Co-expression of cytokeratins and neurofilament proteins in a permanent cell line: cultured rat PC12 cells combine neuronal and epithelial features

Co-expression of intermediate filaments glial fibrillary acidic protein and cytokeratin in pituitary adenoma

PURPOSE

To analyze the co-expression of the intermediate filaments GFAP and cytokeratin in 326 pituitary adenomas with regard to the distribution pattern, the subtype of the adenoma and clinical prognostic data.

METHODS

Tissue from 326 pituitary adenomas and 13 normal anterior pituitaries collected in the Institute of Neuropathology, University Medical Center Hamburg-Eppendorf, between 2006 and 2009 was investigated by immunohistochemistry, immunofluorescence and electron microscopy.

RESULTS

Co-expression of intermediate filaments GFAP and cytokeratin was associated with hormone expression in 62/278 cases (22%), but only found in 2/48 (4%) of null cell adenomas (p < 0.01). Simultaneous co-expression of GFAP and cytokeratin in the same cells was demonstrated in 26 out of 326 pituitary adenomas and in all 13 pituitaries. In pituitary intermediate filaments were demonstrated in a larger area of the cytoplasm than in adenoma (p < 0.01), however, overlapping expression was seen in 2.6% of the total area in both, pituitary and adenoma. Congenially, cells with overlapping expression were found near vessels and in follicles. Furthermore, adenomas with cellular co-expression of GFAP and cytokeratin were associated with a lower recurrence rate (7.7%) compared to adenomas without co-expression of intermediate filaments (17.8%).

CONCLUSIONS

Cellular co-expression of the intermediate filaments GFAP and cytokeratin in pituitary adenomas and the pituitary was demonstrated and shown to be associated with hormone expression and low recurrence rate. The results are discussed with regard to the biology of folliculostellate cells, neural transformation and tumor stem cells. This study may complement the understanding of pituitary adenoma biology.

The Rat Adrenal Medulla. II. Proliferative Lesions

Many strains of rats develop spontaneous or drug-induced adrenal medullary proliferative lesions. However, there is often ambiguity about whether the changes observed are hyperplastic or neoplastic and if the term “pheochromocytoma” is appropriate for the lesion in rodents. Various considerations are presented, and the evolution and morphology of the changes are discussed. The lesions are of practical interest because they have at times impeded drug licensing applications.

293 cells express both epithelial as well as mesenchymal cell adhesion molecules

The 293 cell line, used extensively in various types of studies due to the ease with which these cells can be transfected, was thought to be derived by the transformation of primary cultures of human embryonic kidney cells with sheared adenovirus type 5 DNA. Although the 293 cells were assumed to originate from epithelial cells, the exact origin of these cells remains unknown. Previous attempts to characterize these cells combined immunostaining, immunoblot analysis and microarray analysis to demonstrate that 293 cells express neurofilament subunits, α-internexin, and several other proteins typically found in neurons. These findings raised the possibility that the 293 cell line may have originated from human neuronal lineage cells. Contrary to this suggestion, in this study, we found that the 293 cells expressed N-cadherin and vimentin, which are marker proteins expressed in mesenchymal cells. Furthermore, the 293 cells also expressed E-cadherin, cytokeratins 5/8 and desmoglein 2, which are epithelial cell markers. When the cells, primarily cultured from the kidneys of Clawn miniature swine and passaged 10–15 generations [termed porcine kidney epithelial (PKE) cells] were examined, they were found to be positive for the expression of both mesenchymal and epithelial markers. Thus, transformation by adenovirus was not necessary for the cells to express N-cadherin. Occludin and zonula occludens (ZO)-1, two components of tight junctions in epithelial and endothelial cells, were detected in the 293 and the PKE cells. Thus, the findings of the present study demonstrate that 293 cells retain several characteristics of epithelial cells.

Ferulic acid protects PC12 neurons against hypoxia by inhibiting the p-MAPKs and COX-2 pathways

OBJECTIVES

Hypoxia induces cellular oxidative stress that is associated with neurodegenerative diseases. Here, the protective effects of ferulic acid (FA) on hypoxia-induced neurotoxicity in PC12 cells were evaluated.

MATERIALS AND METHODS

We investigated the effect of FA on PC12 cells subjected to hypoxia stress, in vitro.

RESULTS

FA increased cell viability, prevented membrane damage (LDH release), scavenged free radicals, increased superoxide dismutase (SOD) activity, and attenuated the elevation of intracellular free Ca(2+), lipid peroxidation, apoptosis (evaluated by TUNEL staining) and PGE2 production in hypoxia-stressed PC12 cells. MAPKs were activated during hypoxia. FA reduced p-p38 MAPK, caspase-3, and COX-2 activation which correlated well with diminished LDH release in PC12 cells under hypoxia. Furthermore, FA reduced lipid peroxidation in PC12 cells subjected to hypoxia.

CONCLUSION

Taken together, these results indicate that FA antioxidant effects could partly be involved in inhibition of p38 MAPK pathway and apoptosis through scavenging ROS in hypoxia-stressed PC12 cells.

Atypical pituitary adenoma with neurocytic transformation

Here, we report an example of an atypical prolactin-producing pituitary adenoma showing clear morphologic and immunohistochemical evidence of neurocytic transformation. Its features support the concept that neoplastic neuroendocrine cells, in this case adenohypophyseal cells, are capable of neuronal differentiation and broaden the morphologic spectrum of such rare tumors. Our findings have implications with respect to the nosology of neuronal tumors of the adenohypophysis.

Transcriptional profile of genes involved in oxidative stress and antioxidant defense in PC12 cells following treatment with cerium oxide nanoparticles

BACKGROUND

Thanks to their impressive catalytic properties, cerium oxide nanoparticles (nanoceria) are able to mimic the activity of superoxide dismutase and of catalase, therefore acting as reactive oxygen species (ROS) scavengers in many biological contexts, for instance offering neuroprotection and reduction of apoptosis rate in many types of cells exposed to oxidative stress (stem cells, endothelial cells, epithelial cells, osteoblasts, etc.).

METHODS

We report on the investigation at gene level, through quantitative real time RT-PCR, of the effects of cerium oxide nanoparticles on ROS mechanisms in neuron-like PC12 cells. After three days of treatment, transcription of 84 genes involved in antioxidant defense, in ROS metabolism, and coding oxygen transporters is evaluated, and its relevance to central nervous system degenerative diseases is considered.

RESULTS

Experimental evidences reveal intriguing differences in transcriptional profiles of cells treated with cerium oxide nanoparticles with respect to the controls: nanoceria acts as strong exogenous ROS scavenger, modulating transcription of genes involved in natural cell defenses, down-regulating genes involved in inflammatory processes, and up-regulating some genes involved in neuroprotection.

CONCLUSIONS

Our findings are extremely promising for future biomedical applications of cerium oxide nanoparticles, further supporting their possible exploitation in the treatment of neurodegenerative diseases.

GENERAL SIGNIFICANCE

This work represents the first documented step to the comprehension of mechanisms underlying the anti-oxidant action of cerium oxide nanoparticles. Our findings allow for a better comprehension of the phenomena of ROS scavenging and neuroprotection at a gene level, suggesting future therapeutic approaches even at a pre-clinical level.

Combined gangliocytoma and prolactinoma of the pituitary gland

Gangliocytomas of the pituitary gland are rare lesions that often occur in combination with pituitary adenomas, which are frequently associated with the hypersecretion of pituitary hormones, particularly growth hormones. We report a case of combined gangliocytoma and prolactinoma of the pituitary gland. A 49-year-old male presented with vertigo. Radiological examination revealed an intrasellar tumor with a suprasellar extension, which was removed via the trans-sphenoidal approach. Histologically, the tumor was composed of adenoma cells, mature ganglion cells and cells with features intermediate between those of adenoma cells and ganglion cells (intermediate cells). Immunohistochemical analysis revealed the ganglion cells and intermediate cells as well as adenoma cells to be positive for prolactin. No growth hormone-positive tumor cells were observed. The ganglion cells were positive for synaptophysin and neurofilament. The findings in this case are discussed in relation to hypotheses proposed for histogenesis, and the presence of intermediate cells supports three hypotheses. The first is that adenoma cells transform into ganglion cells, and the second is that both components originate from the embryonal pituitary cell rests, showing intermediate features between ganglion cells and adenoma cells. The last is that their common origin may be the same stem/progenitor cells in normal adult pituitaries.

