Overexpression of Adhesion Molecule L1 in NG108-15 Neuroblastoma × Glioma Hybrid Cells Enhances Dibutyryl Cyclic AMP-Induced Neurite Outgrowth and Functional Synapse Formation with Myotubes

Abstract: The role of adhesion molecule L1 in synapse formation was examined by transient transfection of L1 cDNA in neuroblastoma × glioma hybrid NG108-15 cells. L1 overexpression was found in ∼50% of the transfected NG108-15 cell population. Neurite outgrowth induced by 0.25 m M dibutyryl cyclic AMP (cAMP) was much greater in L1-transfected NG108-15 cells than that in nontransfected and mock-transfected cells. The proportion of cells with neurites and the number of neurites per cells were increased in L1-transfected cells after 2 days of dibutyryl cAMP treatment. The proportion of cells with branched neurites and the average length of neurites were higher at day 4. A significantly higher rate of synapse formation with myotubes was apparent in the late phase of coculture (days 4–7) in L1-transfected cells than in control cells. The miniature end-plate potential frequency in myotubes was the same for the three types of NG108-15 cells. These results show that overexpression of L1 in NG108-15 cells facilitates synaptic connections by enhancing branching and elongation of neurites induced with dibutyryl cAMP, rather than by increasing probability of acetylcholine release.     

Modulation of Neuritogenesis by Ganglioside-Specific Sialidase (Neu 3) in Human Neuroblastoma NB-1 Cells

Plasma membrane-associated sialidase (Neu 3), which specifically hydrolyzes gangliosides, is relatively abundantly present in the nervous system. To understand the role of Neu 3 in neuronal differentiation, we studied the relationship between neurite outgrowth and Neu 3 expression in human neuroblastoma NB-1 cells. The expression of Neu 3 in NB-1 cells increased when neurite outgrowth in these cells was induced by dibutyryl cAMP. While treatment with dibutyryl cAMP alone enhanced the outgrowth of dendrite-like processes, transfection of the Neu 3 gave rise to a more prominent outgrowth of neurites with axon-like characteristics, even in the absence of dibutyryl cAMP. Neu 3 induction by dibutyryl cAMP is probably attributable, in part, to transactivation of the Neu 3 gene through cAMP responsive elements in the 5-upstream region, as revealed by the promotor activity assay using Neu 3 promotor expression plasmid. These results indicate that Neu 3 regulates neurite formation in NB-1 cells, and suggest that this effect may be enhanced by dibutyryl cAMP via a cAMP-dependent pathway.     

Increase in β-1,4-Galactosyltransferase Activity During PC12 Cell Differentiation Induced by Forskolin and 2-Chloroadenosine

Galactosyltransferase (GALTase) activity was measured in differentiating PC12 cells induced by either forskolin or 2-chloroadenosine. The specific activity of GALTase in whole cells and isolated Golgi membranes increased as early as 3 h after initiating treatment with 2-chloroadenosine, and maximal activity was reached at approximately 12 h. In two mutant PC12 cell lines deficient in protein kinase A, both forskolin and 2-chloroadenosine failed to increase GALTase activity. The adenosine A2 receptor antagonist, xanthine amine congener, prevented 2-chloroadenosine stimulation of GALTase, demonstrating that this adenosine derivative was mediating its effect via the A2 receptor. These data suggest that GALTase activity during PC12 cell differentiation is regulated by cyclic AMP (cAMP)- and protein kinase A-dependent processes. In support of the role of cAMP in regulating GALTase activity were studies with murine PC carcinoma cells demonstrating that the greatest stimulation of GALTase activity occurred with cells treated with both retinoic acid and dibutyryl cAMP.     

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.     

Down modulation of N-myc, heat-shock protein 70, and nucleolin during the differentiation of human neuroblastoma cells.

