Magnesium-dependent attachment and neurite outgrowth by PC12 cells on collagen and laminin substrata

We report a study of the substratum and medium requirements for attachment and neurite outgrowth by cells of the pheochromocytoma-derived PC12 line. In attachment medium containing both Ca2+ and Mg2+, more than 50% of cells attached within 1 hr to petri dishes coated with native collagen Types I/III or II, native or denatured collagen Type IV, laminin, wheat germ agglutinin (WGA), or poly-L-lysine; attachment to dishes coated with nerve growth factor (NGF) was only about 20% and attachment to uncoated dishes or to dishes coated with fibronectin or gelatin was almost nil. Neither prior culturing in the presence of NGF nor addition of NGF to the attachment medium significantly affected the extent of attachment to collagen or laminin. With Ca2+ (1 mM) as the sole divalent cation, cells attached normally to WGA, polylysine, and NGF, but failed to attach to collagen or laminin. With Mg2+ (1 mM) as the only divalent cation, attachment to all substrata was about the same as in medium with both Ca2+ and Mg2+. Like the ionic requirements, the kinetics of attachment, insensitivity to protease treatment of the cells, and inhibition by low temperature and sodium azide were similar for PC12 attachment to collagen and laminin, suggesting that a common molecular mechanism may underlie attachment to these substrata. The only significant difference observed was that addition of WGA (30 micrograms/ml) to the attachment medium inhibited attachment to collagen but promoted attachment to laminin. Finally, PC12 cells extended neurites on laminin, on native collagens I/III, II, and IV, and on denatured collagen IV; they did not extend neurites on denatured collagens I/III or II, NGF, or WGA. Neurite outgrowth on collagen and laminin occurred with Mg2+ as the sole divalent cation. These results suggest that the same Mg2+-dependent adhesion mechanism operates at the cell body and at the growth cone.     

Modulation of growth factor induced fiber outgrowth in rat pheochromocytoma (PC12) cells by a fibronectin receptor antibody

Rat pheochromocytoma PC12 cells respond to the binding of nerve growth factor (NGF) and basic fibroblast growth factor (bFGF) by extending neurites in a manner resembling sympathetic neurons. This response requires cell attachment to an appropriate substratum (Fujii et al., J. Neurosci., 2:1157, 1982); attachment factors which function in this capacity include the adhesive proteins fibronectin and laminin. Incubating PC12 cells with a polyclonal antiserum directed against a putative 140-kDa fibroblast cell surface fibronectin receptor (anti-gp140) perturbed spreading but not attachment of the cells to fibronectin and laminin substrates. However, in the presence of anti-gp 140 or its Fab fragments, NGF-stimulated neurite outgrowth was dramatically reduced. The antibody also caused a retraction of previously extended neurites. SDS-PAGE analysis of immunoprecipitates of PC12 cells surface labeled with 125I identified a prominent 120-140-kDa band, suggesting that the site of anti-gp140 action in PC12 cells is also through a fibronectin receptor.     

The neurite-initiating effect of microbial extracellular glycolipids in PC12 cells

The effects of several kinds of microbial extracellular glycolipids on neurite initiation in PC12 cells were examined. Addition of mannosylerythritol lipid-A (MEL-A), MEL-B, and sophorose lipid (SL) to PC12 cells caused significant neurite outgrowth. Other glycolipids, such as polyol lipid (PL), rhamnose lipid (RL), succinoyl trehalose lipid-A (STL-A) and STL-B caused no neurite-initiation. MEL-A increased acetylcholine esterase (AChE) activity to an extent similar to nerve growth factor (NGF). However, MEL-A induced one or two long neurites from the cell body, while NGF induced many neurites. In addition, MEL-A-induced differentiation was transient, and after 48 h, percentage of cells with neurites started to decrease in contrast to neurons induced by NGF, which occurred in a time-dependent manner. MEL-A could induce neurite outgrowth after treatment of PC12 cells with an anti-NGF receptor antibody that obstructed NGF action. These results indicate that MEL-A and NGF induce differentiation of PC12 cells through different mechanisms. This revised version was published online in August 2006 with corrections to the Cover Date.     

Changes in the Expression of β and Actins During Differentiation of PC 12 Cells

Cells of the rat pheochromocytoma line PC12 cease proliferation and develop neurites in response to nerve growth factor (NGF). Quantification of beta and gamma isoforms of nonmuscle actin in extracts of these differentiating cells showed that the beta:gamma ratio decreased from 1.30 +/- 0.05 to 0.99 +/- 0.05 after 6 days of NGF treatment. Cells treated with N6,O2-dibutyryl cyclic AMP (dbcAMP) also showed a shift in the ratio of beta:gamma isoforms, although few of these cells extended neurites. Administration of dbcAMP or both NGF and dbcAMP to cells accelerated the decrease in the beta:gamma actin isoform ratio relative to treatment with NGF alone. Those cells treated with both NGF and dbcAMP also showed an accelerated rate of neurite outgrowth. Suspension-grown PC12 cells treated with NGF showed neither an isoform ratio decrease nor neurite development. Our results suggest that either cyclic AMP may be a "second messenger" for NGF or it may effect the isoform ratio change by an independent mechanism. In addition, our data demonstrate an alteration in actin isoform expression, which accompanies the morphological differentiation of PC12 cells.     