Ganglion cell containing pituitary adenomas: signs of neuronal differentiation in adenoma cells

Ganglion cell containing pituitary adenomas are rare. They represent tumors originating in the sella turcica which are composed of adenomatous and neuronal components. Recently accumulated information suggests a common origin for their neuronal and pituitary constituents. The objective of this study was to report the clinical and morphologic findings of pituitary gangliocytomas and study their immunoprofile using neuronal markers. Seven cases of pituitary gangliocytomas retrieved from 1,322 sellar lesions were studied. All tumors were removed from patients with mild acromegaly. Histologically they were biphasic composed of pituitary adenoma and clusters of ganglion cells embedded in a variably dense neuropil substrate. All adenomas belonged to the category of sparsely granulated somatotroph adenoma and were positive for growth hormone, whereas in five tumors, a few adenoma cells were also positive for prolactin. Ganglion cells were immunoreactive for NSE, synaptophysin and neurofilament protein (NFP). NFP-reactive fibrils were observed in the neuropil substrate and varied in number among the cases. Interestingly, all tumors contained varying numbers of adenoma cells with NFP-positive, dot-like areas of cytoplasmic reactivity, mostly tiny paranuclear, a finding not previously reported in human pituitary gangliocytomas. The presence of NFP in pituitary adenomas indicates neuronal differentiation in adenoma cells, suggesting a common origin for neuronal and pituitary adenoma cell elements in gangliocytomas.

RIFLE: a novel ring zinc finger-leucine-rich repeat containing protein, regulates select cell adhesion molecules in PC12 cells

Cell adhesion molecules play a critical role in cell contacts, whether cell-cell or cell-matrix, and are regulated by multiple signaling pathways. In this report, we identify a novel ring zinc finger-leucine-rich repeat containing protein (RIFLE) and show that RIFLE, expressed in PC12 cells, enhances the Serine (Ser)21/9 phosphorylation of glycogen synthase kinase-3alpha/beta (GSK-3alpha/beta) resulting in the inhibition of GSK-3 kinase activity and increase of beta-catenin levels. RIFLE expression also is associated with elevated E-cadherin protein levels but not N-cadherin. The regulation of these cell adhesion-associated molecules by RIFLE is accompanied by a significant increase in cell-cell and cell-matrix adhesion. Moreover, increase in cell-cell adhesion but not cell-matrix adhesion by RIFLE can be mimicked by selective inhibition of GSK-3. Our results suggest that RIFLE represents a novel signaling protein that mediates components of the Wnt/wingless signaling pathway and cell adhesion in PC12 cells.

A role for intermediate filaments in determining and maintaining the shape of nerve cells

To date, the functions of most neural intermediate filament (IF) proteins have remained elusive. Peripherin is a type III intermediate filament (IF) protein that is expressed in developing and in differentiated neurons of the peripheral and enteric nervous systems. It is also the major IF protein expressed in PC12 cells, a widely used model for studies of peripheral neurons. Dramatic increases in peripherin expression have been shown to coincide with the initiation and outgrowth of axons during development and regeneration, suggesting that peripherin plays an important role in axon formation. Recently, small interfering RNAs (siRNA) have provided efficient ways to deplete specific proteins within mammalian cells. In this study, it has been found that peripherin-siRNA depletes peripherin and inhibits the initiation, extension, and maintenance of neurites in PC12 cells. Furthermore, the results of these experiments demonstrate that peripherin IF are critical determinants of the overall shape and architecture of neurons.

Brush cells of rodent gallbladder and stomach epithelia express neurofilaments

It has been suggested that brush cells (BCs), a distinct type of cell occurring in various epithelia of the respiratory and gastrointestinal tracts, may function as receptor cells. The major characteristics of BCs are a prominent brush border and an unusually highly ordered arrangement of cytoskeletal elements (F-actin, microtubules, and intermediate filaments). In this study we aimed to characterize the nature of the intermediate filaments in BCs by light and electron microscopic immunostaining. Gallbladder and stomach specimens from mice and rats, respectively, were fixed in various solutions, embedded either in paraffin or epoxy resin, and processed for immunodetection. Commercially available, well-characterized antibodies against neurofilaments, peripherin, and cytokeratin peptide 18 were used. The polyclonal antiserum cocktail to neurofilaments was applied as a supplement in a double-labeling procedure with anti-actin and anti-cytokeratin 18 antibodies. The results demonstrate that the BCs of both organs express two types of intermediate filaments, i.e., neurofilaments and cytokeratin 18 filaments, and that these have a compartmentalized distribution in the cytoplasm. BCs do not express peripherin. The immunodetection of intermediate filaments distinctive for mature neurons in BCs supports their putative receptor function. The co-expression of neurofilaments and cytokeratins is shown for the first time in healthy tissues.

Tetraspan vesicle membrane proteins: synthesis, subcellular localization, and functional properties

Tetraspan vesicle membrane proteins (TVPs) are characterized by four transmembrane regions and cytoplasmically located end domains. They are ubiquitous and abundant components of vesicles in most, if not all, cells of multicellular organisms. TVP-containing vesicles shuttle between various membranous compartments and are localized in biosynthetic and endocytotic pathways. Based on gene organization and amino acid sequence similarities TVPs can be grouped into three distinct families that are referred to as physins, gyrins, and secretory carrier-associated membrane proteins (SCAMPs). In mammals synaptophysin, synaptoporin, pantophysin, and mitsugumin29 constitute the physins, synaptogyrin 1-4 the gyrins, and SCAMP1-5 the SCAMPs. Members of each family are cell-type-specifically synthesized resulting in unique patterns of TVP coexpression and subcellular colocalization. TVP orthologs have been identified in most multicellular organisms, including diverse animal and plant species, but have not been detected in unicellular organisms. They are subject to protein modification, most notably to phosphorylation, and are part of multimeric complexes. Experimental evidence is reviewed showing that TVPs contribute to vesicle trafficking and membrane morphogenesis.

Functional interplay between nuclear factor-kappaB and c-Jun integrated by coactivator p300 determines the survival of nerve growth factor-dependent PC12 cells

Nerve growth factor (NGF) activates the transcription factors nuclear factor kappaB (NF-kappaB) and activator protein-1 (AP-1) in sympathetic neurons. Whereas NGF-inducible NF-kappaB is required for the survival of neurons, c-Jun has the ability to promote neuronal death. In this report, we have examined the effect of NGF withdrawal on c-Jun and NF-kappaB transcription factors in PC12 cells differentiated to a neuronal phenotype. We show that the withdrawal of NGF from these cultures results in de novo synthesis of c-Jun, increase in AP-1 activity, and down-regulation of NF-kappaB activity. To investigate how the signal transduction pathways activating c-Jun and NF-kappaB are differentially regulated by NGF, we performed transcriptional analyses. Expression of ReIA (NF-kappaB) suppressed the c-Jun-dependent transcription of c-jun, and this effect was reversed by overexpression of the coactivator p300. RelA's effects on c-Jun transcription were mediated by competitive binding of the carboxy-terminal region of RelA to the CH1 domain of p300, which also binds to c-Jun; deletion of this region abrogated the ability of RelA to inhibit c-Jun activity. Furthermore, the inhibition of endogenous NF-kappaB in NGF-maintained neuronal PC12 cells led to the induction of c-Jun synthesis and a marked increase in cell death. Together, these studies demonstrate a functional interaction between NF-kappaB and c-Jun and suggest a novel mechanism of NF-kappaB-mediated neuroprotection.

Pituitary adenoma with neuronal choristoma: a report of two rare cases

Two rare cases of pituitary adenoma with neuronal choristoma are described. Both patients were female and presented with features of acromegaly with elevated growth hormone and prolactin levels. Radiologically, both lesions were predominantly intrasellar in location with extension into suprasellar region, but hypothalamus was not involved. Histopathological examination revealed a mixture of chromophobe pituitary adenoma cells and neuronal cells. In both cases, the adenoma component was positive for growth hormone and prolactin. Interestingly, immunopositivity for alpha-subunit, cytokeratin and prolactin was seen in the adenoma and neuronal cells in one case. Our findings support the hypothesis that the neuronal cells possibly arise from adenoma cells as a result of metaplasia.

