A sequence of changes in cytoskeletal components during neuroblastoma differentiation

α-Internexin and Peripherin: Expression, Assembly, Functions, and Roles in Disease

α-Internexin and peripherin are neuronal-specific intermediate filament (IF) proteins. α-Internexin is a type IV IF protein like the neurofilament triplet proteins (NFTPs, which include neurofilament light chain, neurofilament medium chain, and neurofilament high chain) that are generally considered to be the primary components of the neuronal IFs. However, α-internexin is often expressed together with the NFTPs and has been proposed as the fourth subunit of the neurofilaments in the central nervous system. α-Internexin is also expressed earlier in the development than the NFTPs and is a maker for neuronal IF inclusion disease. α-Internexin can self-polymerize in vitro and in transfected cells and it is present in the absence of the NFTP in development and in granule cells in the cerebellum. In contrast, peripherin is a type III IF protein. Like α-internexin, peripherin is specific to the nervous system, but it is expressed predominantly in the peripheral nervous system (PNS). Peripherin can also self-assemble both in vitro and in transfected cells. It is as abundant as the NFTPs in the sciatic nerve and can be considered a fourth subunit of the neurofilaments in the PNS. Peripherin has multiple isoforms that arise from intron retention, cryptic intron receptor site or alternative translation initiation. The functional significance of these isoforms is not clear. Peripherin is a major component found in inclusions of patients with amyotrophic lateral sclerosis (ALS) and peripherin expression is upregulated in ALS patients.

Peripherin is a subunit of peripheral nerve neurofilaments: implications for differential vulnerability of CNS and peripheral nervous system axons

Peripherin, a neuronal intermediate filament protein implicated in neurodegenerative disease, coexists with the neurofilament triplet proteins [neurofilament light (NFL), medium (NFM), and heavy (NFH) chain] but has an unknown function. The earlier peak expression of peripherin than the triplet during brain development and its ability to form homopolymers, unlike the triplet, which are obligate heteropolymers, have supported a widely held view that peripherin and neurofilament triplets form separate filament systems. However, here, we demonstrate that, despite a postnatal decline in expression, peripherin is as abundant as the triplet in the adult PNS and exists in a relatively fixed stoichiometry with these subunits. Peripherin exhibits a distribution pattern identical to those of triplet proteins in sciatic axons and colocalizes with NFL on single neurofilaments by immunogold electron microscopy. Peripherin also coassembles into a single network of filaments containing NFL, NFM, and NFH with and without α-internexin in quadruple- or quintuple-transfected SW13vim(-) cells. Genetically deleting NFL in mice dramatically reduces peripherin content in sciatic axons. Moreover, peripherin mutations has been shown to disrupt the neurofilament network in transfected SW13vim(-) cells. These data show that peripherin and the neurofilament proteins are functionally interdependent. The results strongly support the view that, rather than forming an independent structure, peripherin is a subunit of neurofilaments in the adult PNS. Our findings provide a basis for its close relationship with neurofilaments in PNS diseases associated with neurofilament accumulation.

Defective axonal transport of neurofilament proteins in neurons overexpressing peripherin

Peripherin is a type III neuronal intermediate filament detected in motor neuron inclusions of amyotrophic lateral sclerosis (ALS) patients. We previously reported that overexpression of peripherin provokes late-onset motor neuron dysfunction in transgenic mice. Here, we show that peripherin overexpression slows down axonal transport of neurofilament (NF) proteins, and that the transport defect precedes by several months the appearance of axonal spheroids in adult mice. Defective NF transport by peripherin up-regulation was further confirmed with dorsal root ganglia (DRG) neurons cultured from peripherin transgenic embryos. Immunofluorescence microscopy and western blotting revealed that excess peripherin provokes reduction in levels of hyperphosphorylated NF-H species in DRG neurites. Similarly the transport of a green fluorescent protein (GFP)-tagged NF-M, delivered by means of a lentiviral construct, was impaired in DRG neurites overexpressing peripherin. These results demonstrate that peripherin overexpression can cause defective transport of type IV NF proteins, a phenomenon that may account for the progressive formation of ALS-like spheroids in axons.

