The trk proto-oncogene rescues NGF responsiveness in mutant NGF-nonresponsive PC12 cell lines

The trk tyrosine kinase proto-oncogene product gp140prototrk binds nerve growth factor (NGF) and is rapidly and selectively activated by this neurotrophic factor. To determine whether gp140prototrk is involved in transducing a functional NGF signal, PC12 cell mutants (PC12nnr) deficient in high affinity NGF binding and unresponsive to NGF were used. Northern analysis revealed that these mutant cells have greatly reduced levels of trk expression. PC12nnr cultures were transiently transfected with expression vectors encoding the full-length rat trk cDNA and assessed for responsiveness to NGF. Expression of exogenous trk rescued the capacity for NGF-promoted neurite outgrowth, cellular hypertrophy, and serum-free survival by these cells. These results indicate that gp140prototrk is necessary for functional NGF signal transduction.

Behavioral recovery following intrastriatal implantation of microencapsulated PC12 cells

The motor deficits associated with Parkinson's disease may be ameliorated by intrastriatal placement of dopamine-secreting cells in a polymer capsule. Water soluble polyelectrolytes were utilized for membrane encapsulation of dopamine-secreting PC12 cells. Membrane permeability studies revealed exclusion of radiolabeled 69,000 Da albumin, whereas 30,000 Da carbonic anhydrase was able to cross the membrane. No cytolytic activity was observed following incubation of the encapsulated PC12 cells with PC12 cell-directed antiserum and fresh complement. In vitro, dopamine release and the surface area of intact cells per microcapsule, reached a plateau at 4 weeks that was maintained for at least 12 weeks. Viable PC12 cells were observed in microcapsules implanted for 4 and 8 weeks in nonlesioned guinea pig striata. The behavioral effect of intrastriatal dopamine release from microencapsulated PC12 cells was evaluated in the 6-hydroxydopamine unilaterally lesioned rat model. From 1 to 4 weeks postimplantation a significant reduction in rotation behavior under apomorphine challenge was observed with PC12 cell-loaded microcapsules as compared to empty microcapsules. Tyrosine hydroxylase immunopositive PC12 cells were observed 4 weeks postimplantation in all animals exhibiting a reduction in turning behavior. Implantation of polymer-encapsulated cells may provide a means for long-term delivery of neurotransmitters and growth factors to the nervous system.

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.

Multiple agents rescue PC12 cells from serum-free cell death by translation- and transcription-independent mechanisms

Past studies revealed that NGF and fibroblast growth factor (FGF) prevent the death of PC 12 pheochromocytoma cells that otherwise occurs in serum-free medium. Additional agents were tested here for their abilities to promote long-term survival of naive and NGF-pretreated (primed) PC 12 cells in serum-free conditions. Forskolin and permeant cAMP analogs effectively prevented serum-free cell death, as did micromolar levels of insulin and 10-100-nM levels of insulin-like growth factors I and II. In contrast to NGF and FGF, none of these agents caused neuronal differentiation of naive cells or neurite regeneration by primed cells. Each of the agents also prevented rapid cell death in a balanced salt solution, thus apparently ruling out a mechanism dependent on regulation of nutrient uptake. Epidermal growth factor and elevated K+ appeared to slow the rate of cell death, but did not promote long-term survival; phorbol ester, dexamethasone, or vanadate did not prevent cell death. Each of the survival-promoting agents was effective even when macromolecular synthesis was blocked. Because the synthesis inhibitors themselves did not significantly prevent cell death, such findings indicate that survival was promoted by mechanisms that do not require synthesis of RNA or protein. In addition, various lines of experimental evidence (using the kinase inhibitor K-252a or PC 12 cell variants deficient either in protein kinase A activity or in responsiveness to NGF) further suggested that the effective agents maintain survival by independent initial pathways. Regulation of protein kinase activity appears to be a common feature of each pathway and may therefore play a key convergent role in mediating prevention of cell death.

