Production of 1,2-diacylglycerol in PC12 cells by nerve growth factor and basic fibroblast growth factor

Modulation of inositol polyphosphate levels regulates neuronal differentiation

The modulation of inositol pentakisphosphate (IP5) and hexakisphosphate (IP6) intracellular levels controls the differentiation and survival of PC12 cells and primary neurons. These mechanisms are controlled by the levels of the protein kinase IP5-2K responsible for the conversion of IP5 into IP6.

The binding of neurotrophins to tropomyosin receptor kinase receptors initiates several signaling pathways, including the activation of phospholipase C-γ, which promotes the release of diacylglycerol and inositol 1,4,5-trisphosphate (IP₃). In addition to recycling back to inositol, IP₃ serves as a precursor for the synthesis of higher phosphorylated inositols, such as inositol 1,3,4,5,6-pentakisphosphate (IP₅) and inositol hexakisphosphate (IP₆). Previous studies on the effect of neurotrophins on inositol signaling were limited to the analysis of IP₃ and its dephosphorylation products. Here we demonstrate that nerve growth factor (NGF) regulates the levels of IP₅ and IP₆ during PC12 differentiation. Furthermore, both NGF and brain-derived neurotrophic factor alter IP₅ and IP₆ intracellular ratio in differentiated PC12 cells and primary neurons. Neurotrophins specifically regulate the expression of IP₅-2 kinase (IP₅-2K), which phosphorylates IP₅ into IP₆. IP₅-2K is rapidly induced after NGF treatment, but its transcriptional levels sharply decrease in fully differentiated PC12 cells. Reduction of IP₅-2K protein levels by small interfering RNA has an effect on the early stages of PC12 cell differentiation, whereas fully differentiated cells are not affected. Conversely, perturbation of IP₅-2K levels by overexpression suggests that both differentiated PC12 cells and sympathetic neurons require low levels of the enzyme for survival. Therefore maintaining appropriate intracellular levels of inositol polyphosphates is necessary for neuronal survival and differentiation.

Nerve growth factor-induced protein kinase C stimulation contributes to TrkA-dependent inhibition of p75 neurotrophin receptor sphingolipid signaling

Previous studies have established that reciprocal interactions between the low-affinity p75 nerve growth factor (NGF) receptor (p75(NTR)) and the high-affinity TrkA NGF receptor can dictate the cellular response to NGF. As the most important interaction, TrkA signaling was found to inhibit p75(NTR)-mediated sphingomyelinase (SMase) stimulation, ceramide production, and apoptosis. However, the mechanism by which TrkA counteracts p75(NTR)-coupled sphingolipid signaling is still unclear. Considering the stimulatory effect of NGF on protein kinase C (PKC) activity, we investigated the role of PKC in TrkA/p75(NTR) signaling interaction. In this study, we found that, in SK-N-BE cells, which selectively express p75(NTR), phorbol ester-induced PKC stimulation resulted in the abrogation of SMase stimulation and ceramide production induced by NGF. Moreover, in SK-N-BE neuroblastoma cells, which selectively express TrkA, NGF stimulated global PKC activity through two independent pathways involving phospholipase Cgamma (PLCgamma) and phosphoinositide-3 kinase (PI3K). In SH-SY5Y, another neuroblastoma cell line, which coexpresses TrkA and p75(NTR), NGF induced PKC stimulation through a TrkA/PI3K signaling pathway, whereas there was no ceramide production. However, in these cells, the inhibition of TrkA, PI3K, and PKC resulted in the restoration of NGF-induced ceramide production. Thus, our study demonstrates for the first time that TrkA interferes with p75(NTR) signaling through a PI3K/PKC-dependent mechanism.

Distinct protein kinase C isoforms mediate regulation of vascular endothelial growth factor expression by A2A adenosine receptor activation and phorbol esters in pheochromocytoma PC12 cells

Vascular endothelial growth factor (VEGF) stimulates angiogenesis during development and in disease. In pheochromocytoma (PC12) cells, VEGF expression is regulated by A(2A) adenosine receptor (A(2A)AR) activation. The present work examines the underlying signaling pathway. The adenylyl cyclase-protein kinase A cascade has no role in the down-regulation of VEGF mRNA induced by the A(2A)AR agonist, 2-[4-[(2-carboxyethyl)phenyl]ethylamino]-5'-N-ethylcarboxamidoadenosine (CGS21680). Conversely, 6-h exposure of cells to either phorbol 12-myristate 13-acetate (PMA) or protein kinase C (PKC) inhibitors mimicked the CGS21680-induced down-regulation. PMA activated PKCalpha, PKCepsilon, and PKCzeta, and CGS21680 activated PKCepsilon and PKCzeta as assessed by cellular translocation. By 6 h, PMA but not CGS21680 decreased PKCalpha and PKCepsilon expression. Neither compound affected PKCzeta levels. Following prolonged PMA treatment to down-regulate susceptible PKC isoforms, CGS21680 but not PMA inhibited the cobalt chloride induction of VEGF mRNA. The proteasome inhibitor, MG-132, abolished PMA- but not CGS21680-induced down-regulation of VEGF mRNA. Phorbol 12,13-diacetate reduced VEGF mRNA levels while down-regulating PKCepsilon but not PKCalpha expression. In cells expressing a dominant negative PKCzeta construct, CGS21680 was unable to reduce VEGF mRNA. Together, the findings suggest that phorbol ester-induced down-regulation of VEGF mRNA occurs as a result of a reduction of PKCepsilon activity, whereas that mediated by the A(2A)AR occurs following deactivation of PKCzeta.

A diacylglycerol-activated Ca2+ channel in PC12 cells (an adrenal chromaffin cell line) correlates with expression of the TRP-6 (transient receptor potential) protein

The structures, and mechanisms of activation, of plasma membrane intracellular-messenger-activated, non-selective cation channels in animal cells are not well understood. The PC12 adrenal chromaffin cell line is a well-characterized example of a nerve cell. In PC12 cells, 1-oleolyl-2-acetyl-sn-glycerol (OAG), a membrane-permeant analogue of diacylglycerol, initiated the inflow of Ca(2+), Mn(2+) and Sr(2+). Acetylcholine and thapsigargin initiated the inflow of Ca(2+) and Mn(2+), but not of Sr(2+). The activation of bivalent cation inflow by OAG: (i) was mimicked by another membrane-permeant diacylglycerol analogue, 1,2-dioctanoyl-sn-glycerol, but not by the membrane-impermeant analogue 1-stearoyl-2-arachidonyl-sn-glycerol; (ii) was not blocked by staurosporin or chelerythrine, inhibitors of protein kinase C; (iii) was enhanced by RHC80267 and R50922, inhibitors of diacylglycerol lipase and diacylglycerol kinase respectively; and (iv) was inhibited by extracellular Ca(2+). When OAG was added after acetylcholine, the effect of OAG on Ca(2+) inflow was over-and-above that induced by acetylcholine. 2-Aminoethyl diphenylborate (2-APB) inhibited Ca(2+) inflow initiated by either acetylcholine or thapsigargin, but not that initiated by OAG. Flufenamic acid inhibited OAG-initiated, but not acetylcholine-initiated, Ca(2+) and Mn(2+) inflow. OAG-initiated Ca(2+) inflow was less sensitive to inhibition by SK&F96365 than acetylcholine-initiated Ca(2+) inflow. In polyadenylated RNA prepared from PC12 cells, mRNA encoding TRP (transient receptor potential) proteins 1-6 was detected by reverse transcriptase (RT)-PCR, and in lysates of PC12 cells the endogenous TRP-6 protein was detected by Western blot analysis. It is concluded that PC12 cells express a diacylglycerol-activated, non-selective cation channel. Expression of this channel function correlates with expression of the TRP-3 and TRP-6 proteins, which have been shown previously to be activated by diacylglycerol when expressed heterologously in animal cells [Hofmann, Obukhov, Schaefer, Harteneck, Gudermann, and Schultz (1999) Nature (London) 397, 259-263].