Functions of intermediate filaments in neuronal development and disease

Five major types of intermediate filament (IF) proteins are expressed in mature neurons: the three neurofilament proteins (NF-L, NF-M, and NF-H), alpha-internexin, and peripherin. While the differential expression of IF genes during embryonic development suggests potential functions of these proteins in axogenesis, none of the IF gene knockout experiments in mice caused gross developmental defects of the nervous system. Yet, deficiencies in neuronal IF proteins are not completely innocuous. Substantial developmental loss of motor axons was detected in mice lacking NF-L and in double knockout NF-M;NF-H mice, supporting the view of a role for IFs in axon stabilization. Moreover, the absence of peripherin resulted in approximately 30% loss of small sensory axons. Mice lacking NF-L had a scarcity of IF structures and exhibited a severe axonal hypotrophy, causing up to 50% reduction in conduction velocity, a feature that would be very detrimental for large animal species. Unexpectedly, the NF-M rather than NF-H protein turned out to be required for proper radial growth of large myelinated axons. Studies with transgenic mice suggest that some types of IF accumulations, reminiscent of those found in amyotrophic lateral sclerosis (ALS), can have deleterious effects and even cause neurodegeneration. Additional evidence for the involvement of IFs in pathogenesis came from the recent discovery of neurofilament gene mutations linked to ALS and Charcot-Marie-Tooth disease (CMT2E). Conversely, we discuss how certain types of perikaryal neurofilament aggregates might confer protection in motor neuron disease.

Peripherin-mediated death of motor neurons rescued by overexpression of neurofilament NF-H proteins

In previous studies, we showed that overexpression of peripherin, a neuronal intermediate filament (IF) protein, in mice deficient for neurofilament light (NF-L) subunits induced a progressive adult-onset degeneration of spinal motor neurons characterized by the presence of IF inclusion bodies reminiscent of axonal spheroids found in amyotrophic lateral sclerosis (ALS). In contrast, the overexpression of human neurofilament heavy (NF-H) proteins provoked the formation of massive perikaryal IF protein accumulations with no loss of motor neurons. To further investigate the toxic properties of IF protein inclusions, we generated NF-L null mice that co-express both peripherin and NF-H transgenes. The axonal count in L5 ventral roots from 6 and 8-month-old transgenic mice showed that NF-H overexpression rescued the peripherin-mediated degeneration of motor neurons. Our analysis suggests that the protective effect of extra NF-H proteins is related to the sequestration of peripherin into the perikaryon of motor neurons, thereby abolishing the development of axonal IF inclusions that might block transport. These findings illustrate the importance of IF protein stoichiometry in formation, localization and toxicity of neuronal inclusion bodies.

Desmoplastic and spindle cell melanomas express protein markers of the neural crest but not of later committed stages of Schwann cell differentiation

BACKGROUND

The rare desmoplastic and spindle cell variants of malignant melanoma exhibit histological and biochemical features suggestive of early Schwann cell differentiation. These features include a spindle-shaped morphology, neurotropism, and the expression of the low affinity nerve growth factor receptor (p75NGFR).

METHODS

We evaluated by immunohistochemistry (using formalin-fixed, paraffin-embedded tissues) nine desmoplastic and three spindle cell melanomas for the expression of peripherin, p75NGFR, neural cell adhesion molecule (CD56/N-CAM), and growth-associated phosphoprotein-43 (GAP-43). Peripherin is expressed in the neural crest and in neurons, but not in cells committed to the Schwann cell lineage. p75NGFR and CD56/N-CAM also are expressed in early neural crest cells, but persist in unmyelinated and early premyelinating Schwann cells. GAP-43 is expressed in unmyelinated Schwann cells, but is downregulated in the later premyelinating to promyelinating stages of cells committed to the Schwann cell lineage.

