Kinetic analysis of 'rapid onset' neurite formation in NG108-15 cells reveals a dual role for substratum-bound laminin

Optimisation of a PC12 cell-based in vitro stroke model for screening neuroprotective agents

Stroke causes death and disability globally but no neuroprotectant is approved for post-stroke neuronal injury. Neuroprotective compounds can be identified using oxygen glucose deprivation (OGD) of neuronal cells as an in vitro stroke model. Nerve growth factor (NGF)-differentiated PC12 pheochromocytoma cells are frequently used. However, investigators often find their clonal variant undifferentiable and are uncertain of optimal culture conditions. Hence we studied 3 commonly used PC12 variants: PC12 Adh, PC12 from Riken Cell Bank (PC12 Riken) and Neuroscreen-1 (NS-1) cells. We found DMEM the optimal media for PC12 Riken and NS-1 cells. Using a novel serum-free media approach, we identified collagen IV as the preferred adhesive substrate for both cell lines. We found PC12 Adh cells cannot attach without serum and is unable to differentiate using NGF. NS-1 cells differentiated to a maximal 72.7 ± 5.2% %, with substantial basal differentiation. We optimised differentiated NS-1 cells for an in vitro stroke model using 3 h of OGD resulting in ~ 70% viable cells. We screened 5 reported neuroprotectants and provide the first report that serotonin is antiapoptotic in a stroke model and the 5-HT_1A agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) is neuroprotective in PC12 cells. Thus we demonstrate the optimisation and validation for a PC12 cell-based in vitro stroke model.

6-shogaol, a neuroactive compound of ginger (jahe gajah) induced neuritogenic activity via NGF responsive pathways in PC-12 cells

BACKGROUND

Ginger is a popular spice and food preservative. The rhizomes of the common ginger have been used as traditional medicine to treat various ailments. 6-Shogaol, a pungent compound isolated from the rhizomes of jahe gajah (Zingiber officinale var officinale) has shown numerous pharmacological activities, including neuroprotective and anti-neuroinflammatory activities. The aim of this study was to investigate the potential of 6-shogaol to mimic the neuritogenic activity of nerve growth factor (NGF) in rat pheochromocytoma (PC-12) cells.

METHODS

The cytotoxic effect of 6-shogaol was determined by 3-(4,5-dimethythiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The neuritogenic activity was assessed by neurite outgrowth stimulation assay while the concentration of extracellular NGF in cell culture supernatant was assessed by enzyme-linked immunosorbent assay (ELISA). Involvement of cellular signaling pathways, mitogen-activated protein kinase kinase/extracellular signal-regulated kinase1/2 (MEK/ERK1/2) and phosphoinositide-3-kinase/protein kinase B (PI3K/AKT) in 6-shogaol-stimulated neuritogenesis were examined by using specific pharmacological inhibitors.

RESULTS

6-Shogaol (500 ng/ml) induced neuritogenesis that was comparable to NGF (50 ng/ml) and was not cytotoxic towards PC-12 cells. 6-Shogaol induced low level of NGF biosynthesis in PC-12 cells, showing that 6-shogaol stimulated neuritogenesis possibly by inducing NGF biosynthesis, and also acting as a substitute for NGF (NGF mimic) in PC-12 cells. The inhibitors of Trk receptor (K252a), MEK/ERK1/2 (U0126 and PD98059) and PI3K/AKT (LY294002) attenuated the neuritogenic activity of both NGF and 6-shogaol, respectively.

CONCLUSIONS

The present findings demonstrated that 6-shogaol induced neuritogenic activity in PC-12 cells via the activation MEK/ERK1/2 and PI3K/AKT signaling pathways. This study suggests that 6-shogaol could act as an NGF mimic, which may be beneficial for preventive and therapeutic uses in neurodegenerative diseases.

Uridine from Pleurotus giganteus and Its Neurite Outgrowth Stimulatory Effects with Underlying Mechanism

Neurodegenerative diseases are linked to neuronal cell death and impairment of neurite outgrowth. An edible mushroom, Pleurotus giganteus was found to stimulate neurite outgrowth in vitro but the chemical constituents and the underlying mechanism is yet to be elucidated. The chemical constituents of P. giganteus (linoleic acid, oleic acid, cinnamic acid, caffeic acid, p-coumaric acid, succinic acid, benzoic acid, and uridine) were tested for neurite outgrowth activity. Uridine (100 μM) was found to increase the percentage of neurite-bearing cells of differentiating neuroblastoma (N2a) cells by 43.1±0.5%, which was 1.8-fold higher than NGF (50 ng/mL)-treated cells. Uridine which was present in P. giganteus (1.80±0.03 g/100g mushroom extract) increased the phosphorylation of extracellular-signal regulated kinases (ERKs) and protein kinase B (Akt). Further, phosphorylation of the mammalian target of rapamycin (mTOR) was also increased. MEK/ERK and PI3K-Akt-mTOR further induced phosphorylation of cAMP-response element binding protein (CREB) and expression of growth associated protein 43 (GAP43); all of which promoted neurite outgrowth of N2a cells. This study demonstrated that P. giganteus may enhance neurite outgrowth and one of the key bioactive molecules responsible for neurite outgrowth is uridine.

