Pentylenetetrazole-Induced Chemoshock Affects Protein Kinase C and Substrate Proteins in Mouse Brain

Abstract: Protein kinase C (PKC) activity, western blot analysis of PKCα, β, γ, ε, and ζ by isozyme-specific antibodies, and in vitro phosphorylation of endogenous substrate proteins were studied in the mice brain after pentyl-enetetrazole-induced chemoshock. The PKC isozymes and endogenous substrates in the crude cytosolic and membrane fractions were partially purified by DE-52 columns eluted with buffer A containing 100 or 200 m M KCI. This method consistently separates cytosolic and membrane proteins and various PKC isoforms. The 100 m M KCI eluates from DE-52 columns contain more PKC α and β in both cytosol and membrane than the 200 m M KCI eluates, whereas PKCγ, ε, and ζappear in equal amounts in these two eluates. The kinase activity assayed by phosphorylation of exogenous histone was increased in the chemoshocked mice in both the cytosol and membrane of 200 m M KCI eluates. In further analysis by immunoblotting, this increased activity was found to be due to the increase in content of PKC7 isozyme. As for novel-type ε and ζ isozymes, they were not altered in the chemoshocked mice. From autoradiography, the endogenous substrate 17-kDa neurogranin, which was shown below 21 kDa, was mostly eluted by 100 m M KCI from the DE-52 column, whereas 43-kDa neuromodulin, which was also demonstrated in sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis, only appeared in the 200 m M KCI eluates. The in vitro phosphorylation of neuromodulin was found to be increased in the chemoshocked mice. Therefore, the increased phosphorylation of neuromodulin and increased content of the PKCγ isoform were involved in the pentylenetetrazole-induced chemoshock.     

Roles of protein kinase Cα isozyme in the regulation of oxidative stress and neuropeptide Y gene expression in phenylpropanolamine-mediated appetite suppression

Hypothalamic neuropeptide Y (NPY) is an appetite stimulant in the brain. Although regulation of NPY expression has been reported to contribute to the appetite-suppressing effect of phenylpropanolamine (PPA), it is still unknown if protein kinase C (PKC) is involved in this effect. Rats were daily treated with PPA for 4 days. Changes in food intake, hypothalamic NPY, PKC, and proopiomelanocortin (POMC) mRNA levels were assessed and compared. Results showed that the NPY gene was down-regulated following PPA treatment, which was parallel with the decrease of feeding. Moreover, several isotypes of PKC mRNA level (α, βI, βII, γ, δ, η, λ, ε, and ζ) were changed. Among these, α, δ, and λ PKC were up-regulated along with POMC gene expression which coincided with down-regulation of the NPY gene. To further determine if PKCα was involved, infusions of antisense oligonucleotide into the cerebroventricle were performed at 1 h before daily PPA treatment in free-moving rats. Results showed that PKCα knock-down could modify both anorexia induced by PPA and the NPY mRNA levels. Moreover, PKCα knock-down could also modify superoxide dismutase (SOD) gene expression. It is suggested that PKCα participates in the regulation of PPA-mediated appetite suppression via the modulation of NPY and SOD gene expression.     

Induction of a Distinct Morphology and Signal Transduction in TrkB/PC12 Cells by Nerve Growth Factor and Brain-Derived Neurotrophic Factor

Abstract: A clonal cell line stably expressing trkB (TrkB/PC12) was established from rat pheochromocytoma PC12 cells. Brain-derived neurotrophic factor (BDNF), as well as nerve growth factor (NGF), stimulates neurite outgrowth in TrkB/PC12 cells. However, the morphology of BDNF-differentiated cells was clearly different from NGF-differentiated cells. BDNF treatment brought about longer and thicker neurites and induced a flattened soma and an increase in somatic size. This is not explained enough by the quantitative difference in the strength between TrkA and TrkB stimulation, because the level of BDNF-stimulated tyrosine phosphorylation of TrkB was similar to that of TrkA stimulated with NGF in PC12/TrkB cells. There was no difference in major tyrosine phosphorylated proteins induced by NGF and BDNF. Signal proteins such as phosphatidylinositol 3-kinase, phospholipase C-γ1, Shc, and mitogen-activated protein kinase seem to be involved in both TrkA- and TrkB-mediated signaling pathways. However, a tyrosine-phosphorylated 38-kDa protein (pp38) was detected in anti-pan-Trk immunoprecipitation only after NGF stimulation. Immunoprecipitation using three distinct anti-pan-Trk antibodies suggests that pp38 is not a fragment of TrkA. These data indicate that TrkA has a unique signal transduction pathway that is not stimulated through TrkB in TrkB/PC12 cells and suggest distinct functions among neurotrophin receptors.     

