Regulation of neuron-specific enolase isozyme levels during differentiation of murine neuroblastoma cell cultures

Differential expression of neuron-specific enolase mRNA in mouse neuroblastoma cells in response to differentiation inducing agents

1. The mouse neuroblastoma cell line N-115 was used as a model system to study neuronal differentiation induced by treatment of cells with different agents. 2. The extent of morphological differentiation obtained with dibutyryl cyclic AMP (dbc-AMP), dimethyl sulfoxide (DMSO), retinoic acid (RA), and serum-free medium was correlated to the expression of the mRNA for the gamma isoform of the glycolytic enzyme enolase, a recognized neuron-specific marker. 3. A 4-day treatment of the cells with any of the differentiation inducing agents used in this study resulted in the extension of long neurites, though differences in cell body shape were observed depending on the agent used. 4. Northern blot analysis revealed that changes in the level of gamma enolase-specific mRNA correlate with the extent of morphological differentiation, with a 5- to 20-fold increase depending on the differentiation inducing agent used. 5. Finally, we found that a high cell density causes a significative increase in the level of the gamma enolase-specific message in cells maintained in growing conditions.

Adriamycin promotes neurite outgrowth in the "neurite-minus" N1A-103 mouse neuroblastoma cell line

Adriamycin, an anticancer agent acting on topoisomerase II, promotes the arrest of cell division and neurite extension in a "neurite-minus" murine neuroblastoma cell line, N1A-103. This morphological differentiation is accompanied by a blockade in the S phase of the cell cycle, modification of the amount of peripherin, and appearance of the beta 7-tubulin isoform. Yet, adriamycin-induced N1A-103 cells fail to express other neuronal markers, such as long-lasting Ca2+ channels, synaptophysin, and the shift in the proportion of the beta'1 tubulin isoform to the beta'2 isoform, whose appearance parallels the terminal differentiation of the wild type neuroblastoma cell line N1E-115. Hence, a comparison of the behavior of these two cell lines leads to the proposal that there are two programs of neuroblastoma differentiation: one where expression is triggered by the arrest of cell division and which is observed in adriamycin-induced N1A-103 variant cells, and the other, presumably occurring further downstream, which would involve further changes in morphogenesis and acquisition of new electrophysiological properties.

Participation of the mitochondrial genome in the differentiation of neuroblastoma cells

Using clonal cell lines isolated from murine neuroblastoma C1300, we investigated the mitochondrial changes related to neuronal differentiation and, more generally, the role played by the mitochondrion in this phenomenon. By different approaches (measurement of the mitochondrial mass, immunoquantification of specific mitochondrial proteins, or incorporation of Rhodamine 123), the differentiation of the inducible clone, N1E-115, was found associated with an important increase of the cellular content in mitochondria. This increase could be observed with differentiating N1E-115 cells maintained in suspension, i.e. under conditions where neurite outgrowth is prevented but other early stages of (biochemical) differentiation continue to occur. That these mitochondrial changes are likely to be correlated with these stages of neuronal differentiation, rather than with simple progression to the postmitotic stage, stems from comparative experiments with clone N1A-103, a neuroblastoma cell line variant that becomes postmitotic after induction but fails to differentiate and shows no modification in its cellular content in mitochondria. In accordance with these observations, chloramphenicol prevents differentiation when added together with the inducer. This effect is probably related to the inhibition of mitochondrial translation rather than to modification of the bioenergetic needs because oligomycine, a potent inhibitor of the mitochondrial ATP synthetase, shows no effect on neurogenesis. As a working hypothesis and in keeping with independently published models, we postulate that products resulting from mitochondrial translation could be involved in the organization of the cytoskeleton or of certain membrane components whose rearrangements should be the prerequisite or the correlates to early stages of neuronal differentiation.

Growth inhibition of N1E-115 mouse neuroblastoma cells by c-myc or N-myc antisense oligodeoxynucleotides causes limited differentiation but is not coupled to neurite formation

Antisense oligodeoxynucleotides were found to be stable in the culture medium containing fetal calf serum (heat-inactivated 30 minutes at 65 degrees C) and in cells. Antisense oligomer treatment causes cessation of mitoses, but does not lead to morphological differentiation. Under antisense conditions, we have observed an increase in the amount of two neurospecific protein, namely peripherin and gamma-enolase. Comparison of the results obtained with chemical inducers and antisense oligodeoxynucleotides allows us to postulate three phases in N1E-115 differentiation: the first correspond to the arrest of mitosis, the second to the expression of a limited neuronal program, and the third to the morphological and electrophysiological differentiation.

