Protein kinase C iota protects neural cells against apoptosis induced by amyloid beta-peptide

Investigating pathogenic SNP of PKCι in HCV-induced hepatocellular carcinoma

Hepatocellular carcinoma is a leading cause of cancer-related deaths due to its complexity in diagnosis, chemo-resistance, and aggressive nature. Identifying pathogenic single nucleotide polymorphism (SNP) in protein kinase C iota (PKCι) can be a potential biomarker in the prognosis and treatment of HCC. This study investigated the association between a SNP in PRKCI and the Pakistani population's hepatocellular carcinoma (HCC) risk. Obtained samples were first evaluated for ALT measurements and viral load quantification through reverse transcriptase-PCR. The PKCι nsSNP rs1199520604 was evaluated computationally by multiple consensus bioinformatics tools for predicting its potential deleterious effects. Its association with hepatitis C virus- (HCV) mediated HCC was then investigated through ARMS-PCR (Amplification Refractory Mutation System Polymerase Chain Reaction). SNP analysis of rs1199520604 was performed in 100 cases and 100 controls. Variant rs1199520604's homozygous T genotype is a risk factor allele for the HCV-induced HCC (odds ratio: 4.13, relative risk: 2.01, P-value < 0.0001). The heterozygous genotype is determined to protect HCV patients from HCC development (P < 0.001). The study highlighted the disease association of variant rs1199520604 with HCV-induced HCC in the Pakistani populations. This variant, after further validation through high-throughput investigation on a larger cohort, has the potential to be translated at the clinical level.

A phenotypic screen of Marfan syndrome iPSC-derived vascular smooth muscle cells uncovers GSK3β as a new target

Marfan syndrome (MFS) is a rare connective tissue disorder caused by mutations in FBN1. Patients with MFS notably suffer from aortic aneurysm and dissection. Despite considerable effort, animal models have proven to be poorly predictive for therapeutic intervention in human aortic disease. Patient-derived induced pluripotent stem cells can be differentiated into vascular smooth muscle cells (VSMCs) and recapitulate major features of MFS. We have screened 1,022 small molecules in our in vitro model, exploiting the highly proteolytic nature of MFS VSMCs, and identified 36 effective compounds. Further analysis identified GSK3β as a recurring target in the compound screen. GSK3β inhibition/knockdown did not ameliorate the proliferation defect in MFS-VSMCs but improved MFS-VSMC proteolysis and apoptosis and partially rescued fibrillin-1 deposition. To conclude, we have identified GSK3β as a novel target for MFS, forming the foundation for future work in MFS and other aortic diseases.

Unveiling OASIS family as a key player in hypoxia-ischemia cases induced by cocaine using generative adversarial networks

Repeated cocaine use poses many serious health risks to users. One of the risks is hypoxia and ischemia (HI). To restore the biological system against HI, complex biological mechanisms operate at the gene level. Despite the complexity of biological mechanisms, there are common denominator genes that play pivotal roles in various defense systems. Among these genes, the cAMP response element-binding (Creb) protein contributes not only to various aspects of drug-seeking behavior and drug reward, but also to protective mechanisms. However, it is still unclear which Creb members are key players in the protection of cocaine-induced HI conditions. Herein, using one of the state-of-the-art deep learning methods, the generative adversarial network, we revealed that the OASIS family, one of the Creb family, is a key player in various defense mechanisms such as angiogenesis and unfolded protein response against the HI state by unveiling hidden mRNA expression profiles. Furthermore, we identified mysterious kinases in the OASIS family and are able to explain why the prefrontal cortex and hippocampus are vulnerable to HI at the genetic level.

A brain proteomic signature of incipient Alzheimer's disease in young APOE ε4 carriers identifies novel drug targets

Aptamer-based proteomics revealed differentially abundant proteins in Alzheimer’s disease (AD) brains in the Baltimore Longitudinal Study of Aging and Religious Orders Study (mean age, 89 ± 9 years). A subset of these proteins was also differentially abundant in the brains of young APOE ε4 carriers relative to noncarriers (mean age, 39 ± 6 years). Several of these proteins represent targets of approved and experimental drugs for other indications and were validated using orthogonal methods in independent human brain tissue samples as well as in transgenic AD models. Using cell culture–based phenotypic assays, we showed that drugs targeting the cytokine transducer STAT3 and the Src family tyrosine kinases, YES1 and FYN, rescued molecular phenotypes relevant to AD pathogenesis. Our findings may accelerate the development of effective interventions targeting the earliest molecular triggers of AD.

Potential neuroprotective of trans-resveratrol a promising agent tempeh and soybean seed coats-derived against beta-amyloid neurotoxicity on primary culture of nerve cells induced by 2-methoxyethanol

Resveratrol, a natural polyphenol found in tempeh, has not been investigated especially in vitro as a neuroprotective agent against 2-methoxyethanol (2-ME)-induced beta-amyloid cytotoxicity. Beta amyloid peptides (Aβ) could initiate neurotoxic events and neuron-inflammatory response via microglial activation. However, it remains unknown whether the neurotoxic effect of beta-amyloid and/or associated with the potential of 2-ME to induce neurotoxic effects on primary culture of nerve cells induced by 2-ME. This study investigated potential neuroprotective of trans-resveratrol a promising agent tempeh and soybean seed coats-derived against beta-amyloid cytotoxicity on primary culture of nerve cells induced by 2-methoxyethanol. Biotium and MTT assays were used to analyze neurons, which were isolated from the cerebral cortex of fetal mice at gestation day 19 (GD-19). A standard solution of 2-methoxyethanol was dosed at 10 μL. The cultured cells were randomly divided into the following groups: (1) 2-ME group + resveratrol standard, (2) 2-ME group + resveratrol isolated from tempeh, (3) 2-ME group + resveratrol isolated from soybean seed coats, and (4) the control group, without the addition of either 2-ME or resveratrol. Exposure of the primary cortical neuron cells to beta-amyloid monoclonal antibody pre-incubated for 24 h with 10 µL of 4.2 µg/mL resveratrol and 7.5 mmol/l 2-methoxy-ethanol additions. Here, we report that the addition of 2-ME and resveratrol (standard and isolated from tempeh) of cell culture at concentrations of 1.4, 2.8 and 4.2 µg/mL showed that the majority of neurons grew well. In contrast, after exposure to 2-ME and Beta-amyloid, showed that glial activated. These findings demonstrate a role for resveratrol in neuroprotective-neurorescuing action.