Lignosus rhinocerotis (Cooke) Ryvarden mimics the neuritogenic activity of nerve growth factor via MEK/ERK1/2 signaling pathway in PC-12 cells

The traditional application of the sclerotium of Lignosus rhinocerotis (tiger’s milk mushroom) by the indigenous folks as tonic and remedy to treat a variety of ailments has been documented in Malaysia. Indigenous communities claimed to have consumed the decoction to boost their alertness during hunting. Mental alertness is believed to be related to neuronal health and neuroactivity. In the present study, the cell viability and neuritogenic effects of L. rhinocerotis sclerotium hot aqueous and ethanolic extracts, and crude polysaccharides on rat pheochromocytoma (PC-12) cells were studied. Interestingly, the hot aqueous extract exhibited neuritogenic activity comparable to NGF in PC-12 cells. However, the extracts and crude polysaccharides stimulated neuritogenesis without stimulating the production of NGF in PC-12 cells. The involvements of the TrkA receptor and MEK/ERK1/2 pathway in hot aqueous extract-stimulated neuritogenesis were examined by Trk (K252a) and MEK/ERK1/2 (U0126 and PD98059) inhibitors. There was no significant difference in protein expression in NGF- and hot aqueous extract-treated cells for both total and phosphorylated p44/42 MAPK. The neuritogenic activity in PC-12 cells stimulated by hot aqueous and ethanolic extracts, and crude polysaccharides of L. rhinocerotis sclerotium mimicking NGF activity via the MEK/ERK1/2 signaling pathway is reported for the first time.

Neurochemical and morphological studies on differentiation of NG108-15 cells by phorbol ester and forskolin

12-O-tetradecanoylphorbol 13-acetate (TPA), forskolin or dibutyryl cAMP induced neurite outgrowth and inhibition of cell growth in NG108-15 cells. TPA, forskolin and dibutyryl cAMP significantly increased specific activity of choline acetyltransferase. Forskolin markedly stimulated cAMP accumulation, but not TPA, suggesting that forskolin could induce differentiation by increasing the cAMP content via adenylate cyclase activation, but TPA-induced differentiation seems not to be due to the raise of the cAMP level. Incubation of the cells with TPA, forskolin or dibutyryl cAMP for 24 h resulted in enhancement of 50 mM K(+)-evoked Ca(2+) influx and neurite elongation, although incubation with these agents for 1 h didn't affect these events. From these results, it is suggested that TPA and forskolin induce differentiation of NG108-15 cells to acetylcholine neurons via different mechanisms: protein kinase C activation by TPA and cAMP-dependent protein kinase activation by forskolin. In addition, it is likely that Ca(2+) channels in cells differentiated by TPA, forskolin or dibutyryl cAMP become sensitive to depolarization.

Lignosus rhinocerus (Cooke) Ryvarden: A Medicinal Mushroom That Stimulates Neurite Outgrowth in PC-12 Cells

A national treasure mushroom, Lignosus rhinocerus, has been used to treat variety of ailments by local and indigenous communities in Malaysia. The aim of this study was to investigate the potential of the most valuable part of L. rhinocerus, the sclerotium, on neurite outgrowth activity by using PC-12Adh cell line. Differentiated cells with one thin extension at least double the length of the cell diameter were scored positive. Our results showed that aqueous sclerotium L. rhinocerus extract induced neurite outgrowths of 24.4% and 42.1% at 20 μg/mL (w/v) of aqueous extract alone and a combination of 20 μg/mL (w/v) aqueous extract and 30 ng/mL (w/v) of NGF, respectively. Combination of NGF and sclerotium extract had additive effects and enhanced neurite outgrowth. Neuronal differentiation was demonstrated by indirect immunofluorescence of neurofilament protein. Aqueous sclerotium extract contained neuroactive compounds that stimulated neurite outgrowth in vitro. To our knowledge this is the first report on neurite-stimulating activities of L. rhinocerus.

