Clonal hybrid cell lines expressing cholinergic and adrenergic properties

The neuropeptide head activator induces activation and translocation of the growth-factor-regulated Ca2+-permeable channel GRC

The neuropeptide head activator stimulates cell proliferation of neuronal precursor and neuroendocrine cells. The mitogenic signaling cascade requires Ca2+ influx for which, as we show in this paper, the growth-factor-regulated Ca2+-permeable cation channel, GRC, is responsible. GRC is a member of the transient receptor potential channel family. In uninduced cells only low amounts of GRC are present on the plasma membrane but, upon stimulation with head activator, GRC translocates from an intracellular compartment to the cell surface. Head activator functions as an inducer of GRC translocation in neuronal and neuroendocrine cells, which express GRC endogenously, and also in COS-7 cells after transfection with GRC. Head activator is no direct ligand for GRC, but its action requires the presence of a receptor coupled to a pertussis-toxin inhibitable G-protein. Heterologously expressed GRC becomes activated by head activator, which results in opening of the channel and Ca2+ influx. SK&F 96365, an inhibitor specific for TRP-like channels, blocks Ca2+ entry and, consequently, translocation of GRC is prevented. Head activator-induced GRC activation and translocation are also inhibited by wortmannin and KN-93, blockers of the phosphatidylinositol 3-kinase and of the Ca2+/calmodulin-dependent kinase, respectively, which implies a role for both kinases in head-activator signaling to GRC.

Characterization of pressure-induced calcium response in neuronal cell lines

BACKGROUND

Cation channels that respond to mechanical stress have been described in neuronal and nonneuronal cells. These nonselective cation ([C+(SA)]) channels are believed to regulate volume and osmolarity of cells in the central nervous system and are therefore believed to be involved in brain injury, resulting in intracellular calcium accumulation and cell death.

METHODS

Activation of pressure-sensitive channels was monitored as an increase in [Ca2+](i) by flow cytometry using indo-1. Several neuronal cell lines including NH15-CA2 neuroblastoma x glioma cells were stimulated by rectangular pressure increase.

RESULTS

Neuronal cell lines showed a pressure-sensitive increase in [Ca2+](i) but no pressure sensitivity was found in fibroblasts and embryonic P19 cells. [C+(SA)] channels in NH15-CA2 cells were not blocked by inhibitors of voltage-dependent calcium channels and G-proteins. Depletion of extracellular calcium and of internal Ca2+ stores inhibited pressure-induced [Ca2+](i) increase. Elevated [C+(SA)] channel activity was also observed in confluent NH15-CA2 thus accumulated in the G(0)/G(1)-phase of the cell cycle. P19 cells showed occurrence of [C+(SA)] channel activity only after neuronal differentiation.

CONCLUSION

Pressure-sensitive channel activity is present in cells of neuronal origin. This activity depends on neuronal differentiation and might have a pivotal role in neuronal development and differentiation.

Unique expression pattern of a novel mosaic receptor in the developing cerebral cortex

Recently, a new type of transmembrane protein with a unique combination of protein domains was characterized from human, rabbit and chicken. This protein exhibits features of the low-density lipoprotein receptor family and shows homology to the receptor of the neuropeptide head activator isolated from hydra. To study the temporal and spatial pattern of expression of this unusual new receptor we have isolated a murine homolog and, in accordance with its human counterpart, named it mSorLA. Northern blot analysis revealed the highest abundance of mSorLA transcripts in the adult brain, lower levels in a variety of other organs and expression during embryogenesis. In situ hybridization showed predominant localization in neurons of the cortex, the hippocampus and the cerebellum. During embryonic development mSorLA displayed a unique pattern of expression in the cerebral cortex, where a subpopulation of neurons was labeled before final differentiation. Transcripts of mSorLA were also detected outside the central nervous system in regions active in morphogenesis.

A novel G protein-coupled receptor with homology to neuropeptide and chemoattractant receptors expressed during bone development

A novel G protein-coupled receptor was isolated from a cDNA derived from the cell line NH15-CA2 and a cDNA library from adult mouse brain using a PCR cloning strategy. The amino acid sequence of the candidate receptor DEZ showed homology to neuropeptide and chemoattractant receptors. Highest overall homology was found with the orphan receptor GPR-1 (65%), the angiotensin II receptor (62%), and the C5a anaphylatoxin receptor (60%). Northern blot analysis of dez revealed a predominant 2.6 kb mRNA species in NH15-CA2 cells. In situ hybridization experiments showed that dez is differentially regulated during development, with a prominent expression in developing osseous and cartilaginous tissue. It was also detectable in the adult parathyroid glands, hinting at a possible function in bone metabolism.