Cultured human neuroblastoma (GOTO) cells were induced to differentiate by dibutyryl cyclic AMP (Bt2cAMP) and/or retinoic acid (RA). A combination of Bt2cAMP (1 mM) and RA (1 microM) yielded the most significant networks of neurites after 3 to 4 days, this being associated with the reduction of N-myc mRNA levels. Next, we examined several cellular genes that were possibly linked with changes in N-myc gene expression under these conditions. Among the genes examined, both nucleolin and a major heat-shock protein (hsp70) mRNAs showed changes concomitant with those in N-myc mRNA levels when induced by Bt2cAMP and RA. Dibutyryl cAMP alone induced several short cellular processes and caused a marked decrease in N-myc mRNA within 2 days. RA alone induced a few long and straight neurites along the longitudinal axis of individual cells and a significant decrease in growth rate but showed neither network formation nor a decrease in N-myc gene expression. These results indicate differential effects of Bt2cAMP and RA on the regulatory mechanisms of both cell proliferation and differentiation and also indicate a possible association of expression of N-myc gene with those of hsp70 and nucleolin genes.     

Reversible effects of dibutyryl cAMP on laminin and type IV collagen secretion from retinoic acid treated F9 cells

The effects of dibutyryl cAMP on the differentiation of embryonal carcinoma F9 cells were studied mainly using the secretion of laminin and type IV collagen as the marker. For this purpose, F9 cells were labeled with 35S-methionine and radioactive proteins in the medium were analyzed by SDS-polyacrylamide gel electrophoresis. Treatment of F9 cells with retinoic acid alone induced differentiation into cells secreting type IV collagen. The combination of retinoic acid and dibutyryl cAMP stimulated laminin secretion in addition to type IV collagen secretion. This effect of dibutyryl cAMP was observed only 16 h after adding dibutyryl cAMP. Immunofluorescence staining demonstrated that the majority of the cells in culture were converted into cells secreting laminin under these conditions. In contrast to the irreversible effect of retinoic acid, the effect of dibutyryl cAMP on laminin and type IV collagen secretion was reversible at least during the first 5 days of maintaining cells in the medium containing retinoic acid plus dibutyryl cAMP. Removal of dibutyryl cAMP from the culture medium decreased the protein secretion to the basal levels within 2 days. This reversibility was not due to a change in cell number. An in vitro translation assay also suggested the reversible effect of dibutyryl cAMP on the levels of laminin mRNA. Coinciding with variations of the protein secretion, a reversible and homogeneous change in the morphology of retinoic acid generated F9 cells was observed by dibutyryl cAMP.     

Beta-adrenergic stimulation enhances translocation, processing and synthesis of lipoprotein lipase in rat heart cells

Cells isolated from newborn rat hearts were cultured for 10-14 days, and lipoprotein lipase activity was present in an intracellular and heparin-releasable pool. Treatment of the cultures with 10(-7) M isoproterenol for 3 min resulted in a 3-fold increase in heparin-releasable lipoprotein lipase and a concomitant decrease in residual cellular enzyme activity. Similar results were obtained by treatment with dibutyryl cAMP. Treatment with isoproterenol or dibutyryl cAMP for 2 h affected glycosylation of immunoadsorbable lipoprotein lipase, so that the ratio of [3H]galactose to [14C]mannose in the heparin-releasable enzyme increased from 3.8 (control) to 13.0 (isoproterenol-treated). The change in the ratio of the sugars in the cellular fraction of the enzyme was from 3.1 to 9.9. 2 h treatment with isoproterenol did not enhance new enzyme synthesis, as determined by incorporation of [3H]leucine into immunoadsorbable lipoprotein lipase. 24 h after addition of either isoproterenol or dibutyryl cAMP to the culture medium, stimulation of enzyme synthesis was demonstrated. The present results permit three effects of isoproterenol on lipoprotein lipase to be distinguished: stimulation of translocation from a cellular to heparin-releasable pool; enhanced processing of mannose residues and terminal glycosylation; stimulation of synthesis of enzyme protein.     