Effects of soluble laminin on organelle transport and neurite growth in cultured mouse dorsal root ganglion neurons: Difference between primary neurites and branches

Laminin, an extracellular matrix molecule, is known to promote neurite growth. In the present study, the effects of soluble laminin on organelle transport and their relation to neurite growth were investigated in cultured dissociated mouse dorsal root ganglion (DRG) neurons. Laminin added into the extracellular medium was deposited on the surface of DRG neurons. DRG neurons incubated with soluble laminin exhibited branched, long, and thin neurites. Time-lapse study demonstrated that many small-diameter branches were newly formed after the addition of laminin. Thus, the growths of large-diameter primary neuritis, arising from cell bodies and branches extended from growth cones of primary neuritis, were analyzed separately. Laminin decreased the growth rate of primary neurites but increased that of branches. In primary neurites, acute addition of laminin rapidly decreased organelle movement in the neurite shaft and growth cone, accompanied by slowing of the growth cone advance. Branching of primary neurites occurred in response to laminin in some growth cones. In these growth cones, organelles protruded into nascent branches. In branches, soluble laminin increased organelle movement in the growth cone and the distal portion of the shaft. These results suggest that laminin inhibits the elongation of primary neurites but promotes branching and elongation of branches, all of which seem to be closely related to organelle transport.

Neuronal intermediate filament protein alpha-internexin facilitates axonal neurite elongation in neuroblastoma cells

We examined the localization and role of alpha-IN vs. other neuronal intermediate filaments before and during differentiation. Vimentin but not alpha-IN localized within filopodia-like neurites of undifferentiated cells. During differentiation, alpha-IN immunoreactivity accumulated within axonal neurites following vimentin but, as previously describe in neurons in situ, before the appearance of NF-L. We therefore manipulated alpha-IN synthesis, accumulation, and function in attempts to determine whether or not this intermediate filament species played a role in axonal development. Intracellular delivery of anti-alpha-IN antisense oligonucleotides and antibodies was permissive for neuritogenesis, yet compromised neurite elongation; this effect was further reflected in diminished levels of stabilized axonal microtubules. These data suggest that alpha-IN plays a role in the development of neuronal polarity. Relatively more alpha-IN than NF-L accumulated within the plastic axonal neurites induced following serum-deprivation, while stable, dbcAMP-induced neurites treatment contained equivalent levels of each. Protease inhibition increased NF-L and NF-H but not alpha-IN immunoreactivity within serum-deprived neurites, suggesting that proteolysis restricts NF-L accumulation pending neurite stabilization. To test the possibility that NF-H accumulation is dependent upon NF-L and cannot be mediated by alpha-IN, we examined levels of NF-H co-precipitated from cells with alpha-IN and NF-L. Virtually all newly synthesized NF-H co-precipitated with NF-L, while only a small percentage co-precipitated with alpha-IN. Finally, NF-H or NF-M were absent from the axon hillock or perikaryal area at the base of neurites, where alpha-IN immunoreactivity is prominent. These data extend earlier cell-free demonstrations that NF-H preferentially associates with NF-L rather than alpha-IN.

Neuronal laminins and their cellular receptors

The laminins are a family of extracellular matrix glycoproteins expressed throughout developing neural tissues. The laminins are potent stimulators of neurite outgrowth in vitro for a variety of cell types, presumably reflecting an in vivo role in stimulating axon outgrowth. In recent years, the laminins have been shown to occur in several distinct isoforms; currently, the precise functional differences between the laminin variants are not well understood. A variety of neuronal surface receptors have been identified for one laminin isoform, laminin-1. These receptors include several members of the integrin family, as well as non-integrin laminin-binding proteins such as LBP-110, the 67 kDa laminin-receptor, alpha-dystroglycan, and beta 1,4 galactosyltransferase. Little is currently known about receptors for other laminin isoforms.

Rapid regulation of neurite outgrowth and retraction by phospholipase A2-derived arachidonic acid and its metabolites

Arachidonic acid and lipoxygenase metabolites have been proposed to act as retrograde synaptic messengers and as early mediators of neuronal injury, but few studies have analyzed their roles in controlling neurite behavior within a time window of minutes to hours. Phospholipase A2 inhibitors (BPB, ONO-RS-082, quinacrine and AACOCF3) and the lipoxygenase inhibitor AA861 delayed the initial outgrowth of NG108-15 cell neurites on laminin. Inhibitors of diacylglycerol lipase (RHC 80267), cyclooxygenase (indomethacin) and free radicals (N-acetyl cysteine and vitamin E) did not produce similar effects. Phospholipase A2 and lipoxygenase inhibitors also prevented acute neurite retraction in response to lysophosphatidic acid and eight other agents tested, and decreased F-actin staining at cell margins. Conversely, exogenous arachidonic acid (1 microM) enhanced the responses of neurites in outgrowth and retraction assays. Phospholipase A2 and lipoxygenase pathways appear to have a general role in maintaining the ability of neurites to respond rapidly to external stimuli, possibly via regulating the ability of the cytoskeleton to remodel.

