (cAMP), tyrosine kinase (TyrK) and phosphatidylinositol 3-kinase (PI3K) on this effect. We used Gö6976 (100 nM) and low concentration of GF 109203X (GF) (50 nM) to inhibit Ca(2+)-dependent PKC isozymes. For Ca(2+)-independent isozymes, we used 500 nM GF and 10 microM rottlerin (specifically inhibits PKCdelta). Phorbol 12-myristate 13-acetate (PMA) (100 ng/ml) was used to stimulate PKC, and genistein (10 microM) and lavendustin A (1 microM) as unspecific TyrK inhibitors. STI571 10 microM was used to specifically inhibit the activity of Kit, the receptor for stem cell factor, and 10 nM wortmannin as a PI3K inhibitor. Activation of PKC with PMA enhances histamine release in response to NH(4)Cl and ionomycin. PMA increases NH(4)Cl-induced alkalinization and ionomycin-induced Ca(2+) entry. Inhibition of PKCdelta strongly inhibits Ca(2+) entry elicited by ionomycin, but failed to modify histamine release. The effect of cAMP-active drugs was explored with the adenylate cyclase activator forskolin (30 microM), the inhibitor SQ22,536 (1 microM), the cAMP analog dibutyryl cAMP (200 microM), and the PKA blocker H89 (1 microM). Forskolin and dibutyryl cAMP do increase NH(4)Cl-induced alkalinization, and potentiate histamine release elicited by this compound. Our data indicates that alkaline-induced exocytosis is modulated by PKC and cAMP, suggesting that pH could be a modulatory signal itself.

A nerve growth factor-induced retrograde survival signal mediated by mechanisms downstream of TrkA

Considerable evidence suggests that mammalian neurons are always poised to destroy themselves by apoptosis but are blocked by retrograde survival signals triggered in their axon terminals by neurotrophic factors secreted by the target cells they innervate. Studies with nerve growth factor (NGF) and its receptor, TrkA, form the basis of the prevalent theory of retrograde signaling. According to this theory, retrograde survival signals travel to the cell bodies in the form of endosomes produced at the axon terminals with internalized NGF in their lumens bound to phosphorylated TrkA in their membranes. The inhibition of TrkA phosphorylation in the cell bodies of sympathetic neurons in compartmented cultures by K252a blocked retrograde NGF signaling in some studies in accord with this theory, but other studies do not show a block. We report that local block of TrkA phosphorylation in the cell bodies and proximal axons with another kinase inhibitor, Gö6976 (25nM), did not block the survival signal from NGF at distal axons, while Gö6976 at the distal axons completely blocked the retrograde survival signal. These results suggest that downstream signals activated by phosphorylated TrkA in the distal axons carry the retrograde survival signals to the cell bodies, possibly via a downstream type of signaling endosome not necessarily transporting NGF or phosphorylated TrkA. Unlike Gö6976, K252a exerted a survival effect on its own when applied to cell bodies/proximal axons or distal axons of completely NGF-deprived neurons. The latter effect suggests that downstream retrograde survival signals can arise from alterations in one or more kinase activities in the distal axons without activation of TrkA by NGF.

Neurotrophin and GDNF family ligands promote survival and alter excitotoxic vulnerability of neurons derived from murine embryonic stem cells

Embryonic stem (ES) cells are genetically manipulable pluripotential cells that can be differentiated in vitro into neurons, oligodendrocytes, and astrocytes. Given their potential utility as a source of replacement cells for the injured nervous system and the likelihood that transplantation interventions might include co-application of growth factors, we examined the effects of neurotrophin and GDNF family ligands on the survival and excitotoxic vulnerability of ES cell-derived neurons (ES neurons) grown in vitro. ES cells were differentiated down a neural lineage in vitro using the 4-/4+ protocol (Bain et al., Dev Biol 168:342-57, 1995). RT-PCR demonstrated expression of receptors for neurotrophins and GDNF family ligands in ES neural lineage cells. Neuronal expression of GFRalpha1, GFRalpha2, and ret was confirmed by immunocytochemistry. Exposure to 30-100 ng/ml GDNF or neurturin (NRTN) resulted in activation of ret. Addition of NT-3 and GDNF did not increase cell division but did increase the number of neurons in the cultures 7 days after plating. Pretreatment with NT-3 enhanced the vulnerability of ES neurons to NMDA-induced death (100 microM NMDA for 10 min) and enhanced the NMDA-induced increase in neuronal [Ca2+]i, but did not alter expression of NMDA receptor subunits NR2A or NR2B. In contrast, pretreatment with GDNF reduced the vulnerability of ES neurons to NMDA-induced death while modestly enhancing the NMDA-induced increase in neuronal [Ca2+]i. These findings demonstrate that the response of ES-derived neurons to neurotrophins and GDNF family ligands is largely similar to that of other cultured central neurons.