The roles of macromolecular synthesis and phosphorylation in the regulation of a protein kinase activity transiently stimulated by nerve growth factor

Past work identified and characterized an apparently novel protein kinase activity (designated HMK) that is highly and transiently stimulated in PC12 pheochromocytoma cells by nerve growth factor (NGF). In vitro, HMK phosphorylates both high molecular weight microtubule-associated proteins and myelin basic protein. This study investigates the potential mechanisms of HMK regulation in intact PC12 cells and reveals the following. 1) HMK activation is independent of macromolecular synthesis while the subsequent post-induction suppression requires both RNA and protein synthesis. 2) Neither cAMP-dependent nor Ca2+/phospholipid-dependent protein kinases appear to play a role in regulation of HMK activity by NGF. 3) In vitro, HMK activity is inactivated by protein phosphatase 2A. 4) In vivo, HMK activation by NGF is inhibited by the kinase inhibitor, K-252a. (5) Vanadate, a tyrosine phosphatase inhibitor, induces HMK activity in intact cells, while okadaic acid, a serine/threonine phosphatase inhibitor, is much less efficacious. 6) Application of okadaic acid to vanadate-pretreated cells synergistically stimulates HMK activity to a level comparable to that achieved with NGF. (7) Activation of HMK by NGF is not significantly affected when cells are pretreated with okadaic acid. However, the subsequent NGF-promoted deactivation of HMK is greatly accelerated by okadaic acid. (8) NGF down-regulated HMK activity can be heterologously restimulated by exposure to vanadate and okadaic acid. These data suggest that phosphorylation plays a critical role in both the up- and down-regulation of HMK activity in NGF-treated cells. Moreover, suppression of HMK activity requires ongoing macromolecular synthesis and appears to occur by inactivation rather than degradation.

Transplantation of polymer encapsulated neurotransmitter secreting cells: effect of the encapsulation technique

Deficits associated with neurological diseases may be improved by the transplantation within the brain lesioned target structure of polymer encapsulated cells releasing the missing neurotransmitter. Surrounding cells with a permselective membrane of appropriate molecular weight cut-off allows inward diffusion of nutrients and outward diffusion of neurotransmitters, but prevents immunoglobulins or immune cells from reaching the transplant. This technique therefore allows transplantation of post-mitotic cells across species. It also permits neural grafting of transformed cell lines since the polymer capsule prevents the formation of tumors by physically sequestering the transplanted tissue. In the present study, we compared the ability of dopamine-secreting cells, encapsulated by 2 different methods, to reverse experimental Parkinson's disease, a neurodegenerative disease characterized by motor disturbances due to a lack of dopamine within the striatum following degeneration of the dopaminergic nigro-striatal pathway. PC12 cells were loaded in polyelectrolyte-based microcapsules or thermoplastic-based macrocapsules and maintained in vitro or transplanted in a rat experimental Parkinson model for 4 weeks. Chemically-induced depolarization increased the in vitro release of dopamine from macrocapsules over time, while no increase in release was observed from microcapsules. Encapsulated PC12 cells were able to reduce lesion-induced rotational asymmetry in rats for at least 4 weeks, regardless of the encapsulation technique used. With both encapsulation methods, PC12 cell viability was greater in vivo than in vitro which suggests that the striatum releases trophic factors for PC12 cells. More brain tissue damage was observed with microcapsules than macrocapsules, possibly the result of the difficulty of manipulating the more fragile microcapsules.(ABSTRACT TRUNCATED AT 250 WORDS)

The peripherin gene maps to mouse chromosome 15

We have mapped the mouse peripherin gene, Prph, to chromosome 15 by means of Southern analysis of a panel of Chinese hamster/mouse somatic cell hybrids using a rat peripherin cDNA probe. Peripherin is a recently characterized type III intermediate filament expressed in the peripheral and the central nervous system. Although its exact function is not known, peripherin is likely to be involved in the neuronal cytoskeleton, a role it shares with other intermediate filaments, such as the neurofilament proteins. The intermediate filament gene family is believed to have evolved via gene duplication and dispersal throughout the genome; these processes have resulted in clusters of intermediate filament genes on specific chromosomes and conservation of these chromosomal locations among mammalian species.