Prolactin-producing pituitary adenoma and carcinoma with neuronal components--a metaplastic lesion

Recent studies indicate that cells of various epithelial tumors are capable of transformation to neurons. Observing both neurons and neuropil in two prolactin-producing adenohypophyseal tumors, one benign and one malignant, we sought to assess their cellular differentiation, the presence of nerve growth factor receptor, and expression of the dopamine receptor gene using immunocytochemistry, electron microscopy, and in situ hybridization. Light and electron microscopy clearly revealed cells morphologically transitional between adenoma/carcinoma cells and neurons. Large neurons lacked proliferative activity. Neurons in varying number showed immunoreactivity for pituitary hormones including prolactin, growth hormone and alpha subunit in the adenoma and prolactin alone in the carcinoma. The distribution of nerve growth factor receptor staining was similar. In both tumors, in situ hybridization showed mRNAs for prolactin and dopamine receptor within adenohypophyseal cells and neurons. Our results indicate that the occurrence of neurons and neuropil in growth hormone and prolactin-producing pituitary tumors appears to be the result of metaplasia. The process is not limited to benign tumors and may be due to the production of tropic substances by the adenohypophysial cells, which by paracrine/autocrine mechanisms result in transformation of adenoma cells to nerve cells.

Incorporation of NF-L into keratin filaments in transfected epithelial cells

Neurofilaments are the characteristic intermediate filaments of mature neurons; during development and in some neuronal cell lines and neuroendocrine tumors, neurofilament proteins are expressed together with vimentin or cytokeratins. In some cell types, the filamentous arrays formed by neurofilaments and vimentin or cytokeratins do not coincide. However, individual neurofilament proteins co-assemble with vimentin in transfected non-neuronal cells. In order to determine whether individual neurofilament proteins could also co-assemble with cytokeratins in a cellular environment, the light chain of neurofilaments, NF-L, was transfected into MCF-7 cells, in which the only cytoplasmic intermediate filament proteins expressed are cytokeratins. In transfected MCF-7 cells, human NF-L was localized to a prominent filamentous network. This pattern most probably reflected the incorporation of NF-L into the endogenous keratin cytoskeleton as it is unlikely to be due to human NF-L self-assembly since, like its rodent counterpart, human NF-L accumulated into punctate aggregates when transiently transfected in intermediate filament-deficient SW13 vim- cells. These results suggest the existence of a specific mechanism of segregation of neurofilaments and keratin filaments in some cell types.

Immunomicroscopy of neurofilaments in chromaffin cells of the adult bovine adrenal gland

Neurofilaments (NFs) represent a class of intermediate filaments which are highly specific for neurons. The most abundant of the native NFs is the 68 kD subunit (NF-L). Chromaffin cells of the adrenal medulla express NF subunits under culture conditions. However, NF expression in situ is questionable. It has been reported that as chromaffin cell precursors mature and begin to express catecholamine-synthesizing enzymes, their neuronal traits are extinguished and they become endocrine-like cells. This study reports that while NF-L may be lacking in the adrenal medulla of some species, NF-L immunoreactivity is clearly present in the adult bovine adrenal medulla. Immunofluorescence microscopy of bovine chromaffin cells in culture demonstrated NF immunoreactivity localized to both thin, highly ramified filaments present throughout the cell and frequently to an intensely immunofluorescent spot located near the nucleus. Double-label immunofluorescence microscopy and immunoblot analysis also demonstrated NF-L immunoreactivity in mature chromaffin cells of the bovine adrenal gland. In vitro and in situ immunofluorescence results were confirmed by immunogold and immunoperoxidase labelling, respectively. In both cases, NF-L immunoreactivity was associated with filaments in close proximity to the nucleus. Additionally, a spheroidal aggregate of immunogold-labelled NFs was seen adjacent to the nucleus in cultured cells. In conclusion, NF-L in bovine chromaffin cells demonstrates that at least one neuronal trait persists in these catecholamine-producing cells of the mature adrenal gland. In addition, this study emphasizes the fact that interspecies comparisons must be interpreted with caution, especially when attempting to formulate a generalized hypothesis.

Sorting of synaptophysin into special vesicles in nonneuroendocrine epithelial cells

Synaptophysin is a major transmembrane glycoprotein of a type of small vesicle with an electron-translucent content (SET vesicles), including the approximately 50-nm presynaptic vesicles in neuronal cells, and of similar, somewhat larger (< or = approximately 90 nm) vesicles (SLMV) in neuroendocrine (NE) cells. When certain epithelial non-NE cells, such as human hepatocellular carcinoma PLC cells, were cDNA transfected to synthesize synaptophysin, the new molecules appeared in specific SET vesicles. As this was in contrast to other reports that only NE cells were able to sort synaptophysin away from other plasma membrane proteins into presynaptic- or SLMV-type vesicles, we have further characterized the vesicles containing synaptophysin in transfected PLC cells. Using fractionation and immunoisolation techniques, we have separated different kinds of vesicles, and we have identified a distinct type of synaptophysin-rich, small (30-90-nm) vesicle that contains little, if any, protein of the constitutive secretory pathway marker hepatitis B surface antigen, of the fluid phase endocytosis marker HRP, and of the plasma membrane recycling endosomal marker transferrin receptor. In addition, we have found variously sized vesicles that contained both synaptophysin and transferrin receptor. A corresponding result was also obtained by direct visualization, using double-label immunofluorescence microscopy for the endocytotic markers and synaptophysin in confocal laser scan microscopy and in double-immunogold label electron microscopy. We conclude that diverse non-NE cells of epithelial nature are able to enrich the "foreign" molecule synaptophysin in a category of SET vesicles that are morphologically indistinguishable from SLMV of NE cells, including one type of vesicle in which synaptophysin is sorted away from endosomal marker proteins. Possible mechanisms of this sorting are discussed.

Pituitary adenoma with neuronal choristoma (PANCH): composite lesion or lineage infidelity?

Fifteen cases of the rare association of pituitary adenoma and neuronal choristoma (PANCH) were investigated by histology, immunohistochemistry, and electron microscopy. Acromegaly was apparent clinically in 11 patients and was equivocal in 1, and 3 lesions appeared to be nonfunctioning. Histology revealed various proportions of chromophobic PA and nervous tissue consisting of neuronlike cells and neuropil. Immunohistochemistry documented growth hormone (GH) in every PA, including those unassociated with clinical acromegaly. In contrast, the NCH component showed no consistent immunohistochemical profile. Most frequent reactivities were for the pituitary hormone alpha subunit, thyroid-stimulating hormone, and GH, whereas only a few cases displayed scattered positivity for GH-releasing hormone. Low-molecular weight keratin tested positive in PAs and in a few cells and processes of an NCH. A few fibrous bodies were immunoreactive for neurofilament protein. Electron microscopy revealed sparsely granulated GH cell adenoma, neurons, and neuropil. Cells intermediate between PA and neurons were numerous in 1 lesion. The present morphologic findings as well as lack of GH cell hyperplasia and the consistent association of NCH with but one type of PA do not support the causative role of NCH in the initiation of PA, as proposed previously. It appears that NCH is the result of neuronal differentiation within sparsely granulated GH cell adenomas.

Rat pancreatic AR42J cells. Amphicrine cells as an in vitro model to study peptide hormone receptor regulation

The rat pancreatic acinar tumor cell line, AR42J, is widely used to study pancreatic acinar cell biology and biochemistry. In addition to the well-documented exocrine cell features, we have identified by immunofluorescence and by electron microscopy the co-expression of small neuroendocrine (NE) vesicles using the NE vesicle-specific markers synaptophysin and "protein S.V.2." AR24J cells store [3H]GABA, which is secreted upon potassium depolarization in a calcium-dependent manner. In addition, we found the expression of the receptor for the neurotransmitter substance P by using a receptor-specific cDNA probe. Glucocorticoid treatment, which profoundly inhibits cellular growth and induces differentiation, results in a rapid decrease of substance P receptor (SPR) gene expression as assessed by Northern blot analysis. Intracellular Ca2+ mobilization was then determined in response to substance P in control cells and glucocorticoid-pretreated cells by dual wavelength spectrophotometry using fura-2 in single cells. Glucocorticoid-mediated down-regulation of substance P receptors resulted in a dose- and time-dependent decrease of the intracellular Ca2+ mobilization stimulated by substance P. In summary, these data indicate that AR42J cells display an amphicrine phenotype with two differentially regulated secretory pathways; during glucocorticoid-induced differentiation, the cells become less sensitive to substance P stimulation as a consequence of reduced gene expression of the substance P receptor.