Retinoic acid affects basement membrane formation of the seminiferous cords in 14-day male rat gonads in vitro

The vitamin A derivative retinoic acid (RA) has been previously shown to have teratogenic effects and an ability to modulate cell differentiation in vivo and in vitro. In this study bilateral testicular primordia with the mesonephroi attached were isolated from rat fetuses at 14.5 days of gestation. The gonads were cultured on agar-coated grids in a synthetic medium. RA was added to male rat embryonic gonad cultures at a final concentration of 10(-6) M for 3 h. Two types of controls were prepared: (1) by omitting RA from the culture medium (alcohol controls) and (2) by using plain medium (untreated controls). When applied to gonad cultures RA was found to affect basement membrane development and disturb the general appearance of the tissue. All controls exhibited normal morphology. In order to evaluate the morphological changes observed due to the RA treatment, constituents of the basement membrane, laminin and collagen IV, were localized immunohistochemically at the light microscope level. Basement membrane was also studied at the electron microscope level in control and RA-treated cultures. We propose that one of the effects RA has on rat testicular morphogenesis is the irreversible suppression of seminiferous cord basement membrane formation and the disruption of normal testicular morphogenesis.

Neurite outgrowth from cultured CNS neurons is promoted by inhibitors of protein and RNA synthesis

We examined the effects of changes caused by the blocking of protein and RNA synthesis on neurite outgrowth from neurons of the central nervous system (CNS) in primary culture. Exposure to cycloheximide and actinomycin-D led to dramatic increases in the length of neurites in cultures of neurons from various rat or chick CNS regions. Inhibitor-induced neurite outgrowth was observed (1) from dopaminergic neurons in mixed cultures of the rat substantia nigra or (2) in pure cultures of rat and chick neurons grown on a polyornithine/laminin substratum. These results suggest that neurite outgrowth from CNS neurons is kept restricted, at least in culture, by the continuous production of a labile neurite-inhibiting protein intrinsic to the neurons, which rapidly decays following inhibition of protein or RNA synthesis.

Shapes of cells spreading on fibronectin: measurement of the stellation of BHK21 cells induced by raising cyclic AMP, and of its reversal by serum and lysophosphatidic acid

In common with many other animal cells in culture, BHK21, CHO and NIH-3T3 cells adopt bizarre stellate or arborized shapes when exposed, in the absence of serum, to agents which increase cytoplasmic cyclic AMP (cAMP). Dibutyryl cAMP, 3-isobutyl-1-methylxanthine, 5′-deoxy-5′-methylthioadenosine, cholera toxin and the invasive adenylate cyclase from Bordetella pertussis all induce similar shapes. Time lapse video recording of BHK21 cells spreading on fibronectin shows that stellate shapes are generated by outgrowth of neurite-like processes led by small fans of ruffling membrane. These structures stain strongly for F actin, and their outgrowth is completely inhibited by cytochalasin D. Thus if stellation is caused by microfilament depletion, this must be selective for subsets of microfilaments. We have quantified the shape changes of BHK21 cells using the parameter dispersion. They are prevented by low concentrations (1% by volume and below) of bovine sera. The inhibitory component of foetal bovine serum acts humorally, behaves as a macromolecule and is itself inhibited by suramin, but platelet-derived growth factor, insulin, vasopressin and bradykinin are inactive. The inhibitory activity of serum may be due to phospholipids, since it can be replaced by lysophosphatidic acid in the presence of serum albumin.

Monensin-sensitive cellular events modulate neurite extension on laminin: an example of higher-order regulation of cell motility

NG108-15 cells extend "rapid-onset" neurites vigorously within the first hour after plating in minimal serum-free medium on Petri dishes coated with polylysine and laminin (1 ng/mm2). We recently reported that the initial rates of neurite formation and cell translocation are further accelerated in this system when non-specific substratum attachment sites are partially blocked by polyglutamate, bovine serum albumin, or polyethylene glycol polymers [Smalheiser, N. R. (1991): Dev. Brain Res. 62:81-89]. When cells were plated in the presence of the monovalent cation ionophore monensin (1-5 microM) or hypertonic sucrose (50-100 mM), the initial rate of outgrowth on laminin/polylysine-treated Petri dishes was not affected, yet the acceleration produced by polyglutamate was strongly inhibited. These data indicate that monensin-sensitive intracellular events can regulate neurite extension on laminin indirectly, through modulating the effects exerted on cells by nonspecific substratum sites. Although the critical events affected by monensin remain to be identified, movements of laminin receptors (their clustering, internalization, and recycling) are likely targets for further study.