Regulation of peripherin and neurofilament expression in regenerating rat motor neurons

Northern blotting, in situ hybridization and immunocytochemistry were used to study the changes in levels of mRNA coding for peripherin and in immunoreactivity of peripherin, a type III neuronal intermediate filament, in rat spinal motor neurons following axotomy of the sciatic nerve. For comparison, parallel studies examined the biology of neurofilament (NF) proteins in this model. The sciatic nerve was crushed at the junction of the L4-L5 spinal nerves. Levels of messenger RNA (mRNA) coding for peripherin in the motor neurons doubled by 4 days postaxotomy and remained elevated for a period of 6 weeks. Within 4-7 days of injury peripherin immunoreactivity increased significantly in cell bodies of motor neurons and remained elevated through 6 weeks. In contrast, no changes were detected in NF-M immunoreactivity over the same time period. By 8 weeks postaxotomy, levels of peripherin mRNA and protein returned to control values. The increases in the expression of peripherin parallel those of beta-tubulin and actin, and these changes are quite different from the alterations in neurofilament mRNA that decrease after axotomy. The contrasting responses of peripherin and NF to nerve injury indicates that each of these intermediate filaments may play distinct roles in nerve growth and regeneration.

Nerve growth factor and fibroblast growth factor selectively activate a protein kinase that phosphorylates high molecular weight microtubule-associated proteins. Detection, partial purification, and characterization in PC12 cells

A cell-free assay has been developed to detect and characterize a nerve growth factor (NGF)-stimulated protein kinase activity in PC12 cells that phosphorylates high molecular weight microtubule-associated proteins (HMW-MAPs). The activity was partially purified and separated from other endogenous nonregulated HMW-MAP kinase activities by chromatography on heparin-Sepharose and Mono-Q resin. Characterization of the NGF-activated kinase (designated HMK) revealed the following features. 1) Both MAP1 and MAP2 are phosphorylated with approximately equal efficiencies. 2) Activation reaches a plateau within 3 min of NGF treatment and persists for approximately 60 min; subsequently, a substantial decline occurs by 5 h. 3) Maximal activation reaches 15-20-fold; activation is nearly as high with fibroblast growth factor, an agent that mimics NGF in promoting PC12 cell neuronal differentiation. 4) Epidermal growth factor and depolarizing levels of K+ stimulate HMK activity by only 2-4-fold; additional agents without PC12 cell differentiation activity (insulin, phorbol ester, and a permeant cAMP analogue) do not stimulate HMK activity. 5) The divalent cation requirement shows a preference for Mn2+ over Mg2+. 6) There is inhibition by 10 mM 2-aminopurine but not by 6-thioguanine, heparin, or NaF. 7) HMW-MAPs and myelin basic protein are effective substrates while histones IIIs and H1, dephospho-beta-casein, and S6 protein are not phosphorylated by HMK. These and other features appear to distinguish HMK from a variety of other well-characterized protein kinases as well as from other previously described NGF-activated kinases. The properties of HMK indicate that it could play a role in the signaling pathway for growth-factor-promoted neuronal differentiation.

Capillary hemangioma of the maxilla. A report of two cases in which angiography and embolization were used

This article presents two clinical cases of capillary hemangiomas of the maxilla. Such lesions are rare, as demonstrated by the review of the literature included in this article. The presentation, differential diagnosis, histopathology, management, and follow-up for each case are discussed. Our rationale for approaching these types of lesions, as well as our opinion that microembolization should be considered as a first line approach to treatment, is presented.

Induction of ornithine decarboxylase by nerve growth factor in PC12 cells: dissection by purine analogues

Purine analogues were used to probe the mechanism by which nerve growth factor (NGF) and other agents regulate cellular ornithine decarboxylase (ODC) activity. Exposure of cultured rat pheochromocytoma PC12 cells to NGF causes a 10-50-fold induction of ODC activity within 4-6 h. We recently found that purine analogues block this induction as well as other, but not all, actions of NGF and have provided evidence that the inhibitory actions of the analogues may be due in part to the suppression of an NGF-activated protein kinase activity (Volonté, C., Rukenstein, A., Loeb, D. M., and Greene, L. A. (1989) J. Cell Biol. 109, 2395-2403). The present results show that the purine analogues also suppress the induction of ODC mRNA. One of the analogues used was 6-thioguanine (6-TG). Although 6-TG was effective when applied simultaneously with NGF, if NGF was administered for as little as 1-3 min before 6-TG, ODC induction was unimpaired. This suggests that 6-TG blocks an early step in the NGF mechanism, and that once this step is triggered, the ODC induction pathway is no longer sensitive to this analogue. In contrast, another purine analogue, 2-aminopurine (2-AP), effectively inhibited ODC induction even if applied only during the last hour of a 5-h exposure to NGF. It is hypothesized that this increased period of sensitivity to 2-AP may be due to its broader range (as compared to 6-TG) as an inhibitor of protein kinase activities. Epidermal growth factor (EGF) and cAMP derivatives also induce ODC activity in PC12 cells, and these effects were suppressed by 6-TG and 2-AP at concentrations similar to those that affect responses to NGF. However, short term (less than 30 min) pretreatment with EGF or a cAMP derivative did not protect induction of ODC activity by these agents from inhibition by 6-TG. This suggests that there are both convergent and divergent elements in the mechanistic pathways used by NGF, cAMP analogues, and EGF to induce ODC.