Establishment and characterization of two Merkel cell tumor cultures

Two Merkel cell tumor cultures (MC-MA1, MC-MA2) have been established from metastases of typical Merkel cell tumors. The mestastases in vivo were characterized by co-expression of cytokeratins 8, 18, 19, 20 and neurofilaments, presence of intermediate filament whirls, expression of synaptophysin, neuron-specific enolase, and chromogranin A, rare and weak immunostaining for plakoglobin but absence of cadherins and desmoplakins. Both cultures grow, using supplemented RPMI medium on human irradiated fibroblast feeder layers, as loosely arranged floating small aggregates. Their karyotypes are mostly hyperdiploid. The mean doubling times were about 84 h in the first 8 months and later increased. Ultrastructural and immunoelectron microscopic studies of the Merkel cell tumor cells in vitro (MC-MA1, MC-MA2) revealed sparse membrane-bound neuroendocrine granules and typical IFs that were partly arranged in paranuclear whirls and were labeled by antibodies against cytokeratins and neurofilaments. In immunocytochemical studies using antibodies to cytokeratins 8, 18, 19, and 20 and neurofilament protein NF-L, Merkel cell tumor cells in vitro showed a uniform staining appearing as paranuclear whirls and cytoplasmic fibrils as well. Double-labeling experiments showed a co-localization of both intermediate filament types in most cells. Biochemically we found cytokeratins 8, 18, 19, and 20, and NF-L in tumor cells in vitro. Immunocytochemical staining was negative for desmoplakins, various cadherins, and cell adhesion molecules, whereas plakoglobin was only rarely detectable in some Merkel cell tumor cells in vitro. By immunoluminometric assay chromogranin A was detected in cell homogenates and culture supernatants as well. Immunocytochemically, synaptophysin and neuron-specific enolase were detectable additionally in some of the cells. These established cell cultures will allow further studies devoted to the biology, differentiation, and hormone secretion of Merkel cell tumors that may also increase our knowledge about normal Merkel cells.

Expression of Wnt-1 in PC12 cells results in modulation of plakoglobin and E-cadherin and increased cellular adhesion

The Wnt-1 gene plays an essential role in fetal brain development and encodes a secreted protein whose signaling mechanism is presently unknown. In this report we have investigated intracellular mechanisms by which the Wnt-1 gene induces morphological changes in PC12 pheochromocytoma cells. PC12 cells expressing Wnt-1 show increased steady-state levels of the adhesive junction protein plakoglobin, and an altered distribution of this protein within the cell. This effect appears similar to a modulation of the plakoglobin homolog, Armadillo, that occurs in Drosophila embryos in response to the Wnt-1 homolog, wingless (Riggleman, B., P. Schedl, and E. Wieschaus. 1990. Cell. 63:549-560). In addition, PC12/Wnt-1 cells show elevated expression of E-cadherin and increased calcium-dependent cell-cell adhesion. These results imply evolutionary conservation of cellular responses to Wnt-1/wingless and indicate that in certain cell types Wnt-1 may act to modulate cell adhesion mechanisms.

Reorganization of brain spectrin (fodrin) during differentiation of PC12 cells

Fodrin has been shown to redistribute dynamically between cytoplasmic and plasma membrane-associated compartments upon the differentiation of T lymphocytes. We studied the changes of distribution of fodrin in PC12 cells upon neuronal differentiation induced by nerve growth factor. To visualize preferentially the elements that were tightly associated with cytoskeletal structures, we performed immunofluorescence and immunoelectron microscopy on saponin-extracted cells. In undifferentiated PC12 cells, fodrin was distributed mostly underneath the plasma membrane. However, after the administration of nerve growth factor, perinuclear spot-like aggregates of fodrin appeared. Double-labeling immunofluorescence revealed that the cytoplasmic fodrin spot was co-localized with the intermediate filament proteins, peripherin and neurofilament. Immunogold electron microscopy showed that fodrin and neurofilament were localized in close association in the perinuclear regions enriched with intermediate filaments. With prolonged exposure to nerve growth factor, fodrin and intermediate filaments spread to the cytoplasm and neurites. These results suggest that there is a dynamic reorganization of fodrin during differentiation of PC12 cells, and that fodrin is first recruited in the perinuclear region closely associated with intermediate filaments. This dynamic reorganization of fodrin may represent important, previously unrecognized aspects of the morphological differentiation of neurons.

A role of retinoic acid in the regulation of the morphology and the levels of intermediate filament proteins and mRNAs in PC12 cells

An adrenal tumor-derived cell line (PC12W) cultured in the presence of nerve growth factor exhibited a spindle-shaped cell morphology resembling neuronal cells. The shape of these cells can be specifically changed in vitamin A-depleted medium supplemented with retinoic acid. Retinoic acid promoted an epithelial-like cell morphology except for occasional neuronal processes. These morphological results were correlated with differential expression of intermediate filaments at the mRNA and protein levels in these cells. Retinoic acid suppressed the synthesis of peripherin, an intermediate filament protein predominantly found in peripheral nerve cells, but a high level of simple keratins, normally found in simple epithelial cells, was present in retinoic acid-treated PC12 cells. The neurofilaments typically expressed in neurons remained virtually unaffected under the same conditions. In contrast, nerve growth factor induced the production of neurofilaments, but suppressed the synthesis of simple keratins. Since intermediate filament expression is known to be tissue-specific, these changes in expression together with the cell morphology changes are consistent with PC12 cells undergoing an epithelial-like differentiation in the presence of retinoic acid and a neuronal-like differentiation in the presence of nerve growth factor. These results suggest that retinoic acid and nerve growth factor are both effective regulators of PC12 cell differentiation but stimulate opposing pathways.

Age-related immunoreactivity pattern in medulloblastoma

Thirty-five paraffin-embedded medulloblastomas (19 from children and 16 from adults; 24 classic medulloblastomas, 10 desmoplastic medulloblastomas, 1 tumor with neuronal differentiation) were examined for reactions with antibodies against glial fibrillary acidic protein (GFAP), cytokeratins KL1 and MNF116, desmin, and vimentin. Only the tumor from the youngest patient, a 152-day-old boy, showed a positive immunoreaction for cytokeratins. Because of this age-related expression of cytokeratins in medulloblastomas primarily in very young children, cytokeratin positivity was interpreted as a sign of tumor immaturity. Five medulloblastomas showed scattered GFAP-positive reactive astrocytes and/or other positive, probably neoplastic, cells. Only two tumors showed GFAP immunoreactivity in unequivocally neoplastic cells. Of six tumors that reacted with vimentin, three showed strong reactivity throughout, one being the tumor from the 152-day-old boy. The remaining three demonstrated nests of vimentin-positive cells with weak or intense somatic immunoreactivity for vimentin. None of the 35 cases showed positivity for desmin; indicating that mesenchymal differentiation is restricted to the rare so-called medullomyoblastomas.

Immunohistochemistry of primitive neuroectodermal tumors in infants with special emphasis on cytokeratin expression

Eleven primitive neuroectodermal tumor (PNET) biopsies from infants under the age of 3 years were studied for the presence of various differentiation markers for neuroectodermal stem cells. Special emphasis was placed on the expression of cytokeratin proteins. The tumor cells expressed different cytokeratin proteins (CK8, CK13, CK18, CK19, KL1, AE1/AE3, MNF16) in 3 of 11 cases. These cases were furthermore characterized by a strong expression of glial fibrillary acidic protein, S-100 protein and vimentin. Vimentin and cytokeratin proteins were co-expressed; cross-reactivity between these two intermediate filaments could be excluded by immunoblotting. It is noteworthy that the three positive tumors were all from infants in their 1st year. We assume that PNETs in early infancy are characterized by a particularly wide range of differentiation patterns. The presence of cytokeratin proteins in these cases seems to be associated with the expression of vimentin and must be regarded as an indicator of an early developmental stage of the tumor cells.