Neurite outgrowth from N18TG2 neuroblastoma induced by H-7, a protein kinase inhibitor, in the presence of colchicine

Our previous studies have demonstrated that the protein kinase inhibitor H-7 promotes neurite outgrowth from mouse neuroblastoma N18TG2 cells as well as from primary cerebellar cells, and also that the neurites induced by H-7 were more tolerant of colchicine (COL) than those induced by dibutyryl cAMP (dB-cAMP). In the present study, we tested the effects of H-7 and dB-cAMP on neurite growth from N18TG2 cells in the presence of COL. We found that only H-7 promoted neurite formation in the presence of COL. The percentage of cells with neurites induced by H-7 in the presence of COL (H-7 + COL) was similar to that induced by H-7 alone. The neurites induced by H-7 + COL grew straight. They were very thin (less than 1 micron in diameter) and had round varicosities, as did the neurites induced by H-7 alone. By transmission electron microscopy, the neurites induced by H-7 + COL were found to contain longitudinally arranged intermediate filaments (IF). Microtubules (MT) were not observed within the neurites. We also examined the effect of cytochalasin B (CB) on the neurites induced by H-7 + COL and by H-7 alone. The neurites induced by H-7 + COL were tolerant to CB, but those induced by H-7 were resorbed completely within 24 h after CB was applied. Neurites tolerant to CB contained longitudinally IF. Simultaneous application of CB with H-7 + COL or with H-7 alone did not induce neurite formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Morphometric and time lapse analyses of rapid-onset neurites stimulated by cycloheximide in NG108-15 cells

We previously reported that the laminin-induced outgrowth of neurites in the first 4 hr after plating ('rapid-onset neurites') is markedly stimulated by inhibitors of protein and RNA synthesis, including cycloheximide, puromycin and actinomycin D. Our original interpretation of this finding was that inhibiting protein synthesis led to metabolic changes in the cell which converged upon the intracellular pathway used by laminin to stimulate neurite formation. Alternatively, Preston et al. (1987, Proc. natn. Acad. Sci. U.S.A. 84, 5247-5251) suggested that cycloheximide acts by inhibiting neurite retraction. In order to resolve these conflicting interpretations, we decided to re-examine the effects of cycloheximide using time lapse analyses of NG108-15 cells grown on laminin, together with morphometric analyses of cultures fixed at 1.5 or 3 hr after plating. Cycloheximide was found to cause both an increase in neurite initiation within the first 1.5 hr after plating, and a decrease in the occurrence of neurite retractions between 1 and 3 hr. Investigators should be aware of the effects of biosynthetic inhibitors on neurite growth, since these agents are employed widely in studies of cultured neural cells, particularly those involving receptor metabolism and phenotypic differentiation.

Sequential effects of astroglial-derived factors on neurite outgrowth: initiation by protease inhibitors and potentiation by extracellular matrix components

Astroglial-conditioned medium (GCM) induced two distinct, but intimately related, phases of neuritogenesis in NB2a/d1 neuroblastoma cells--a "rapid-outgrowth," unstable phase, and a delayed, relatively stable phase, which are apparently regulated by glial-derived protease inhibitors and laminin, respectively. The initial rapid outgrowth (less than 4 hr) may be mediated by inhibition of a thrombin-like protease, present as a serum component and/or adsorbed to the outer neuronal surface, since (1) a similar effect was obtained by serum removal or by adding the specific thrombin inhibitor, hirudin; (2) exogenous thrombin inhibited the rapid outgrowth of neurites by GCM; and (3) cell-free enzyme assays confirmed the presence of thrombin-inhibitory activity in GCM. Although neurites induced by removal of serum removal or hirudin addition are rapidly resorbed following serum replenishment or hirudin depletion, GCM-induced neurites continued to elongate after GCM removal, indicating that GCM contained additional neurite-promoting factors. Anti-laminin antiserum did not inhibit the initial elaboration of neurites by GCM but prevented their continued elongation. Anti-laminin antiserum had no affect on neurite outgrowth induced by serum deprivation. The more protracted, second phase of neurite outgrowth could also be achieved by the addition of soluble purified laminin to undifferentiated cells. Unlike neurites at 4 hr, neurites at 24 hr were no longer dependent on the protease inhibitors in GCM, since exogenous thrombin no longer caused them to retract. Simultaneous addition of thrombin and anti-laminin antiserum with GCM had identical inhibitory effects on continued neurite elaboration at 24 hr as did anti-laminin antiserum without thrombin.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of laminin in stimulating rapid-onset neurites in NG108-15 cells: relative contribution of attachment and motility responses