Differential action of nerve growth factor and phorbol ester TPA on rat synaptosomal PKC isoenzymes

The subcellular redistribution of protein kinase C family members (alpha, beta, gamma, delta, epsilon and zeta isoforms) was examined in response to treatment with 12-O-tetradecanoyl-phorbol-13 acetate (TPA) or nerve growth factor (NGF) in a synaptosomal-enriched P2 fraction from rat brain. Treatment with TPA affected members of the classical-PKC family (alpha, beta and gamma), resulting in a final loss of total protein of each isoenzyme. The kinetics of changes of members of the novel-PKC family are different, the delta isoform being translocated, but not down-regulated, while the epsilon isoform showing only a slight diminishing of immunoreactivity in the soluble and particulate fractions. The atypical-PKC zeta isoform was not translocated in response to TPA. Incubation with NGF induced a loss of immunoreactivity of the cytosolic alpha, beta and epsilon isoforms, but the membrane fractions of these isoforms were not appreciably affected. In contrast, a marked translocation from cytosol to membrane was observed in the case of the gamma and delta isoforms. The zeta isoform presented a slight translocation from the particulate fraction to the soluble fraction. Thus, the results show that the effects of TPA and NGF on PKC isoforms are not coincident in synaptosomes, the 6 isoform being activated and not down-regulated by both treatments, whereas the gamma isoform is only down-regulated in the case of TPA, but presents sustained translocation with NGF, indicating that PKC isoform-specific degradation pathways exist in synaptic terminals. The effects of NGF on PKC isoforms coexist with an increase in NGF-induced polyphosphoinositide hydrolysis, suggesting the participation of phospholipases.

Ceramides modulate protein kinase C activity and perturb the structure of Phosphatidylcholine/Phosphatidylserine bilayers

We studied the effects of natural ceramide and a series of ceramide analogs with different acyl chain lengths on the activity of rat brain protein kinase C (PKC) and on the structure of bovine liver phosphatidylcholine (BLPC)/dipalmitoylphosphatidylcholine (DPPC)/dipalmitoylphosphatidylserine (DPPS) (3:1:1 molar ratio) bilayers using (2)H-NMR and specific enzymatic assays in the absence or presence of 7.5 mol % diolein (DO). Only a slight activation of PKC was observed upon addition of the short-chain ceramide analogs (C(2)-, C(6)-, or C(8)-ceramide); natural ceramide or C(16)-ceramide had no effect. In the presence of 7.5 mol % DO, natural ceramide and C(16)-ceramide analog slightly attenuated DO-enhanced PKC activity. (2)H-NMR results demonstrated that natural ceramide and C(16)-ceramide induced lateral phase separation of gel-like and liquid crystalline domains in the bilayers; however, this type of membrane perturbation has no direct effect on PKC activity. The addition of both short-chain ceramide analogs and DO had a synergistic effect in activating PKC, with maximum activity observed with 20 mol % C(6)-ceramide and 15 mol % DO. Further increases in C(6)-ceramide and/or DO concentrations led to decreased PKC activity. A detailed (2)H-NMR investigation of the combined effects of C(6)-ceramide and DO on lipid bilayer structure showed a synergistic effect of these two reagents to increase membrane tendency to adopt nonbilayer structures, resulting in the actual presence of such structures in samples exceeding 20 mol % ceramide and 15 mol % DO. Thus, the increased tendency to form nonbilayer lipid phases correlates with increased PKC activity, whereas the actual presence of such phases reduced the activity of the enzyme. Moreover, the results show that short-chain ceramide analogs, widely used to study cellular effects of ceramide, have biological effects that are not exhibited by natural ceramide.

Anandamide stimulates phospholipase D activity in PC12 cells but not in NIH 3T3 fibroblasts

The endogenous cannabinoid arachidonoylethanolamide was previously reported to have no effects on the phospholipase D activity in Chinese hamster ovary cells expressing the human brain-specific cannabinoid receptor, while in mouse peritoneal cells, delta9-tetrahydrocannabinol stimulated this enzyme. In this work, arachidonoylethanolamide (0.1-1 microM) was found to stimulate the phospholipase D-mediated phospholipid hydrolysis in rat adrenal pheochromocytoma PC12 cells, but not in mouse NIH 3T3 fibroblasts. The phospholipase D-activating effects of arachidonoylethanolamide were comparable to those elicited by phorbol ester and nerve growth factor, while arachidonic acid (1 microM) had no effects. The results show that, depending on the cell type, arachidonoylethanolamide can be an activator of the phospholipase D system.

Synergistic effects of diacylglycerols and fatty acids on membrane structure and protein kinase C activity

The synergistic effects of diacylglycerol (DAG) and fatty acid (FA) in activating protein kinase C have been investigated by correlating their individual and combined effects on enzymatic activity and on membrane structure in phosphatidylcholine/phosphatidylserine (4:1) lipid mixtures using a combination of specific enzymatic assays and 31P and 2H NMR. Addition of DAGs and unsaturated FAs to the bilayers synergistically increased the tendency of the lipids to form nonbilayer phases with a concomitant increase in PKC activity until a maximum was achieved. Further increases in the DAG/FA concentration led to the formation of the nonbilayer lipid phases under the conditions of the PKC activity assays and correlated with decreased activity. The nonbilayer lipid phases still supported PKC activity, although with less than 50% efficiency as compared with the bilayer lipids. Long-chain saturated FA increased DAG-induced PKC activity by causing a lateral phase separation of gel (Lbeta) and liquid-crystalline (Lalpha) domains. Due to the preferential partitioning of DAGs into liquid-crystalline domains, the local DAG concentration increased in these domains, leading to an increase in PKC activity. Because a wide range of lipophilic compounds is capable of altering curvature stress, and therefore the tendency for nonbilayer phase formation in cellular membranes, these compounds would be expected to modulate PKC activity and the activities of a number of other membrane-associated enzymes that are sensitive to biophysical properties of lipid membranes.