Antiapoptotic effects of vasopressin in the neuronal cell line H32 involve protein kinase Cα and β

Activation of V1 vasopressin (VP) receptors prevents serum deprivation-induced apoptosis in neuronal H32 cells, partially through mitogen-activated protein kinase (MAPK) mediated Bad phosphorylation. In this study, we investigated the role of protein kinases C (PKC) and B (PKB) mediating VP-induced antiapoptosis in H32 cells. Serum deprivation increased PKCδ but not PKCα or PKCβ activity, while VP increased PKCα and PKCβ without affecting PKCδ activity. Inhibition of PKCδ prevented caspase 3 activation, indicating that PKCδ mediates the pro-apoptotic actions of serum deprivation. Simultaneous inhibition of PKCα and β and MAPK abolished VP-induced Bad phosphorylation, but it only partially prevented caspase 3 inhibition. Complete abolition of the protective effect of VP on serum deprivation-induced caspase 3 activity required additional blockade of phosphoinositide 3 kinase (PI3K)/protein kinase B. The data demonstrate that VP exerts antiapoptosis through multiple pathways; while PKCα and β together with extracellular signal-regulated kinases/MAPK activation mediates Bad phosphorylation (inactivation), the full protective action of VP requires additional activation of PKB (PI3K/protein kinase B) pathway.     

Involvement of alpha5beta1 integrins in interleukin 8 production induced by oral viridans streptococcal protein I/IIf in cultured endothelial cells

Using human endothelial cells, we define a mechanism that accounts for the induction of interleukin 8 (IL-8) by protein I/IIf, an adhesin from Streptococcus mutans serotype f. We report that protein I/IIf interactions with endothelial cells increased the tyrosine phosphorylation of three cellular components with relative mass of 145 000, 125 000 and 70 000 in endothelial cells. These proteins were identified as phospholipase Cγ (PLCγ), focal adhesion kinase (FAK) and paxillin after immunoprecipitation with monoclonal antibodies (mAbs) and immunoblotting with antiphosphotyrosine mAbs. These results suggested that β1 integrins could be one of the components implicated in the modulin activity of protein I/IIf. By incubating protein I/IIf with either purified α5β1 integrins or with α5β1 integrins overexpressing CHO cells, we demonstrated that α5β1 integrins act as cell receptors for protein I/IIf. We also showed that protein I/IIf interactions with α5β1 integrins lead to IL-8 secretion. Using specific inhibitors, we demonstrated that protein I/IIf-induced IL-8 release involves mitogen-activated protein kinases (MAPKs), and that PLCγ and PKC also seem to contribute to protein I/IIf stimulation. However, PI-3K activation is not involved in IL-8 release. Altogether, these results indicate that, after binding to α5β1 integrins, protein I/IIf induces IL-8 release by activating the MAPKs signalling pathways.     

Role of Protein Kinase C α in Nerve Growth Factor-Induced Arachidonic Acid Release from PC12 Cells

Abstract: Nerve growth factor (NGF) increases arachidonic acid (AA) release by PC12 pheochromocytoma cells. To explore the role of protein kinase C (PKC) in this action of NGF, PKC was down-regulated by long-term treatment of the cells with phorbol 12-myristate 13-acetate (PMA). Such prolonged exposure to PMA (1 µ M ) resulted in the inhibition of NGF-induced AA release. Moreover, pretreatment of PC12 cells with the protein kinase inhibitor staurosporine or with calphostin C, a specific inhibitor of PKC, also blocks the increase of AA release induced by NGF. These data, as well as that PMA alone can induce AA release in PC12 cells, suggest that PKC is necessary for NGF-induced AA release. Immunoblot analysis of whole cell lysates by using antibodies against various PKC isoforms revealed that our PC12 cells contained PKCs α, δ, ε, and ζ. PMA down-regulation depleted PKCs α, δ, and ε, and partially depleted ζ. To see which isoform was involved in NGF-induced AA release, an isoform-specific PKC inhibitor was used. GO 6976, a compound that inhibits PKCs α and β specifically, blocked NGF-induced AA release. In addition, thymeleatoxin, a specific activator of PKCs α, β, and γ, induced AA release from PC12 cells in amounts comparable with those seen with NGF. Taken together, these data suggest that PKC α plays a role in NGF-induced AA release.     