Attenuation of amyloid-β generation by atypical protein kinase C-mediated phosphorylation of engulfment adaptor PTB domain containing 1 threonine 35

Amyloid-β (Aβ) is derived from the proteolytic processing of amyloid precursor protein (APP), and the deposition of extracellular Aβ to form amyloid plaques is a pathologic hallmark of Alzheimer's disease (AD). Although reducing Aβ generation and accumulation has been proposed as a means of treating the disease, adverse side effects and unsatisfactory efficacy have been reported in several clinical trials that sought to lower Aβ levels. Engulfment adaptor phosphotyrosine-binding (PTB) domain containing 1 (GULP1) is a molecular adaptor that has been shown to interact with APP to alter Aβ production. Therefore, the modulation of the GULP1-APP interaction may be an alternative approach to reducing Aβ. However, the mechanisms that regulate GULP1-APP binding remain elusive. As GULP1 is a phosphoprotein, and because phosphorylation is a common mechanism that regulates protein interaction, we anticipated that GULP1 phosphorylation would influence GULP1-APP interaction and thereby Aβ production. We show here that the phosphorylation of GULP1 threonine 35 (T35) reduces GULP1-APP interaction and suppresses the stimulatory effect of GULP1 on APP processing. The residue is phosphorylated by an isoform of atypical PKC (PKCζ). Overexpression of PKCζ reduces both GULP1-APP interaction and GULP1-mediated Aβ generation. Moreover, the activation of PKCζ via insulin suppresses APP processing. In contrast, GULP1-mediated APP processing is enhanced in PKCζ knockout cells. Similarly, PKC ι, another member of atypical PKC, also decreases GULP1-mediated APP processing. Intriguingly, our X-ray crystal structure of GULP1 PTB-APP intracellular domain (AICD) peptide reveals that GULP1 T35 is not located at the GULP1-AICD binding interface; rather, it immediately precedes the β1-α2 loop that forms a portion of the binding groove for the APP helix αC. Phosphorylating the residue may induce an allosteric effect on the conformation of the binding groove. Our results indicate that GULP1 T35 phosphorylation is a mechanism for the regulation of GULP1-APP interaction and thereby APP processing. Moreover, the activation of atypical PKC, such as by insulin, may confer a beneficial effect on AD by lowering GULP1-mediated Aβ production.-Chau, D. D.-L., Yung, K. W.-Y., Chan, W. W.-L., An, Y., Hao, Y., Chan, H.-Y. E., Ngo, J. C.-K., Lau, K.-F. Attenuation of amyloid-β generation by atypical protein kinase C-mediated phosphorylation of engulfment adaptor PTB domain containing 1 threonine 35.

Preclinical testing of 5-amino-1-((1R,2S,3S,4R)-2,3-dihydroxy-4-methylcyclopentyl)-1H-imidazole-4-carboxamide: a potent protein kinase C-ι inhibitor as a potential prostate carcinoma therapeutic

Protein kinase C-iota (PKC-ι) is an oncogene overexpressed in many cancer cells including prostate, breast, ovarian, melanoma, and glioma. Previous in-vitro studies have shown that 5-amino-1-((1R,2S,3S,4R)-2,3-dihydroxy-4-methylcyclopentyl)-1H-imidazole-4-carboxamide (ICA-1s), a PKC-ι specific inhibitor, is effective against some cancer cell lines by decreasing cell growth and inducing apoptosis. To assess ICA-1s as a possible therapeutic, in-vivo studies using a murine model were performed. ICA-1s was tested for stability in blood serum and results demonstrated that ICA-1s was stable in human plasma at 25 and 37°C over a course of 2 h. Toxicity of ICA-1s was tested for both acute and subacute exposure. The acute exposure showed patient surviving after 48 h of doses ranging from 5 to 5000 mg/kg. Subacute tests exposed the patients to 14 days of treatment and were followed by serum and tissue collection. Aspartate aminotransferase, alkaline phosphatase, γ-glutamyl transpeptidase, troponin, and C-reactive protein serum levels were measured to assess organ function. ICA-1s in plasma serum was measured over the course of 24 h for both oral and intravenous treatments. Heart, liver, kidney, and brain tissues were analyzed for accumulation of ICA-1s. Finally, athymic nude mice were xenografted with DU-145 prostate cancer cells. After tumors reached ~0.2 cm², they were either treated with ICA-1s or left as control and measured for 30 days or until the tumor reached 2 cm². Results showed tumors in treated mice grew at almost half the rate as untreated tumors, showing a significant reduction in growth. In conclusion, ICA-1s is stable, shows low toxicity, and is a potential therapeutic for prostate carcinoma tumors.

Inhibition of atypical protein kinase C‑ι effectively reduces the malignancy of prostate cancer cells by downregulating the NF-κB signaling cascade

Prostate cancer (PC) is the most common type of cancer among men. Aggressive and metastatic PC results in life- threatening tumors, and represents one of the leading causes of mortality in men. Previous studies of atypical protein kinase C isoforms (aPKCs) have highlighted its role in the survival of cultured prostate cells via the nuclear factor (NF)-κB pathway. The present study showed that PKC-ι was overexpressed in PC samples collected from cancer patients but not in non-invasive prostate tissues, indicating PKC-ι as a possible prognostic biomarker for the progression of prostate carcinogenesis. Immunohistochemical staining further confirmed the association between PKC-ι and the prostate malignancy. The DU-145 and PC-3 PC cell lines, and the non-neoplastic RWPE-1 prostatic epithelial cell line were cultured and treated with aPKC inhibitors 2-acetyl-1,3-cyclopentanedione (ACPD) and 5-amino-1-(1R,2S,3S,4R)-2,3-dihydroxy-4-methylcyclopentyl)-1H-imidazole-4-carboxamide (ICA-1). Western blot data demonstrated that ICA-1 was an effective and specific inhibitor of PKC-ι and that ACPD inhibited PKC-ι and PKC-ζ. Furthermore, the two inhibitors significantly decreased malignant cell proliferation and induced apoptosis. The inhibitors showed no significant cytotoxicity towards the RWPE-1 cells, but exhibited cytostatic effects on the DU-145 and PC-3 cells prior to inducing apoptosis. The inhibition of aPKCs significantly reduced the translocation of NF-κB to the nucleus. Furthermore, this inhibition promoted apoptosis, reduced signaling for cell survival, and reduced the proliferation of PC cells, whereas the normal prostate epithelial cells were relatively unaffected. Overall, the results suggested that PKC-ι and PKC-ζ are essential for the progression of PC, and that ACPD and ICA-1 can be effectively used as potential inhibitors in targeted therapy.