The protein kinase C inhibitor Go6976 [12-(2-cyanoethyl)-6,7,12,13-tetrahydro-13-methyl-5-oxo-5H-indolo(2,3-a)pyrrolo(3,4-c)-carbazole] potentiates agonist-induced mitogen-activated protein kinase activation through tyrosine phosphorylation of the epidermal growth factor receptor

Protein kinase C (PKC) isoforms are important transducers of signals from G protein-coupled receptors (GPCRs) to diverse cellular targets, including extracellular signal-regulated kinases 1 and 2 (ERK1/2). Clone 9 rat hepatocytes (C9 cells) express receptors for angiotensin II (Ang II) type 1, lysophosphatidic acid (LPA), and epidermal growth factor (EGF), and their stimulation causes transient ERK1/2 phosphorylation through transactivation of the epidermal growth factor receptor (EGF-R). Inhibition of PKC by Go6983 [2-[1-(3-dimethylaminopropyl)-5-methoxyindol-3-yl]-3-(1H-indol-3-yl)maleimide], or PKC depletion by prolonged phorbol 12-myristate 13-acetate (PMA) treatment, attenuated ERK1/2 activation by Ang II and PMA, but not by LPA and EGF. In contrast, another PKC inhibitor, Go6976 [12-(2-cyanoethyl)-6,7,12,13-tetrahydro-13-methyl-5-oxo-5H-indolo(2,3-a)pyrrolo(3,4-c)-carbazole], enhanced basal and agonist-stimulated phosphorylation of ERK1/2, which was not caused by alteration in receptor binding and internalization, stimulation of inositol phosphate production, or activation of Pyk2 and Src tyrosine kinases. However, Go6976 enhanced agonist-induced tyrosine phosphorylation of the EGF receptor, possibly through inhibition of protein tyrosine phosphatase (PTP), because the PTP inhibitor sodium orthovanadate mimicked the effects of Go6976. Selective blockade of EGF-R kinase by AG1478 [4-(3-chloroanilino)6,7-dimethoxyquinazoline] abolished the ERK1/2 activation induced by Go6976. Similar experiments were conducted in human embryonic kidney 293 cells, which express receptors for LPA and EGF but exhibit no significant cross-communication between them. Although Go6976 caused a significant increase in EGF-induced tyrosine phosphorylation of the EGF-R and subsequent ERK1/2 activation, it had no such effects on LPA-induced responses. In Chinese hamster ovary cells, which express receptors for LPA but not for EGF, Go6976 also had no significant effect on LPA-induced ERK1/2 activation. These data indicate that Go6976 potentiates agonist-induced ERK1/2 activation through stimulation of tyrosine phosphorylation of the EGF-R.

Arsenite stimulated glucose transport in 3T3-L1 adipocytes involves both Glut4 translocation and p38 MAPK activity

The protein-modifying agent arsenite stimulates glucose uptake in 3T3-L1 adipocytes. In the current study we have analysed the signalling pathways that contribute to this response. By subcellular fractionation we observed that arsenite, like insulin, induces translocation of the GLUT1 and GLUT4 glucose transporters from the low-density membrane fraction to the plasma membrane. Arsenite did not activate early steps of the insulin receptor (IR)-signalling pathway and the response was insensitive to inhibition of phosphatidylinositol-3'-kinase (PI-3') kinase by wortmannin. These findings indicate that the 'classical' IR-IR substrate-PI-3' kinase pathway, that is essential for insulin-induced GLUT4 translocation, is not activated by arsenite. However, arsenite-treatment did induce tyrosine-phosphorylation of c-Cbl. Furthermore, treatment of the cells with the tyrosine kinase inhibitor, tyrphostin A25, abolished arsenite-induced glucose uptake, suggesting that the induction of a tyrosine kinase by arsenite is essential for glucose uptake. Both arsenite and insulin-induced glucose uptake were inhibited partially by the p38 MAP kinase inhibitor, SB203580. This compound had no effect on the magnitude of translocation of glucose transporters indicating that the level of glucose transport is determined by additional factors. Arsenite- and insulin-induced glucose uptake responded in a remarkably similar dose-dependent fashion to a range of pharmacological- and peptide-inhibitors for atypical PKC-lambda, a downstream target of PI-3' kinase signalling in insulin-induced glucose uptake. These data show that in 3T3-L1 adipocytes both arsenite- and insulin-induced signalling pathways project towards a similar cellular response, namely GLUT1 and GLUT4 translocation and glucose uptake. This response to arsenite is not functionally linked to early steps of the IR-IRS-PI-3' kinase pathway, but does coincide with c-Cbl phosphorylation, basal levels of PKC-lambda activity and p38 MAPK activation.