Constitutive expression of the mature array of neurofilament proteins by a CNS neuronal cell line

Neurofilament protein expression was examined immunochemically in a neuronal cell line derived from postnatal day 21 septal tissue. The SN48.1p cell line was found to constitutively synthesize an array of neurofilament proteins typical of a mature neuron. All three neurofilament subunits (NF-L, NF-M, and NF-H) as well as differentially phosphorylated isoforms (P-, P+, P++, and P ) of NF-M and NF-H were identified by immunoblot analysis. Immunofluorescence studies revealed that the neurofilament proteins were components of discrete, filamentous structures. Abnormal intracellular aggregations of neurofilament proteins were never observed. Some SN48.1p cells apportioned specific isoforms into selected intracellular regions based on the molecular weight and phosphorylation level of the protein. NF-L was preferentially localized to perikarya and proximal neurites; NF-M[P++] and NF-H[P ] were distributed to distal aspects of neurites. The expression of these differentiated features of neurofilament proteins and, presumably, the synthesis of the kinases and phosphatases required for normal neurofilament metabolism occurred in the absence of growth factors, differentiating agents, and specialized culture substrates. In addition, the non-neuronal intermediate filaments glial fibrillary acidic protein and epithelial cytokeratin proteins were absent. These data demonstrate that SN48.1p cells exhibit a neurofilament phenotype characteristic of mature neurons and provide a unique model to examine the expression and function of neurofilaments in differentiated neuronal cells.

Unexpected immunoreactivities of intermediate filament antibodies in human brain and brain tumors

Immunoreactivities of 35 different monoclonal antibodies (MAbs) that detect intermediate filaments were studied systematically on serial cryostat sections of 14 well-defined human gliomas (five astrocytomas, three oligodendrogliomas, six glioblastomas) and on normal brain. Glial fibrillary acidic protein (GFAP), vimentin, desmin, neurofilaments, and broad-specificity keratin MAbs, as well as MAbs that recognize several or only single keratin polypeptides, were used. Unexpected reactivities were surprisingly frequent. As these may lead to diagnostic confusion and misinterpretation on this material, the authors investigated these phenomena more thoroughly. Four major sources of artifactual staining were found: 1) positive staining attributable to the rabbit gamma G immunoglobulins used in the alkaline phosphatase anti-alkaline phosphatase technique; 2) certain desmin and keratin MAbs cross-reacted with astrocytic glia and with other brain-specific epitopes; 3) technical difficulties; 4) some MAbs directed against neurofilaments and keratins showed unexpected reactivities only on individual anaplastic gliomas. The implications of these findings for intermediate filament typing of neuropathologic material are discussed.

The synaptophysin-encoding gene in rat and man is specifically transcribed in neuroendocrine cells

Synaptophysin (SY) is an integral membrane protein of presynaptic small (30-80-nm) translucent vesicles also present in dispersed neuroendocrine cells. As the occurrence of this type of vesicle is specific for two major pathways of differentiation, the neuronal and neuroendocrine-epithelial information on the regulation of SY synthesis should contribute to an understanding of regulatory principles common to both pathways. Isolation and comparison of the complete rat and human single-copy genes showed that despite the difference in size (16 kb in rat vs. 13 kb in man) intron/exon boundaries are precisely conserved. Surprisingly, intron VI is located in the 3'-noncoding region in both species. The major transcriptional start point, as determined by primer extension and S1-nuclease protection analyses in rat pheochromocytoma-derived PC12 cells and rat brain, mapped to a site 27 nt 5' of the first methionine codon. Unexpectedly, the 5' upstream region is devoid of any TATA or CAAT boxes, but shows instead typical features of 'housekeeping' genes, i.e., G + C-rich islands and four Sp1-binding motifs. Using 'nuclear run-on' assays, we have identified examples in which SY synthesis is regulated at the transcriptional level. Reporter gene constructs showed that approx. 1.2 kb of the immediate upstream region contains promoter enhancer elements that were, however, insufficient to confer cell-type specific expression, whereas sequences farther upstream were able to suppress thymidine kinase promoter activity in a cell-type-dependent fashion.

Lewy bodies in parkinsonism share components with intraneuronal protein bodies of normal brains

Histochemical characteristics of the Lewy bodies, in catecholamine neurons of 10 Parkinsonian patients, were compared to those of the spherical protein bodies, the basic protein-rich markers of catecholamine neurons in man. Special methods for proteins and lipids showed that the core of the Lewy bodies, in the neurons of the locus coeruleus and the substantia nigra, contains basic proteins and lipids normally found in the protein bodies. Acid fuchsin and the lipid-soluble fluorescent dye rhodamine B stained the entire core of the Lewy body in the parkinsonian brains and the entire sphere of the protein body in the control brains. Bromsulfophthalein, another acidic dye, which selectively binds to the enzyme gluthathione-S-transferase, had affinity only for a ring-like lamina at the outer layer of the core of the Lewy body and for the outer rim of the protein body. These results demonstrate that Lewy bodies and protein bodies contain similar macromolecular components, that is lipids and two different types of proteins, which also show similar stratification in the two structures. On the other hand, the presence in several neurons of the Parkinsonian patients, of aggregates representing transitional forms between protein bodies and Lewy bodies, indicates that abnormalities of protein bodies precede, and are somehow linked to Lewy body production.

Constitutive and basal secretion from the endocrine cell line, AtT-20

A variant of the ACTH-secreting pituitary cell line, AtT-20, has been isolated that does not make ACTH, sulfated proteins characteristic of the regulated secretory pathway, or dense-core secretory granules but retains constitutive secretion. Unlike wild type AtT-20 cells, the variant cannot store or release on stimulation, free glycosaminoglycan (GAG) chains. In addition, the variant cells cannot store trypsinogen or proinsulin, proteins that are targeted to dense core secretory granules in wild type cells. The regulated pathway could not be restored by transfecting with DNA encoding trypsinogen, a soluble regulated secretory protein targeted to secretory granules. A comparison of secretion from variant and wild type cells allows a distinction to be made between constitutive secretion and basal secretion, the spontaneous release of regulated proteins that occurs in the absence of stimulation.

Synaptophysin. A widespread constituent of small neuroendocrine vesicles and a new tool in tumor diagnosis

Synaptophysin, a vesicular integral membrane protein, is specifically expressed in neuroendocrine tissues. According to cDNA cloning studies, it has a molecular weight of 33,300 Dalton, one potential N-glycosylation site at the vesicle inside, four major hydrophobic domains as well as a C-terminus containing approximately 90 amino acids. The C- and N-termini of synaptophysin are located on the cytoplasmic side of the vesicle membrane. No signal sequence is found. Transfection of non-neuroendocrine cells with synaptophysin cDNA leads to the synthesis of synaptophysin-containing vesicles, which contain this protein in highly enriched form and have biophysical properties similar to presynaptic vesicles of neurons. So far, the vesicular content has only been determined in rat neurons, where classical neurotransmitters such as biogenic amines and transmitter-active amino acids were found. Reconstitution of the purified protein in liposomes suggests a possible channel function of synaptophysin. Using mono- and polyvalent antibodies against synaptophysin, a considerable number of studies in several laboratories have shown that this protein is a reliable marker molecule for neuroendocrine tumors of various degrees of differentiation.