Protein kinase Cι/λ is dispensable for platelet function in thrombosis and hemostasis in mice

Platelet activation at sites of vascular injury is crucial for hemostasis, but it may also cause myocardial infarction or ischemic stroke. Upon platelet activation, cytoskeletal reorganization is essential for platelet secretion and thrombus formation. Members of the protein kinase C family, which includes 12 isoforms, are involved in most platelet responses required for thrombus formation. The atypical protein kinase Cι/λ (PKCι/λ) has been implicated as an important mediator of cell polarity, carcinogenesis and immune cell responses. PKCι/λ is known to be associated with the small GTPase Cdc42, an important mediator of multiple platelet functions; however, its exact function in platelets is not known. To study the role of PKCι/λ, we generated platelet- and megakaryocyte-specific PKCι/λ knockout mice (Prkci^{fl/fl, Pf4-Cre}) and used them to investigate the function of PKCι/λ in platelet activation and aggregation in vitro and in vivo. Surprisingly, lack of PKCι/λ had no detectable effect on platelet spreading and function in vitro and in vivo under all tested conditions. These results indicate that PKCι/λ is dispensable for Cdc42-triggered processes and for thrombosis and hemostasis in mice.

Extracellular signal-related kinase 2/specificity protein 1/specificity protein 3/repressor element-1 silencing transcription factor pathway is involved in Aroclor 1254-induced toxicity in SH-SY5Y neuronal cells

Polychlorinated biphenyls (PCBs) cause a wide spectrum of toxic effects in the brain through undefined mechanisms. Exposure to the PCB mixture Aroclor-1254 (A1254) increases the repressor element-1 silencing transcription factor (REST) expression, leading to neuronal death. This study sought to understand the sequence of some molecular mechanisms to determine whether A1254 could increase REST expression and the cytoprotective effect of the phorbol ester tetradecanoylphorbol acetate (TPA) on A1254-induced toxicity in SH-SY5Y cells. As shown by Western blot analysis, A1254 (10 µg/ml) downregulates extracellular signal-related kinase 2 (ERK2) phosphorylation in a time-dependent manner, thereby triggering the binding of specificity protein 1 (Sp1) and Sp3 to the REST gene promoter as revealed by chromatin immunoprecipitation analysis. This chain of events results in an increase in REST mRNA and cell death, as assessed by quantitative real-time polymerase chain reaction and dimethylthiazolyl-2-5-diphenyltetrazolium-bromide assay, respectively. Accordingly, TPA prevented both the A1254-induced decrease in ERK2 phosphorylation and the A1254-induced increase in Sp1, Sp3, and REST protein expression. After 48 hr, TPA prevented A1254-induced cell death. ERK2 overexpression counteracted the A1254-induced increase in Sp1 and Sp3 protein expression and prevented A1254-induced Sp1 and Sp3 binding to the REST gene promoter, thus counteracting the increase in REST mRNA expression induced by the toxicant. In neuroblastoma SH-SY5Y cells, ERK2/Sp1/SP3/REST is a new pathway underlying the neurotoxic effect of PCB. The ERK2/Sp1/Sp3/REST pathway, which underlies A1254-induced neuronal death, might represent a new drug signaling cascade in PCB-induced neuronal toxicity.

Altered expression of atypical PKC and Ryk in the spinal cord of a mouse model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive paralysis due to the selective death of motor neurons of unknown causes. Increasing evidence indicates that Wnt signaling is altered in ALS. In this study, we focused on two non-canonical Wnt signaling components, atypical PKC (aPKC) and a Wnt receptor, Ryk, in a mouse model of ALS, SOD1 (G93A). aPKC mediates Wnt signaling to regulate growth cone guidance, axon differentiation and cell survival. Ryk is a Wnt repulsive receptor that regulates axon guidance and inhibits regeneration after spinal cord injury. aPKC expression was increased in motor neurons of the lumbar spinal cord in SOD1 (G93A) mice at both early and late stages. Interestingly, aPKC was co-localized with SOD1 in motor neuron cell bodies and extracellular aggregates, and aPKC-containing extracellular aggregates increased with disease progression. Biochemical fractionation showed that aPKC protein level was increased in the detergent-insoluble protein fraction in SOD1 (G93A) mice at late stage but decreased in the detergent-soluble fraction at symptomatic stage. These results suggest that aPKC may be sequestered in SOD1 aggregates, impairing its ability to protect motor neurons from death. Ryk expression was also increased in the motor neurons and the white matter in the ventral lumbar spinal cord of mutant SOD1 mice with a peak at early stage. These observations indicate that Wnt/aPKC and Wnt/Ryk signaling are altered in SOD1 (G93A) mice, suggesting that changed Wnt signaling may contribute to neurodegeneration in ALS.

Genistein inhibits Aβ₂₅₋₃₅ -induced neurotoxicity in PC12 cells via PKC signaling pathway

Protein kinase C (PKC) signaling pathway is recognized as an important molecular mechanism of Alzheimer's disease (AD) in the regulation of neuronal plasticity and survival. Genistein, the most active molecule of soy isoflavones, exerts neuroprotective roles in AD. However, the detailed mechanism has not been fully understood yet. The present study aimed to investigate whether the neuroprotective effects of genistein against amyloid β (Aβ)-induced toxicity in cultured rat pheochromocytoma (PC12) cells is involved in PKC signaling pathway. PC12 cells were pretreated with genistein for 2 h following incubation with Aβ(25-35) for additional 24 h. Cell viability was assessed by MTT. Hoechst33342/PI staining was applied to determine the apoptotic cells. PKC activity, intracellular calcium level and caspase-3 activity were analyzed by assay kits. The results showed that pretreatment with genistein significantly increased cell viability and PKC activity, decreased the levels of intracellular calcium, attenuated Hoechst/PI staining and blocked caspase-3 activity in Aβ(25-35)-treated PC12 cells. Pretreatment of Myr, a general PKC inhibitor, significantly attenuated the neuroprotective effect of genistein against Aβ(25-35)-treated PC12 cells. The present study indicates that PKC signaling pathway is involved in the neuroprotective action of genistein against Aβ(25-35)-induced toxicity in PC12 cells.