The tyrosine-phosphorylated hepatocyte growth factor/scatter factor receptor associates with phosphatidylinositol 3-kinase.

The receptor for hepatocyte growth factor, also known as scatter factor (HGF/SF), has recently been identified as the 190-kDa heterodimeric tyrosine kinase encoded by the MET proto-oncogene (p190MET). The signaling pathway(s) triggered by HGF/SF are unknown. In A549 cells, a lung epithelial cell line, nanomolar concentrations of HGF/SF induced tyrosine phosphorylation of the p190MET receptor. The autophosphorylated receptor coprecipitated with phosphatidylinositol 3-kinase (PI 3-kinase) activity. In GTL16 cells, a cell line derived from a gastric carcinoma, the p190MET receptor, overexpressed and constitutively phosphorylated on tyrosine, coprecipitated with PI 3-kinase activity and with the 85-kDa PI 3-kinase subunit. In these cells activation of protein kinase C or the increase of intracellular [Ca2+] inhibits tyrosine phosphorylation of the p190MET receptor as well as the association with both PI 3-kinase activity and the 85-kDa subunit of the enzyme. In an in vitro assay, tyrosine phosphorylation of the immobilized p190MET receptor was required for binding of PI 3-kinase from cell lysates. These data strongly suggest that the signaling pathway activated by the HGF/SF receptor includes generation of D-3-phosphorylated inositol phospholipids.     

Enhanced generation of Alzheimer's amyloid-β following chronic exposure to phorbol ester correlates with differential effects on alpha and epsilon isozymes of protein kinase C

Alzheimer's amyloid precursor protein (APP) sorting and processing are modulated through signal transduction mechanisms regulated by protein phosphorylation. Notably, protein kinase C (PKC) appears to be an important component in signaling pathways that control APP metabolism. PKCs exist in at least 11 conventional and unconventional isoforms, and PKCα and PKCε isoforms have been specifically implicated in controlling the generation of soluble APP and amyloid-β (Aβ) fragments of APP, although identification of the PKC substrate phospho-state-sensitive effector proteins remains challenging. In the current study, we present evidence that chronic application of phorbol esters to cultured cells in serum-free medium is associated with several phenomena, namely: (i) PKCα down-regulation; (ii) PKCε up-regulation; (iii) accumulation of APP and/or APP carboxyl-terminal fragments in the trans Golgi network; (iv) disappearance of fluorescence from cytoplasmic vesicles bearing a green fluorescent protein tagged form of APP; (v) insensitivity of soluble APP release following acute additional phorbol application; and (vi) elevated cellular APP mRNA levels and holoprotein, and secreted Aβ. These data indicate that, unlike acute phorbol ester application, which is accompanied by lowered Aβ generation, chronic phorbol ester treatment causes differential regulation of PKC isozymes and increased Aβ generation. These data have implications for the design of amyloid-lowering strategies based on modulating PKC activity.     

Parvovirus interference with intracellular signalling: mechanism of PKCeta activation in MVM-infected A9 fibroblasts

Autonomous parvoviruses are strongly dependent on the phosphorylation of the major non-structural protein NS1 by members of the protein kinase C (PKC) family. Besides being accompanied with changes in the overall phosphorylation pattern of NS1 and acquiring new modifications at consensus PKC sites, ongoing minute virus of mice (MVM) infections lead to the appearance of new phosphorylated cellular protein species. This prompted us to investigate whether MVM actively interferes with phosphoinositol-dependent kinase (PDK)/PKC signalling. The activity, subcellular localization and phosphorylation status of the protein kinases PDK1, PKCη and PKCλ were measured in A9 cells in the presence or absence of MVM infection. Parvovirus infection was found to result in activation of both PDK1 and PKCη, as evidenced by changes in their subcellular distribution and overall (auto)phosphorylation. We show evidence that activation of PKCη by PDK1 is driven by atypical PKCλ. By modifying the hydrophobic motif of PKCη, PKCλ appeared to control docking and consecutive phosphorylation of PKCη's activation-loop by PDK1, a process that was inhibited in vivo in the presence of a dominant-negative PKCλ mutant.     