Coexpression patterns of vimentin and glial filament protein with cytokeratins in the normal, hyperplastic, and neoplastic breast

The authors studied by immunohistochemistry the intermediate filament (IF) protein profile of 66 frozen samples of breast tissue, including normal parenchyma, all variants of fibrocystic disease (FCD), fibroadenomas, cystosarcoma phylloides, and ductal and lobular carcinomas. Monoclonal antibodies (MAbs) to cytokeratins included MAb KA 1, which binds to polypeptide 5 in a complex with polypeptide 14 and recognizes preferentially myoepithelial cells; MAb KA4, which binds to polypeptides 14, 15, 16 and 19; individual MAbs to polypeptides 7, 13, and 16, 17, 18, and 19, and the MAb mixture AE1/AE3. The authors also applied three MAbs to vimentin (Vim), and three MAbs to glial filament protein (GFP). Selected samples were studied by double-label immunofluorescence microscopy and by staining sequential sections with some of the said MAbs, an MAb to alpha-smooth muscle actin, and well-characterized polyclonal antibodies for the possible coexpression of diverse types of cytoskeletal proteins. Gel electrophoresis and immunoblot analysis also were performed. All samples reacted for cytokeratins with MAbs AE1/AE3, although the reaction did not involve all cells. Monoclonal antibody KA4 stained preferentially the luminal-secretory cells in the normal breast and in FCD, whereas it stained the vast majority of cells in all carcinomas. Monoclonal antibody KA1 stained preferentially the basal-myoepithelial cells of the normal breast and FCD while staining tumor cell subpopulations in 4 of 31 carcinomas. Vimentin-positive cells were found in 8 of 12 normal breasts and in 12 of 20 FCD; in most cases, Vim-reactive cells appeared to be myoepithelial, but occasional luminal cells were also stained. Variable subpopulations of Vim-positive cells were noted in 9 of 20 ductal and in 1 of 7 lobular carcinomas. Glial filament protein-reactive cells were found in normal breast lobules and ducts and in 15 of 20 cases of FCD; with rare exceptions, GFP-reactivity was restricted to basally located, myoepithelial-appearing cells. Occasional GFP-reactive cells were found in 3 of 31 carcinomas. Evaluation of sequential sections and double-label immunofluorescence microscopy showed the coexpression of certain cytokeratins (possibly including polypeptides 14 and 17) with vimentin and alpha-smooth muscle actin together with GFP in some myoepithelial cells. The presence of GFP in myoepithelial cells was confirmed by gel electrophoresis and immunoblotting. Our results indicate that coexpression of cytokeratin with vimentin and/or GFP is comparatively frequent in normal basal-myoepithelial cells of the breast.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of functional nerve growth factor-receptors in a CNS glial cell line: monoclonal antibody 217c recognizes the nerve growth factor-receptor on C6 glioma cells

The biological effects of nerve growth factor (NGF) have been shown to be mediated by the high-affinity form of the nerve growth factor receptor (NGF-R) in sympathetic and sensory neurons, and in PC12 cells. We report here that the central nervous system C6 rat glioma cell line likewise expresses functional high-affinity NGF-Rs. The expression of NGF-R mRNA in C6 cells can be up-regulated by cycloheximide and its own ligand, NGF; and it can be rapidly down-regulated by epidermal growth factor (EGF). Furthermore, C6 cells display NGF responsiveness by expressing c-fos mRNA within 30 minutes of treatment with NGF; and after 4-5 days of NGF exposure, C6 cells cease dividing as measured by [3H]-thymidine uptake, change shape, and reveal neurite-like processes. Scatchard analysis of [125I]-labelled NGF bound to solubilized C6 cells confirms the presence of both high- and low-affinity receptor protein. Crosslinking radiolabeled NGF to its receptor in the presence or absence of excess unlabeled NGF, followed by immunoprecipitation with monoclonal antibody (mAb) 192-IgG (a known anti-NGF-R antibody) and SDS-PAGE reveals a 100 kD band corresponding to the NGF/NGF-R complex. An identical band is observed when the immunoprecipitation is carried out with mAb 217c, suggesting that the 217c epitope is related to NGF-R. The 217c antibody was generated against C6 cells and shown to be a cell surface antibody (Peng et al., Science 215:1102-4, 1982); several investigators have used it subsequently as an immunocytochemical marker for Schwann cells. The significance of NGF-Rs in a CNS glial cell line is unclear, but association of NGF with the control of proliferation and/or differentiation of primitive glial cells is suggested.

Similarities between neuronal Lewy bodies in parkinsonism and hepatic Mallory bodies in alcoholism

The aim of the present study was to identify components of the Lewy body, which is a characteristic neuronal lesion in idiopathic Parkinsonism, using histochemical methods that selectively stain the Mallory body, a characteristic lesion of the hepatocyte in alcoholism. Our observation that Lewy bodies stain with phosphotungstic acid hematoxylin, the dye originally used for demonstrating alcoholic hyaline (Mallory bodies), promoted this study. The material consisted of formalin-fixed, brain stem tissue from Parkinsonian subjects, and of similarly preserved liver tissues from alcoholic individuals. The methods selected were Roque's chromotrope 2R-aniline blue, and Liisberg's rhodamine B, which stains Mallory bodies due to its affinity for sites of tissue keratinization. Hence, skin was also included in this study as control tissue. Our results showed that Lewy bodies in the brain, Mallory bodies in the liver and stratum corneum in the skin have identical staining properties with the dyes used, indicating the presence of histochemically similar components. Taking into account the reactions of these dyes with model substances, we suggest that the similar components shared by Lewy bodies and Mallory bodies are arginine-rich proteins and lipids associated with keratinization. Similar findings in both, a toxin-induced lesion of the liver, and a spontaneous lesion of the brain may offer clues for understanding the latter's mode of formation.

Sorting during transport to the surface of PC12 cells: divergence of synaptic vesicle and secretory granule proteins

PC12 cells, a cell line derived from a rat pheochromocytoma, have both regulated and constitutive secretory pathways. Regulated secretion occurs via large dense core granules, which are related to chromaffin granules and are abundant in these cells. In addition, PC12 cells also contain small electron-lucent vesicles, whose numbers increase in response to nerve growth factor and which may be related to cholinergic synaptic vesicles. These could characterize a second regulated secretory pathway. We have investigated the trafficking of protein markers for both these organelles. We have purified and characterized the large dense core granules from these cells using sequential velocity and equilibrium gradients. We demonstrate the copurification of the major PC12 soluble regulated secretory protein (secretogranin II) with this organelle. As a marker for the synaptic vesicle-like organelles in this system, we have used the integral membrane glycoprotein p38 or synaptophysin. We show that the p38-enriched fraction of PC12 cells comigrates with rat brain synaptic vesicles on an equilibrium gradient. We also demonstrate that p38 purifies away from the dense core granules; less than 5% of this protein is found in our dense granule fraction. Finally we show that p38 does not pass through the dense granule fraction in pulse-chase experiments. These results rule out the possibility of p38 reaching the small clear vesicles via mature dense granules and imply that these cells may have two independently derived regulated pathways.

Cytokeratins and cytokeratin filaments in subpopulations of cultured human and rodent cells of nonepithelial origin: modes and patterns of formation

Using immunofluorescence microscopy, we observed that in several established cell culture lines derived from different nonepithelial tissues and species, cells spontaneously emerge, usually at low frequencies, which contain cytoplasmic structures decorated by antibodies specific for cytokeratins 8 and 18. This phenomenon was further examined at both the protein (gel electrophoreses of cytoskeletal proteins, followed by immunoblotting) and the RNA (Northern blots, "nuclear run-on" analysis, in situ hybridization) level. Positive cell lines included simian virus (SV40)-transformed human fibroblasts (HF-SV80, WI-38 VA13), human astrocytic glioma cells (U333 CG/343MG), rat (RVF-SMC) and hamster (BHK-21/13) cells derived from vascular smooth muscle and murine sarcoma MS-180 cells. In two cell lines (HF-SV80 and BHK-21/13), the frequency of the cytokeratin-containing cells and of the cytokeratin fibril arrays per cell was drastically increased upon treatment with 5-azacytidine. The structural appearance of the cytokeratins was variable in the different cell lines but could also differ among cells of the same culture: While small granular or comma-shaped structures or bizarrely shaped filament arrays prevailed in WI-38, RVF and normally grown BHK-21 cells, most of the other lines revealed extended normal-looking, fibrillar arrays. In one line (MS-180), the appearance of cytokeratins was associated with a morphological change, as it was only found in a subpopulation of cells that had lost their typical elongated and spindle-shaped phenotype and assumed a rounded ("coccoid") shape. Our results show that the expression of the genes encoding cytokeratins 8 and 18 is not necessarily restricted to programs of epithelial differentiation and that factors stochastically effective appear in cultured cell lines that allow the synthesis of these cytoskeletal components. Mechanisms possibly involved in this spontaneous and selective advent of cytokeratins 8 and 18 and implications for tumor diagnosis are discussed.