Green tea polyphenols precondition against cell death induced by oxygen-glucose deprivation via stimulation of laminin receptor, generation of reactive oxygen species, and activation of protein kinase Cε

As the development of synthetic drugs for the prevention of stroke has proven challenging, utilization of natural products capable of preconditioning neuronal cells against ischemia-induced cell death would be a highly useful complementary approach. In this study using an oxygen-glucose deprivation and reoxygenation (OGD/R) model in PC12 cells, we show that 2-day pretreatment with green tea polyphenols (GTPP) and their active ingredient, epigallocatechin-3-gallate (EGCG), protects cells from subsequent OGD/R-induced cell death. A synergistic interaction was observed between GTPP constituents, with unfractionated GTPP more potently preconditioning cells than EGCG. GTPP-induced preconditioning required the 67-kDa laminin receptor (67LR), to which EGCG binds with high affinity. 67LR also mediated the generation of reactive oxygen species (ROS) via activation of NADPH oxidase. An exogenous ROS-generating system bypassed 67LR to induce preconditioning, suggesting that sublethal levels of ROS are indeed an important mediator in GTPP-induced preconditioning. This role for ROS was further supported by the fact that antioxidants blocked GTPP-induced preconditioning. Additionally, ROS induced an activation and translocation of protein kinase C (PKC), particularly PKCε from the cytosol to the membrane/mitochondria, which was also blocked by antioxidants. The crucial role of PKC in GTPP-induced preconditioning was supported by use of its specific inhibitors. Preconditioning was increased by conditional overexpression of PKCε and decreased by its knock-out with siRNA. Collectively, these results suggest that GTPP stimulates 67LR and thereby induces NADPH oxidase-dependent generation of ROS, which in turn induces activation of PKC, particularly prosurvival isoenzyme PKCε, resulting in preconditioning against cell death induced by OGD/R.

Knocking down the transcript of protein kinase C-lambda modulates hypothalamic glutathione peroxidase, melanocortin receptor and neuropeptide Y gene expression in amphetamine-treated rats

It has been reported that neuropeptide Y (NPY) contributes to the behavioral response of amphetamine (AMPH), a psychostimulant. The present study examined whether protein kinase C (PKC)-λ signaling was involved in this action. Moreover, possible roles of glutathione peroxidase (GP) and melanocortin receptor 4 (MC4R) were also examined. Rats were given AMPH daily for 4 days. Hypothalamic NPY, PKCλ, GP and MC4R were determined and compared. Pretreatment with α-methyl-para-tyrosine could block AMPH-induced anorexia, revealing that endogenous catecholamine was involved in regulating AMPH anorexia. PKCλ, GP and MC4R were increased with maximal response on Day 2 during AMPH treatment, which were concomitant with the decreases in NPY. cAMP response element binding protein (CREB) DNA binding activity was increased during AMPH treatment, revealing the involvement of CREB-dependent gene transcription. An interruption of cerebral PKCλ transcript could partly block AMPH-induced anorexia and partly reverse NPY, MC4R and GP mRNA levels to normal. These results suggest that PKCλ participates in regulating AMPH-induced anorexia via a modulation of hypothalamic NPY gene expression and that increases of GP and MC4R may contribute to this modulation. Our results provided molecular evidence for the regulation of AMPH-induced behavioral response.

Partial neuroprotection by 17-β-estradiol in neonatal γ-irradiated rat cerebellum

Acute and long-term complications can occur in patients receiving radiation therapy. It has been suggested that cytoprotection might decrease the incidence and severity of therapy-related toxicity in these patients. Developing cerebellum is highly radiosensitive and for that reason it is a useful structure to test potential neuroprotective substances to prevent radiation induced abnormalities. Recent studies have shown that estrogen can rapidly modulate intracellular signalling pathways involved in cell survival. Thus, it has been demonstrated that estrogens mediate neuroprotection by promoting growth, cell survival and by preventing axonal pruning. The aim of this work was to evaluate the effect of the treatment with 17-β-estradiol on the motor, structural and biochemical changes induced by neonatal ionizing radiation exposure, and to investigate the participation of nitric oxide and protein kinase C, two important intracellular messengers involved in neuronal activity. Our results show that perinatal chronic 17-β-estradiol treatment partially protects against radiation-induced cerebellar disorganization and motor abnormalities. PKC and NOS activities could be implicated in its neuroprotective mechanisms. These data provide new evidence about the mechanisms underlying estrogen neuroprotection, which could have therapeutic relevance for patients treated with radiotherapy.

The role of Wnt signaling in neuronal dysfunction in Alzheimer's Disease

Recent evidence supports a neuroprotective role for Wnt signaling in neurodegenerative disorders such as Alzheimer's Disease (AD). In fact, a relationship between amyloid-beta-peptide (Abeta)-induced neurotoxicity and a decrease in the cytoplasmic levels of beta-catenin has been observed. Apparently Abeta binds to the extracellular cysteine-rich domain of the Frizzled receptor (Fz) inhibiting Wnt/beta-catenin signaling. Cross-talk with other signaling cascades that regulate Wnt/beta-catenin signaling, including the activation of M1 muscarinic receptor and PKC, the use of Ibuprofen-ChE bi-functional compounds, PPAR alpha, gamma agonists, nicotine and some antioxidants, results in neuroprotection against Abeta. These studies indicate that a sustained loss of Wnt signaling function may be involved in the Abeta-dependent neurodegeneration observed in Alzheimer's brain. In conclusion the activation of the Wnt signaling pathway could be proposed as a therapeutic target for the treatment of AD.

Activation of p38MAPK contributes to expanded polyglutamine-induced cytotoxicity

Background

The signaling pathways that may modulate the pathogenesis of diseases induced by expanded polyglutamine proteins are not well understood.

Methodologies/Principal Findings

Herein we demonstrate that expanded polyglutamine protein cytotoxicity is mediated primarily through activation of p38MAPK and that the atypical PKC iota (PKCι) enzyme antagonizes polyglutamine-induced cell death through induction of the ERK signaling pathway. We show that pharmacological blockade of p38MAPK rescues cells from polyglutamine-induced cell death whereas inhibition of ERK recapitulates the sensitivity observed in cells depleted of PKCι by RNA interference. We provide evidence that two unrelated proteins with expanded polyglutamine repeats induce p38MAPK in cultured cells, and demonstrate induction of p38MAPK in an in vivo model of neurodegeneration (spinocerebellar ataxia 1, or SCA-1).

Conclusions/Significance

Taken together, our data implicate activated p38MAPK in disease progression and suggest that its inhibition may represent a rational strategy for therapeutic intervention in the polyglutamine disorders.

Involvement of PKC-iota in glioma proliferation

Atypical protein kinase C-iota (PKC-iota) protects cells against apoptosis and may play a role in cell proliferation. However, in vivo, the status and function of PKC-iota in human normal brain tissue, gliomas, benign and malignant meningiomas as well as its in vitro status in proliferating and confluent glioma cells, remains unknown.

OBJECTIVES

The objectives of our research were to determine whether expression of PKC-iota is altered either in gliomas or in benign and malignant meningiomas, compared to normal brain. In addition, we wished to establish the expression of PKC-iota in proliferating plus in cell cycle-arrested glioma cell lines, as well as the relationship between PKC-iota siRNA on PKC-iota protein content and cell proliferation.

MATERIALS AND METHODS

Western blot analyses for PKC-iota were performed on 12 normal brain biopsies, 15 benign meningiomas, three malignant meningiomas and three gliomas.

