Desmoplakin is involved in organization of an adhesion complex in peripheral nerve regeneration after injury

Peripheral nerves have the unique capability to regenerate after injury. Insights into regeneration of peripheral nerves after injury may have implications for neurodegenerative diseases of the nervous system. In this study, we analyzed the expression and function of desmoplakin in peripheral nerve regeneration. Desmoplakin was upregulated in spinal cord motoneurons after sciatic nerve injury. Conditional ablation of desmoplakin in motoneurons demonstrated that desmoplakin is necessary for normal motor regeneration. SiRNA and desmoplakin deletion-constructs revealed a role of desmoplakin in neurite extension in vitro. A complex of N-cadherin, plakoglobin, desmoplakin and vimentin was shown in motoneuronal cell cultures and peripheral nerves after injury in vivo. Motor nerve fiber regeneration and localization of N-cadherin and vimentin to axonal growth fronts were reduced in conditionally desmoplakin-ablated mice. These data indicate a function of desmoplakin in motor nerve regeneration by linking N-cadherin to intermediate filaments in regenerating motor axons.

Mutation analysis in Chariot-Marie Tooth disease type 1: point mutations in the MPZ gene and the GJB1 gene cause comparable phenotypic heterogeneity

Charcot-Marie-Tooth disease type 1 (CMT1) is a demyelinating peripheral neuropathy most commonly caused by a DNA duplication on chromosome 17p11.2 including the peripheral myelin protein 22 (PMP22). Point mutations in the myelin protein zero gene (MPZ) and gap junction protein, beta-1 gene (GJB1) are also found in association with CMT1 or the subclass of CMT type X (CMTX), respectively. Recently point mutations in these genes have been found in patients showing the axonal variant of CMT, CMT type 2 (CMT2). We here describe the clinical and electro-physiological findings caused by two novel and two recently described MPZ mutations and six GJB1 mutations. Different MPZ and GJB1 mutations were associated with different grades of severity in CMT1 and CMTX. The novel MPZ Glu141st op mutation was associated with the axonal CMT2. We conclude that the clinical and electrophysiological heterogeneity among CMT patients carrying point mutations in MPZ and GJB1 is similar. Thus for clinical purposes CMT1 and CMT2 patients should be screened for mutations in these two genes after duplication on chromosome 17p11.2 has been excluded as the disease causing mutation.

Kinetic parameters of 3-[(123)I]iodo-L-alpha-methyl tyrosine ([(123)I]IMT) transport in human GOS3 glioma cells

The radiolabelled amino acid 3-[(123)I]iodo-L-alpha-methyl tyrosine ([(123)I]IMT) is a promising tool for the diagnosis and monitoring of brain tumors using single-photon emission tomography (SPECT). However, little is known about the precise kinetics of [(123)I]IMT uptake in human glioma cells. The kinetic analysis of [(123)I]IMT transport in human GOS3 glioma cells yielded a high-affinity apparent Michaelis constant (K(m) = 20.1 +/- 1.5 microM). The maximum transport velocity (V(max)) amounted to 34.8 +/- 1.9 nmol/mg protein/10 min. Competitive inhibition experiments revealed that [(123)I]IMT transport is mediated principally by the sodium-independent system L.

Complete inhibition of in vivo glioma growth by oncostatin M

We describe here the oncostatin M (OSM)-dependent inhibition of in vivo tumour formation after intracerebral inoculation of glioblastoma cells in mice. We generated human glioblastoma cells transfected with the OSM gene under the control of a tetracycline-response promoter. Upon removal of tetracycline from the medium, cells exhibited a differentiated cell morphology, while proliferation was significantly inhibited. After implantation of these cells into nude mice brains, large tumours developed in animals lacking OSM expression, whereas no tumour formation was observed in mice with induced OSM expression. Our results suggest that OSM exerts pronounced antitumorigenic effects on glioblastoma cells in vivo and provide arguments for a therapeutic application of OSM in humans.

Characterization of 3-[(123)I]iodo-L-alpha-methyl tyrosine transport in astrocytes of neonatal rats

3-[(123)I]Iodo-L-alpha-methyl tyrosine ((123)I-IMT) is used for diagnosis and monitoring of brain tumours by means of single-photon emission tomography. As recently shown, (123)I-IMT is predominantly mediated into rat C6 glioma cells by sodium-independent system L for large neutral amino acids. Until now, (123)I-IMT transport in non-neoplastic glial cells has not been examined. Therefore, the aim of this study was to examine the cellular pathways and precise transport kinetics of (123)I-IMT uptake into astrocytes of neonatal rats. In particular sodium-independent (123)I-IMT transport into neonatal astrocytes was compared with sodium-independent (123)I-IMT uptake into neoplastic rat C6 glioma cells. Competitive inhibition experiments showed that (123)I-IMT is exclusively transported via sodium-independent system L into the neonatal astrocytes (92%). Kinetic analysis of sodium-independent (123)I-IMT uptake into neonatal astrocytes and into C6 glioma cells revealed apparent Michaelis constants K(M) = 13.9 +/- 0.5 microM and K(M) = 33.9 +/- 4.1 microM, respectively, which are in the same range of K(M) values as those recently determined for amino acid transport into neoplastic and non-neoplastic glial cells. Indeed, the K(M) values in the micromolar range correspond to the expression of the LAT-1 subunit of system L both in the neonatal astrocytes and in C6 glioma cells. However, sodium-independent maximum transport velocities (V(max)) differed significantly between neonatal astrocytes and C6 glioma cells (11.1 +/- 0.3 and 39.9 +/- 3.3 nmol/mg protein/10 min, respectively).