Control of membrane phosphatidylcholine biosynthesis by diacylglycerol levels in neuronal cells undergoing neurite outgrowth

Phospholipids are the major components of cell membranes and are required for cellular growth. We studied membrane phosphatidylcholine (PtdCho) biosynthesis in neuronal cells undergoing neurite outgrowth, by using PC12 cells as a model system. When neurite outgrowth was induced by exposing PC12 cells to nerve growth factor for 2 and 4 days, the amounts of [14C]choline incorporated into [14C]phosphatidylcholine per cell (i.e., per DNA) increased approximately 5- and 10-fold, respectively, as compared with control cells, reflecting increases in the rate of PtdCho biosynthesis. [14C]choline uptake was not affected. Analysis of the three major PtdCho biosynthetic enzymes showed that the activity of CDPcholine:1,2-diacylglycerol cholinephosphotransferase was increased by approximately 50% after nerve growth factor treatment, but the activities of choline kinase or choline-phosphate cytidylyltransferase were unaltered; the cholinephosphotransferase displayed a high Km value ( approximately 1,200 microM) for diacylglycerol. Moreover, free cellular diacylglycerol levels increased by approximately 1.5- and 4-fold on the second and fourth days, respectively. These data indicate that PtdCho biosynthesis is enhanced when PC12 cells sprout neurites, and the enhancement is mediated primarily by changes in cholinephosphotransferase activity and its saturation with diacylglycerol. This suggests a novel regulatory role for diacylglycerol in membrane phospholipid biosynthesis.

Single step purification of biologically active recombinant rat basic fibroblast growth factor by immobilized metal affinity chromatography

The construction and use of a plasmid which allows the expression and single step purification of recombinant rat basic fibroblast growth factor (bFGF) is described. A cDNA encoding rat bFGF was subcloned into the expression plasmid pQE-9 (Qiagen) in such a way that the bFGF which is produced from the resulting construct contains 6 histidine residues near the amino terminus. The resulting plasmid, pQE-9-bFGF, was expressed in the E. coli strain M15[pREP4] and the 6 x His-bFGF was purified to homogeneity from the soluble fraction of the bacterial cell lysate in a single step by affinity chromatography on a nickel chelate resin. About 5 mg of 6 x His-bFGF was obtained from the soluble fraction from one liter of bacterial cell culture. Testing of the 6 x His-bFGF in a PC12 cell differentiation assay showed that its activity was comparable to the activities for native bFGF and recombinant bFGF purified by multistep methods.

A neuronal protein tyrosine phosphatase induced by nerve growth factor

A new protein tyrosine phosphatase (PC12-PTP1) was identified in nerve growth factor (NGF)-treated PC12 cells. The mRNA level of PC12-PTP1 is increased 9-fold over the initial 8 h of NGF treatment and then decreases dramatically after 24 h of treatment. In rat brain, three transcripts corresponding to 1.5, 2.6, and 3.0 kilobases (kb) in size are detected by Northern blot analysis. Although the 1.5- and 2.6-kb transcripts are present in brain and other tissues, the 3-kb transcript is exclusively expressed in brain and the expression of this transcript alone increases following NGF treatment. PC12-PTP1 is a non-receptor protein tyrosine phosphatase (PTP) with a 50% sequence homology in the phosphatase domain with several other non-receptor PTPs. PC12-PTP1 fusion protein exhibits tyrosine phosphatase activity, and in vitro translation of the PC12-PTP1 transcript produces a major protein of 39 kDa. The data presented suggest that NGF regulates the expression of PC12-PTP1 during periods of neuronal growth and differentiation.

The mitogenic action of recombinant basic FGF in Swiss 3T3 cells is independent of early diradylglycerol production and downregulatable protein kinase C activity

In this study we have investigated the requirement for phosphoinositide metabolism, diradylglycerol (DG) production and protein kinase C (PKC) activation in recombinant basic fibroblast growth factor (rbFGF)-mediated reinitiation of DNA synthesis in Swiss 3T3 cells. We have assessed the involvement of PKC activation in rbFGF-induced DNA synthesis by two approaches; enzymic inhibition by H7 and down-regulation by prolonged phorbol-ester treatment. In both conditions we observed that rbFGF was able to sustain a significant component of its mitogenic response, therefore denying an exclusive role for the activation of downregulatable and H7-sensitive PKC isoforms in rbFGF-induced reinitiation of DNA synthesis. Moreover, we have found no evidence for diacylglycerol accumulation in response to rbFGF by 3T3 cells. In previous studies, we observed that rbFGF caused a moderate and slow accumulation of total inositol phosphates. This effect was significant only after a 60 min incubation. It is our contention that rbFGF, in our culture system, does not exert a direct effect on phosphoinositide metabolism.

A bryostatin-sensitive protein kinase C required for nerve growth factor activity

Nerve growth factor (NGF) stimulates rat pheochromocytoma cells (PC12) to differentiate into a neuronal-like cell that exhibits neurite extensions. The role of protein kinase C in signal transduction has been examined in PC12 cells treated with phorbol 12-myristate 13-acetate (PMA) and bryostatin, a macrocyclic lactone that activates protein kinase C at both the nuclear and the plasma membranes [Hocevar, B. A., & Fields, A. P. (1991) J. Biol. Chem. 266, 28-33]. In contrast to PMA down-regulation [Reinhold, D. S., & Neet, K. E. (1989) J. Biol. Chem. 264, 3538-3544], chronic (24 h) treatment with bryostatin blocked the formation of neurites in response to NGF or basic fibroblast-derived growth factor stimulation, but, like PMA, bryostatin did not block the induction of c-fos or c-jun protooncogenes by NGF. Chronic bryostatin treatment down-regulated protein kinase C activity in the cytosolic, membrane, and nuclear fractions. Acute (60 min) bryostatin or NGF treatment activated cytosolic and nuclear protein kinase C activity, suggesting possible translocation to the nucleus. Bryostatin did not induce neurite outgrowth, either alone or in combination with PMA. Thus, the bryostatin-sensitive protein kinase C is distinct from PMA- or K252a-sensitive kinases previously described. The bryostatin-sensitive protein kinase C is necessary, but not sufficient, for neurite outgrowth and acts in the nucleus in a manner independent of c-fos and c-jun transcription.

HOE-BAY 946 has distinct effects on spontaneous and FGF induced proliferation of epithelial and neuroblastoma cell lines

We have studied in vitro the effects of HOE-BAY 946, a specific inhibitor of tyrosine kinase C, on spontaneous and basic FGF-induced proliferation of the epithelial cell lines A549 and HELA as well as the neuroblastoma cell line SY5Y using a fully automated colorimetric assay for determinations of cell numbers. HOE-BAY suppressed spontaneous proliferation of the epithelial lines, but not the neuroblastoma line, both in the presence and absence of serum. In contrast, the drug completely abolished the mitogenic effect of basic FGF on all cell lines. This suggests an involvement of a tyrosine kinase C activity in the transduction of the FGF signal both in the epithelial and neuroblastoma lines. Since the action of FGF on non-transformed neuronal cells is accompanied by a down-regulation of kinase C, and kinase C activation blocks the FGF effects, our data indicate that differentiative and mitogenic effects of FGF on neuronal cells may employ different transduction mechanisms.