RESULTS

Results demonstrated no (n = 9) or very weak (n = 3) detection of PKC-iota in normal brain tissue. In comparison, PKC-iota was robustly present in the majority of the benign meningiomas. Similarly, PKC-iota was abundant in all malignant meningiomas and gliomas. Western blotting for PKC-iota in confluent or proliferating glioma cell lines depicted substantial quantities of PKC-iota in proliferating T98G and U-138MG glioma cells. In contrast, confluent cells had either 71% (T98G) or 21% (U-138MG) less PKC-iota than proliferating cells. T98 and U-138 MG glioma cells treated with 100 nm PKC-iota siRNA had lower levels of cell proliferation compared to control siRNA-A and complete down-regulation of PKC-iota protein content.

CONCLUSION

These results support the concept that presence of PKC-iota may be required for cell proliferation to take place.

Conventional protein kinase C isoforms mediate neuroprotection induced by phorbol ester and estrogen

Rapid signal transduction pathways play a prominent role in mediating neuroprotective actions of estrogen in the CNS. We have previously shown that estrogen-induced neuroprotection of primary cerebrocortical neurons from beta-amyloid peptide (Abeta) toxicity depends on activation of protein kinase C (PKC). PKC activation with phorbol-12-myristate-13-acetate (PMA) also provides neuroprotection in this paradigm. Because the PKC family includes several isoforms that have opposing roles in regulating cell survival, we sought to identify which PKC isoforms contribute to neuroprotection induced by PMA and estrogen. We detected protein expression of multiple PKC isoforms in primary neuron cultures, including conventional (alpha, betaI, betaII), novel (delta, epsilon, theta) and atypical (zeta, iota/lambda) PKC. Using a panel of isoform-specific peptide inhibitors and activators, we find that novel and atypical PKC isoforms do not participate in the mechanism of either PMA or estrogen neuroprotection. In contrast, a selective peptide activator of conventional PKC isoforms provides dose-dependent neuroprotection against Abeta toxicity. In addition, peptide inhibitors of conventional, betaI, or betaII PKC isoforms significantly reduce protection afforded by PMA or 17beta-estradiol. Taken together, these data provide evidence that conventional PKC isoforms mediate phorbol ester and estrogen neuroprotection of cultured neurons challenged by Abeta toxicity.

Effects of the PKC inhibitor PD 406976 on cell cycle progression, proliferation, PKC isozymes and apoptosis in glioma and SVG-transformed glial cells

It is well established that protein kinase C (PKC) isozymes are involved in the proliferation of glioma cells. However, reports differ on which PKC isozymes are responsible for glioma proliferation. As a means to further elucidate this, the objectives of our research were to determine how inhibition of PKC-alpha, PKC-beta and PKCmu with PD 406976 regulates the cell cycle, cell proliferation and PKC during glioma growth and development. To establish the cell cycle effects of PD 406976 on brain cells (SVG, U-138MG and U-373MG glioma cells), specimens were treated with either dimethylsulfoxide (DMSO; control) or PD 406976 (2 microm). Results from flow cytometry demonstrated that PD 406976 delayed the entry DNA synthesis phase in SVG cells and delayed the number of cells entering and exiting the DNA synthesis phase in both U-138MG and U-373MG cells, indicating that PD 406976 may inhibit G(1)/S and S phase progression. Assessment of cell viability demonstrated a cytostatic effect of PD 406976 on SVG, U-138MG and U-373MG glioma cell proliferation. The PD 406976-induced decreased proliferation was sustained at 48-96 h. A PKC activity assay was quantified and demonstrated that exposure of SVG and U-373MG glioma cells to PD 406976 suppressed PKC activity. Western blotting demonstrated reduced PKC-beta1, PKC-gamma and PKC-tau protein content in cells treated with PD 406976. We determined that the growth inhibitory effect of PD 406976 was not as a result of apoptosis.

Nicergoline, a drug used for age-dependent cognitive impairment, protects cultured neurons against beta-amyloid toxicity

Nicergoline, a drug used for the treatment of Alzheimer's disease and other types of dementia, was tested for its ability to protect neurons against beta-amyloid toxicity. Pure cultures of rat cortical neurons were challenged with a toxic fragment of beta-amyloid peptide (betaAP(25-35)) and toxicity was assessed after 24 h. Micromolar concentrations of nicergoline or its metabolite, MDL, attenuated betaAP(25-35)-induced neuronal death, whereas MMDL (another metabolite of nicergoline), the alpha1-adrenergic receptor antagonist, prazosin, or the serotonin 5HT-2 receptor antagonist, methysergide, were inactive. Nicergoline increased the basal levels of Bcl-2 and reduced the increase in Bax levels induced by beta-amyloid, indicating that the drug inhibits the execution of an apoptotic program in cortical neurons. In mixed cultures of rat cortical cells containing both neurons and astrocytes, nicergoline and MDL were more efficacious than in pure neuronal cultures in reducing beta-amyloid neurotoxicity. Experiments carried out in pure cultures of astrocytes showed that a component of neuroprotection was mediated by a mechanism of glial-neuronal interaction. The conditioned medium of cultured astrocytes treated with nicergoline or MDL for 72-96 h (collected 24 h after drug withdrawal) was neuroprotective when transferred to pure neuronal cultures challenged with beta-amyloid. In cultured astrocytes, nicergoline increased the intracellular levels of transforming-growth factor-beta and glial-derived neurotrophic factor, two trophic factors that are known to protect neurons against beta-amyloid toxicity. These results raise the possibility that nicergoline reduces neurodegeneration in the Alzheimer's brain.

Neuroprotective effects of sigma-1 receptor agonists against beta-amyloid-induced toxicity

Prolonged exposure of cultured cortical neurons to the residue 25-35 fragment of beta-amyloid protein, in the presence of dizocilpine, an antagonist of the N-methyl-D-aspartate receptor, and of 6,7-dinitroquinoxaline-2,3-dione, an antagonist of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate receptors, resulted in the expression of the proapoptotic protein Bax and neuronal death. Beta-amyloid protein(25-35)-induced neuronal death was substantially attenuated by the sigma1 receptor agonist 2-(4-morpholinethyl)1-phenylcyclohexanecarboxylate. The neuroprotective action of 2-(4-morpholinethyl)1-phenylcyclohexanecarboxylate was mimicked by the sigma1 ligand methyl (1S,2R)-2-[1-adamantyl(methyl)amino]methyl-1-phenylcyclopropanecarboxylate and was antagonized by the sigma1 receptor antagonist N,N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)-phenyl]-ethylamine monohydrochloride. These results suggest that sigma1 receptor agonists might function as neuroprotectant agents in Alzheimer's disease.