The present paper analyzed how attachment and motility responses contribute to the initial formation of rapid-onset neurites in undifferentiated NG108-15 cells. Attachment responses played a positive role in stabilizing neurites against slippage, but exerted a negative effect upon active motility--which appears to be the major rate-determining event in initial outgrowth. The role of laminin in this paradigm was elucidated by analyzing the effects of polyglutamate and other agents (bovine serum albumin and polyethylene glycol chain derivatives) which reduced the number of passive substratum attachment sites, but which did not affect cells directly nor affect the binding of laminin to the substratum. Polyglutamate decreased attachment and spreading of cells, yet greatly accelerated the initial laminin-dependent formation of rapid-onset neurites, and greatly enhanced active neurite remodelling and cell translocation as well. Together with data presented in previous studies in this series, these findings indicate that laminin stimulates rapid-onset neurites primarily by stimulating active motility responses. Insofar as rapid-onset neurites appear to provide a valid model of how neuronal growth cones are regulated, it is likely that these findings will be relevant to developing primary neurons as well.

Multiple proteases regulate neurite outgrowth in NB2a/dl neuroblastoma cells

Mouse NB2a/dl neuroblastoma cells elaborate axonal neurites in response to various chemical treatments including dibutyryl cyclic AMP and serum deprivation. Hirudin, a specific inhibitor of thrombin, initiated neurite outgrowth in NB2a/dl cells cultured in the presence of serum; however, these neurites typically retracted within 24 h. The cysteine protease inhibitors leupeptin and N-acetyl-leucyl-leucyl-norleucinal (CI; preferential inhibitor of micromolar calpain but also inhibits millimolar calpain) at 10(-6) M considerably enhanced neurite outgrowth induced by serum deprivation, but could not induce neuritogenesis in the presence of serum. A third cysteine protease inhibitor, N-acetyl-leucyl-leucyl-methional (CII; preferential inhibitor of millimolar calpain but also inhibits micromolar calpain), had no detectable effects by itself. Cells treated simultaneously with hirudin and either leupeptin, CI, or CII elaborated stable neurites in the presence of serum. Cell-free enzyme assays demonstrated that hirudin inhibited thrombin but not calpain, CI and CII inhibited calpain but not thrombin, and leupeptin inhibited both proteases. These results imply that distinct proteolytic events, possibly involving more than one protease, regulate the initiation and subsequent elongation and stabilization of axonal neurites. Since the addition of exogenous thrombin or calpain to serum-free medium did not modify neurite outgrowth, the proteolytic events affected by these inhibitors may be intracellular or involve proteases distinct from thrombin or calpain.

Cell attachment and neurite stability in NG108-15 cells: what is the role of microtubules?

Undifferentiated NG108-15 cells forming rapid-onset neurites were acutely exposed to nocodazole or trypsin. Resorption, cell rounding and detachment were delayed or prevented by 5'-deoxy,5'-methylthioadenosine (MTA), which selectively enhanced the strength of attachment responses. However, taxol, which stabilized microtubules, did not protect cell shape appreciably when trypsin or mechanical stimuli were used to decrease the strength of attachment. Together with numerous control experiments, this evidence suggests that the mechanical properties of microtubules do not contribute acutely to maintaining cell shape, though microtubules may play an indirect regulatory role (e.g. through their interactions with actin and substratum attachment sites). Patterns of trypsin-induced resorption resembled those seen 'spontaneously' in NG108-15 cells growing on laminin, and in fibroblastic CHO cells, suggesting that these results may be both physiologically relevant and applicable widely to many cell types.