RESULTS

Peripherin was expressed in 7/12 (58%), p75NGFR in 4/12 (33%), and CD56/N-CAM in 6/12 (50%) of the desmoplastic and spindle cell melanomas. GAP-43 was not expressed (0%) in any of the 12 melanomas (chi2, p = 0.05).

CONCLUSIONS

Desmoplastic and spindle cell melanomas express protein markers common to cells of the neural crest and to neurons similar to the immunophenotype previously reported for epithelioid cell melanomas. The expression of peripherin and the lack of expression of GAP-43 further define that these rare subtypes of melanoma do not recapitulate the later committed stages of Schwann cell differentiation.

Differential expression of the intermediate filament peripherin in cutaneous neural lesions and neurotized melanocytic nevi

Peripherin is an intermediate filament involved in growth and development of the peripheral nervous system, and is produced by neurons and the beta cells of the islets of Langerhans. Recently, malignant melanomas and some melanocytic nevi have been shown to express peripherin. It is unknown if Schwann cells, also derived from the neural crest, express peripherin. Expression of peripherin was evaluated by immunohistochemistry in cutaneous lesions characterized by a prominent Schwann cell component including 26 neurofibromas (NF), 10 schwannomas (SCH), seven granular cell tumors, and five palisaded encapsulated neuromas (PEN); 13 neurotized melanocytic nevi (NMN) also were evaluated because these lesions contain Wagner-Meissnerlike structures and type C nevus cells, which exhibit a "schwannian" phenotype. Peripherin was detected in the axons of normal peripheral nerves. NF and PEN contained numerous axons dispersed throughout the lesions, whereas only scattered small nerves were seen in GCT. In SCH, only rare axons were labeled, mostly at the periphery of the lesions. All other cells in these four types of lesions, therefore including Schwann cells, were not labeled. In most NMN, labeled axons were identified within the lesions. In a few cases, rare epithelioid melanocytes within the superficial portions of the nevi were labeled. The Wagner-Meissnerlike structures and type C nevus cells (schwannian) were not labeled in any lesion; however, numerous labeled axons invested these areas. Because there are different relative numbers of peripherin-labeled axons throughout NF, PEN, some nevi, and SCH, analysis of peripherin expression may be helpful in the diagnosis of these lesions. Neurons and some epithelioid melanocytes, in contrast to type C nevus cells and Schwann cells of NF and SCH, express peripherin, providing further evidence for a transition from a more neuronal to a more schwannian phenotype during the normal maturation sequence of melanocytes in nevi.

The intermediate filament peripherin is expressed in cutaneous melanocytic lesions

Peripherin is an intermediate filament involved in growth and development of the peripheral nervous system and is localized to neurons, some other cells derived from neural tube and neural crest, and some neuroendocrine cells (e.g. beta cells of islets of Langerhans). Peripherin also has been demonstrated in neuroblastomas and cutaneous neuroendocrine (Merkel cell) carcinomas. The expression of peripherin by other cells derived from the neural crest is unknown. We evaluated by immunohistochemistry 74 cutaneous melanocytic lesions including primary invasive malignant melanoma (IMM), melanoma in situ (MIS), atypical nevus (nevus with architectural disorder and cytologic atypia of melanocytes) (AN), spindle and epithelioid cell nevus (Spitz nevus) (SN), blue nevus (BN), and common intradermal benign melanocytic nevus (BMN) for expression of peripherin. Peripherin was detected in a cytoplasmic distribution within tumor cells in 14/14 IMM and 8/10 MIS. For IMM, peripherin localized to both the intraepidermal and invasive dermal components. Peripherin was detected in 10/10 AN and 9/9 SN, being localized to the intraepidermal component and, focally, to the superficial dermal component of the lesions. The dendritic nevus cells in 15/15 BN also expressed peripherin. For most of the BMN, expression of peripherin was absent or limited to rare, scattered cells in the superficial portion of the lesions. Melanocytes in adjacent normal skin were not labeled in any of the lesions studied. These results indicate that expression of peripherin is common in both benign and malignant melanocytic lesions, but not in normal resting adult melanocytes. Among benign lesions, expression of peripherin in the dermal component is rare except in the dendritic cells of BN. These findings provide evidence that the expression of peripherin, a marker of neuronal differentiation, is maintained by IMM, MIS, and BN, but is lost in the normal maturational sequence of the dermal component of other melanocytic lesions.