Gö6976 inhibits LPS-induced microglial TNFalpha release by suppressing p38 MAP kinase activation

Microglial responses to endotoxin, including the synthesis of inflammatory factors, contribute to gliosis and neuron degeneration in cultured brain tissue. We have previously shown that Gö6976, a protein kinase C (PKC) inhibitor, suppressed the lipopolysaccharide (LPS)-induced production of inflammatory factors in microglia and afforded marked protection of neurons from glia-mediated cytotoxicity. The purpose of this study was to identify the signal transduction pathway underlying the neuroprotective effect of Gö6976. Gö6976 suppressed the LPS-induced release of tumor necrosis factor alpha (TNFalpha) in the microglial cell line, BV2. We show in this study the inhibitory effect of Gö6976 on TNFalpha release occurring through suppression of p38 mitogen-activated protein kinase (MAPK) phosphorylation and not through a PKC mechanism. While Gö6976 did not inhibit the activity of p38 MAPK directly, it did suppress its activation by phosphorylation, indicating the target of action of Gö6976 is a signaling event upstream of p38 MAPK. Although Gö6976 is considered a selective inhibitor of certain PKC isozymes, suppression of TNFalpha production was not mediated through inhibition of PKC activity. Gö6976 appears to play a novel role in neuroprotection by suppressing the release of pro-inflammatory factors by inhibiting the activation of p38 MAPK in microglia, rather than a PKC isoform.

Putative conventional protein kinase C inhibitor Gödecke 6976 [12-(2-cyanoethyl)-6,7,12,13-tetrahydro-13-methyl-5-oxo-5H-indolo(2,3-a)pyrrolo(3,4-c)-carbazole] stimulates transglutaminase activity in primary mouse epidermal keratinocytes

Much data in the literature suggest a role for protein kinase C (PKC) in regulating keratinocyte proliferation and differentiation. Nevertheless, the exact role of this family of isoenzymes is unclear, since PKC agonists (e.g., phorbol esters) are known to stimulate expression of both proliferative and differentiative markers in keratinocytes. Similarly, PKC inhibitors have been demonstrated both to inhibit [2-[1-3(aminopropyl)indol-3-yl]-3(1-methyl-1H-indol-3-yl)maleimide, acetate (Ro 31-7549) and 3-[1-[3-(amidinothio)propyl-1H-indol-3-(1-methyl-1H-indol-3yl) maleimide (Ro 31-8220)] and to induce (staurosporine) keratinocyte differentiation. In this study, we examined the role of the PKC inhibitor, Gödecke 6976 (Gö6976) [12-(2-cyanoethyl)-6,7,12,13-tetrahydro-13-methyl-5-oxo-5H-indolo(2,3-a)pyrrolo (3,4-c)-carbazole], on keratinocyte proliferation, as measured by DNA synthesis, and differentiation, as monitored by transglutaminase activity. This compound is reported to be selective for the conventional PKC isoforms, of which keratinocytes express only PKCalpha, and for protein kinase D (PKD; also known as PKCmu). We report that Gö6976 stimulated transglutaminase activity. Consistent with this effect, Gö6976 also potently inhibited [(3)H]thymidine incorporation (a half-maximal inhibitory concentration of approximately 0.1 microM). In addition, Gö6976 (1 microM) was able to enhance the stimulation of transglutaminase activity by 1,25-dihydroxyvitamin D(3) but had no effect on D(3)-induced expression of keratin-1. Conversely, Gö6983 [2-[1-(3-dimethylaminopropy)-5-methoxyindol-3-yl]-3-(1H-indol-3-yl)maleimide], a similar compound that also selectively inhibits conventional PKCalpha, but not PKD, had little or no effect on DNA synthesis or transglutaminase activity (up to 1 microM). The effect of Gö6976 was not due to cytotoxicity as its effect on thymidine incorporation was largely reversible, and its stimulation of transglutaminase activity could be inhibited by another general PKC inhibitor, bisindolylmaleimide I. Therefore, our results suggest a proproliferative, antidifferentiative role for PKD in epidermal maturation.