Synaptophysin and chromogranins/secretogranins--widespread constituents of distinct types of neuroendocrine vesicles and new tools in tumor diagnosis

Normal and neoplastic neuroendocrine (NE) cells have been identified for many years by morphological criteria only. With the advent of immunocytochemistry, antibodies against NE-specific polypeptides have been used to identify NE cells that had been missed by conventional techniques, thus improving the diagnosis of NE cells. In this review article we discuss (i) the biochemical, cell biological and molecular biological data obtained so far for two major types of NE markers, synaptophysin, which is characteristic of the small "transparent-looking" neurosecretory vesicles, and the chromogranins/secretogranins, which are widespread constituents of the larger "dense-cored" secretory granules; (ii) the immunohistochemical data obtained for these marker proteins in normal and neoplastic human NE cells and tissues; and (iii) future possible developments involving these as well as other proteins that are associated with these two distinct secretory organelles of NE cells and may serve as potential markers in NE cell diagnosis.

Topogenesis and sorting of synaptophysin: synthesis of a synaptic vesicle protein from a gene transfected into nonneuroendocrine cells

Diverse nonneuroendocrine (non-NE) cells were forced to express synaptophysin (SY), the major and typical transmembrane glycoprotein of small (30-80 nm) neurotransmitter vesicles of NE cells, using microinjection of RNA synthesized in vitro from cDNA or transient and stable transfections with cDNA brought under SV40 promoter control. The glycoprotein synthesized in non-NE cells is indistinguishable from SY of NE cells and is integrated with similar, if not identical, orientation in the membranes of a specific, novel type of small cytoplasmic vesicle that structurally resembles synaptic vesicles and in which SY is the only major protein detected. A non-N-glycosylated form of SY generated by site-directed mutagenesis showed the same behavior and specific distribution in small vesicles. The results show that the information contained in this protein alone is sufficient to secure its sorting into a special type of vesicle in a heterotypic context, i.e., in the absence of other NE-specific components.

An epithelium-type cytoskeleton in a glial cell: astrocytes of amphibian optic nerves contain cytokeratin filaments and are connected by desmosomes

In higher vertebrates the cytoskeleton of glial cells, notably astrocytes, is characterized (a) by masses of intermediate filaments (IFs) that contain the hallmark protein of glial differentiation, the glial filament protein (GFP); and (b) by the absence of cytokeratin IFs and IF-anchoring membrane domains of the desmosome type. Here we report that in certain amphibian species (Xenopus laevis, Rana ridibunda, and Pleurodeles waltlii) the astrocytes of the optic nerve contain a completely different type of cytoskeleton. In immunofluorescence microscopy using antibodies specific for different IF and desmosomal proteins, the astrocytes of this nerve are positive for cytokeratins and desmoplakins; by electron microscopy these reactions could be correlated to IF bundles and desmosomes. By gel electrophoresis of cytoskeletal proteins, combined with immunoblotting, we demonstrate the cytokeratinous nature of the major IF proteins of these astroglial cells, comprising at least three major cytokeratins. In this tissue we have not detected a major IF protein that could correspond to GFP. In contrast, cytokeratin IFs and desmosomes have not been detected in the glial cells of brain and spinal cord or in certain peripheral nerves, such as the sciatic nerve. These results provide an example of the formation of a cytokeratin cytoskeleton in the context of a nonepithelial differentiation program. They further show that glial differentiation and functions, commonly correlated with the formation of GFP filaments, are not necessarily dependent on GFP but can also be achieved with structures typical of epithelial differentiation; i.e., cytokeratin IFs and desmosomes. We discuss the cytoskeletal differences of glial cells in different kinds of nerves in the same animal, with special emphasis on the optic nerve of lower vertebrates as a widely studied model system of glial development and nerve regeneration.

Laminin induces formation of neurite-like processes and potentiates prolactin secretion by GH3 rat pituitary cells

Tumor-derived GH3 rat pituitary cell lines are widely utilized to study mechanisms of prolactin secretion and responsiveness to secretagogues. These cells served here as a model with which to study relationships between shape and function. When GH3 cells were routinely grown in serum-supplemented medium, they exhibited the polygonal phenotype of epithelial cells, with scarce secretory granules. In contrast, when seeded in a serum-free medium, they attached loosely and contained more secretory granules. In both cases, they released prolactin in a nonpolarized manner. We show in the present work that laminin extracted from Englebreth-Holm-Swarm (EHS) tumors was a potent attachment and spreading factor for GH3/B6 cells seeded in serum-free medium. Moreover, it induced the formation of neurite-like processes, which were increased in number and length by chronic treatment with a specific secretagogue, thyroliberin (TRH). These changes in cell shape were correlated with a potentiation of prolactin secretion, both basal and TRH-stimulated. Furthermore, using immunocytochemistry and electron microscopy, we revealed--at the dilated tip of processes--an accumulation not only of prolactin, but also of synaptophysin, a vesicle membrane marker, and of several organelles, such as secretory granules, smooth vesicles, dense bodies and mitochondria. The cytoplasmic processes contained long parallel bundles of microtubules and showed a strong immunoreactivity for beta 2-tubulin. In addition, we found immunocyto-chemical evidence for the presence of 200-k Da neurofilament protein in GH3/B6 cell processes as well as in neurites of cultured hypothalamic neurons. We conclude that, in GH3/B6 cells, laminin induced the differentiation of neurite-like processes, which were the site of polarized organelle transport and exhibited some neuronal markers.

Regulation of the differentiation of PC12 pheochromocytoma cells

The PC12 clone, developed from a pheochromocytoma tumor of the rat adrenal medulla, has become a premiere model for the study of neuronal differentiation. When treated in culture with nanomolar concentrations of nerve growth factor, PC12 cells stop dividing, elaborate processes, become electrically excitable, and will make synapses with appropriate muscle cells in culture. The changes induced by nerve growth factor lead to cells that, by any number of criteria, resemble mature sympathetic neurons. These changes are accompanied by a series of biochemical alterations occurring in the membrane, the cytoplasm, and the nucleus of the cell. Some of these events are independent of changes in transcription, while others clearly involve changes in gene expression. A number of the alterations seen in the cells involve increases or decreases in the phosphorylation of key cellular proteins. The information available thus far allows the construction of a hypothesis regarding the biochemical basis of PC12 differentiation.

Differential response of myofibrillar and cytoskeletal proteins in cells treated with phorbol myristate acetate

Muscle-specific and nonmuscle contractile protein isoforms responded in opposite ways to 12-o-tetradecanoyl phorbol-13-acetate (TPA). Loss of Z band density was observed in day-4-5 cultured chick myotubes after 2 h in the phorbol ester, TPA. By 5-10 h, most I-Z-I complexes were selectively deleted from the myofibril, although the A bands remained intact and longitudinally aligned. The deletion of I-Z-I complexes was inversely related to the appearance of numerous cortical, alpha-actinin containing bodies (CABs), transitory structures approximately 3.0 microns in diameter. Each CAB consisted of a filamentous core that costained with antibodies to alpha-actin and sarcomeric alpha-actinin. In turn each CAB was encaged by a discontinuous rim that costained with antibodies to vinculin and talin. Vimentin and desmin intermediate filaments and most cell organelles were excluded from the membrane-free CABs. These curious bodies disappeared over the next 10 h so that in 30-h myosacs all alpha-actin and sarcomeric alpha-actinin structures had been eliminated. On the other hand vinculin and talin adhesion plaques remained prominent even in 72-h myosacs. Disruption of the A bands was first initiated after 15-20 h in TPA (e.g., 15-20-h myosacs). Thick filaments of apparently normal length and structure were progressively released from A segments, and by 40 h all A bands had been broken down into enormous numbers of randomly dispersed, but still intact single thick filaments. This breakdown correlated with the formation of amorphous cytoplasmic aggregates which invariably colocalized antibodies to myosin heavy chain, MLC 1-3, myomesin, and C protein. Complete elimination of all immunoreactive thick filament proteins required 60-72 h of TPA exposure. The elimination of the thick filament-associated proteins did not involve the participation of vinculin or talin. In contrast to its effects on myofibrils, TPA did not induce the disassembly of the contractile proteins in stress fibers and microfilaments either in myosacs or in fibroblastic cells. Similarly, TPA, which rapidly induces the translocation of vinculin and talin to ectopic sites in many types of immortalized cells, had no gross effect on the adhesion plaques of myosacs, primary fibroblastic cells, or presumptive myoblasts. Clearly, the response to TPA of contractile protein and some cytoskeletal isoforms not only varies among phenotypes, but even within the domains of a given myotube the myofibrils respond one way, the stress fibers/microfilaments another.