Coexistence of cholinergic, catecholaminergic, serotonergic, and glutamatergic neurotransmitter markers in mouse clonal hybrid neurons derived from the septal region

Two clonal immortalized neurons designated SN6.1b and SN6.2a were isolated by limiting dilution from a mouse embryonic septal cholinergic neuronal hybrid cell line SN6 (Hammond et al., 1986). In the serum-containing medium without extra differentiating agents, one-third of SN6.1b cells stably exhibited a morphology of differentiated neurons with extensive elaborate neurites, while a majority of SN6.2a cells, along with the parent cell line SN6, were round in shape with poorly branched short processes. Neurochemical studies showed that both clones synthesized choline acetyltransferase (ChAT), dopamine, norepinephrine, serotonin, and glutamate. Immunocytochemically, they expressed a number of neuronal antigens, such as 200-kDa neurofilament protein, neuron-specific enolase, microtubule-associated protein 2, tau protein, tubulin, neural cell adhesion molecule, Thy-1.2, saxitoxin-binding sodium channel protein, ChAT, tyrosine hydroxylase, serotonin, and glutamate. The coexistence of cholinergic, catecholaminergic, serotonergic, and glutamatergic neurotransmitter markers in the clonal hybrid septal neurons that express a variety of immunocytochemical properties of differentiated neurons suggests that embryonic septal cholinergic neurons are potentially multiphenotypic with respect to neurotransmitter synthesis.

Expression of intracisternal A-particle-related retroviral element-encoded envelope proteins detected in cell lines

Intracisternal A-particle (IAP) retrotransposons of rodents express gag and pol proteins for assembly of intracellular viruslike particles but lack an env gene. The recently described IAP-related family of retroviral elements contains a reading frame with close resemblance to retroviral env genes (IAPEs) (F. U. Reuss and H. C. Schaller, J. Virol. 65:5702-5709, 1991). I now report the analysis of cellular IAPE mRNAs and detection of IAPE env proteins. IAPE elements are transcribed in cell lines NH15-CA2 and AtT20. Four major transcripts of 4.2, 3.9, 2.8, and 1.3 kb are detected and characterized by probes specific for defined regions of the cloned IAPE-1 cDNA. The 2.8-kb mRNA is shown to lack gag and pol genes but comprises an env gene and U3 region, as expected for a subgenomic env mRNA. Polymerase chain reaction amplification and cloning of such mRNAs confirmed the absence of gag and pol genes 5' from the env gene and implicates env mRNA generation by a splicing event. A polyclonal anti-IAPE env antiserum, raised against a bacterial IAPE-env fusion protein, specifically detects N-glycosylated env proteins of 91 kDa or less in cell lines positive for IAPE mRNA. IAPE env proteins of different sizes represent independent translation products. After inhibition of N-glycosylation, env proteins in the size predicted from the env gene sequence or smaller are present. These results provide evidence that putative IAPE env proteins are synthesized in vivo. Envelope protein expression by an IAP-related retroviral element identifies IAPEs as a possible missing link between IAP retrotransposons and retroviruses.

cDNA sequence and genomic characterization of intracisternal A-particle-related retroviral elements containing an envelope gene

Intracisternal A-particle retrotransposons (IAPs) are retroviruslike elements that are defective in envelope protein synthesis and exist without an extracellular stage. We have isolated a novel class of cDNAs that are related to known IAP elements in the nucleotide and deduced protein sequence of gag and pol genes but also contain a previously unidentified reading frame between the pol gene and putative U3 region. Analysis of the deduced protein sequence reveals features of the putative protein that are characteristic of retroviral envelope proteins. The isolated cDNAs represent transcripts of multiple retroid elements in the mouse genome that were termed IAPE (intracisternal A-particle-related elements coding for envelope). IAPE env genes exist in approximately 200 copies per haploid genome as integral parts of the majority of these retroid elements. Four major IAPE subgroups could be distinguished after EcoRI digestion of genomic DNA.