Laminin-mediated process formation in neuronal cells involves protein dephosphorylation

Laminin mediates neural adhesion and process formation. A possible signal transduction pathway for laminin was investigated in both NG108-15 and PC12 neuronal cells using radiolabeling studies as well as various stimulators and inhibitors of phosphatases and kinases. Using [32P]-ortho-phosphate, laminin caused a decrease in the TCA-precipitable counts. Further, laminin stimulated dephosphorylation of laminin binding proteins of 110 kDa, 67 kDa, and 45 kDa and this dephosphorylation was blocked by the phosphatase inhibitor, okadaic acid, and the protein kinase C stimulator, TPA. The phosphatase inhibitors okadaic acid and vanadate, as well as the protein kinase C stimulators, TPA and DAG, blocked laminin-mediated process formation. Inhibitors of kinase activity such as H-7, H-8, and H-9 increased laminin-mediated neural process formation. Since phosphate incorporation into laminin-binding proteins is decreased by laminin and because both phosphatase inhibitors and kinase stimulators inhibit laminin-mediated process formation, we conclude that dephosphorylation events promote the neural cell response to laminin.

Effect of cytochalasin D on the adhesion of a neuroblastoma x glioma cell line (NG108-15) to laminin and plastic substrates

Adhesion of the neuronal cell surface to its underlying substrate plays an important role in neurite outgrowth in vitro. I have investigated the adhesive basis for neurite outgrowth in the presence of cytochalasin D, a disruptor of actin-containing microfilaments, and in the presence of vinblastine, a depolymerizer of microtubules. Scanning electron microscopy shows that cytochalasin D does not alter the branching configuration of filopodia on a laminin substrate, although processes are shorter and tapered distally in the presence of the drug. Using a standard attachment assay for the neuroblastoma x glioma cell line (NG108-15) I show that vinblastine does not influence attachment of NG108-15 cells to either plastic or laminin. Cytochalasin D-treated cells normally attach to high concentrations of a laminin substrate (20 micrograms/ml). However, when cell are seeded on a laminin substrate at lower concentrations (0.001-10 micrograms/ml), or on YIGSR, a fragment of laminin, cytochalasin D increases cell attachment. Cytochalasin D increases attachment in a dose-dependent manner when cells are seeded on plain polystyrene plastic, so that the number of cells attached to plastic in 1 microM cytochalasin D is similar to the number attached to laminin (20 micrograms/ml). Combining low concentrations of cytochalasin D and laminin results in greater attachment than with either agent alone. Mild trypsinization of the cell surface reduces the CD-enhanced attachment to plastic, indicating that a protein on the cell surface may be involved. The effect of cytochalasin D appears to be cell specific since cytochalasin D does not affect the attachment of a fibroblast cell line (NIH 3T3) to laminin and plastic.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell attachment and neurite stability in NG108-15 cells: effects of 5'-deoxy, 5'-methyl thioadenosine (MTA) compared with laminin, kinase inhibitor H-7, and Mn2+ ions

Methylation inhibitors such as 5'-deoxy, 5'-methyl thioadenosine (MTA) have been shown to exert an intriguing spectrum of effects upon neural cells: inhibiting responses to nerve growth factor in PC12 cells; stimulating outgrowth of rapid-onset neurites in NG108-15 cells; inhibiting the resorption and remodelling of these rapid-onset neurites; and inducing fibroblasts to extend long, multipolar, branched processes. To learn whether the apparently diverse effects of these agents might reflect some common underlying cellular sites of action, we examined simpler, short-term effects of MTA upon cell attachment and stability of rapid-onset neurites in NG108-15 cells, and compared the effects with those produced by the kinase inhibitor H-7, substratum-bound laminin, or Mn2+ ions. MTA was shown to selectively enhance the response of cells and their neurites in attaching to their substrata, without inducing other 'adhesive' responses such as cell spreading or motility. The data suggest that MTA activates or increases the effectiveness of 'attachment receptors', and that this at least partially explains its neurite-promoting effects. While it is still premature to propose a common mechanism of action for MTA and related agents, all of their known effects thus appear to involve modulating responses generated at cell-surface receptors. A further clue is that kinase C activity appears to be critical, since cells pretreated with phorbol esters for 24 h (which down-regulated levels of kinase C) selectively failed to extend neurites in response to MTA, but responded normally to laminin and Mn2+ ions.

Altered cell shapes in fibroblasts treated with 5'-deoxy-5'-methylthioadenosine: relation to morphogenesis of neural cells

In the present study, mouse 3T3 fibroblasts and primary human foreskin fibroblasts exposed to MTA (5'-deoxy-5'-methylthioadenosine) were found to achieve neural-like cell shapes and to extend long, multipolar processes rapidly and reversibly. Time lapse recordings and pharmacologic studies revealed that process formation in MTA-treated fibroblasts was mechanistically related to the rapid-onset mode of neurite formation previously characterized in neural hybrid NG108-15 cells. These data, together with evidence presented elsewhere, indicate that MTA selectively reorganizes the mode of expression of a specific cytoplasmic machinery that is active in many types of cells, and which is involved in regulating cell shape and neurite formation in developing neurons.