Inhibition of protein kinase C prevents Purkinje cell death but does not affect axonal regeneration

In organotypic cultures, mouse Purkinje cells regenerate their axons from embryonic day 18 (E18) to postnatal day 0 (P0), die of apoptosis between P1 and P7, and survive but do not regenerate at P10. This particular behavior of Purkinje cells did not allow us to find out when the developmental switch between regeneration and lack of regeneration occurs. This work was undertaken to suppress Purkinje cell apoptosis and to investigate whether the same molecules that prevent apoptosis could also influence axonal growth, regeneration, or both. We show that brain-derived neurotrophic factor, neurotrophin 3, and insulin-like growth factor I have marginal effects on P3 Purkinje cell death. The use of Gö6976 [a protein kinase C (PKC) inhibitor] or a transgenic mouse line, in which a pseudosubstrate PKC inhibitor has been specifically targeted to Purkinje cells, prevents the massive Purkinje cell death in P3 organotypic cultures. In addition, Gö6976 promotes axotomized Purkinje cell survival up to P7. Thus, the inhibition of PKC activity is able to prevent Purkinje cell apoptosis in organotypic cultures. Furthermore, Gö6976 increases the outgrowth of dendrites and axon collateralization, as shown after gene gun enhanced green fluorescent protein transfection. In contrast, PKC inhibitors do not influence the axonal regenerative capability of Purkinje cell during development; the latter decreases between E18 and P7 after the same time course in control and Gö6976-treated slices. Thus, because inhibition of PKC prevents Purkinje cell death but does not affect axonal regeneration, these two events (cell death and axonal regeneration) seem to be differentially regulated.

Protein kinase C inhibitors as novel anticancer drugs

The role of PKC isoforms in signal transduction pathways involved in regulation of the cell cycle, apoptosis, angiogenesis, differentiation, invasiveness, senescence and drug efflux are reviewed, along with the clinical results on the current crop of PKC inhibitors, including midostaurin (PKC-412, CGP 41251, N -benzoylstaurosporine), UCN-01 (7-hydroxystaurosporine), bryostatin 1, perifosine, ilmofosine, Ro 31-8220, Ro 32-0432, GO 6976, ISIS-3521 (CGP 64128A) and the macrocyclic bis (indolyl) maleimides (LY-333531, LY-379196, LY-317615). An appreciation of the complex, often contradictory roles of PKC isoforms in signal transduction pathways involved in cancer is important for interpreting the clinical results observed with PKC inhibitors of varying selectivity. An antisense oligonucleotide, ISIS-3521 and two orally available small molecule inhibitors, LY 333531 and midostaurin, have now advanced to latter stage development for cancer and/or other indications. These compounds have varying levels of selectivity for the PKC isoforms and for the kinase and initial safety and early clinical efficacy have been encouraging. At this stage, the potential of PKC inhibition for the treatment of cancer has not been fully realised. The concurrent inhibition of multiple PKC isoforms may yet provide an improved clinical outcome in treating cancers in view of the complex interrelated roles of the PKC isoforms.

Testosterone- and phorbol ester-stimulated proliferation in human cultured prostatic stromal cells

Prostatic stromal proliferation may be commonly associated with the development of benign prostatic hyperplasia. In this study, we investigate the role of testosterone and protein kinase C in stimulating cultured stromal cell proliferation. Testosterone increased the uptake of [(3)H]-thymidine into the human cultured prostatic stromal cells, this was reduced by the protein kinase C inhibitors, bisindolylymaleimide (10 nM) and myristoylated protein kinase C inhibitor (mPKCi, 20 microM), but not by Gö 6983 (1 microM) or Gö 6976 (1 microM). Cells responded to the addition of the PKC activators phorbol 12,13 dibutyrate (PDB), phorbol 12,13 diacetate (PDA), 12-deoxyphorbol 13-acetate (DPA) and 12-deoxyphorbol 13-tetradecanoate (DPT) with proliferation (order of potency DPT> or =PDB>>PDA=DPA). The DPT-stimulated proliferative response was inhibited after cells were electroporated with PKCalpha antisense, but not mismatch oligonucleotides (8 microM). These results indicate that PKCalpha is involved in the proliferative response of human cultured prostatic stromal cells.