Elevated levels of head activator in human brain tumors and in serum of patients with brain and other neurally derived tumors

In normal human tissue high concentrations of the neuropeptide head activator are found in the hypothalamus, in the retina, and in the gastro-intestinal tract. Up to 100-fold elevated levels of head activator over neighbouring tissue were found in tumors of the brain, especially in tumors of neural origin like astrocytoma and glioblastoma, but also in meningioma. Coincident with elevated tissue levels, an increased secretion into the general circulation was observed. Elevated levels of head activator in the blood were also observed in patients with tumors in peripheral locations, especially in tumors of gastrointestinal tract and/or of neuroendocrine origin. After tumor removal, the head activator levels in the blood dropped to normal values suggesting a possible role of head activator in neuroendocrine tumorigenesis.

Production and characterization of monoclonal antibodies recognizing head activator in precursor form and immunocytochemical localization of head activator precursor and head activator peptide in the neural cell line NH15-CA2 and in hydra

A synthetic gene for the hydra neuropeptide head activator (HA) was used to produce large amounts of an HA bacterial fusion protein. From this protein an HA-containing fragment was cleaved out, attached in high copy number to carrier proteins, and used as an immunogen to produce monoclonal antibodies able to recognize head activator in precursor form. Using such antibodies and others with different specificities for HA epitopes in combination with different fixation procedures, we detected HA immunoreactivity in three locations in the HA-rich neural cell line NH15-CA2. A precursor-like HA immunoreactivity was present in the cytoplasm of cells and detected, independent of fixation procedure, by monoclonal antibodies characterized as HA-precursor-specific. With antibodies specific for the HA peptide, two immunoreactivities could be distinguished, one within cells and one at the outer cell membrane. HA was detected within differentiated cells with long processes when crosslinkers such as carbodiimide or glutaraldehyde were applied together with agents like methanol. HA peptide bound to target cells was restricted to small round cells with an undifferentiated morphology, especially to those in the process of cell division. In hydra HA precursor immunoreactivity was localized in interstitial cells and in developing nerve cells. HA peptide immunoreactivity was present in nerve cells, but was more concentrated on and in target cells such as interstitial cells and epithelial cells. In tissue sections immunoreactive cells were especially abundant in regions of high HA content such as hypostome, subhypostomal region, and the future head region of developing buds.

Neuronal properties of clonal hybrid cell lines derived from central cholinergic neurons

Clonal cell lines derived from specific types of central neurons can be used to identify and characterize properties specific to those neurons. With somatic cell fusion techniques, nine clonal hybrid cell lines have been developed from the septal region of the mouse basal forebrain. Two lines express characteristics typical of cholinergic neurons--choline acetyltransferase activity and immunoreactivity, neurite formation with neurofilament protein immunoreactivity, and aggregation in rotation-mediated cell culture. These cell lines may be useful for studying the trophic interactions that support the development and maintenance of central cholinergic connections.

Neuroblastoma X glioma hybrid cells synthesize enkephalin-like opioid peptides

Partially purified extracts from neuroblastoma X glioma hybrid cells 108CC15 inhibit, like opioids, the prostaglandin E1-evoked formation of cyclic AMP in a dose-dependent manner in the same hybrid cells. The inhibition is prevented by the opioid antagonist naloxone. In addition, the same extract competes with [3H]naloxone and [3H]Leu-enkephalin for binding to opioid receptors of hybrid cell membranes and to a specific antiserum, respectively. The opioid activity in the extracts is destroyed by carboxypeptidase A and leucine aminopeptidase, but not by trypsin. Further purification of the extracts by HPLC, TLC, or high-voltage paper electrophoresis reveals in each case two active fractions which behave like Met- and Leu-enkephalin. The Met-enkephalin-like, but not the Leu-enkephalin-like, fraction is inactivated by treatment with BrCN. Dimethylaminonaphtylsulfonyl (dansyl) derivatives of Met- and Leu-enkephalin correspond to [3H]dansyl derivatives of Met-like substances from hybrid cells. Three to four times as much Met-enkephalin-like as Leu-enkephalin-like material is present in the extract. The overall concentration of opioid peptides in the hybrid cells varies between 0.03 and 1.0 pmol Leu-enkephalin equivalents per mg protein. The amount of opioids in the hybrid cells is strongly dependent on the cell density. The findings suggest that neuroblastoma X glioma hybrid cells contain opioid peptides that are very similar, if not identical, to Met- and Leu-enkephalin. Opioid activity can also be detected in other neuronal cell lines and even in glioma cells.