Protein kinase C isozymes that mediate enhancement of neurite outgrowth by ethanol and phorbol esters in PC12 cells

Using PC12 cells to study ethanol's effects on growth of neural processes, we found that ethanol enhances NGF- and basic FGF-induced neurite outgrowth. Chronic ethanol exposure selectively up-regulates delta and epsilon protein kinase C (PKC) and increases PKC-mediated phosphorylation in PC12 cells. Since PKC regulates differentiation, we investigated the role of PKC in enhancement of neurite outgrowth by ethanol. Like ethanol, 0.3-10 nM phorbol 12-myristate, 13-acetate (PMA) increased NGF-induced neurite outgrowth. However, higher concentrations did not, and immunoblot analysis demonstrated that 100 nM PMA markedly depleted cells of beta, delta and epsilon PKC. PMA (100 nM) also down-regulated beta, delta and epsilon PKC in ethanol-treated cells and completely prevented enhancement of neurite outgrowth by ethanol. In contrast, the cAMP analogue 8-bromoadenosine cAMP did not completely mimic the effects of ethanol on neurite outgrowth, and ethanol was able to enhance neurite formation in mutant PC12 cells deficient in protein kinase A (PKA). These findings implicate beta, delta or epsilon PKC, but not PKA, in the neurite-promoting effects of ethanol and PMA. Since chronic ethanol exposure up-regulates delta and epsilon, but not beta PKC, these findings suggest that delta or epsilon PKC regulate neurite outgrowth.

Attenuation of insulin actions in primary rat hepatocyte cultures by phenylarsine oxide

Phenylarsine oxide (PAO), a trivalent arsenical which complexes vicinal dithiols, prevented the action of insulin in primary cultured adult rat hepatocytes. Simultaneous short-term treatment of 48-h old cells with insulin and 2 microM PAO resulted in complete attenuation of the insulin-dependent increase in the level of fructose 2,6-bisphosphate and the activation of phosphofructokinase 2, pyruvate kinase, glucokinase flux and glycolysis. Basal rates of glucose transport and glycolysis were not affected. PAO also abolished stimulation of glycogen synthesis and amino-acid transport and the decrease of glycogenolysis evoked by insulin. The 20-fold activation of the insulin receptor tyrosine kinase by insulin was, however, not reduced by PAO. The data suggest that in differentiated hepatocytes insulin signal transduction involves vicinal sulhydryls located at a post-receptor step.

Nerve growth factor stimulates the production of inositol 1,3,4- and 1,4,5-trisphosphate and inositol 1,3,4,5-tetrakisphosphate in PC12 cells

In PC12 cells, preincubated with [3H]inositol, nerve growth factor (NGF) stimulated an approximately 100% increase in the levels of [3H]inositol 1,3,4-trisphosphate ([3H]-Ins(1,3,4)P3], [3H]inositol 1,4,5-trisphosphate ([3H]Ins(1,4,5)P3], and [3H]inositol 1,3,4,5-tetrakisphosphate ([3H]Ins(1,3,4,5)P4] as early as 5-15 s after addition of NGF. This NGF-mediated response was apparent only when the cells had been cultured in the absence of fetal bovine serum (FBS). PC12 cells cultured in FBS-containing medium did not display NGF-mediated increases in [3H]Ins(1,3,4)P3, [3H]Ins(1,4,5)P3, and [3H]Ins(1,3,4,5)P4 levels. Using cells cultured in the absence of FBS, epidermal growth factor (EGF) and fibroblast growth factor also stimulated production of [3H]Ins(1,3,4)P3, [3H]Ins(1,4,5)P3, and [3H]Ins(1,3,4,5)P4. Lavendustin A, a tyrosine kinase inhibitor, inhibited both the EGF- and NGF-stimulated increases in the levels of these tritiated inositol phosphates. These results suggest that NGF stimulates the production of Ins(1,3,4)P3, Ins(1,4,5)P3, and Ins(1,3,4,5)P4 and that this response is dependent on tyrosine kinase activity. Furthermore, although the production of Ins(1,3,4)P3, Ins(1,4,5)P3, and Ins(1,3,4,5)P4 may be a common response to factors stimulating neuronal differentiation, it is not sufficient for stimulation of neuronal differentiation.

Phenylarsine oxide (PAO) blocks antigen receptor-induced calcium response and tyrosine phosphorylation of a distinct group of proteins

Antigen receptor (AgR) crosslinking by antigens or AgR-specific antibodies induces a cascade of enzymatic events in lymphocytes which involves activation of several non-receptor tyrosine- and serine/threonine kinases, phosphatases, phospholipases, etc. Here we show data demonstrating that a thiol group-reactive protein tyrosine phosphatase (PTP) inhibitor, phenylarsine oxide (PAO), uncouples a crucial part of the signaling events induced by anti-IgM or anti-Leu-4 (CD3) in human tonsil B lymphocytes, BL41 and Daudi B cell lines and Jurkat T lymphoma cells. PAO treatment (10 microM) resulting in distinct modification of AgR-induced tyrosine phosphorylation pattern inhibited the AgR-mediated calcium response (Ca++ release and influx) of all of these cells completely. Since this treatment did not alter the cell viability and the binding capacity of the AgR crosslinking antibodies, alteration of the tyrosine phosphorylation pattern and blockage of the calcium response indicate prompt inactivation of essential signal transduction element(s).

Immunocytochemical analysis of phosphatidylinositol-specific phospholipase C in PC12 cells: predominance of the delta isoform during neural differentiation

The rat pheochromocytoma PC12 cell line, which differentiates into sympathetic neurons under nerve growth factor (NGF) treatment, contains at least three phosphoinositidase C (PIC) isozymes, PIC beta, PIC gamma, PIC delta. These isozymes have been previously shown to display a different subcellular localization. To determine whether or not NGF induces changes in the presence and/or distribution of PIC isozymes during PC12 neural differentiation, studies were carried out by means of in situ immunocytochemistry. After NGF administration the proliferative activity was progressively reduced to very low levels, as measured by bromodeoxy Uridine incorporation, and a neuron-like morphology was displayed by almost all cells. In unstimulated PC12 cells, PIC beta was detected in the nucleus whereas PIC delta was only cytoplasmic; PIC gamma was found in both cell compartments. In cells treated with NGF for 3 days, neural processes extended to twice the diameter of the cell body; the gamma isoform was concentrated near the nucleus, while the immunoreactivity of the beta form remained constant and the delta form was increased. After 10 days of treatment with NGF, PIC beta was hardly detectable and PIC gamma immunostaining was considerably decreased. On the contrary, PIC delta progressively increased and, after 14 days of NGF exposure, fully differentiated cells displayed an intense labelling of cell body and neurites. In the same cells, PIC beta and PIC gamma were almost negative. These results suggest that NGF dependent neural differentiation is related to the selective down regulation of PIC beta and gamma and the increase of PIC delta isozyme associated with the decrease of cell proliferation.