Purine analogs inhibit nerve growth factor-promoted neurite outgrowth by sympathetic and sensory neurons

Past studies have shown that purine analogs block certain, but not all, responses of cultured rat PC12 pheochromocytoma cells to nerve growth factor (NGF). In the present work, newborn rat sympathetic and sensory neurons were exposed to NGF in the presence or absence of the purine analogs 6-thioguanine and 2-aminopurine. These compounds reversibly suppressed NGF-dependent neurite outgrowth by the neurons and did so at concentrations comparable to those effective on PC12 cells. In contrast to their effects on neurites, neither compound significantly blocked NGF-promoted neuronal survival. Similar effects were seen with cultures of chick embryo sympathetic ganglia. These findings show that purine analog effects on NGF responses can be extended to mammalian and avian neurons. Moreover, the differential effects of the analogs on neurite outgrowth and survival indicate that these 2 actions of NGF can be dissected from one another and may represent different mechanistic pathways.

Multiple pathways of N-kinase activation in PC12 cells

Past work established a cell-free assay for a nerve growth factor (NGF)-activated protein kinase activity (designated N-kinase) that utilizes tyrosine hydroxylase and histone H1 as substrates and that is distinct from a variety of well-characterized kinases. This study explores the specificity and mechanistic pathway(s) by which N-kinase activity is regulated in PC12 rat pheochromocytoma cells. N-kinase is rapidly activated in these cells by treatment with NGF, epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), phorbol ester, or dibutyryl cyclic AMP. Our data indicate that the stimulated activity is the same for each agent by several criteria: It exhibits the same characteristic biphasic elution pattern by Mono S fast protein liquid chromatography (FPLC), except for the case of dibutyryl cyclic AMP in which one of the activity peaks is somewhat shifted; it shows the same elution pattern by FPLC on a Superose 12 column; it possesses identical substrate specificity; and, except in the case of dibutyryl cyclic AMP, it does not show additivity when each agent is added simultaneously with NGF. The multiple forms of N-kinase are interconvertible in that rechromatography on a Mono S column yields a single peak of activity. Also, when NGF and dibutyryl cyclic AMP are simultaneously presented to cells, the chromatographic profile resembles that with NGF alone. Activation occurs through several independent initial pathways. Down-regulation of protein kinase C by phorbol ester pretreatment prevents N-kinase activation by phorbol ester, but not by the other agents. A PC12 cell-derived line deficient in cyclic AMP-dependent protein kinase II activity exhibits N-kinase activation by all treatments except dibutyryl cyclic AMP. The properties of N-kinase suggests that it is similar or identical to the ribosomal S6 protein kinase described by Blenis and Erikson. Additional experiments revealed that N-kinase activity can be stimulated in several cell lines in addition to PC12 cells. These findings indicate that the N-kinase can be activated via multiple second-messenger pathways and that it could therefore potentially play a significant role in mediating shared intracellular responses to various extracellular signals.

Ontogeny of the neuronal intermediate filament protein, peripherin, in the mouse embryo