Phosphatidylinositide 3-kinase and protein kinase C zeta mediate retinoic acid induction of DARPP-32 in medium size spiny neurons in vitro

Mature striatal medium size spiny neurons express the dopamine and cAMP-regulated phosphoprotein, 32 kDa (DARPP-32), but little is known about the mechanisms regulating its levels, or the specification of fully differentiated neuronal subtypes. Cell extrinsic molecules that increase DARPP-32 mRNA and/or protein levels include retinoic acid (RA), brain-derived neurotrophic factor, and estrogen (E₂). We now demonstrate that RA regulates DARPP-32 mRNA and protein in primary striatal neuronal cultures. Furthermore, DARPP-32 induction by RA in vitro requires phosphatidylinositide 3-kinase, but is independent of tropomyosin-related kinase B, cyclin-dependent kinase 5, and protein kinase B. Using pharmacologic inhibitors of various isoforms of protein kinase C (PKC), we also demonstrate that DARPP-32 induction by RA in vitro is dependent on PKC zeta (PKCζ). Thus, the signal transduction pathways mediated by RA are very different than those mediating DARPP-32 induction by brain-derived neurotrophic factor. These data support the presence of multiple signal transduction pathways mediating expression of DARPP-32 in vitro , including a novel, important pathway via which phosphatidylinositide 3-kinase regulates the contribution of PKCζ.     

Hepatocyte growth factor-induced differential activation of phospholipase cgamma 1 and phosphatidylinositol 3-kinase is regulated by tyrosine phosphatase SHP-1 in astrocytes

Hepatocyte growth factor (HGF) elicits pleiotropic effects on various types of cells through the c-Met receptor tyrosine kinase. However, the mechanisms underlying the diverse responses of cells remain unknown. We show here that HGF promoted chemokinesis of rat primary astrocytes through the activation of phosphatidylinositol 3 (PI3)-kinase without any influence on mitogenesis of the cells. Under the same condition, phospholipase Cgamma1 (PLCgamma1), which is another signal mediator of c-Met, was not tyrosine-phosphorylated during HGF stimulation. However, treatment of the cells with orthovanadate, a tyrosine phosphatase inhibitor, restored the HGF-induced tyrosine phosphorylation of PLCgamma1. A tyrosine phosphatase, SHP-1, was associated with both PI3-kinase and PLCgamma1 before HGF stimulation, but it was dissociated only from PI3-kinase after the stimulation. Furthermore, transfectants of catalytically inactive mutant of SHP-1 showed tyrosine phosphorylation of PLCgamma1 and mitogenic responses to HGF, and the mitogenic response was blocked with, an inhibitor of phosphatidylinositol-specific PLC, and calphostin C, an inhibitor of protein kinase C downstream of the PLCgamma1. These results indicate that PLCgamma1 is selectively prevented from being a signal mediator by constitutive association of SHP-1, and that this selective inhibition of PLCgamma1 may determine the cellular response of astrocytes to HGF.     

Binding of Protein Kinase C Isoforms to Actin in Aplysia

Abstract: Recently, two of the 10 vertebrate protein kinase C (PKC) isoforms, PKCβII and PKCε, have been shown to bind specifically to actin filaments, suggesting that these kinases may regulate cytoskeletal dynamics. Here, we present evidence that two PKCs from the marine mollusk Aplysia californica , PKC Apl I, a Ca²⁺-activated PKC, and PKC Apl II, a Ca²⁺-independent PKC most similar to PKCε and η, also bind F-actin. First, they both cosedimented with purified actin filaments in a phorbol ester-dependent manner. Second, they both translocated to the Triton-insoluble fraction of the nervous system after phorbol ester treatment. PKC Apl II could also partially translocate to actin filaments and associate with the Triton-insoluble fraction in the absence of phorbol esters. Translocation to purified actin filaments was increased in the presence of a PKC inhibitor, suggesting that PKC phosphorylation reduces PKC bound to actin. Although both kinases bound F-actin, actin was not sufficient to activate the kinases. In support of a physiological role for actin-PKC interactions, immunochemical localization of PKC Apl II in neuronal growth cones revealed a striking colocalization with F-actin. Our results are consistent with a role for actin-PKC interactions in regulating cytoskeletal dynamics in Aplysia .     