Developmental effect of dimethyl sulfoxide on hypothalamo-neurohypophysial neurons in vitro

Primary dissociated cultures were established from diencephalic tissue of 14-day-old fetal rats. Neurons exhibiting immunocytochemical staining for neurophysin appeared in these cultures after 6 days of cultivation. Addition of dimethyl sulfoxide (DMSO) to the culture medium resulted in a slight decrease in total neuronal cell mass as assessed by immunocytochemistry and radio-immunometric quantitation of neuron-specific enolase. In contrast, in DMSO-treated cultures the number of neurophysin-immunoreactive neurons was more than doubled as compared to control cultures. [3H]Thymidine labeling and autoradiography in conjunction with immunocytochemistry for neurophysin showed that this was not due to a mitogenic effect of DMSO on precursor cells. Time-course analysis of the action of DMSO revealed a 6-day time lag between the initiation of treatment and the appearance of increased numbers of neurophysin-immunoreactive cells. These findings suggest that DMSO, which has previously been reported to have a differentiation-inducing effect on malignant transformed cells, may also modulate cellular processes that control differentiation in specific types of neurons in primary culture.

Isolation of murine neuron-specific and non-neuronal enolase cDNA clones

cDNA clones corresponding to subunits of neuron-specific (gamma gamma and alpha gamma) and non-neuronal (alpha alpha) enolase isozymes were characterized from two mouse brain cDNA libraries. Our hybridization data revealed a partial homology of the coding sequences of mouse alpha, mouse gamma and rat gamma mRNAs. The noncoding sequences, however, appear to be specific for each mouse mRNA. Although coding for two polypeptides of the same molecular weight, the mRNA for the gamma subunit (2600 bases) is larger than that for the alpha subunit (1900 bases). The noncoding sequences for neuron-specific gamma mRNA (about 1300 bases) are therefore longer than those of the non-nervous tissue specific alpha mRNA (about 600 bases).

Dissociated cells of foetal rat pallium grown in culture medium supplemented with noradrenaline: effects on the expression of neuron-specific enolase and cell adhesion molecule L1

The possible influence of noradrenaline (NA) upon cell differentiation has been studied by comparing NA-supplemented cultures of foetal pallial cells with control cultures grown in normal medium. Two days after plating, the cultures were processed for immunocytochemical detection of either an adhesion molecule and marker of early stages of neuronal differentiation (L1) or a marker expressed at relatively late stages (gamma-enolase). In both cases, the NA supplement reduced the expression of the antigen. The effects were more clear-cut for the late than for the early marker. In conclusion, the NA supplement to the culture medium, in our model, seemed to have a 'differentiation regulating' rather than a 'neurotrophic' function sensu stricto. It remains to be clarified, however, to which extent this finding can be generalized to in vivo situations.

Neuron-specific enolase: complete structure of rat mRNA, multiple transcriptional start sites, and evidence suggesting post-transcriptional control

The protein encoded by a randomly selected rat brain cDNA clone was identified as neuron-specific enolase (NSE; 4.2.1.11; gamma subunit), based on homology to yeast enolase sequences and the presence of the corresponding 2.5-kb mRNA in rat brain but not in liver, kidney, or muscle tissue. The 2,222-nucleotide NSE and mRNA sequence presented identifies a 68-nucleotide 5' noncoding region, a 1,302-nucleotide open reading frame (corresponding to a primary translation product of 434 amino acids), and 852 noncoding 3' bases. Evolutionary implications based on sequence comparisons to yeast enolase and non-neuronal enolase are discussed. Primer extension analysis indicated the presence of several alternative initiation sites for transcription within 60 nucleotides on the NSE gene. The developmental onset of NSE mRNA expression correlates with the appearance of NSE protein; however, the mRNA reaches adult levels by postnatal week 3, whereas the protein continues to accumulate over the next few months, suggesting regulatory mechanisms in addition to transcriptional control.