The expression of peripherin, a type III neuron-specific intermediate filament protein, and the middle neurofilament subunit were studied in the mouse embryo using immunofluorescence staining. The earliest staining for both proteins is seen at embryonic day 9 in the myelencephalon, initially as fiber staining followed by cell body staining in the developing facial and acoustic nuclei. As the embryo develops, there is rostral as well as caudal extension of peripherin and staining is seen in the trigeminal ganglia, nerve fibers and in the enteric nervous system. As the spinal cord forms there is anti-peripherin staining in developing motoneurons of the anterior horns while little cell body staining is seen for the middle neurofilament subunit. Both antibodies stain the developing dorsal root and its entry zone, but peripherin is found in the secondary sensory and commissural fibers while the middle neurofilament subunit is not. While both proteins are found in the neurons of the dorsal root ganglia, their distribution varies. The larger peripheral cells of the ganglia contain both proteins while the smaller more central cells, constituting over 60% of the cells in the ganglia, contain only peripherin. A similar picture is found in the sympathetic ganglia where there are cells which contain peripherin. middle neurofilament subunit or both, but where the majority of the neurons have only peripherin in their cell bodies. Peripherin is not found in the developing retina or in the adrenal medulla. Peripherin is also completely absent from cell bodies in the cerebral and cerebellar cortices. These results indicate that peripherin is found in development only in regions in which it is found in the adult. It can either co-exist with neurofilaments in the same neuron or the two may be independently expressed.

Nerve growth factor (NGF) responses by non-neuronal cells: detection by assay of a novel NGF-activated protein kinase

Past work described the partial purification and characterization of a novel serine protein kinase activity designated protein kinase N (PKN) that is activated by nerve growth factor (NGF) in cultured PC12 cells [Rowland et al. (1987) J. Biol. Chem. 262; 7504-7513]. We have now devised a rapid, sensitive technique for partially purifying and assaying PKN activity in cell extracts. This methodology was applied to the IARC-EW-1 osteosarcoma and several additional non-neuronal cell lines that possess NGF receptors but that lack both morphological and a variety of additional biochemical responses to NGF. In each case, NGF significantly elevated PKN activity. The assay also revealed activation of PKN activity in IARC-EW-1 cells by additional agents, including epidermal growth factor, fibroblast growth factor, phorbol ester, and a cAMP analog. Also tested were an NGF-receptor-deficient PC12 cell variant and sublines thereof into which human NGF receptors had been introduced [Hempstead et al. (1989) Science 243; 373-375]. Acquisition of the NGF receptors resulted in NGF-activatable PKN activity. These findings indicate that detection of PKN activity may serve as a sensitive means to test NGF responsiveness in cells lacking macroscopic responses to the factor and that non-neuronal cells may be useful for studying primary signaling events in the NGF mechanism of action.

An outbreak of waterborne cryptosporidiosis caused by post-treatment contamination

An outbreak of waterborne cryptosporidiosis affecting 27 persons, diagnosed stool positive, occurred in Ayrshire in April 1988. Twenty-one in 27 confirmed cases required some form of fluid replacement therapy. Local general practitioners indicated a two- to fivefold increase in diarrhoeal disease during the outbreak, and following enquiries made by Environmental Health Officers it became apparent that many hundreds of people had suffered a diarrhoeal illness at that time. Cryptosporidium spp. oocysts were detected in the treated chlorinated water supply system, in the absence of faecal bacterial indicators. Oocyst contamination of a break-pressure tank containing final water for distribution was the cause of this waterborne outbreak. An irregular seepage of oocyst-containing water, which increased during heavy rains, was the cause of the break-pressure tank contamination, rather than a failure of the water-treatment processes. The waterborne route should be considered when clusters of cryptosporidiosis-associated with potable water occur. Waterborne cryptosporidiosis can occur in the absence of other faecal indicators of contamination.

Differential inhibition of nerve growth factor responses by purine analogues: correlation with inhibition of a nerve growth factor-activated protein kinase

Purine analogues were used in this study to dissect specific steps in the mechanism of action of nerve growth factor (NGF). Protein kinase N (PKN) is an NGF-activated serine protein kinase that is active in the presence of Mn++. The activity of PKN was inhibited in vitro by purine analogues, the most effective of which was 6-thioguanine (apparent Ki = 6 microM). Several different criteria indicated that 6-thioguanine is not a general inhibitor of protein kinases and that it is relatively specific for PKN. For instance, it did not affect protein kinases A or C and was without effect on the overall level and pattern of protein phosphorylation by either intact or broken PC12 cells. Since purine analogues rapidly and effectively enter cells, they were also assessed for their actions on both transcription-dependent and -independent responses of PC12 cells to NGF. NGF-promoted neurite regeneration was reversibly suppressed by the analogues and at concentrations very similar to those that inhibit PKN. Comparable concentrations of the analogues also blocked NGF-stimulated induction of ornithine decarboxylase activity. In contrast to its inhibition of neurite regeneration and ornithine decarboxylase induction, 6-thioguanine did not suppress NGF-dependent induction of c-fos mRNA expression. Thus, purine analogues such as 6-thioguanine appear capable of differentially suppressing some, but not other actions of NGF. These findings suggest the presence of multiple pathways in the NGF mechanism and that these can be dissected with purine analogues. Moreover, these data are compatible with a role for protein kinase N in certain of these pathways.