Down-regulation of phosphatidylinositol response to BDNF and NT-3 in cultures of cortical neurons

The hydrolysis of phosphatidyl 4,5-bisphosphate (PI), which is involved in the transduction mechanism of neurotransmitters and growth factors, is stimulated by brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) in primary cultures of fetal brain neurons. In the present study we sought to examine the effect of pretreatment with these factors on their acute stimulation capabilities and, furthermore, to substantiate that the effects of BDNF and NT-3 reflect actions on neurons rather than glial cells. Pretreatment with BNDF and NT-3 for 4 days followed by 1 day without growth factor abolished the effect of an acute stimulation with these factors. The growth factors were mutually effective so that BDNF pretreatment abolished the acute response to NT-3 and vice versa. In contrast, the effects of bFGF (basic fibroblast growth factor, a non-neurotrophin growth factor) also stimulating PI hydrolysis in these culture systems, were not reduced by neurotrophin pretreatment. Pretreatment with K-252b, at concentrations known to inhibit trk receptors, did not alter the acute stimulation of PI hydrolysis induced by the neutrophins. PI hydrolysis stimulated by BDNF and NT-3 in cultures grown in presence of cytosine arabinoside C, containing > 95% neurons, was higher than in cultures containing non-neuronal cells, indicating that the neurotrophin stimulation occurs in neuronal cells. No stimulatory effect was detected in bFGF treated pure neuronal cultures. The findings suggest that prolonged exposure of responsive neurons to BDNF and NT-3 down-regulates their stimulatory effects on PI hydrolysis.

Rapid phosphorylation of phospholipase C gamma 1 by brain-derived neurotrophic factor and neurotrophin-3 in cultures of embryonic rat cortical neurons

Phospholipase C gamma 1 (PLC-gamma 1) is involved at an early step in signal transduction of many hormones and growth factors and catalyzes the hydrolysis of phosphatidylinositol (PI) 4,5-bisphosphate to diacylglycerol and inositol trisphosphate, two potent intracellular second messenger molecules. The transformation of PC12 cells into neuron-like cells induced by nerve growth factor is preceded by a rapid stimulation of PLC-gamma 1 phosphorylation and PI hydrolysis. The present study analyzed the effects of brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) on phosphorylation of PLC-gamma 1 in primary cultures of embryonic rat brain cells. BDNF and NT-3 stimulated the phosphorylation of PLC-gamma 1, followed by hydrolysis of PI. The stimulation of PLC-gamma 1 phosphorylation occurred within 20 s after addition of BDNF or NT-3 and lasted up to 30 min, with a peak after 4 min. ED50 values were similar for BDNF and NT-3, with approximately 25 ng/ml. Phosphorylation of PLC-gamma 1 by BDNF and NT-3 was found in cultures from all major brain areas. K-252b, a compound known to inhibit selectively neutrophin actions by interfering with the phosphorylation of trk-type neutrophin receptors, prevented the BDNF- and NT-3-stimulated phosphorylation of PLC-gamma 1. Receptors of the trk type were coprecipitated with anti-PLC-gamma 1 antibodies. The presence of trkB mRNA in the cultures was substantiated by northern blot analysis. The action of BDNF and NT-3 seems to be neuron specific because no phosphorylation of PLC-gamma 1 was observed in cultures of nonneuronal brain cells. The results provide evidence that developing neurons of the cerebral cortex and other brain areas are responsive to BDNF and NT-3, and they indicate that the transduction mechanism of BDNF and NT-3 in the brain involves rapid phosphorylation of PLC-gamma 1 followed by PI hydrolysis.

Effect of nerve growth factor and fibroblast growth factor on PC12 cells: inhibition by orthovanadate

Sodium orthovanadate, an inhibitor of protein tyrosine phosphatases, causes increased levels of tyrosine phosphorylation and blocks, at noncytotoxic concentrations, the differentiative response of rat pheochromocytoma (PC12) cells to beta-nerve growth factor (beta NGF) and basic fibroblast growth factor (bFGF) in a reversible manner. It also prevents growth factor-induced neurite proliferation in primed cells and causes the retraction of previously formed neurites, even in the presence of beta NGF or bFGF. It is equally effective in blocking neurite proliferation by 8-Br-cAMP. Zinc chloride and ammonium molybdate, two other inhibitors of tyrosine phosphatases, also cause parallel decreases in neurite proliferation. Orthovanadate generally reduces the transcription of immediate early response genes (TIS 8 and c-fos) and secondary response genes (ornithine decarboxylase (ODC), acetyl-cholinesterase (AChE) and SCG 10) induced by beta NGF, bFGF, EGF, and PMA, albeit in a variable fashion. There was no observed effect on the kinetics of expression as judged by TIS 8 induction by beta NGF and protein kinase C (PKC) downregulation did not change the levels of inhibition by orthovanadate seen in control cells. Orthovanadate does not affect the production of diacylglycerol induced by beta NGF or bFGF. These observations are consistent with the view that growth factor stimulation of differentiation in PC12 cells involves at least one other PKC independent pathway, and that cAMP and PMA (and their active analogs) activate tyrosine kinases (albeit probably secondarily), which are at least partially responsible for their actions. Although the exact site(s) of action of orthovanadate that lead to the inhibition of growth factor-induced neurite proliferation are unknown, the results presented suggest that it prolongs tyrosine phosphorylations by nonreceptor tyrosine kinases that act downstream from the receptor kinases.

Stimulation of phosphatidylinositol hydrolysis by brain-derived neurotrophic factor and neurotrophin-3 in rat cerebral cortical neurons developing in culture

Phosphatidylinositol (PI) breakdown represents a powerful system participating in the transduction mechanism of some neurotransmitters and growth factors and producing two second messengers, diacylglycerol and inositol trisphosphate. The transformation of PC12 neuroblastoma cells into neuron-like cells induced by nerve growth factor (NGF) is preceded by a rapid stimulation of PI breakdown; however, it was not known whether PI breakdown mediates actions of other members of the neurotrophin family. The present study analyzed the effects of NGF, brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3) on PI breakdown in primary cultures of embryonic rat brain cells. Cultures were grown for 7 days; PI was then labeled by incubating cultures with myo-[3H]inositol, which then were exposed acutely to growth factors. BDNF and NT-3, but not NGF, elevated the levels of labeled inositol phosphates within 10-15 min after addition to the cultures in a dose-dependent manner. ED50 values for BDNF and NT-3 were 12.4 and 64.5 ng/ml, respectively. Comparable effects were found in cultures of cortical, striatal, and septal cells. The actions of BDNF and NT-3 probably reflect actions on neurons, because no effects were seen in cultures of nonneuronal cells. In contrast, basic fibroblast growth factor induced a marked stimulation of PI breakdown in cultures of nonneuronal cells. K252b, which selectively blocks neurotrophin actions by inhibiting trk-type receptor proteins, prevented the PI breakdown mediated by BDNF and NT-3. The findings suggest that rapid and specific induction of PI breakdown is involved in the signal transduction of BDNF and NT-3, and they provide evidence that cortical neurons are functionally responsive to BDNF and NT-3 during development.