Ultrastructural effects of nerve growth factor on PC 12 pheochromocytoma cells in spinner culture

PC12 pheochromocytoma cells treated with nerve growth factor (NGF) for two weeks in spinner cultures quickly begin to form processes after plating on an appropriate substrate, while cells freshly exposed to NGF in monolayer culture initiate neurite outgrowth only after a lag period of several days. The present ultrastructural studies indicate that PC 12 cells treated with NGF in spinner cultures do not form neurites, but do form short extensions comparable to those which have been reported within the first two days of exposure to NGF in monolayer cultures. These extensions contain organelles believed to be required for locomotion and for transport of cytoskeletal and membrane components and neurotransmitters. They also form bulbous distensions in which numerous chromaffin-type granules accumulate. These findings suggest that NGF may affect cells in spinner cultures by promoting development or activation of axonal transport mechanisms, and that the existence of these mechanisms may contribute to the neurite outgrowth which the cells exhibit when plated. NGF-treated PC 12 cells in spinner cultures do not accumulate the agranular synaptic-like vesicles, which are typically found in comparably treated monolayer cultures and which have been hypothesized to be sites of acetylcholine storage. These and other data demonstrate that attachment to a substrate can selectively modulate the responses of PC 12 cells to NGF.     

Acidic fibroblast growth factor stimulates adrenal chromaffin cells to proliferate and to extend neurites, but is not a long-term survival factor

Acidic fibroblast growth factor (aFGF) is a heparin-binding polypeptide that is a mitogen for endothelial cells and glial cells, as well as a differentiation factor for PC12 cells and certain neurons. We show here that aFGF is as potent as nerve growth factor (NGF) in stimulating both neuritic outgrowth and proliferation in adrenal chromaffin cells from young rats, but it fails to support long-term survival. Heparin strongly potentiates aFGF-dependent neuritic outgrowth but not aFGF-dependent proliferation. As is the case with NGF, phorbol myristate acetate depresses aFGF-induced cell division and increases the outgrowth of neurites. On the other hand, dexamethasone antagonizes neuritic outgrowth elicited by both NGF and aFGF but inhibits only proliferation induced by NGF. The effects of basic FGF (bFGF) are similar but not identical to those of aFGF. Thus the regulatory pathways controlled by aFGF, bFGF, and NGF are partially distinct.     

Clonal variants of PC12 pheochromocytoma cells with altered response to nerve growth factor

We describe the isolation and characterization of clonal variants of PC12 pheochromocytoma cells which have been selected for loss of response to nerve growth factor (NGF). PC12 cells mutagenized with ethyl methanesulfonate were cultured in the presence of NGF, causing normal cells to cease proliferation and allowing the isolation of cell clones which do not show growth inhibition by NGF. Some but not all of these clones also failed to respond morphologically to NGF. Forty clones were isolated and characterized. Many exhibited altered morphologies of a variety of types, including clones with an NGF-independent formation of neurites and clones with various types of flattened epithelial morphology. Variant clones appeared to be mutants since their frequency of occurrence was increased by mutagen, the clones were generally phenotypically stable and no alteration in chromosomal composition was observed. Three clones lacked NGF receptor. Some clones responded morphologically to NGF (by forming neurites) without inhibition of proliferation. Several clones which did not otherwise respond to NGF nevertheless responded with transient membrane ruffling. Thus transient changes in cell surface morphology caused by NGF binding do not necessarily lead to subsequent responses. Several alternative hypotheses concerning the nature of the mutations induced are discussed.     

PC12 cell mutants that possess low- but not high-affinity nerve growth factor receptors neither respond to nor internalize nerve growth factor