Transcriptional activation of the neuronal peripherin-encoding gene depends on a G + C-rich element that binds Sp1 in vitro and in vivo

Peripherin (Prph) is a type-III intermediate filament (IF) protein principally synthesized in peripheral nervous system neurons. We have previously shown that three regulatory elements, PER1, PER2 and PER3, in the first 98 bp of the Prph gene promoter, were sufficient to direct cell-type specific expression of a reporter gene [Desmarais et al., EMBO J. 11 (1992) 2971-2980]. Of these elements, PER1 was found to be important for cell-type specificity, but required the presence of other elements for transcriptional activity. Here, we show that PER3 is a stronger activator than PER2 and that it can stimulate cell-type-specific transcription when combined with PER1. We have characterized the G + C-rich PER3 element for its ability to bind trans-acting factors. Gel retardation and methylation interference (MI) assays show that PER3 binds transcription factor Sp1. In addition, an anti-Sp1 antibody recognizes the PER3 DNA-binding protein. A 3-bp mutation abrogating the capacity of PER3 to bind Sp1 in vitro completely abolished expression of the reporter gene construct containing only PER3 and PER1, while in a construct containing the first 256 bp of the Prph promoter, it led to an 80% decrease with respect to the control wild-type construct. Finally, by co-transfection of a Sp1-expressing plasmid, we show that Sp1 can stimulate transcription from a reporter gene containing the PER3 sequence. Together, these results indicate that interactions between Sp1 and the proteins binding PER1 are involved in the control of the Prph gene.

Selective expression of peripherin in gonadotropin-releasing hormone-synthesizing neurons of the rat

Immunofluorescent double stainings for gonadotropin-releasing hormone (GnRH) and peripherin, vimentin, or neurofilament-70 were used to determine the identity of the intermediate filaments in GnRH neurons of the adult rat. The results show that GnRH cells are unique neurons in the septum-rostral hypothalamus in that they express peripherin and vimentin but not neurofilament-70. Both peripherin and vimentin form a dense perinuclear network from which peripherin extends only into the proximal neurites, while vimentin can be seen in certain GnRH terminals in the median eminence. The presence of peripherin and vimentin in GnRH neurons as well as in olfactory receptor neurons suggests close ties between these cell types and supports the view that both cell types arise from a common ancestor.

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.

The peripherin gene maps to mouse chromosome 15

We have mapped the mouse peripherin gene, Prph, to chromosome 15 by means of Southern analysis of a panel of Chinese hamster/mouse somatic cell hybrids using a rat peripherin cDNA probe. Peripherin is a recently characterized type III intermediate filament expressed in the peripheral and the central nervous system. Although its exact function is not known, peripherin is likely to be involved in the neuronal cytoskeleton, a role it shares with other intermediate filaments, such as the neurofilament proteins. The intermediate filament gene family is believed to have evolved via gene duplication and dispersal throughout the genome; these processes have resulted in clusters of intermediate filament genes on specific chromosomes and conservation of these chromosomal locations among mammalian species.

Regulation of peripherin and neurofilament expression in regenerating rat motor neurons

Northern blotting, in situ hybridization and immunocytochemistry were used to study the changes in levels of mRNA coding for peripherin and in immunoreactivity of peripherin, a type III neuronal intermediate filament, in rat spinal motor neurons following axotomy of the sciatic nerve. For comparison, parallel studies examined the biology of neurofilament (NF) proteins in this model. The sciatic nerve was crushed at the junction of the L4-L5 spinal nerves. Levels of messenger RNA (mRNA) coding for peripherin in the motor neurons doubled by 4 days postaxotomy and remained elevated for a period of 6 weeks. Within 4-7 days of injury peripherin immunoreactivity increased significantly in cell bodies of motor neurons and remained elevated through 6 weeks. In contrast, no changes were detected in NF-M immunoreactivity over the same time period. By 8 weeks postaxotomy, levels of peripherin mRNA and protein returned to control values. The increases in the expression of peripherin parallel those of beta-tubulin and actin, and these changes are quite different from the alterations in neurofilament mRNA that decrease after axotomy. The contrasting responses of peripherin and NF to nerve injury indicates that each of these intermediate filaments may play distinct roles in nerve growth and regeneration.