Functional receptors for nerve growth factor on Ewing's sarcoma and Wilm's tumor cells

Quantification of changes in levels of c-fos RNA was used as an indicator of the presence of functional responses to nerve growth factor in several human non-neuronal cell lines which have previously been shown to express high levels of NGF receptors. Four Ewing's sarcomas, one Wilm's tumor, and one melanoma were examined. Of these cell lines, the Ewing's sarcoma IARC-EW1 showed greatly increased levels (10-20-fold) of c-fos RNA after 1 hour of exposure to NGF. Except for the melanoma line, the other tumor lines exhibited small, but reproducible, elevation of c-fos RNA expression. In IARC-EW1 cells, this induction was analyzed for kinetics, dose-response, and suppression by selective inhibitors of NGF action. The results indicate that these cells bear high-affinity receptors for NGF, which utilize signal pathways similar to NGF receptors on PC12 cells. Thus, we report new types of cells with functional responses to NGF and indicate that these may constitute a new model which will usefully complement those presently used for studying the mechanism of action of NGF.

A new neuronal intermediate filament protein

It would be an understatement to say that the vertebrate nervous system appears complex. The characterization and classification of its components rely, in addition to its gross anatomy, on analyses of the differential expression of cytoskeletal and other cellular structures and products. In this brief review Lloyd Greene describes the discovery of a novel intermediate filament protein.

Phosphorylation of the peripherin 58-kDa neuronal intermediate filament protein. Regulation by nerve growth factor and other agents

Peripherin, a recently described member of the intermediate filament multigene family, is present in peripheral and certain central nervous system neurons as well as in cultured neuron-like cell lines, including PC12 pheochromocytoma cells. In PC12 cells, peripherin appears to be the major intermediate filament protein and its relative levels and synthesis are specifically increased during nerve growth factor (NGF)-promoted neuronal differentiation. The present study examines the phosphorylation of peripherin and the regulation thereof by nerve growth factor and other agents in cultured PC12 cells. Immunoblotting experiments using a peripherin-specific antiserum show five distinct isoforms of this protein in whole cell and cytoskeletal extracts resolved by two-dimensional isoelectric focusing sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Three of these isoforms incorporate detectable quantities of [32P]phosphate during metabolic radiolabeling. The small proportion (approximately 6%) of total cellular peripherin that is extractable with 1% Triton X-100, does not appear to incorporate phosphate. NGF increases peripherin phosphorylation by 2-3-fold within 1-2 h of treatment. Epidermal growth factor and insulin have no effect. The relative levels of phosphorylated peripherin are markedly elevated (17-fold) by long term NGF exposure, and peripherin becomes a major cytoskeletal phosphoprotein. Activators of protein kinases A and C and treatment with depolarizing levels of K+ also enhance peripherin phosphorylation by 2-3-fold, in cultures both with and without prior long term NGF treatment. Evidence is presented that NGF regulates peripherin phosphorylation by a mechanism independent of protein kinases A and C and of depolarization. The large increase in phosphorylated peripherin brought about by NGF treatment suggests that this neuronal filament protein may play a role in the elaboration and maintenance of neurites. The presence of multiple independent pathways that acutely enhance peripherin phosphorylation indicates that this role is subject to modulation by extrinsic signals.

Relationship between the nerve growth factor-regulated clone 73 gene product and the 58-kilodalton neuronal intermediate filament protein (peripherin)

Exposure of PC12 cells to nerve growth factor (NGF) has been shown to induce an mRNA that encodes a novel neuronal intermediate filament protein. The findings presented here concern the identity of this filament protein. The major protein in NGF-treated PC12 cell cytoskeletons derived by extraction with 1% Triton X-100 is of apparent Mr = 58,000, focuses by isoelectric focusing as several closely spaced spots of pl 5.6-5.8, and is elevated relative to non-NGF-treated cells. Partial microsequencing of this material reveals 2 internal sequences that are identical to a 14-residue sequence encoded by the NGF-regulated clone 73 mRNA, but not to sequences of other known proteins. An antiserum raised against a 19-residue synthetic peptide corresponding to the deduced C-terminus of the protein encoded by the NGF-regulated clone 73 mRNA specifically recognizes the 58,000-Mr protein. Properties of the 58-kilodalton protein strongly suggest that it corresponds to an intermediate filament protein (peripherin) previously identified in PC12 cells and in peripheral and certain CNS neurons. Identification of the intermediate filament protein encoded by an NGF-induced message should facilitate studies of its regulation and function.