Activation of adenylate cyclase system enzymes and lysosomal acid phosphatase in target cells interacting with T-killer cells

The interaction of T-killers with target cells was studied to reveal the biochemical changes in the latter. On specific binding of target cells with T-killers the activity in target cells of cAMP phosphodiesterase increased 2.1-fold, the level of cAMP decreased 1.5-fold, the adenylate cyclase activity decreased 2.0-fold, the phosphorylation of intracellular proteins decreased 1.8-fold, the cAMP-dependent protein kinase activity decreased 1.7-fold. No change in the activity of lysosomal enzymes was observed. At the "independent target cells lysis" stage the level of cAMP increased 1.8-fold, the phosphodiesterase activity decreased 1.7-fold, the cAMP-dependent protein kinase activity increased 1.8-fold, the released activity of acid phosphatase increased up to 40% compared with the control cells. In the presence of 1 mM dibutyryl cAMP the released activity of the acid phosphatase in target cells was inhibited by 29%, the target cells lysis was decreased by 23,5%. The data obtained allowed to suppose that the activation of the host lysosomal enzymes causes target cells autolysis and that cAMP takes part in the regulation of these processes.     

Alteration in gene expression at the onset of human Y-79 retinoblastoma cell differentiation

We have tested the hypothesis that differentiation and growth arrest of Y-79 human retinoblastoma cells in culture is associated with a modification of gene expression. We first examined proteins translated from mRNAs isolated from Y-79 cells growing in suspension and in attachment cultures in serum-containing medium and found them to be markedly different. This suggests that membrane-substrate interactions are of major consequence in the biochemical differentiation of these cells. Secondly, we examined the patterns of proteins translated from attached cells which had been induced to morphologically differentiate into neuronal-like and glial-like cells by serum-withdrawal and dibutyryl cAMP treatment respectively. The in vitro translatable proteins of mRNAs isolated from these cultures were found to be markedly different from those of the suspension and attachment cultures. Thirdly, we found that treatment of cells growing in attachment culture in serum-containing medium supplemented with 8-bromo cAMP, butyrate and retinoic acid as well as dibutyryl cAMP resulted in discreet alterations in proteins translated in vitro from extracted mRNAs. Although all these substances inhibit the growth of Y-79 cells, only dibutyryl cAMP and butyrate result in morphological differentiation of cells. Our results suggest that (1) attachment and morphological differentiation of Y-79 cells are both related to specific alterations in gene expression and (2) differentiation and inhibition of cell growth by various agents can be correlated with changes in translatable mRNA species although all agents do not act in the same mode.     

Cyclic AMP dependent regulation of mitosis in human lymphoid cells

Intracellular levels of cyclic AMP (cAMP), cAMP-dependent phosphodiesterase activity, and adenylate cyclase activity are examined in an established line of human lymphoid cells synchronized by either excess thymidine or by colcemid treatment. cAMP levels and adenylate cyclase activities during the two G periods are high when compared with the values in M. cAMP-dependent phosphodiesterase activity, which is low during early G 2, is shown to increase during G 2 and reach a maximum activity during M. Agents such as dibutyryl cAMP, 1-methyl-3-isobutyl xanthine, noradrenaline, and isopropyl noradrenaline, which increase the levels of intracellular cAMP were examined to determine their effects on mitosis and on DNA synthesis. In thymidine-synchronized cells the onset of mitosis is prevented by increasing or maintaining high levels of cAMP during G 2. The specificity of inhibition of DNA synthesis or mitosis by dibutyryl cAMP is a function of the time, during the cell cycle, when the analogue is added. The elevation of cAMP by methyl xanthine results in a more general inhibition of nucleic acid synthesis and mitosis. Although both catecholamine hormones inhibit mitosis, isopropylnoradrenaline also inhibits DNA synthesis while noradrenaline treatment does not result in such inhibition.     