Four mutant PC12 pheochromocytoma cell lines that are nerve growth factor (NGF)-nonresponsive (PC12nnr) have been selected from chemically mutagenized cultures by a double selection procedure: failure both to grow neurites in the presence of NGF and to survive in NGF-supplemented serum-free medium. The PC12nnr cells were deficient in all additional NGF responses surveyed: abatement of cell proliferation, changes in glycoprotein composition, induction of ornithine decarboxylase, rapid changes in protein phosphorylation, and cell surface ruffling. However, PC12nnr cells closely resembled non-NGF-treated PC12 cells in most properties tested: cell size and shape; division rate; protein, phosphoprotein, and glycoprotein composition; and cell surface morphology. All four PC12nnr lines differed from PC12 cells in three ways in addition to failure of NGF response: PC12nnr cells failed to internalize bound NGF by the normal, saturable, high-affinity mechanism present in PC12 cells. The PC12nnr cells bound NGF but entirely, or nearly entirely, at low-affinity sites only, whereas PC12 cells possess both high- and low-affinity NGF binding sites. The responses to dibutyryl cyclic AMP that were tested appeared to be enhanced or altered in the PC12nnr cells compared to PC12 cells. Internalization of, and responses to, epidermal growth factor were normal in the PC12nnr cells ruling out a generalized defect in hormonal binding, uptake, or response mechanisms. These findings are consistent with a causal association between the presence of high-affinity NGF receptors and of NGF responsiveness and internalization. A possible relationship is also suggested between regulation of cAMP responses and regulation of NGF responses or NGF receptor affinity.     

Synergistic effects of cyclic AMP and nerve growth factor on neurite outgrowth and microtubule stability of PC12 cells

The outgrowth of neurites from rat PC12 cells stimulated by combined treatment of nerve growth factor (NGF) with cAMP is significantly more rapid and extensive than the outgrowth induced by either factor alone. We have compared the responses of PC12 cells under three different growth conditions, NGF alone, cAMP alone, and combined treatment, with respect to surface morphology, rapidity of neurite outgrowth, and stability of neurite microtubules, to understand the synergistic action of NGF and cAMP on PC12. Surface events at early times in these growth conditions varied, suggesting divergent pathways of action of NGF and cAMP. This suggestion is strongly supported by the finding that cells exposed to saturating levels of dibutyryl cAMP without substantial neurite outgrowth initiated neurites within 5 min of NGF. This response has been adopted as a convenient assay for NGF. Neurites that regenerated in the three growth conditions showed marked differences in stability to treatments that depolymerize microtubules. The results indicate that microtubules in cells treated with both NGF and cAMP are significantly more stable than in either growth factor alone. We suggest that a shift of the assembly equilibrium favoring tubulin assembly is a necessary prerequisite for the initiation of neurites by PC12.     

A Nerve Growth Factor-Dependent Protein Kinase That Phosphorylates Microtubule-Associated Proteins In Vitro: Possible Involvement of Its Activity in the Outgrowth of Neurites from PC12 Cells

We have established a subline of PC12 cells (PC12D) that extend neurites very quickly in response not only to nerve growth factor (NGF) but also to cyclic AMP (cAMP) in the same way as primed PC12 cells (NGF-pretreated cells). When phosphorylation of brain microtubule proteins by extracts of these cells was monitored, two distinct kinase activities were found to be increased [from three- to eightfold in terms of phosphorylation of microtubule-associated protein (MAP) 2] by a brief exposure of cells to NGF or to dibutyryl cAMP(dbcAMP). The effect of the combined stimulation with both NGF and dbcAMP was additive in terms of the phosphorylation of MAP2. The apparent molecular mass of the kinase activated by dbcAMP was 40 kDa, and this kinase appears to be cAMP-dependent protein kinase. The molecular mass of the kinase activated by NGF was 50 kDa. The latter was activated to a measurable extent after 5 min of exposure of cells to NGF; it required Mg²⁺ for activity but not Mn²⁺ or Ca²⁺. This kinase appears to be distinct from previously reported kinases in PC12 cells, and it has been designated as NGF-dependent MAP kinase, although its physiological substrates are not known at present. An inhibitor of protein kinases, K-252a, selectively inhibited the outgrowth of neurites from PC12D cells in response to NGF but not to dbcAMP. When this inhibitor was added to the incubation medium of cells exposed simultaneously to NGF or dbcAMP, the increase in activity of the NGF-dependent MAP kinase was selectively abolished. We isolated several mutant clones of PC12D cells that were deficient in the ability to induce neurites in response to either of the two stimulators. In these variant cells, the activity of the relevant protein kinase was decreased, in parallel with the deficiency in the neurite response to NGF or dbcAMP. These observations suggest that the NGF-dependent MAP kinase may play an important role in the outgrowth of neurites from PC12 cells in response to NGF.     