Reversal of heroin neurobehavioral teratogenicity by grafting of neural progenitors

A major objective in identifying the mechanisms underlying neurobehavioral teratogenicity in an animal model is the possibility of designing therapies that reverse or offset teratogen-induced neural damage. In our previous studies, we identified deficits in hippocampal muscarinic cholinergic receptor-induced translocation of protein kinase C (PKC) γ as the likely central factor responsible for the adverse behavioral effects of pre-natal heroin exposure. Neural progenitors (NP) have the ability to recover behavioral deficits after focal hippocampal damage. Therefore, we explored whether behavioral and synaptic defects could be reversed in adulthood by neural progenitor grafting. Pregnant mice were injected daily with 10 mg/kg of heroin on gestational days 9–18. In adulthood, offspring showed deficits in the Morris maze, a behavior dependent on the integrity of septohippocampal cholinergic synaptic function, along with the loss of the PKCγ and PKCβII responses to cholinergic stimulation. Mice that were exposed pre-natally to heroin and vehicle control mice were then grafted in adulthood with NP. Importantly, most grafted cells differentiated to astrocytes. NP reversed the behavioral deficits ( p  =   0.0043) and restored the normal response of hippocampal PKCγ and PKCβII ( p  =   0.0337 and p  =   0.0265 respectively) to cholinergic receptor stimulation. The effects were specific as the PKCα isoform, which is unrelated to the behavioral deficits, showed almost no changes. Neural progenitor grafting thus offers an animal model for reversing neurobehavioral deficits originating in septohippocampal cholinergic defects elicited by pre-natal exposure to insults.     

Negative regulation of phosphatidylinositol 3-kinase and Akt signalling pathway by PKC

Although substantial studies have begun to explore the regulation of phosphatidylinositol 3-kinase/Akt cascade by different signalling pathways, whether protein kinase C (PKC) activity plays a crucial role remains as yet unclear. In this study, we found that in A549 and HEK293 cells non-selective PKC inhibitors Ro 31-8220 and bisindolylmaleimide VIII, and PKCbeta inhibitor LY 379196, caused Akt/PKB phosphorylation at Ser 473 and increased the upstream activator, integrin-linked kinase (ILK) activity. The increased Akt phosphorylation was blocked by phosphatidylinositol 3-kinase inhibitor wortmannin and the newly identified PIP(3)-dependent kinases (PDK) inhibitor SB 203580. In contrast to the Akt stimulation caused by PKC inhibitors, PMA attenuated Akt/PKB phosphorylation. We also found that this stimulating effect on Akt phosphorylation by PKC inhibitors was not the result of phosphatase inhibition, since treatment with PP2A, PP2B and tyrosine phosphatase inhibitors (okadaic acid, FK506 and sodium orthovanadate, respectively) had no effect. We conclude that phosphatidylinositol 3-kinase/Akt signalling pathway is regulated by PKC in a negative manner.     

Protein kinase C modulates negatively the hepatocyte growth factor-induced migration, integrin expression and phosphatidylinositol 3-kinase activation

Previously, we reported that, in hepatocyte growth factor (HGF)-induced HepG2 cells, protein kinase C (PKC) decreased the duration of intensive Erk1/Erk2 MAP kinase activation. This study shows that the inhibition of PKC enhanced significantly the HGF-induced integrin expression. Beside the prolonged activation of Erk1/Erk2, the activity of phosphatidylinositol 3-kinase (PI 3K) was required for growth factor-induced integrin expression. PI 3-kinase was activated to a higher extent in response to HGF than to epidermal growth factor (EGF), though the activation was transient in both cases. In EGF-induced cells, PI 3K activation was terminated by the loss of phosphotyrosine docking sites for PI 3K. To the contrary, the decrease of PI 3K activation, which followed the HGF-induced increase was not accompanied by the loss of phosphotyrosine docking sites and was prevented by the inhibition of PKC. The negative modulator effects of PKC on integrin expression and PI 3-kinase activation correlated with its ability to limit the HGF-induced motogen response.     