Rapid growth cone translocation on laminin is supported by lamellipodial not filopodial structures

To determine the relationship between growth cone structure and motility, we compared the neurite extension rate, the form of individual growth cones, and the organization of f-actin in embryonic (E21) and postnatal (P30) sympathetic neurons in culture. Neurites extended faster on laminin than on collagen, but the P30 nerites were less than half as long as E21 neurites on both substrata. Growth cone shape was classified into one of five categories, ranging from fully lamellipodial to blunt endings. The leading margins of lamellipodia advanced smoothly across the substratum ahead of any filopodial activity and contained meshworks of actin filaments with no linear f-actin bundles, indicating that filopodia need not underlie lamellipodia. Rapid translocation (averaging 0.9-1.4 microns/min) was correlated with the presence of lamellipodia; translocation associated with filopodia averaged only 0.3-0.5 microns/min. This relationship extended to growth cones on a branched neurite where the translocation of each growth cone was dependent on its shape. Growth cones with both filopodial and lamellipodial components moved at intermediate rates. The prevalence of lamellipodial growth cones depended on age of the neurites; early in culture, 70% of E21 growth cones were primarily lamellipodial compared to 38% of P30 growth cones. A high percentage of E21 lamellipodial growth cones were associated with rapid neurite elongation (1.2 mm/day), whereas a week later, only 16% were lamellipodial, and neurites extended at 0.5 mm/day. Age-related differences in neurite extension thus reflected the proportion of lamellipodial growth cones present rather than disparities in basic structure or in the rates at which growth cones of a given type moved at different ages. Filopodia and lamellipodia are each sufficient to advance the neurite margin; however, rapid extension of superior cervical ganglion neurites was supported by lamellipodia independent of filopodial activity.

Morphologic plasticity of rapid-onset neurites in NG108-15 cells stimulated by substratum-bound laminin

Undifferentiated NG108-15 cells, when replated onto laminin-coated substrata, extend multipolar, highly branched neurite-like extensions up to 200 microns in length within 4 h; morphologic and pharmacologic properties of these 'rapid-onset neurites' have been described recently. The present study has extended these observations, using time lapse video recordings of their dynamic behavior and additional pharmacologic studies. Rapid-onset neurites and neuronal growth cones were shown to be regulated in an identical manner in all respects examined, including inhibition of outgrowth by cytochalasin B. Of particular interest was the observation that rapid-onset neurites in contact with laminin exhibited an extremely high rate of turnover, which was inhibited by 5'-deoxy-5'-methylthioadenosine (MTA). This system provides a uniquely favorable in vitro preparation in which neuritic plasticity can be elicited, directly observed and experimentally modulated under controlled conditions.

Analysis of slow-onset neurite formation in NG108-15 cells: implications for a unified model of neurite elongation

When undifferentiated NG108-15 cells are plated onto polylysine coated Petri dishes in serum-free medium, they form neurites within 1-4 h if plated in the presence of laminin or 5'-deoxy-5'-methylthioadenosine (rapid-onset neurites). In the absence of such agents, serum-deprived NG108-15 cells extend axon-like neurites onto polylysine over several days; here we characterize the dynamic behavior of this slow-onset outgrowth pattern in detail. Individual cells plated on laminin expressed a gradual multipolar-to-unipolar transition due to rapid-onset neurites becoming remodelled into the appearance of slow-onset neurites. This phenomenon reflected the selective stabilization of certain rapid-onset neurites, along with the restriction of motility to their distal tips. Based upon the properties and interactions of both rapid- and slow-onset neurites in NG108-15 cells, a unified model for neurite formation is presented.

Cranin: a laminin-binding protein of cell membranes

We report that a 120-kDa glycoprotein is the predominant laminin-binding protein detected within plasma membranes of rodent NG108-15 neural hybrid cells, embryonic chicken brain, and mouse 3T3 fibroblasts. This protein was detected when membrane extracts were separated by PAGE, transferred to nitrocellulose, and incubated with laminin at concentrations as low as 2.8 X 10(-11) M, under conditions of physiological ionic strength and pH and in the presence of calcium ions. It behaves as an integral membrane component, and its laminin-binding moiety is accessible to the external face of the cell surface. Moreover, it appears to bind to a site on laminin that is very sensitive to proteolysis. The properties of this protein, which we have termed "cranin," distinguish it from other known laminin receptors and make it a candidate to mediate some of the effects of laminin upon cells.