Nerve growth factor regulates both the phosphorylation and steady-state levels of microtubule-associated protein 1.2 (MAP1.2)

This study characterizes effects of nerve growth factor (NGF) on the steady-state level and phosphorylation of a high molecular mass microtubule-associated protein in PC12 rat pheochromocytoma cells. Past work showed that NGF significantly raises the relative levels of this phosphoprotein, designated MAP1.2, with a time course similar to that of neurite outgrowth. To study this in greater detail, MAP1.2 in PC12 cell lysates was resolved by SDS-PAGE in gels containing 3.25% acrylamide/4 M urea and identified by comigration with material immunoprecipitated from the lysates by MAP1 antibodies. Quantification by metabolic radiolabeling with [35S]methionine or by silver staining revealed a 3.0-3.5-fold increase in MAP1.2 levels relative to total cell protein after NGF treatment for 2 wk or longer. A partial increase was detectable after 3 d, but not after 2 h of NGF exposure. As measured by incorporation of [32P]phosphate, NGF had a dual effect on MAP1.2. Within 15 min to 2 h, NGF enhanced the incorporation of phosphate into MAP1.2 by two- to threefold relative to total cell phosphoproteins. This value slowly increased thereafter so that by 2 wk or more of NGF exposure, the average enhancement of phosphate incorporation per MAP1.2 molecule was over fourfold. The rapid action of NGF on MAP1.2 could not be mimicked by either epidermal growth factor, a permeant cAMP derivative, phorbol ester, or elevated K+, each of which alters phosphorylation of other PC12 cell proteins. SDS-PAGE revealed multiple forms of MAP1.2 which, based on the effects of alkaline phosphatase on their electrophoretic mobilities, differ, at least in part, in extent of phosphorylation. Before NGF treatment, most PC12 cell MAP1.2 is in more rapidly migrating, relatively poorly phosphorylated forms. After long-term NGF exposure, most is in more slowly migrating, more highly phosphorylated forms. The effects of NGF on the rapid phosphorylation of MAP1.2 and on the long-term large increase in highly phosphorylated MAP1.2 forms could play major functional roles in NGF-mediated neuronal differentiation. Such roles may include effects on microtubule assembly, stability, and cross-linking and, possibly for the rapid effects, nuclear signaling.

Growth cone configuration and advance: a time-lapse study using video-enhanced differential interference contrast microscopy

We have analyzed the dynamics of growth cone configuration using video-enhanced contrast differential interference contrast microscopy. Regenerating neurites from NGF-treated PC12 cells and sympathetic neurons were observed in real time during their elongation and reviewed by time-lapse video recordings. This technique provided a high-resolution view of motile growth cone elements including filopodia, microspikes, lamellipodia and ruffles. On the basis of our observations, a multistage model for growth cone advance is proposed. Elongation commences with lamellipodial spreading. If the newly extended lamellipodium does not retract or lift off the substrate in the form of a ruffle, a second phase--consolidation--occurs, in which the lamellipodium thickens as it fills with cytoplasm and organelles. The consolidated area then undergoes further transformation into an area of neuritic shaft as new lamellipodia form at the leading and peripheral zones of the distal process. We never observed filopodia or microspikes contracting to propel the growth cone forward. We also noted that elongating tips generally had large varicosities within 20 micron of their leading edges. These may play a role in neurite outgrowth and in the formation of smaller, synaptic vesicle-containing varicosities. The dynamic behavior of the growth cone was under the control of NGF. Withdrawal of NGF resulted in the disappearance of motile structures and cessation of growth, while readdition of NGF triggered the rapid reappearance of these structures and the resumption of growth. The high-resolution video microscopy of living growth cones provides necessary baseline information, as well as a bioassay paradigm, for future studies on the molecular mechanisms of nerve growth.