Immunocytochemical localization of the intermediate filament protein peripherin in adult mouse adrenal chromaffin cells in culture

Peripherin is the main intermediate filament protein in sympathetic neurons. Immunoreactivity to peripherin was studied in mouse adrenal chromaffin cells after 6 days in culture, and compared to immunoreactivity to tyrosine hydroxylase used as a general marker of chromaffin cells in culture. Most of the cells immunoreactive to tyrosine hydroxylase were rounded, with a glandular phenotype and a few of them had processes. The cells reactive to peripherin only constituted a small proportion of the chromaffin cells (2%), and most of them sent out processes. However, not all the cells with processes were reactive for peripherin. These results did not change in the presence of nerve growth factor. The discussion focuses on the significance of the sub-population of cells reactive to peripherin. We suggest that these cells resemble the small granule chromaffin cells, regarded as an intermediate cell type between glandular cells and neurons. The cells that expressed peripherin here are compared to those selected to form the PC12 clone. The presence of peripherin in only a few of the cells sending out neurite-like processes is discussed in relation to the expression of other neurofilament proteins in developing cells and to the influence of non-chromaffin cells.

Structure of the gene encoding peripherin, an NGF-regulated neuronal-specific type III intermediate filament protein

We have cloned the rat gene encoding peripherin, a neuronal-specific intermediate filament protein that is NGF-regulated. Determination of the complete sequence, including 821 nucleotides of the 5'-flanking region, allows us to make conclusions about the evolutionary origin of the peripherin gene, its homology with other intermediate filament proteins, and possible mechanisms of regulation of peripherin expression in neurons. The positions of the eight peripherin gene introns correspond to the intron patterns of desmin, vimentin, and GFAP, with one example of intron sliding. Together with protein sequence homologies, this conclusively demonstrates that peripherin is a type III intermediate filament protein. The peripherin promoter contains sequences homologous to regions of other NGF-regulated promoters, which may function in peripherin induction by NGF.

Localization of cytokeratins in tissues of the rainbow trout: fundamental differences in expression pattern between fish and higher vertebrates

Using a panel of antibodies against different cytokeratins in immunofluorescence microscopy on frozen tissue sections and two-dimensional gel electrophoresis of cytoskeletal proteins from these tissues, we have studied the tissue distribution of cytokeratins in a fish, the rainbow trout Salmo gairdneri. We have distinguished at least 14 different cytokeratin polypeptides in only a limited number of tissues, thus demonstrating the great complexity of the cytokeratin pattern in a fish species. The simplest cytokeratin pattern was that present in hepatocytes, comprising one type-II (L1) and two type-I (L2, L3) polypeptides that appear to be related to mammalian cytokeratins 8 and 18, respectively. Two or all three cytokeratins of this group were also identified in several other epithelial tissues, such as kidney. Epithelia associated with the digestive tract contained, in addition, other major tissue-specific cytokeratins, such as components D1-D3 (stomach, intestine and swim bladder) and B1 and B2 (biliary tract). With the exception of D1, all these polypeptides were also found in a cultured cell line (RTG-2). Epidermal keratinocytes contained D1 and six other major cytokeratins, termed E1-E6. The most complex cytokeratin pattern was that found in the gill epithelium. Surprisingly, antibodies specific for cytokeratins of the L1-L3 group also reacted with certain cell-sheet-forming tissues that are not considered typical epithelia and in higher vertebrates express primarily, if not exclusively, vimentin. Such tissues were (a) endothelia, including the pillar cells of the "gill filaments", (b) scale-associated cells, and (c) the ocular lens epithelium, and also several nonepithelial cell types, such as (d) fibroblasts and other mesenchymal cells, (e) chondrocytes, (f) certain vascular smooth muscle cells, and (g) astroglial cells of the optic nerve. The differences between the patterns of cytokeratin expression in this fish species and those of higher vertebrates are discussed. It is concluded that the diversity of cytokeratins has already been established in lower vertebrates such as fish, but that the tissue-expression pattern of certain cytokeratins has been restricted during vertebrate evolution. We discuss the value of antibodies specific for individual cytokeratin polypeptides as marker molecules indicating cell and tissue differentiation in fish histology, embryology, and pathology.

Fractionation of synaptophysin-containing vesicles from rat brain and cultured PC12 pheochromocytoma cells

Synaptophysin is a transmembrane glycoprotein of neuroendocrine vesicles. Its content and distribution in subcellular fractions from cultured PC12 cells, rat brain and bovine adrenal medulla were determined by a sensitive dot immunoassay. Synaptophysin-containing fractions appeared as monodispersed populations similar to synaptic vesicles in density and size distribution. Membranes from synaptic vesicles contained approximately 100-times more synaptophysin than chromaffin granules. In conclusion, synaptophysin is located almost exclusively in vesicles of brain and PC12 cells which are distinct from dense core granules.

Relationship between the nerve growth factor-regulated clone 73 gene product and the 58-kilodalton neuronal intermediate filament protein (peripherin)

Exposure of PC12 cells to nerve growth factor (NGF) has been shown to induce an mRNA that encodes a novel neuronal intermediate filament protein. The findings presented here concern the identity of this filament protein. The major protein in NGF-treated PC12 cell cytoskeletons derived by extraction with 1% Triton X-100 is of apparent Mr = 58,000, focuses by isoelectric focusing as several closely spaced spots of pl 5.6-5.8, and is elevated relative to non-NGF-treated cells. Partial microsequencing of this material reveals 2 internal sequences that are identical to a 14-residue sequence encoded by the NGF-regulated clone 73 mRNA, but not to sequences of other known proteins. An antiserum raised against a 19-residue synthetic peptide corresponding to the deduced C-terminus of the protein encoded by the NGF-regulated clone 73 mRNA specifically recognizes the 58,000-Mr protein. Properties of the 58-kilodalton protein strongly suggest that it corresponds to an intermediate filament protein (peripherin) previously identified in PC12 cells and in peripheral and certain CNS neurons. Identification of the intermediate filament protein encoded by an NGF-induced message should facilitate studies of its regulation and function.

Smooth muscle cells can express cytokeratins of "simple" epithelium. Immunocytochemical and biochemical studies in vitro and in vivo

Cytokeratins are a set of 19 proteins that together constitute the class of intermediate filament protein expressed by epithelial cells and tumors. Using a panel of 9 different monoclonal anti-cytokeratin antibodies, the authors have performed immunocytochemistry on methanol-fixed, frozen sections and methacarn-fixed, paraffin-embedded tissue of human myometrial specimens. Anomalous cytokeratin expression (ACE) by smooth muscle cells was found in all specimens. Immunoblots of this tissue confirmed the presence of cytokeratin 19, and possibly 8. In addition, immunocytochemical studies demonstrated ACE in human fetal tissues within the intestinal muscularis and the heart, especially in the region of the aortic outflow tract, and in 8 of 19 cases of leiomyosarcoma from adults. Indirect immunofluorescence studies were also performed on cells explanted from myometrial tissue; the overwhelming majority of cells derived from these cultures were smooth muscle cells as verified by expression of muscle actins, and a subpopulation of these cells was found to be cytokeratin-positive. ACE was confirmed in vitro by double labeling experiments demonstrating simultaneous expression of muscle actins and cytokeratins within the same cell. The significance of this smooth muscle cell ACE is unknown, but it may be a phenotypic marker of smooth muscle in a proliferative state. ACE could be a source of confusion in the immunocytochemical analysis of poorly differentiated malignancies if a complete panel of antibodies is not employed.