Activation of phosphatidylinositol 3-kinase by epidermal growth factor, basic fibroblast growth factor, and nerve growth factor in PC12 pheochromocytoma cells

Epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), and nerve growth factor (NGF), which stimulate the phosphorylation of proteins on tyrosine in PC12 cells, initiate these modifications through ligand-specific cell surface receptors that contain the causative tyrosine kinases. One apparent substrate for these enzymes is phosphatidylinositol 3-kinase (PI 3-kinase), an enzyme that phosphorylates the D-3 position of the inositol ring and associates with several protein tyrosine kinases, as indicated by the fact that it is immunoprecipitated from EGF-, bFGF-, and NGF-stimulated PC12 cells by an anti-phosphotyrosine antibody. All three growth factors increase immunoprecipitable PI 3-kinase activity after 2 min of addition at concentrations able to stimulate either mitogenic or neurotrophic responses in PC12 cells. The level of stimulation of PI 3-kinase activity by EGF, bFGF, and NGF is 15- to 20-fold, 2- to 3-fold, and 8- to 10-fold, respectively. Moreover, tyrosine phosphorylation of PI 3-kinase was detected in EGF-, bFGF-, and NGF-stimulated PC12 cells, and the amount of the phosphorylation correlated with the level of stimulation of enzyme activity. In contrast, phosphatidylinositol 4-kinase, which produces the inositol phospholipids cleaved by phospholipase C-gamma to yield diacylglycerol and inositol-1,4,5-trisphosphate, is not affected by these growth factors. The pattern of stimulation of PI 3-kinase does not correlate with the induction of neurite outgrowth but rather with the mitotic responses, suggesting that PI 3-kinase and its products may be more important for signaling in cell division than in trophic processes. However, the levels of phosphatidylinositol 3-phosphate do not coincide with the stimulation of [3H]thymidine incorporation by these growth factors, rendering its role in mitotic functions, at least in PC12 cells, also uncertain.

Effect of diacylglycerols on the activity of cobra venom, bee venom, and pig pancreatic phospholipases A2

The effects of a series of diacylglycerols (DAGs) with varying acyl chain lengths and degree of unsaturation on the activity of cobra venom, bee venom, and pig pancreatic phospholipases A2 (PL-A2S) were studied using two lipid substrates: dipalmitoylphosphatidylcholine (DPPC) or bovine liver phosphatidylcholine (BL-PC). The activities of the phospholipases critically depended on the chain length and degree of unsaturation of the added DAGs and on the chemical composition of the substrate. The effects of DAGs on cobra or bee venom PL-A2S were similar, but significantly different from the pig pancreatic PL-A2. The data, taken together with our previous NMR studies on physicochemical effects of these DAGs on lipid bilayer structure [De Boeck, H., & Zidovetzki, R. (1989) Biochemistry 28, 7439; (1992) Biochemistry 31, 623], allowed detailed correlation of the type of a bilayer perturbation induced by DAG with the activation or inhibition of the phospholipase on the same system. In general, the activation of the phospholipases correlated with the DAG-induced defects of the lipid bilayer structure. The results, however, argue against general designation of DAGs as "activators" or "inhibitors" of PL-A2S. Thus, for example, diolein activated phospholipases with the BL-PC lipid substrate, but inhibited them with the DPPC substrate. Dihexanoylglycerol and dioctanoylglycerol inhibited pig pancreatic PL-A2 with both lipid substrates and inhibited cobra or been venom PL-A2 with the DPPC substrate, but activated the latter two enzymes with the BL-PC substrate. Longer-chain DAGs (C greater than 12), which induce lateral phase separation of the bilayers into the regions of different fluidities, activated all PL-A2S with both lipid substrates.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of active serum albumin on PC12 cells: I. Neurite retraction and activation of the phosphoinositide second messenger system

Vertebrate blood sera contain a factor that triggers oscillatory chloride currents in Xenopus oocytes through activation of the phosphoinositide/Ca2+ second system. The active serum component consists of lipids bound to an isoform of serum albumin that we have named active serum albumin (ASA). In undifferentiated PC12 cells, micromolar concentrations of ASA inhibit the early morphological changes induced by NGF, whereas in differentiated PC12 cells ASA caused a rapid withdrawal of neurites, which was reversible and dependent upon culture age. In contrast to normal serum, plasma and thrombin did not cause neurite retraction. Preincubation of ASA with monospecific antibodies to serum albumin suppressed its ability to induce neurite retraction in a dose dependent fashion. As in the oocyte, ASA activated the phosphatidylinositol second messenger system of PC12 cells, causing a several fold increase in Ins1,4,5P3 levels within minutes of application. The Ins1,4,5P3 increase was also blocked, in a titratable fashion, when ASA was preincubated with monospecific antibodies to serum albumin. This suggests that ASA-induced neurite retraction in PC12 cells may depend, at least in part, on activation of the phosphatidylinositol second messenger system. Results involving albumin-depleted sera show that ASA is the main factor responsible for serum vulnerability of neurites in PC12 cells. These findings point to some limitations in the use of serum in culture media, and raise the possibility that the serum factor may impair neuronal plasticity in disorders that are accompanied by the activation of blood coagulation together with a breakdown of the blood-brain barrier.

The effect of active serum albumin on PC12 cells: II. Intracellular Ca2+ transients and their role in neurite retraction

In the preceding paper it was shown that an isoform of serum albumin (ASA; active serum albumin) causes a rapid retraction of neurites and increases intracellular content of Ins1,4,5P3 in PC12 cells. Here we examined whether ASA's effects in nerve growth factor-differentiated PC12 cells were mediated through the Ins1,4,5P3/Ca2+ second messenger pathway by monitoring intracellular Ca2+ (Ca2+i) with Fura2. It was found that ASA caused a dose-dependent increase in Ca2+i. In Ca(2+)-free medium, the increase in Ca2+i elicited by ASA was smaller, but the rise in Ins1,4,5P3 content was not appreciably changed. The small Ca2+i increase seen in Ca(2+)-free medium was probably due to the release of Ca2+ from Ins1,4,5P3-sensitive intracellular stores. In Ca(2+)-containing medium the Ca2+ transient induced by ASA was not affected by organic Ca2+ channel blockers, but decreased when Co2+, Mn2+ or Zn2+ were present in the extracellular medium. The effect of other ligands, such as carbachol and bradykinin, whose receptors are coupled to the phosphoinositide system was also investigated. Carbachol at concentrations from 2 to 200 microM, and bradykinin at a concentration of 2 microM did not cause neurite retraction, whereas 200 microM bradykinin caused an approximately 40% decrease in neurite length. Thapsigargin, a Ca(2+)-ATPase inhibitor, caused a sustained elevation of Ca2+i and retraction of neurites, whereas depolarization of the cells by high K+ gave only a transient elevation of Ca2+i, and no neurite retraction. Therefore, a sustained elevation in Ca2+i might be a sufficient trigger to induce neurite retraction in differentiated PC12 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Veratridine causes the Ca(2+)-dependent increase in diacylglycerol formation and translocation of protein kinase C to membranes in cultured bovine adrenal medullary cells

Our previous studies suggested that protein kinase C is involved in the veratridine (an activator of voltage-dependent Na+ channels)-induced phosphorylation and activation of tyrosine hydroxylase as well as the synthesis of catecholamines in adrenal medulla (Uezono et al. 1989). In the present study, we investigated whether treatment of cultured bovine adrenal medullary cells with veratridine causes the accumulation of diacylglycerol, a physiological activator of protein kinase C and the translocation of protein kinase C from cytosol to membrane, a process required for protein kinase C activation. Veratridine (100 mumol/l) increased diacylglycerol level about 2.2 fold in a monophasic manner, with peaking at 5 min and declining toward the basal level within 20 min. Veratridine also increased membrane protein kinase C from 15.6% to 26.9% of total protein kinase C in a time-course similar to that of diacylglycerol accumulation. Both stimulatory effects of veratridine were inhibited by tetrodotoxin and not observed in Ca(2+)-free, EGTA-containing medium. Amiloride, an inhibitor of Na+/Ca2+ and Na+/H+ exchange, did not alter veratridine-induced events. These results suggest that veratridine-induced Ca2+ influx contributes to the accumulation of diacylglycerol and the activation of protein kinase C in adrenal medullary cells.