Neuroprotective effects of anti-aging oriental medicine Lycium barbarum against β-amyloid peptide neurotoxicity

As aged population dramatically increases in these decades, efforts should be made on the intervention for curing age-associated neurodegenerative diseases such as Alzheimer's disease (AD). Natural plant extracts of Lycium barbarum are well-known to exhibit anti-aging effects. We therefore hypothesized that they exhibit neuroprotective effects against toxins in aging-related neurodegenerative diseases. In this study, we aimed to investigate whether extracts from L. barbarum have neuroprotective effects against toxicity of fibrillar Abeta(1-42) and Abeta(25-35) fragments. Primary rat cortical neurons exposed to Abeta peptides resulted in apoptosis and necrosis. Pre-treatment with extract isolated from L. barbarum significantly reduced the release of lactate dehydrogenase (LDH). In addition, it attenuated Abeta peptide-activated caspases-3-like activity. The extract elicited a typical dose-dependent neuroprotective effect. Effective dosage of this extract was wider than that of a well-known western neuroprotective medicine lithium chloride (LiCl). We have further examined the underlying mechanisms of the neuroprotective effects. In agreement with other laboratories, Abeta peptides induce a rapid activation of c-Jun N-terminal kinase (JNK) by phosphorylation. Pre-treatment of aqueous extract markedly reduced the phosphorylation of JNK-1 (Thr183/Tyr185) and its substrates c-Jun-I (Ser 73) and c-Jun-II (Ser 63). Taken together, we have proved our hypothesis by showing neuroprotective effects of the extract from L. barbarum. Study on anti-aging herbal medicine like L. barbarum may open a new therapeutic window for the prevention of AD.

Aloe-emodin modulates PKC isozymes, inhibits proliferation, and induces apoptosis in U-373MG glioma cells

Aloe-emodin (1,8-dihydroy-3-[hydroxymethyl]-anthraquione) purified from Aloe vera leaves has been reported to have antitumor activity. The objectives of our research were to determine how aloe-emodin regulates the cell cycle, cell proliferation and protein kinase C (PKC) during glioma growth and development. To establish the cell cycle effects of aloe-emodin on brain cells [transformed glia cell line (SVG) and human glioma U-373MG cell line (U-373MG)], cells were treated with either dimethylsulfoxide (DMSO; control) or aloe-emodin (40 microM). Results from flow cytometry demonstrated that aloe-emodin delayed the number of cells entering and exiting DNA synthesis (S) phase in both SVG and U-373MG cells indicating that aloe-emodin may inhibit S phase progression. Assessment of cell viability demonstrated that SVG and U-373MG glioma cell were highly sensitive to aloe-emodin. The aloe-emodin-induced decreased proliferation was sustained at 48-96 h. A PKC activity assay was quantified to establish the role of PKC in aloe-emodin's mode of action. Exposure of SVG and U-373MG glioma cells to aloe-emodin suppressed PKC activity and reduced the protein content of most of the PKC isozymes. We determined that cancer growth inhibition by aloe-emodin was due to apoptosis (i.e., programmed cell death). Taken together, these results support the hypothesis that aloe-emodin represents a novel antitumor chemotherapeutic drug.

Neuroprotective effects of resveratrol against beta-amyloid-induced neurotoxicity in rat hippocampal neurons: involvement of protein kinase C

1. Resveratrol, an active ingredient of red wine extracts, has been shown to exhibit neuroprotective effects in several experimental models. 2. The present study evaluated the neuroprotective effects of resveratrol against amyloid beta(Abeta)-induced toxicity in cultured rat hippocampal cells and examined the role of the protein kinase C (PKC) pathway in this effect. 3. Pre-, co- and post-treatment with resveratrol significantly attenuated Abeta-induced cell death in a concentration-dependent manner, with a concentration of 25 microm being maximally effective. 4. Pretreatment (1 h) of hippocampal cells with phorbol-12-myristate-13-acetate, a PKC activator, at increasing concentrations (1-100 ng x ml(-1)), resulted in a dose-dependent reduction in Abeta-induced toxicity, whereas the inactive 4alpha-phorbol had no effect. 5. Pretreatment (30 min) of hippocampal cells with GF 109203X (1 microm), a general PKC inhibitor, significantly attenuated the neuroprotective effect of resveratrol against Abeta-induced cell death. 6. Treatment of hippocampal cells with resveratrol (20 microm) also induced the phosphorylation of various isoforms of PKC leading to activation. 7. Taken together, the present results indicate that PKC is involved in the neuroprotective action of resveratrol against Abeta-induced toxicity.

Cyclin-dependent kinase activating kinase/Cdk7 co-localizes with PKC-iota in human glioma cells

Cyclin-dependent kinase activating kinase (CAK) is a trimeric complex composed of cdk7, cyclin H and MAT1. CAK/cdk7 functions as a master cell cycle regulator by phosphorylating cyclin-dependent kinases for cell cycle progression. We have previously reported that protein kinase C-iota (PKC-iota) associates with CAK/cdk7. In this investigation, immunofluorescence confocal microscopy was used to provide further evidence for the co-localization of PKC-iota with CAK/cdk7. PKC-iota was labeled with Alexa Fluor 488 (green fluorescent dye) and CAK/cdk7 was labeled with Alexa Fluor 555 (red fluorescent dye). The fusion of the red and green fluorescent colors produced a yellow color, which was used to quantify co-localization of PKC-iota and CAK/cdk7. Confocal microscopy revealed the co-localization of PKC-iota with CAK/cdk7 in both the cytoplasm and nucleus of U-373 MG cells.

Signal transduction during amyloid-β-peptide neurotoxicity: role in Alzheimer disease

Alzheimer's disease (AD) is a neurodegenerative disorder with progressive dementia accompanied by two main structural changes in the brain: intracellular protein deposits termed neurofibrillary tangles (NFT) and extracellular amyloid protein deposits surrounded by dystrophic neurites that constitutes the senile plaques. Currently, it is widely accepted that amyloid beta-peptide (A beta) metabolism disbalance is crucial for AD progression. A beta deposition may be enhanced by molecular chaperones, including metals like copper and proteins like acetylcholinesterase (AChE). At the neuronal level, several AD-related proteins interact with transducers of the Wnt/beta-catenin signaling pathway, including beta-catenin and glycogen synthase kinase 3 beta (GSK-3 beta) and both in vitro and in vivo studies suggest that Wnt/beta-catenin signaling is a target for A beta toxicity. Accordingly, activation of this signaling by lithium or Wnt ligands in AD-experimental animal models or in primary hippocampal neurons attenuate A beta neurotoxicity by recovering beta-catenin levels and Wnt-target gene expression of survival genes such as bcl-2. On the other hand, peroxisomal proliferator-activated receptor gamma (PPAR gamma) and muscarinic acetylcholine receptor (mAChR) agonists also activate Wnt/beta-catenin signaling and they have neuroprotective effects on hippocampal neurons. Our studies are consistent with the idea that a sustained loss of function of Wnt signaling components would trigger a series of events, determining the onset and development of AD and that modulation of this pathway through the activation of cross-talking signaling cascades should be considered as a possible therapeutic strategy for AD treatment.