神经营养因子诱导分化的神经元样PC12细胞分裂的研究

神经营养因子（nerve growth factor,NGF）诱导PC12细胞分化产生的神经元样细胞一直被认为属于分裂后的细胞,没有分裂能力。然而在本研究中,我们观察了一些已经发生分化的PC12细胞,这些细胞长有很长的神经突起,在形态上属于神经元样细胞。在这些细胞中,我们不仅检测到DNA合成,而且观察到这些细胞的分裂现象。更令人感兴趣的是,除了胞体发生分裂外,位于胞体分裂位置的突起也一分为二,分别分配给两个子细胞。这些结果说明,形态发生分化的神经元样PC12细胞仍有分裂能力。本研究首次报道神经元样PC12细胞及其突起能发生分裂。     

Nitric oxide underlies the differentiation of PC12 cells induced by depolarization with high KCl

Nitric oxide (NO) acts as a cytostatic agent to induce neuronal differentiation of PC12 cells after nerve growth factor (NGF) treatment. We newly subcloned PC12K cells that extended neurites after depolarization with high KCl. Here we present evidence that the neuronal differentiation of PC12K cells caused by depolarization with high KCl is mediated by endogenous NO. The outgrowth of neurites was significantly inhibited by 2 mM N-nitro-L-arginine methyl ester (L-NMAE), and 10 mM L-NAME was necessary for complete inhibition. The inhibition of NGF-dependent neurite outgrowth by L-NAME was abolished by depolarization of cells with KCl. The expression of neuronal- and endothelial-NO-synthase in PC12K cells was confirmed by immuno-cytochemical and immuno-blotting analyses with the respective monoclonal antibodies. However, the expression of inducible-NO synthase was not observed in PC12K cells cultured with high KCl under the depolarization conditions with 45 mM KCl. We observed the increase of NO in the differentiated PC12K cells using diaminofluorescein, a novel fluorescent indicator for NO.     

Enhanced expression and activation of CTP:phosphocholine cytidylyltransferase beta2 during neurite outgrowth

During differentiation neurons increase phospholipid biosynthesis to provide new membrane for neurite growth. We studied the regulation of phosphatidylcholine (PC) biosynthesis during differentiation of two neuronal cell lines: PC12 cells and Neuro2a cells. We hypothesized that in PC12 cells nerve growth factor (NGF) would up-regulate the activity and expression of the rate-limiting enzyme in PC biosynthesis, CTP:phosphocholine cytidylyltransferase (CT). During neurite outgrowth, NGF doubled the amount of cellular PC and CT activity. CTbeta2 mRNA increased within 1 day of NGF application, prior to the formation of visible neurites, and continued to increase during neurite growth. When neurites retracted in response to NGF withdrawal, CTbeta2 mRNA, protein, and CT activity decreased. NGF specifically activated CTbeta2 by promoting its translocation from cytosol to membranes. In contrast, NGF did not alter CTalpha expression or translocation. The increase in both CTbeta2 mRNA and CT activity was inhibited by U0126, an inhibitor of mitogen-activated kinase/extracellular signal-regulated kinase kinase 1/2 (MEK1/2). In Neuro2a cells, retinoic acid significantly increased CT activity (by 54%) and increased CTbeta2 protein, coincident with neurite outgrowth but did not change CTalpha expression. Together, these data suggest that the CTbeta2 isoform of CT is specifically up-regulated and activated during neuronal differentiation to increase PC biosynthesis for growing neurites.     

Iron promotes the survival and neurite extension of serum-starved PC12 cells in the presence of NGF by enhancing cell attachment

Delayed death of serum-starved PC12 cells on a poly-L-lysine (PLL) matrix was observed, even in the presence of NGF. NGF blocked the apoptotic death of attached but not detached cells, which suggests that delayed death may be related to cell detachment from the PLL matrix. Iron selectively blocked this anoikis-like death by increasing cell attachment. Interestingly, the addition of > 10 microM FeCl2 to the culture medium generated gelatinous iron precipitates, and the removal of the precipitates abolished the iron effect. Attachment experiments using poly-HEMA supported the role of iron precipitates on cell-to-matrix adhesion. The expression of integrin beta1, neither N-cadherin nor alpha/beta-catenin, was also significantly increased by iron. In addition to its effect on cell viability, iron promoted the outgrowth of neurites. Our results collectively indicate that iron functions as a necessary co-element for NGF by enhancing cell attachment, survival, and neurite extension.     

Reconstituted basement membrane enhances neurite outgrowth in PC12 cells induced by nerve growth factor

Rat pheochromocytoma cells (PC12) respond to nerve growth factor (NGF) by elaborating neurites. We have studied the effect of extracellular matrix proteins on responsiveness of PC12 cells to NGF. NGF elicited neurite outgrowth in cells plated on collagen, fibronectin, or laminin within 48-72 h. In contrast, cells entrapped in reconstituted basement membrane prepared from the Engelbreth-Holm-Swarm tumor (EHS-BM) responded within 24 h. Cells plated on collagen or fibronectin required a minimal dose of 50 ng/ml NGF to achieve the same effect as cells entrapped in EHS-BM at 1 ng/ml NGF. Neurites displayed by cells plated in EHS-BM were more extensively branched and remained intact up to 21 days following a single administration of NGF.