Neurotrophins require distinct extracellular signals to promote the survival of CNS neurons in vitro

Althoughthe neurotrophins BDNF and NT-3 have been recognized as potent survival factors for distinct neuronal populations in the peripheral nervous system, they seem to have only minor effects on the survival of CNS neurons. In the present study, we provide evidence that BDNF and NT-3 require distinct additional extracellular signals in order to effectively promote the survival of several established populations of target neurons in the CNS. In dissociated cell cultures of the embryonic rat mesencephalon, BDNF promoted dopaminergic cell survival only after a delay of several days. Even after prolonged cultivation, survival promoting effects were completely absent with NT-3. Irrespective of the cultivation time, survival promoting effects of both BDNF and NT-3 on dopaminergic neurons were induced or potentiated upon simultaneous depolarization of cultured mesencephalic cells with NMDA or upon activation of cAMP/PKA-dependent signaling pathways with dibutyryl cAMP. Dibutyryl cAMP (dbcAMP), but not NMDA, also potentiated or induced the survival promoting effects of BDNF and NT-3 on cultured cerebellar granule cells. None of these substances, either alone or in combination, affected the survival of cultured cortical neurons. However, cortical cell survival increased upon depolarization with elevated potassium; an effect known to involve the induction of an autocrine BDNF loop. In both cerebellar and mesencephalic neurons, but not in cortical neurons, dbcAMP also potentiated neurotrophin-induced c-fos response, indicating intimate cross-coupling of signaling pathways activated by these different factors. Together these findings suggest that in the CNS, neurotrophins preferentially promote the survival of functionally active neurons. Our findings further reveal that the neuronal response to neurotrophins is modulated in a brain region-specific manner.

TrkB activation by brain-derived neurotrophic factor inhibits the G protein-gated inward rectifier Kir3 by tyrosine phosphorylation of the channel

G protein-activated inwardly rectifying potassium channels (Kir3) are widely expressed throughout the brain, and regulation of their activity modifies neuronal excitability and synaptic transmission. In this study, we show that the neurotrophin brain-derived neurotrophic factor (BDNF), through activation of TrkB receptors, strongly inhibited the basal activity of Kir3. This inhibition was subunit dependent as functional homomeric channels of either Kir3.1 or Kir3.4 were significantly inhibited, whereas homomeric channels composed of Kir3.2 were insensitive. The general tyrosine kinase inhibitors genistein, Gö 6976, and K252a but not the serine/threonine kinase inhibitor staurosporine blocked the BDNF-induced inhibition of the channel. BDNF was also found to directly stimulate channel phosphorylation because Kir3.1 immunoprecipitated from BDNF-stimulated cells showed enhanced labeling by anti-phosphotyrosine-specific antibodies. The BDNF effect required specific tyrosine residues in the amino terminus of Kir3.1 and Kir3.4 channels. Mutations of either Tyr-12, Tyr-67, or both in Kir3.1 or mutation of either Tyr-32, Tyr-53, or both of Kir3. 4 channels to phenylalanine significantly blocked the BDNF-induced inhibition. The insensitive Kir3.2 was made sensitive to BDNF by adding a tyrosine (D41Y) and a lysine (P32K) upstream to generate a phosphorylation site motif analogous to that present in Kir3.4. These results suggest that neurotrophin activation of TrkB receptors may physiologically control neuronal excitability by direct tyrosine phosphorylation of the Kir3.1 and Kir3.4 subunits of G protein-gated inwardly rectifying potassium channels.