M1 muscarinic receptor activation protects neurons from β-amyloid toxicity. A role for Wnt signaling pathway

Amyloid-beta-peptide (Abeta) deposits are one of the hallmark features of Alzheimer's disease. Signal transduction alterations are implicate in the neuronal responses to Abeta, which include neurotransmitter systems and pathways involved in the maintenance of the nervous system. In this context, we have recently found that Abeta-neurotoxicity triggers a loss of Wnt signaling. We report here that M1-acetylcholine-muscarinic-receptor (mAChR) activation protects neurons from Abeta-toxicity. Concomitant with this effect, a modulation of the Wnt signaling was observed. M1 mAChR activation inhibits glycogen-synthase-kinase-3beta (GSK-3beta) activity, stabilizes cytoplasmic and nuclear beta-catenin, and induces the expression of the Wnt target genes engrailed and cyclin-D1, reverting the switch off of the Wnt pathway caused by Abeta-toxicity. Neurons from mice that overexpress GSK-3beta allow us to establish that M1 mAChR stimulation leads to GSK-3beta inactivation. We conclude that the cross-talk between the muscarinic signaling and Wnt components underlie the neuroprotective effect of the M1 mAChR activation.

Estrogen activates protein kinase C in neurons: role in neuroprotection

It has been previously demonstrated that estrogen can protect neurons from a variety of insults, including beta-amyloid (Abeta). Recent studies have shown that estrogen can rapidly modulate intracellular signaling pathways involved in cell survival. In particular, estrogen activates protein kinase C (PKC) in a variety of cell types. This enzyme plays a key role in many cellular events, including regulation of apoptosis. In this study, we show that 17beta-estradiol (E2) rapidly increases PKC activity in primary cultures of rat cerebrocortical neurons. A 1 h pre-treatment with E2 or phorbol-12-myristate-13-acetate (PMA), a potent activator of PKC, protects neurons against Abeta toxicity. Protection afforded by both PMA and E2 is blocked by pharmacological inhibitors of PKC. Further, depletion of PKC levels resulting from prolonged PMA exposure prevents subsequent E2 or PMA protection. Our results indicate that E2 activates PKC in neurons, and that PKC activation is an important step in estrogen protection against Abeta. These data provide new understanding into the mechanism(s) underlying estrogen neuroprotection, an action with therapeutic relevance to Alzheimer's disease and other age-related neurodegenerative disorders.

Phosphorylation of 69-kDa choline acetyltransferase at threonine 456 in response to amyloid-beta peptide 1-42

Choline acetyltransferase synthesizes acetylcholine in cholinergic neurons. In the brain, these neurons are especially vulnerable to effects of beta-amyloid (A beta) peptides. Choline acetyltransferase is a substrate for several protein kinases. In the present study, we demonstrate that short term exposure of IMR32 neuroblastoma cells expressing human choline acetyltransferase to A beta-(1-42) changes phosphorylation of the enzyme, resulting in increased activity and alterations in its interaction with other cellular proteins. Using mass spectrometry, we identified threonine 456 as a new phosphorylation site in choline acetyltransferase from A beta-(1-42)-treated cells and in purified recombinant ChAT phosphorylated in vitro by calcium/calmodulin-dependent protein kinase II (CaM kinase II). Whereas phosphorylation of choline acetyltransferase by protein kinase C alone caused a 2-fold increase in enzyme activity, phosphorylation by CaM kinase II alone did not alter enzyme activity. A 3-fold increase in choline acetyltransferase activity was found with coordinate phosphorylation of threonine 456 by CaM kinase II and phosphorylation of serine 440 by protein kinase C. This phosphorylation combination was observed in choline acetyltransferase from A beta-(1-42)-treated cells. Treatment of cells with A beta-(1-42) resulted in two phases of activation of choline acetyltransferase, the first within 30 min and associated with phosphorylation by protein kinase C and the second by 10 h and associated with phosphorylation by both CaM kinase II and protein kinase C. We also show that choline acetyltransferase from A beta-(1-42)-treated cells co-immunoprecipitates with valosin-containing protein, and mutation of threonine 456 to alanine abolished the A beta-(1-42)-induced effects. These studies demonstrate that A beta-(1-42) can acutely regulate the function of choline acetyltransferase, thus potentially altering cholinergic neurotransmission.

The establishment of a reliable cytotoxic system with SK-N-SH neuroblastoma cell culture

A reliable in vitro cytotoxic system is essential in neurocytotoxic and neuroprotective research. The present study examined four cytotoxic insults with the SK-N-SH human neuroblastoma cell line. These were beta-amyloid protein (Abeta), 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), high density culture, and serum deprivation induced neuronal death. These insults induced significant reduction in cell numbers after 96 h culture, in a concentration dependent manner. Among all the insults, MPTP, serum deprivation, and high density culture induced apoptosis after 96 h, while Abeta presumably induced necrotic neuronal death since apoptosis was not detectable. The p38 MAP kinase inhibitor, SB203580 (1 microM), and the PKC inhibitor, chelerythrine (5 microM) successfully inhibited the loss in viability caused by Abeta and the high density culture, respectively. Other kinase inhibitors, including the non-specific protein kinase inhibitor, H7, the PKA inhibitor 14-22 Amide, the PKG inhibitor, KT5823, and the protein tyrosine kinase inhibitor, AG18 had no effect on any of the four cytotoxic models. This system allows the study of neuroprotection under conditions where the different pathways and mechanisms of the neurons can be considered within one cellular system, removing variations which may be due to different cell type studied. The present studies describe an effective model system for screening potential neuroprotective agents.