Flt3 mutations from patients with acute myeloid leukemia induce transformation of 32D cells mediated by the Ras and STAT5 pathways

Somatic mutations of the receptor tyrosine kinase Flt3 consisting of internal tandem duplications (ITD) occur in 20% of patients with acute myeloid leukemia. They are associated with a poor prognosis of the disease. In this study, we characterized the oncogenic potential and signaling properties of Flt3 mutations. We constructed chimeric molecules that consisted of the murine Flt3 backbone and a 510-base pair human Flt3 fragment, which contained either 4 different ITD mutants or the wild-type coding sequence. Flt3 isoforms containing ITD mutations (Flt3-ITD) induced factor-independent growth and resistance to radiation-induced apoptosis in 32D cells. Cells containing Flt3-ITD, but not those containing wild-type Flt3 (Flt3-WT), formed colonies in methylcellulose. Injection of 32D/Flt3-ITD induced rapid development of a leukemia-type disease in syngeneic mice. Flt3-ITD mutations exhibited constitutive autophosphorylation of the immature form of the Flt3 receptor. Analysis of the involved signal transduction pathways revealed that Flt3-ITD only slightly activated the MAP kinases Erk1 and 2 and the protein kinase B (Akt) in the absence of ligand and retained ligand-induced activation of these enzymes. However, Flt3-ITD led to strong factor-independent activation of STAT5. The relative importance of the STAT5 and Ras pathways for ITD-induced colony formation was assessed by transfection of dominant negative (dn) forms of these proteins: transfection of dnSTAT5 inhibited colony formation by 50%. Despite its weak constitutive activation by Flt3-ITD, dnRas also strongly inhibited Flt3-ITD-mediated colony formation. Taken together, Flt3-ITD mutations induce factor-independent growth and leukemogenesis of 32D cells that are mediated by the Ras and STAT5 pathways. (Blood. 2000;96:3907-3914)

Activation of the Jak-Stat- and MAPK-pathways by oncostatin M is not sufficient to cause growth inhibition of human glioma cells

We have recently described that oncostatin M (OSM), a member of the IL-6 family of cytokines, induces the differentiation of human glioma cells in culture. In order to extend this studies, we analyzed the effect of OSM on other human glioma cell lines including A172, U343-MG and T98G. All of these cell lines express the receptor components of OSM and leukemia inhibitory factor (LIF) gp130, LIFR and the OSM specific OSMRbeta. Therefore, we expected these cell lines to respond to OSM and LIF. Using specific antibodies recognizing proteins of the janus kinase (Jak-)/signal transducers and activator of transcription (Stat-) signaling cascade that has been shown to transduce the signals of the IL-6 cytokines to the nucleus, we could show that Jak1, Jak2 and Tyk2, as well as the Stat proteins Stat1, Stat3 and Stat5b were phosphorylated in all three cell lines by OSM and, at least in part, by LIF. Activation of the Stat proteins was also detected by EMSA which revealed complex formation on the Stat3 DNA-binding element and on a Stat5 binding site. Consistent with our recent findings, OSM treatment also induced the activation of the MAPK erk2 and the tyrosine phosphatase SHP-2 in cells of the A172, T98G and U343-MG cell lines. Although this activation pattern was very close to what we had observed in the GOS3 glioma cells, only T98G showed a growth inhibition in response to OSM while the A172 and the U343-MG cell lines did not respond to OSM treatment in terms of growth inhibition.

Oncostatin M-mediated growth inhibition of human glioblastoma cells does not depend on stat3 or on mitogen-activated protein kinase activation

Oncostatin M (OSM) and other members of the interleukin-6 cytokines, like ciliary neurotrophic factor and leukemia inhibitory factor, can induce differentiation of glial cells. We have recently described that OSM inhibited the growth of human glioma cells in vitro and induced a cell morphology resembling that of mature astrocytes. Using the glioblastoma cell line 86HG39, we demonstrated that treatment of the glioma cells with OSM also leads to a differentiation of the malignant glioma cells as judged by a strong increase in glial fibrillary acidic protein expression. The differentiation and the growth inhibition were not significantly blocked by expression of a dominant-negative (dn) signal transducer and activator of transcription (Stat) 3 protein. OSM exerted a reduction in DNA synthesis even in the presence of a high expression level of dnStat3. Moreover, inhibition of the ras-raf-mitogen-activated protein kinase (MAPK) pathway by the MAPK kinase 1 inhibitor PD98059 resulted in a synergistic enhancement of the OSM effect, indicating that the activation of this pathway counteracts the activity of the cytokine.