Post-transcriptional inhibition of lipopolysaccharide-induced expression of inducible nitric oxide synthase by Gö6976 in murine microglia

Glia in the brain respond to various toxins with an increased expression of inducible nitric oxide synthase (iNOS) and an increased production of nitric oxide (NO). Here, we report that lipopolysaccharide (LPS)-induced expression of iNOS was down-regulated post-transcriptionally through the destabilization of iNOS mRNA by the indolocarbazole compound, Gö6976, in murine microglia. This Gö6976 effect is specific for iNOS since tumor necrosis factor alpha was unaffected by the compound. Interestingly, the post-transcriptional effects ascribed to Gö6976 were not observed with other inhibitors of protein kinase A, C (PKC), G, or protein tyrosine kinases. Instead, these kinases appear to affect the iNOS/NO system at the transcriptional level. In the past, Gö6976 has been reported to be a rather specific inhibitor of PKC in vitro. Results from our experiments, through prolonged treatment with phorbol esters and with the various PKC inhibitors including phorbol ester-insensitive PKC isotype inhibitor, suggest that the Gö6976-mediated post-transcriptional regulation of iNOS gene expression and NO production in microglia is not mediated through its reputed effects on PKC activity. Since the effects of various neurotoxins and certain neurodegenerative diseases may be manifested through alterations in the iNOS/NO system, post-transcriptional control of this system may represent a novel strategy for therapeutic intervention.

The indolocarbazole Gö6976 protects neurons from lipopolysaccharide/interferon-gamma-induced cytotoxicity in murine neuron/glia co-cultures

The expression of inducible nitric oxide synthase (iNOS) and the production of nitric oxide (NO) after exposure to endotoxins has been implicated in immune-mediated neurotoxicity. The indolocarbazole compound Gö6976, which has been described as a selective protein kinase C (PKC) inhibitor in vitro, rescued neurons from lipopolysaccharide/interferon-gamma (LPS/IFNgamma)- or interleukin-1alpha/tumor necrosis alpha/IFNgamma (IL-1alpha/TNFalpha/IFNgamma)-induced cytotoxicity in murine primary neuron-glia co-cultures. Other compounds known to inhibit PKC, Ro31-8220, GF109203X, Gö7874, H7, staurosporine and H89, failed to rescue neurons from the LPS/IFNgamma-induced cytotoxicity. These results suggest that the neuroprotection by Gö6976 from the LPS/IFNgamma-induced neuronal cell death is not mediated through its reputed effects on PKC activity. The neuroprotection paralleled the inhibition of iNOS gene expression and NO production. However, further analyses correlating NO production with the extent of neurotoxicity suggested that additional mechanism(s) besides the inhibition of the iNOS/NO system may be responsible for the neuroprotective effects of Gö6976. An understanding of the mechanism underlying the neuroprotective effect of Gö6976 may provide key insights into potential interventions for immune-mediated neurodegenerative diseases.

Prevention of neuronal apoptosis by phorbol ester-induced activation of protein kinase C: blockade of p38 mitogen-activated protein kinase

Consistent with previous studies on cell lines and non-neuronal cells, specific inhibitors of protein kinase C induced mouse primary cultured neocortical neurons to undergo apoptosis. To examine the complementary hypothesis that activating protein kinase C would attenuate neuronal apoptosis, the cultures were exposed for 1 h to phorbol-12-myristate-13-acetate, which activated protein kinase C as evidenced by downstream enhancement of the mitogen-activated protein kinase pathway. Exposure to phorbol-12-myristate-13-acetate, or another active phorbol ester, phorbol-12,13-didecanoate, but not to the inactive ester, 4alpha-phorbol-12,13-didecanoate, markedly attenuated neuronal apoptosis induced by serum deprivation. Phorbol-12-myristate-13-acetate also attenuated neuronal apoptosis induced by exposure to beta-amyloid peptide 1-42, or oxygen-glucose deprivation in the presence of glutamate receptor antagonists. The neuroprotective effects of phorbol-12-myristate-13-acetate were blocked by brief (non-toxic) concurrent exposure to the specific protein kinase C inhibitors, but not by a specific mitogen-activated protein kinase 1 inhibitor. Phorbol-12-myristate-13-acetate blocked the induction of p38 mitogen-activated protein kinase activity and specific inhibition of this kinase by SB 203580 attenuated serum deprivation-induced apoptosis. c-Jun N-terminal kinase 1 activity was high at rest and not modified by phorbol-12-myristate-13-acetate treatment. These data strengthen the idea that protein kinase C is a key modulator of several forms of central neuronal apoptosis, in part acting through inhibition of p38 mitogen-activated protein kinase regulated pathways.