Ontogeny of the neuronal intermediate filament protein, peripherin, in the mouse embryo

The expression of peripherin, a type III neuron-specific intermediate filament protein, and the middle neurofilament subunit were studied in the mouse embryo using immunofluorescence staining. The earliest staining for both proteins is seen at embryonic day 9 in the myelencephalon, initially as fiber staining followed by cell body staining in the developing facial and acoustic nuclei. As the embryo develops, there is rostral as well as caudal extension of peripherin and staining is seen in the trigeminal ganglia, nerve fibers and in the enteric nervous system. As the spinal cord forms there is anti-peripherin staining in developing motoneurons of the anterior horns while little cell body staining is seen for the middle neurofilament subunit. Both antibodies stain the developing dorsal root and its entry zone, but peripherin is found in the secondary sensory and commissural fibers while the middle neurofilament subunit is not. While both proteins are found in the neurons of the dorsal root ganglia, their distribution varies. The larger peripheral cells of the ganglia contain both proteins while the smaller more central cells, constituting over 60% of the cells in the ganglia, contain only peripherin. A similar picture is found in the sympathetic ganglia where there are cells which contain peripherin. middle neurofilament subunit or both, but where the majority of the neurons have only peripherin in their cell bodies. Peripherin is not found in the developing retina or in the adrenal medulla. Peripherin is also completely absent from cell bodies in the cerebral and cerebellar cortices. These results indicate that peripherin is found in development only in regions in which it is found in the adult. It can either co-exist with neurofilaments in the same neuron or the two may be independently expressed.

A new neuronal intermediate filament protein

It would be an understatement to say that the vertebrate nervous system appears complex. The characterization and classification of its components rely, in addition to its gross anatomy, on analyses of the differential expression of cytoskeletal and other cellular structures and products. In this brief review Lloyd Greene describes the discovery of a novel intermediate filament protein.

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.

Changes in some myelin protein markers and in cytoskeletal components during Wallerian degeneration of mouse sciatic nerve

After transection of the mouse sciatic nerve, the sequence of events occurring in the distal degenerating segment was followed by the biochemical changes related to the cytoskeletal components and to the myelin protein markers. The components of the intermediate filaments and of the microtubules undergo early changes. Within 3 days, the neurofilament triplet and the peripherin disappear whereas many peptides bearing the antigenic determinant common to all classes of intermediate filaments accumulate. Several of them persist after 1 month. The tubulin pattern changes from a high level of microheterogeneity--reflecting mostly the axonal contribution--to a lower level displayed by the predominant Schwann cells. A decrease in the amount of the myelin markers is also observed. However, a month after transection, immunoreactive basic protein is still present in the degenerated segment homogenate.

Is the induction of neuroblastoma differentiation by CCA mediated by its effects on the electrochemical gradient?

Various mitochondrial inhibitors are tested in neuroblastoma cells. Their effects on the mit-proteins and some cytoskeletal proteins are compared to those of CCA, a differentiation inducer. This comparison favours the hypothesis that the primary effect of CCA induction is an alteration of the electrochemical gradient.

Changes in mitochondrial proteins during neuroblastoma differentiation

The evolution of three major mit-proteins was followed in neuroblastoma cells cultured in different conditions of differentiation. 1 methyl cyclohexane carboxylic acid (CCA) was found to stimulate the synthesis of the three mit-protein markers. This result, compared to the effects of oligomycin, an inhibitor of mitochondrial function, favours the hypothesis that CCA induces in vitro neurogenesis through a general metabolic alteration.