Induction of axon-like and dendrite-like processes in neuroblastoma cells

Neuroblastoma cells are widely utilized models for the study of the neuritic outgrowth phase of neuronal differentiation, but relatively few such studies have attempted to identify the nature of the process outgrowths. This identification will be necessary in developing strategies for utilizing these models to distinguish the underlying mechanisms involved in axonogenesis vs dendritogenesis. In an effort to identify procedures for inducing specific types of neurite outgrowth, and for distinguishing axon- from dendrite-like processes, we have subjected two neuroblastoma cell lines to a variety of stimuli previously shown to induce neurite outgrowth in these cells. These include neuraminidase, ionomycin, KCl+dibutyryl cAMP, cholera toxin B subunit, retinoic acid, dibutyryl cAMP (alone), GM1 ganglioside, and low serum. The first four of these (group 1) gave rise to neurites with axon-like characteristics, including immunostaining that was positive for phosphorylated high molecular weight neurofilament protein (NF-H) and synaptic vesicle protein-2 (SV2), but negative for microtubule-associated protein-2 (MAP2). The next three treatments (group 2) resulted in dendrite-like processes, as evidenced in immunostaining that was positive for MAP2 and negative for NF-H and SV2. Neurites produced by low serum had mixed properties. These cytoskeletal differences were supported by immunoblot analysis with antisera to the above cytoskeletal proteins. Striking morphological differences were also noted, group 2-induced neurites being significantly shorter with more branch points than those generated by group 1 stimulants. Time of exposure to stimulatory agent was crucial in determining expression of the neuritic phenotype. Correlation with previous studies suggests that axon-like neurites result from stimulants which elevate intracellular Ca2+, a dependence not previously reported to our knowledge. Dendrite-like process outgrowth, on the other hand, does not appear to depend on altered intracellular Ca2+.     

REGULATION OF A GLUCOSE TRANSPORT SYSTEM IN STICHOCOCCUS BACILLARIS1

Glucose and related non-metabolizable analogs were transported into cells of Stichococcus bacillaris Naeg. By a specific and active transport system. Glucose transport capacity was stimulated eight-fold by incubation in medium of low osmotic potential (0.09 osM). Stimulation occurred over 24 h in the dark and over 72 h in low osmotic medium. Inhibition of protein synthesis prevented any transport, stimulation from occurring. Kinetic studies revealed that the stimulation caused an increase in Ike maximal velocity of transport and did not affect the half-saturation constant for transport. It was concluded that incubation of cells in the dark or in low osmolar medium induces a synthesis of the transport system. The glucose analog 2-deoxy-D-glucose was only phosphorylated to a limited extent upon entry into the cells, and the free sugar accumulated linearly in dark pre-incubated tells for a period of at least six minutes to reach an intracellular/extracellular concentration ratio of almost 300. Glucose, in contrast, was rapid h converted to sucrose and other cell constituents. Cells incubated 24 h with, glucose or 6-deoxy-D-glucose did not exhibit any altered transport system activity. Cells incubated 24 h with 7 mM dibutyryl cAMP exhibited a 2.5-fold stimulation of transport activity. No stimulation was observed in cells treated only 30 min with dibutyryl cAMP.     

Neurite development in vitro. I. The effects of adenosine 3′5′-cyclic monophosphate (cyclic AMP)

Elevated levels of 3′5′ adenosine monophosphate (cyclic AMP) stimulate a wide variety of cellular events including aggregation, differentiation, morphological expression, pigment migration, and secretion. The role of cyclic AMP in these events prompted our present study of embryonic chick dorsal root ganglia. Test substances were applied to cultures during the routine feeding procedure. Their development was quantitatively evaluated on the basis of explant size, length of glial-like outgrowth, distribution of growth, neurite number, length, diameter, and degree of arborization. These parameters were all shown to be independent of each other. The high variability of in vitro neurite development necessitated the use of over 100 cultures per treatment group. Cultures treated with 5′ AMP exhibited no significant differences from controls. Those treated with cyclic AMP, dibutyryl cyclic AMP, or Nerve Growth Factor (NGF) exhibited statistically significant increases in area of outgrowth, the number of neurites per culture, and in diameters, lengths, and degree of neurite arborization. The growth promoting activity of dibutyryl cyclic AMP and NGF were greater than those of cyclic AMP. Electron microscopic study shows neurites formed under the influence of cyclic AMP or its dibutyryl derivative to resemble those grown in NGF. These studies suggest the possibility that cyclic AMP stimulates neurite growth by mediating the process of microtubule (MT) assembly. They further prompt us to speculate that one way NGF enhances neurite development is by stimulating MT assembly via a “Second Messenger System”.     