Activation of Wnt signaling rescues neurodegeneration and behavioral impairments induced by beta-amyloid fibrils

Alzheimer's disease (AD) is a progressive neurodegenerative disorder, which is probably caused by the cytotoxic effect of the amyloid beta-peptide (Abeta). We report here molecular changes induced by Abeta, both in neuronal cells in culture and in rats injected in the dorsal hippocampus with preformed Abeta fibrils, as an in vivo model of the disease. Results indicate that in both systems, Abeta neurotoxicity resulted in the destabilization of endogenous levels of beta-catenin, a key transducer of the Wnt signaling pathway. Lithium chloride, which mimics Wnt signaling by inhibiting glycogen synthase kinase-3beta promoted the survival of post-mitotic neurons against Abeta neurotoxicity and recovered cytosolic beta-catenin to control levels. Moreover, the neurotoxic effect of Abeta fibrils was also modulated with protein kinase C agonists/inhibitors and reversed with conditioned medium containing the Wnt-3a ligand. We also examined the spatial memory performance of rats injected with preformed Abeta fibrils in the Morris water maze paradigm, and found that chronic lithium treatment protected neurodegeneration by rescuing beta-catenin levels and improved the deficit in spatial learning induced by Abeta. Our results are consistent with the idea that Abeta-dependent neurotoxicity induces a loss of function of Wnt signaling components and indicate that lithium or compounds that mimic this signaling cascade may be putative candidates for therapeutic intervention in Alzheimer's patients.

Protein kinase C inhibits amyloid beta peptide neurotoxicity by acting on members of the Wnt pathway

Current evidence supports the notion that the amyloid beta-peptide (Abeta) plays a major role in the neurotoxicity observed in the brain in Alzheimer's disease. However, the signal transduction mechanisms involved still remain unknown. In the present work, we analyzed the effect of protein kinase C (PKC) on some members of the Wnt signaling pathway and its implications for Abeta neurotoxicity. Activation of PKC by phorbol 12-myristate 13-acetate protected rat hippocampal neurons from Abeta toxicity. This effect was accomplished by inhibition of glycogen synthase kinase-3beta (GSK-3beta) activity, which led to the accumulation of cytoplasmic beta-catenin and transcriptional activation via beta-catenin/T-cell factor/lymphoid enhancer factor-1 (TCF/LEF-1) of Wnt target genes, which in the present study were engrailed-1 (en-1) and cyclin D1 (cycD1,). In contrast, inhibition of Ca2+-dependent PKC isoforms activated GSK-3beta and offered no protection from Ab neurotoxicity. Wnt-3a and lithium salts, classical activators of the Wnt pathway, mimicked PKC activation. Our results suggest that regulation of members of the Wnt signaling pathway by Ca2+-dependent PKC isoforms may be important in controlling the neurotoxic process induced by Ab.

Regulation of airway tight junctions by proinflammatory cytokines

Epithelial tight junctions (TJs) provide an important route for passive electrolyte transport across airway epithelium and provide a barrier to the migration of toxic materials from the lumen to the interstitium. The possibility that TJ function may be perturbed by airway inflammation originated from studies reporting (1) increased levels of the proinflammatory cytokines interleukin-8 (IL-8), tumor necrosis factor alpha (TNF-alpha), interferon gamma (IFN-gamma), and IL-1beta in airway epithelia and secretions from cystic fibrosis (CF) patients and (2) abnormal TJ strands of CF airways as revealed by freeze-fracture electron microscopy. We measured the effects of cytokine exposure of CF and non-CF well-differentiated primary human airway epithelial cells on TJ properties, including transepithelial resistance, paracellular permeability to hydrophilic solutes, and the TJ proteins occludin, claudin-1, claudin-4, junctional adhesion molecule, and ZO-1. We found that whereas IL-1beta treatment led to alterations in TJ ion selectivity, combined treatment of TNF-alpha and IFN-gamma induced profound effects on TJ barrier function, which could be blocked by inhibitors of protein kinase C. CF bronchi in vivo exhibited the same pattern of expression of TJ-associated proteins as cultures exposed in vitro to prolonged exposure to TNF-alpha and IFN-gamma. These data indicate that the TJ of airway epithelia exposed to chronic inflammation may exhibit parallel changes in the barrier function to both solutes and ions.

Protein kinase C isoforms in normal and transformed cells of the melanocytic lineage

Enzymes belonging to the protein kinase C (PKC) family represent one of the major mediators of signal transduction in melanocytes. To identify PKC isoforms that may be associated with the process of malignant transformation and metastasis, we investigated the expression pattern of 11 different PKC isoforms (alpha, beta I, beta II, gamma, delta, epsilon, eta, theta, zeta, lambda, and iota) in melanoma lymph node metastases, in cell lines established from these metastases, in primary cell cultures from normal melanocytes, and in permanent cell lines established from spontaneously transformed melanocytes. PKC alpha, beta I, beta II, delta, epsilon, eta, zeta, lambda and iota were found to be expressed in total lysates from melanoma metastases. In permanent cell lines established from these metastases, the expression levels of PKC beta I, beta II, delta, epsilon, and eta were lower or undetectable when compared with initial expression in tumour lysates. In normal primary melanocyte cultures, the PKC isoforms beta II, delta, epsilon, eta and iota were undetectable. PKC gamma and theta isoforms were undetectable in all melanocytic cell types examined. PKC iota was the only isoform exclusively detected in tumour lysates, in spontaneously transformed melanoma cells and melanoma cell lines, but not in normal melanocytes, and may therefore be associated with the transformed phenotype in human melanoma in vitro and in vivo.

Dual role for p75(NTR) signaling in survival and cell death: can intracellular mediators provide an explanation?

Several recent reports support a dual role of p75(NTR) in cell death, as well as survival, depending on the physiological or developmental stage of the cells. Coexpression of the TrkA receptor with p75(NTR) further enhances the complexity of nerve growth factor (NGF) signaling. Recent identification of serine/threonine kinases that interact with the p75(NTR) provides an explanation for the lack of an apparent kinase domain needed for signaling. In this report, we review the possible roles of the intracellular proteins that directly interact with the p75(NTR), atypical protein kinase C (PKC) binding protein, p62 and second messengers in the functional antagonism exhibited by TrkA and p75(NTR) with an emphasis on the nuclear factor-kappa B activation pathway.

Nerve growth factor activates kinases that phosphorylate atypical protein kinase C

Activation of atypical protein kinase C by nerve growth factor (NGF) involves phosphorylation. In order to identify kinases that regulate atypical PKC (aPKC), we surveyed PC12 cell lysates for protein kinases that are activated by NGF and which could phosphorylate aPKC. Employing an in-gel kinase assay where aPKC-zeta was copolymerized within the gel matrix as a substrate, three kinases, pp175, pp87 and pp60, were identified as enzymes that phosphorylated aPKC. Phosphorylation of aPKC by these three kinases coincided with NGF-induced activation of the enzyme. Each kinase possessed a unique subcellular distribution pattern and could be activated by either ceramide or H(2)0(2), second messengers that mimic NGF signaling events. Upstream, pp175 and pp60 lie in a ras pathway, whereas pp87 lies in a pathway dependent upon src. Altogether, these findings reveal that the aPKCs are subject to regulation by a novel group of kinases.