Identification of an activator of the microtubule-associated protein 2 kinases ERK1 and ERK2 in PC12 cells stimulated with nerve growth factor or bradykinin

Treatment of PC12 pheochromocytoma cells with nerve growth factor (NGF) or bradykinin leads to the activation of extracellular signal-regulated kinases ERK1 and ERK2, two isozymes of microtubule-associated protein 2 (MAP) kinase that are present in numerous cell lines and regulated by diverse extracellular signals. The activation of MAP kinase is associated with its phosphorylation on tyrosine and threonine residues, both of which are required for activity. In the present studies, we have identified a factor in extracts of PC12 cells treated with NGF or bradykinin, named MAP kinase activator, that, when reconstituted with inactive MAP kinase from untreated cells, dramatically increased MAP kinase activity. Activation of MAP kinase in vitro by this factor required MgATP and was associated with the phosphorylation of a 42- (ERK1) and 44-kDa (ERK2) polypeptide. Incorporation of 32P into ERK1 and ERK2 occurred primarily on tyrosine and threonine residues and was associated with a single tryptic peptide, which is identical to one whose phosphorylation is increased by treatment of intact PC12 cells with NGF. Thus, the MAP kinase activator identified in PC12 cells is likely to be a physiologically important intermediate in the signaling pathways activated by NGF and bradykinin. Moreover, stimulation of the activator by NGF and bradykinin suggests that tyrosine kinase receptors and guanine nucleotide-binding protein-coupled receptors are both capable of regulating these pathways.

ERK1 and ERK2, two microtubule-associated protein 2 kinases, mediate the phosphorylation of tyrosine hydroxylase at serine-31 in situ

Tyrosine hydroxylase (TH) is phosphorylated at four sites in situ and in vivo, and the protein kinases that phosphorylate three of these sites (Ser8,Ser19,Ser40) have been identified. In intact cells, the phosphorylation of the fourth site (Ser31) is increased in response to phorbol esters or nerve growth factor (NGF). Here, we show that Ser31 is phosphorylated by ERK1 and ERK2, two myelin basic protein and microtubule-associated protein kinases. Extracts of NGF- or bradykinin-treated PC12 rat pheochromocytoma cells were fractionated on Mono Q columns. Protein kinase activity toward Ser31 in TH was present in two peaks corresponding to myelin basic protein kinase activities previously identified as ERK1 and ERK2. Phosphorylation of purified TH in vitro by both kinases was selective for Ser31 up to at least 0.6 mol of phosphate per mol of TH subunit. Treatment of intact PC12 cells with bradykinin or NGF increased both the phosphorylation of TH-Ser31 in situ and the catalytic activity of ERKs (measured subsequently in vitro with myelin basic protein as substrate). Pretreatment of the cells with genistein (a protein-tyrosine kinase inhibitor) decreased the bradykinin- but not the NGF-induced changes in both TH-Ser31 phosphorylation and ERK activity. Genistein also inhibited the increases in Ser31 phosphorylation produced by phorbol dibutyrate, muscarine, and Ba2+. The data indicate that ERK activity is responsible for phosphorylating TH at Ser31 in intact cells and suggest that TH-Ser31 phosphorylation may be regulated by multiple signaling pathways that converge at or prior to the activation of the ERKs.

Early and late effects of NGF may be mediated by different pathways in transdifferentiating chromaffin cells

Nerve growth factor (NGF) causes cultured adrenal chromaffin cells to extend neurites and, after about two weeks of exposure, to 'transdifferentiate' into mature sympathetic neurons. The molecular events leading to these responses are not fully understood, but one possible mediator of NGF's actions is protein kinase C (PKC), which can be directly activated by phorbol esters, including phorbol myristate acetate (PMA). Chronic exposure to PMA mimics the early effects of NGF, that is, it elicits the outgrowth of neurites and an enhanced rate of proliferation. However, while the initial responses to NGF and PMA are similar, after 10 days in culture striking differences become apparent: (1) cells in PMA fail to differentiate into sympathetic neuron-like cells and appear to remain in a transitional state. Even after more than 5 weeks in PMA, cells appear morphologically the same as those grown in PMA for only one week; cells fail to form a dense neuritic network or to exhibit the somatic hypertrophy characteristic of sympathetic neurons. (2) Cells continue to proliferate for at least 4 weeks in PMA, while cells in NGF become postmitotic after about two weeks. (3) While NGF supports and causes the further neuronal differentiation of cells grown in PMA, PMA cannot support NGF-dependent cells. These results suggest that different second messenger systems may be operating in the early and late effects of NGF.

Testing the in vivo role of protein kinase C and c-fos in neurite outgrowth by microinjection of antibodies into PC12 cells

To define the molecular bases of growth factor-induced signal transduction pathways, antibodies known to block the activity of either protein kinase C (PKC) or the fos protein were introduced into PC12 cells by microinjection. The antibody against PKC significantly inhibited neurite outgrowth when scored 24 h after microinjection and exposure to nerve growth factor (NGF). Microinjection of antibodies to fos significantly increased the percentage of neurite-bearing cells after exposure to either NGF or basic fibroblast growth factor (bFGF) but inhibited the stimulation of DNA synthesis by serum, suggesting that in PC12 cells, fos is involved in cellular proliferation. Thus, activation of PKC is involved in the induction of neurite outgrowth by NGF, but expression of the fos protein, which is induced by both NGF and bFGF, is not necessary and inhibits neurite outgrowth.

Activation of microtubule-associated protein kinase in PC12D cells in response to both fibroblast growth factor and epidermal growth factor and concomitant stimulation of the outgrowth of neurites

When PC12D cells, a subline of PC12 cells, were cultured with nerve growth factor (NGF), outgrowth of neurites was promoted even when RNA synthesis was blocked. This property of PC12D cells may enable us to resolve the mechanism of the outgrowth of neurites that is induced in a transcription-independent manner. The outgrowth of neurites from PC12D cells was also stimulated in response to fibroblast growth factor (FGF) and was slightly stimulated in response to epidermal growth factor (EGF). The brief exposure of intact PC12D cells not only to NGF but also to FGF or to EGF stimulated a protein kinase activity in extracts of such cells that catalyzed phosphorylation of microtubule-associated protein 1 (MAP-1) and MAP-2 in vitro. Similar dose-response relationships for the effects of NGF and of FGF on the activation of the kinase and on the outgrowth of neurites were observed. The effects of combinations of NGF and GFG or EGF were not additive in terms of either the outgrowth of neurites or the increase in the kinase activity. Treatment of cells with phorbol 12-myristate 13-acetate (PMA) also stimulated the kinase activity that phosphorylated MAPs in vitro. However, the level of the enzymatic activity that resulted from the combined treatment of cells with PMA and NGF was additive, as is the case with dibutyryl cyclic AMP and NGF. These findings suggest that NGF, FGF, and EGF may stimulate the activity of the same MAP kinase.(ABSTRACT TRUNCATED AT 250 WORDS)

Nerve growth factor induces proliferation and enhances fiber regeneration in oligodendrocytes isolated from adult pig brain

Mature oligodendrocytes (OL) isolated from adult pig brains start to regenerate their fibers after 4-5 days in vitro (DIV); after 14 DIV a network of OL fibers is formed. Growth factors, of which it was known that they play an important part during proliferation and differentiation of OL progenitor cells, were used to study their influence on the regeneration of mature OL. For this purpose, OL were treated at 6 DIV with different concentrations of various growth factors. At 24 h intervals the [3H]thymidine incorporation was measured and at 8 DIV the OL fiber production evaluated. None of these factors did influence the regenerative process to any significant extent except nerve growth factor (NGF). For the first time it could be shown that NGF enhanced the OL fiber regeneration considerably and induced the proliferation of a subset of OL. These results may have important implications for the remyelinating process in demyelinating diseases such as multiple sclerosis.