Two conventional protein kinase C isoforms, alpha and beta I, are involved in the ATP-induced activation of volume-regulated anion channel and glutamate release in cultured astrocytes

Volume-regulated anion channels (VRACs) are activated by cell swelling and are permeable to inorganic and small organic anions, including the excitatory amino acids glutamate and aspartate. In astrocytes, ATP potently enhances VRAC activity and glutamate release via a P2Y receptor-dependent mechanism. Our previous pharmacological study identified protein kinase C (PKC) as a major signaling enzyme in VRAC regulation by ATP. However, conflicting results obtained with potent PKC blockers prompted us to re-evaluate the involvement of PKC in regulation of astrocytic VRACs by using small interfering RNA (siRNA) and pharmacological inhibitors that selectively target individual PKC isoforms. In primary rat astrocyte cultures, application of hypoosmotic medium (30% reduction in osmolarity) and 20 μM ATP synergistically increased the release of excitatory amino acids, measured with a non-metabolized analog of l -glutamate, d -[³H]aspartate. Both Go6976, the selective inhibitor of Ca²⁺-sensitive PKCα, βI/II, and γ, and MP-20-28, a cell permeable pseudosubstrate inhibitory peptide of PKCα and βI/II, reduced the effects of ATP on d -[³H]aspartate release by ∼45–55%. Similar results were obtained with a mixture of siRNAs targeting rat PKCα and βI. Surprisingly, down-regulation of individual α and βI PKC isozymes by siRNA was completely ineffective. These data suggest that ATP regulates VRAC activity and volume-sensitive excitatory amino acid release via cooperative activation of PKCα and βI.     

Inhibition of Phosphatidylinositol 3-Kinase Activity Blocks Cellular Differentiation Mediated by Glial Cell Line-Derived Neurotrophic Factor in Dopaminergic Neurons

Abstract: Glial cell line-derived neurotrophic factor (GDNF) is a potent survival factor for midbrain dopaminergic neurons. To begin to understand the intracellular signaling pathways used by GDNF, we investigated the role of phosphatidylinositol 3-kinase activity in GDNF-stimulated cellular function and differentiation of dopaminergic neurons. We found that treatment of dopaminergic neuron cultures with 10 ng/ml GDNF induced maximal levels of Ret phosphorylation and produced a profound increase in phosphatidylinositol 3-kinase activity, as measured by western blot analysis and lipid kinase assays. Treatment with 1 µ M 2-(4-morpholinyl)-8-phenylchromone (LY294002) or 100 n M wortmannin, two distinct and potent inhibitors of phosphatidylinositol 3-kinase activity, completely inhibited GDNF-induced phosphatidylinositol 3-kinase activation, but did not affect Ret phosphorylation. Furthermore, we examined specific biological functions of dopaminergic neurons: dopamine uptake activity and morphological differentiation of tyrosine hydroxylase-immunoreactive neurons. GDNF significantly increased dopamine uptake activity and promoted robust morphological differentiation. Treatment with LY294002 completely abolished the GDNF-induced increases of dopamine uptake and morphological differentiation of tyrosine hydroxylase-immunoreactive neurons. Our findings show that GDNF-induced differentiation of dopaminergic neurons requires phosphatidylinositol 3-kinase activation.     

Characterization of TrkB Receptor-Mediated Signaling Pathways in Rat Cerebellar Granule Neurons: Involvement of Protein Kinase C in Neuronal Survival

Abstract: TrkB belongs to the Trk family of tyrosine kinase receptors and mediates the response to brain-derived neurotrophic factor (BDNF) and neurotrophin-4/5 (NT-4/5). Here, we report that both truncated and full-length forms of TrkB receptors are expressed in developing cerebellar granule neurons. BDNF and NT-4/5 increased the survival of cultured cerebellar granule neurons. BDNF and NT-4/5 also induced an autophosphorylation of TrkB receptors and subsequently resulted in a phosphorylation and binding of phospholipase C-γ (PLC-γ) and SH2-containing sequence to the autophosphorylated TrkB receptors. Both contain src homology 2 (SH2) regions. In keeping with a signaling function of PLC-γ, BDNF increased the phosphatidylinositol (PI) turnover and elevated intracellular calcium levels. To investigate the involvement of protein kinase C (PKC) in the survival of granular neurons, we show here activation of PKC after BDNF or TPA treatment and blocking of the observed survival-promoting effects of BDNF and TPA with calphostin C, a specific PKC inhibitor. In addition, BDNF activated c- ras in a concentration-dependent manner. These results suggest that two different pathways, the c- ras and the PLC-γ pathway, are activated by TrkB receptors in primary neurons and that PKC activation is involved in the survival promoting effect of BDNF.