Induction of neural-like cells and acetylcholinesterase activity in cultures of F9 teratocarcinoma treated with retinoic acid and dibutyryl cyclic adenosine monophosphate

Cultures of F9 embryonal carcinoma cells treated with retinoic acid showed partial differentiation to endoderm cells as previously reported [Strickland, S., and Mahdavi, V. (1978).Cell15, 393–403]. Addition of dibutyryl cAMP to cultures pretreated with retinoic acid led to a second distinctive change in the cell population, with the formation of many neural-like cells. The appearance of these cells coincided with large increases in specific acetylcholinesterase activity of the cultures. Provided the cultures had been exposed to retinoic acid for at least 48 hr beforehand, the morphological and enzymatic changes became apparent between 24 and 48 hr after the addition of dibutyryl cAMP. The changes proceeded more abruptly and extensively when cells were grown in nongelatinized culture dishes. On gelatin-coated surfaces, the differentiated cells occasionally showed local areas of ordered arrangements. It is suggested that this system may be useful in analyzing early events in neural differentiation.     

Specific protein phosphorylation during cyclic AMP-mediated morphological reversion of transformed cells

Treatment of transformed Chinese hamster ovary cells with dibutyryl cAMP or other agents that elevate cAMP results in the acquisition of growth and morphology characteristic of normal fibroblasts. The role of specific protein phosphorylation in this process of morphological reversion has been examined using metabolic labelling of Chinese hamster ovary (CHO) cells with ³²P-orthophosphate in the presence or absence of N⁶O^2′-dibutyryladenosine 3′:5′-cyclic monophosphoric acid (Bt₂cAMP). Analysis of labelled cultures by SDS gel electrophoresis and radioautography demonstrate dramatic changes in the phosphorylation of only 2 cellular proteins during reverse transformation. A 55,000 dalton protein (pp55) was phosphorylated and a 20,000 dalton protein (pp20) was dephosphorylated. The time course of these events was consistent with the kinetics of morphological reversion. The lower molecular weight species, pp20, was dephosphorylated within 15–30 minutes, prior to all morphological changes except membrane tranquilization. The higher molecular weight protein, pp55, was maximally phosphorylated over 1–2 hours following addition of Bt₂cAMP, paralleling early stages in the establishment of fibroblastic form. The phosphorylated forms of pp20 and pp55 were both extracted from cellular cytoskeletons by 0.5% Triton X-100, but analysis of ³⁵S-methioninelabelled cultures suggested that unphosphorylated pp 20 may be bound to the cytoskeleton. Since pp20 was found to comigrate with the 20,000 dalton myosin light chain, it is possible that dephosphorylation of CHO cell myosin induced by cAMP may alter its interaction with actin microfilaments and modulate the assembly of stress fibers during morphological reversion.     

Involvement of Growth-Associated Protein-43 with Irreversible Neurite Outgrowth by Dibutyryl Cyclic AMP and Phorbol Ester in NG108–15 Cells

Simultaneous treatment with 12-O-tetradecanoylphorbol 13-acetate (TPA) and dibutyryl cyclic AMP (diBu-cAMP) for 72 h induced neurites in NG108-15 cells significantly longer than treatment with each alone. Treatment for 72 h with both drugs induced irreversible neurite extension and a decline in protein kinase C activity, although neurites extended by diBu-cAMP alone disappeared after the withdrawal of the drug. The expression of growth-associated protein-43 (GAP-43) mRNA was also observed by a combined application of TPA and diBu-cAMP. The increased level of GAP-43 mRNA induced by treatment with both drugs for 72 h was maintained at least 24 h after withdrawal of the drugs. In cells transfected with GAP-43 cDNA, neurites induced by treatment with diBu-cAMP alone for 72 h were maintained at least 48 h after removal of the drugs. These results suggest that GAP-43 could be involved in the maintenance of elongated neurites and that a decline in protein kinase C activity may be involved in the accumulation of GAP-43.     