Vanadate amplifies receptor-mediated accumulation of inositol trisphosphates and inhibits inositol tris- and tetrakis-phosphatase activities

Lithium ion, which inhibits hydrolytic degradation of inositol monophosphates, is the most common therapeutic agent used in the control of bipolar disorder. There exists evidence that elevated elemental vanadium levels may play an etiological role in at least some forms of manic-depression. Here we demonstrate that vanadate treatment of intact cells from several different clonal lines synergistically induces substantial augmentation in neurotransmitter receptor-mediated or growth factor receptor-triggered inositol trisphosphate accumulation in situ. Furthermore, studies done using cellular extracts indicate that effects of vanadate treatment in situ may be due to its ability to inhibit hydrolysis of inositol 1,4,5-trisphosphate inositol 1,3,4-trisphosphate, and inositol 1,3,4,5-tetrakisphosphate in vitro. These results suggest that vanadate treatment may facilitate characterization of inositol phosphate metabolism and intracellular signaling.

Ethanol enhances growth factor-induced neurite formation in PC12 cells

Ethanol can injure the nervous system by disturbing the growth of neural processes. PC12 cells, which form neurites in response to nerve growth factor (NGF), fibroblast growth factor (FGF), and cAMP analogues, were used to study mechanisms by which ethanol alters process outgrowth. Ethanol potentiated NGF-induced neurite outgrowth in cells cultured on different substrata and in serum-containing or defined medium. Ethanol did not increase NGF receptor binding or internalization of NGF. Neurite outgrowth induced by basic FGF was also increased by ethanol but outgrowth induced by forskolin was not. Ethanol potentiated NGF-induced expression of Thy-1, but not of neural cell adhesion molecule (N-CAM), indicating that some, but not all actions of NGF are enhanced by ethanol. In some brain regions, chronic exposure to ethanol increases the growth of dendrites. This has been explained as a compensatory response of surviving neurons to the loss of neighboring cells, and not as a direct effect of ethanol. The present findings suggest that, in some cells, ethanol directly promotes growth factor-mediated neurite formation. This could harm the nervous system by disturbing the balanced development and organization of synapses.

Nerve growth factor potentiates bradykinin-induced calcium influx and release in PC12 cells

To investigate how the response to agonists changes during neuronal differentiation, we examined the effect of nerve growth factor (NGF) on bradykinin-induced calcium increases in PC12 cells. Short-term (1 h) treatment with NGF increased the potency of bradykinin to raise intracellular calcium by about 10-fold, whereas long-term (1 week) treatment, which was associated with the expression of the differentiated phenotype, increased the potency about 100-fold. Neither treatment affected the maximal response to bradykinin. NGF alone had no acute effect on calcium levels. Short-term potentiation appeared to be mainly a result of greater release of calcium from intracellular stores, whereas the effect of long-term treatment apparently was due to increases in both release from intracellular stores and calcium influx. [3H]Bradykinin binding to intact PC12 cells was unaltered by short-term NGF treatment, whereas differentiated cells displayed a 50% increase in receptor number and about a twofold increase in affinity as compared with cells not treated with NGF. The production of inositol phosphates in response to bradykinin correlated poorly with the calcium transients, in that large calcium responses were associated with small increases in inositol phosphates. Neither NGF treatment had a significant effect on the appearance of inositol phosphates in response to bradykinin. Experiments with permeabilized cells revealed that differentiated cells did not display a heightened response to exogenously added inositol 1,4,5-trisphosphate. Our results demonstrate that NGF modulates the bradykinin signaling pathway without acutely activating this pathway itself.

Carbachol stimulates a different phospholipid metabolism than nerve growth factor and basic fibroblast growth factor in PC12 cells

We have examined 1,2-diglycerides (DGs) generated in PC12 cells in response to the muscarinic agonist carbachol and compared them with those generated in response to the differentiation factors nerve growth factor and basic fibroblast growth factor. Whereas carbachol stimulates a greater release of inositol phosphates, all three agonists generate similar levels of DGs. In this report, we have analyzed the molecular species of PC12 DGs generated in response to these three agonists. Additionally, we have analyzed the molecular species of PC12 phospholipids. The data indicate that 1) after 1 min of either nerve growth factor or basic fibroblast growth factor stimulation, DGs arise primarily from phosphoinositide hydrolysis; 2) in contrast, after 1 min of carbachol stimulation, DG are generated equally by both phosphoinositide and phosphatidylcholine hydrolysis; and 3) after 15 min of stimulation by any of these agonists, DGs are generated largely by phosphatidylcholine hydrolysis, with a smaller component arising from the phosphoinositides. These results suggest that at least part of the mechanism by which PC12 cells distinguish between different agonists is via alterations in phospholipid sources and kinetics of DG generation.

Microinjection of a p21ras antibody into PC12 cells inhibits neurite outgrowth induced by nerve growth factor and basic fibroblast growth factor

The role of p21ras in signal transduction in PC12 cells was studied using an antibody that blocks its function. Native cells were microinjected with either a control solution or a solution containing the monoclonal antibody Y13-259. Treatment of the cells with growth factors appeared to enhance the ability of the cells to survive the microinjection procedure. Of the cells microinjected with the control solution 66-69% of those treated with either nerve growth factor (NGF) or basic fibroblast growth factor (bFGF) were still present 24 h post-injection, compared with only 57% for those not treated with growth factor after microinjection. This effect of the growth factors was inhibited by introduction of the Y13-259 antibody, suggesting that it occurs through a pathway that involves p21ras. Similarly, introduction of the Y13-259 antibody into cells also resulted in a statistically significant decrease in the percentage of neurite-bearing cells; 25-36% of the cells microinjected with the control solution had neurites, whereas 12-14% of the cells microinjected with the antibody solution had neurites. This decrease suggests that the induction of neurite outgrowth and the maintenance of established neurites by these growth factors is dependent on a functional p21ras pathway. As well as complementing the finding that p21ras is apparently involved in the mechanism of action of NGF in PC12 cells, these results further establish (1) that p21ras is also involved in the mechanism of action of bFGF, and (2) that the effect of NGF and bFGF on the number of labeled cells still present 24 h postinjection requires a functional p21ras protein.