τ and Microtubule-Associated Protein 2c Transfection and Neurite Outgrowth in ND 7/23 Cells

Abstract: Neuronal hybrid ND 7/23 cells, which display sensorylike properties, develop neurites when cultured in the presence of either dibutyryl cyclic AMP plus nerve growth factor (DBcAMP + NGF) or retinoic acid or a phorbol ester derivative, although they express only trace amounts of the microtubule-associated τ proteins and low levels of microtubule-associated protein 2c (MAP2c). Nondifferentiated ND cells transfected with τ cDNAs did not develop neurites, whereas very short cell processes were formed in MAP2c-transfected cells. τ and MAP2 antibodies labeled microtubule bundles displayed in a ring array underneath the surface of the transfected cells and short microtubules starting from the cell center. After differentiation in the presence of DBcAMP + NGF, the same bundle organization was observed in the transfected cells. In addition, τ and MAP2 antibodies stained a short section of the formed neurites. These data demonstrate that the expression of τ protein is not sufficient to induce neurite extension and that other proteins induced by morphogens are more important to initiate morphological differentiation of this cell line.     

Differentiation of a cell line of mouse myeloid leukemia : I. Simultaneous induction of lysosomal enzyme activities and phagocytosis

Induction of phagocytic activity in the Ml cell line of mouse myeloid leukemia, on being exposed to a conditioned medium from cultured embryo cells, was accompanied by an increment in the activities of both lysosomal acid phosphatase and acid protease. The activity of these lysosomal enzymes, as well as that of phagocytosis, was not induced when Ml cells were incubated either with the conditioned medium subjected to heat treatment or in the presence of 5-bromodeoxyuridine (BUdR). The levels of these induced enzyme activities in Ml cells were comparable to those in normal mouse peritoneal macrophages. The lysosomal enzyme activity in Mm-1 cells, which were spontaneously differentiated from Ml cells and exhibiting a higher phagocytic activity, were reminiscent of those in peritoneal macrophages. Based on these observations, it was concluded that both phagocytosis and lysosomal enzyme activity occur simultaneously during the course of differentiation. This differentiation, morphological or functional, in Ml cells in the presence of the conditioned medium was further supported by biochemical evidence.     

Differential regulation of keratin 8 and 18 messenger RNAs in differentiating F9 cells

F9 embryonal carcinoma cells (F9EC) can be induced to differentiate in vitro into epithelial cells expressing keratin 8 (K8) and keratin 18 (K18). cDNAs corresponding to K8 and K18 mRNAs were cloned and used to study the change in the abundance of these mRNAs during differentiation of F9 cells into parietal endoderm-like cells by treatment with retinoic acid (RA) or with RA and dibutyryl cAMP (Bt₂cAMP). Using an RNase protection assay, it was determined that K8 mRNA was induced slightly before K18 mRNA and that it accumulated to a greater extent than K18 mRNA. Furthermore, differentiation in presence of Bt₂cAMP plus RA resulted in an earlier induction of the two mRNAs and a higher level of expression of K8 mRNA. These results indicate that K8 and K18 mRNAs are regulated differently in F9 cells.     

Direct effects of trypan blue on thyroid secretion.

Trypan blue directly inhibited in vitro thyroid secretion (butanol soluble 125I release to the media) induced by both thyroid stimulating hormone (TSH) and dibutyryl cAMP. Intracellular colloid droplet counts were also decreased. Inhibition was directly proportional to dye concentration and could be overcome by supramaximal TSH and dibutyryl cAMP. Inhibition could be observed as early as 20 min of incubation, was not increased by preincubation, and could even be demonstrated after TSH in vivo. Trypan blue, in vivo, produced similar inhibition of thyroid secretion. Incubation of 125I-thyroglobulin with lysosomal enzymes revealed inhibition with much lower concentrations of dye. Inhibition of lysosomal enzyme(s) would not appear to explain the marked decreases in colloid droplets, and this may represent two separate effects of trypan blue on thyroid secretion.