CNTF and its receptor subunits in human gliomas

Ciliary neurotrophic factor (CNTF) promotes the survival of various neuronal cell populations. It is produced by astrocytes and influences the development and differentiation of glial cells. CNTF and related neuropoietic cytokines affect growth and differentiation of various neoplasms. Moreover, they induce the reactive transformation of astrocytes (gliosis) and influence growth and differentiation of neuroectodermal tumor cell lines in vitro. However, their role in gliomas is largely unknown. We studied the expression of CNTF and its receptor subunits in human astrocytomas and glioblastomas. In more than 95% of the tumors, CNTF transcripts were found by RNAase protection assay; in more than 80% of the cases, tumor cells were CNTF immunoreactive. CNTF receptor alpha (CNTFR alpha), the specific component of the tripartite CNTF receptor system, was detectable by Northern blot analysis in 80% of the cases. In situ hybridization revealed CNTFR alpha mRNA in the cytoplasm of neoplastic cells. Transcripts of the remaining two components of the CNTF receptor system, gp130 and LIFR beta, were found by Northern blotting in 83% and 70% of the tumors, respectively. Simultaneous expression of CNTF and all its receptor components was detected in approximately half of the tumors. These results indicate that CNTF and its receptor components are expressed by human glioma cells. The simultaneous expression of ligands and receptor subunits suggests that CNTF might act on human glioma cells via an auto- or paracrine mechanism.

Expression of matrix metalloproteinase-2 in glial and neuronal tumor cell lines: inverse correlation with proliferation rate

The expression of matrix metalloproteinases (MMPs) has been found to be positively correlated to the degree of malignancy in gliomas, indicating that poorly differentiated brain tumor cells produce more MMPs than differentiated ones. We determined the production of active MMP-2 in five glial (U138MG, U373MG, A172, C6, GOS-3), two neuronal (SK-N-SH, SK-N-MC), and two pluripotent cell lines with facultative neuronal and glial differentiation (P19 and NT2) by gelatin zymography. The MMP-2 activity profiles were compared to the proliferative activities of the cell lines. MMP-2 expression varied from barely existent (P19 cells) to strong (U138MG and SK-N-SH). Interestingly, for the cell lines with high MMP-2 expression levels, low proliferative activities were recorded, and vice versa. Retinoic acid induced neuronal differentiation and a reduction of proliferation of P19 cells; the differentiated cells produced significantly more MMP-2 than untreated cells. Upon confluency, GOS-3 cells showed reduced proliferation, but increased MMP expression. Thus, proliferative activity was inversely correlated to MMP-2 expression in the tumor cell lines analyzed.

Kinetics of 3-[(123)I]iodo-l-alpha-methyltyrosine transport in rat C6 glioma cells

3-[(123)I]Iodo-l-alpha-methyltyrosine ((123)I-IMT) is used for the diagnosis and monitoring of brain tumours by means of single-photon emission tomography (SPET). To date, little has been known about the system for the transport of (123)I-IMT into brain tumour cells. It is assumed that (123)I-IMT is transported by a specific carrier for large, neutral amino acids (L-system). In this study, rat C6 glioma cells were used to characterize the uptake system of (123)I-IMT and to investigate its precise kinetics. The time course of (123)I-IMT uptake into the cells was examined for a range of 1-60 min. (123)I-IMT uptake rates with varying concentrations of (123)I-IMT (2. 5-50 microM) in the medium were quantified to assess the kinetic parameters of (123)I-IMT transport. Furthermore, competition of (123)I-IMT with other amino acids was investigated to identify the distinct transport systems involved in (123)I-IMT uptake. (123)I-IMT uptake into C6 glioma cells was linear for approximately 10 min and reached a steady-state level within 30 min. The analysis of the rate of uptake of (123)I-IMT at different concentrations was concordant with the predominance of a single uptake system. The apparent Michaelis constant (K(m)) of (123)I-IMT was 26.2+/-1.9 microM, and the maximum transport velocity (V(max)) was 35.4+/-1.7 nmol/mg protein per 10 min. 77%+/-10% of (123)I-IMT transport was sodium independent and 23%+/-3% was sodium dependent. Competitive inhibition of (123)I-IMT uptake by 2-aminobicyclo[2.2. 1]heptane-2-carboxylic acid, alpha-(methylamino)isobutyric acid and naturally occurring amino acids revealed a major (123)I-IMT transport via the sodium-independent system L (72%) and a minor uptake via the sodium-dependent system B(0,+) (17%). Our results show that (123)I-IMT transport into C6 glioma cells is principally mediated by the L-system and to a minor extent by the B(0,+)-system. The kinetic parameters of (123)I-IMT uptake are in the range of those of naturally occurring amino acids.

Activation of Jak-Stat and MAPK2 pathways by oncostatin M leads to growth inhibition of human glioma cells

Oncostatin M (OSM) is a cytokine of the IL-6 family that modulates the growth of various cell types, at least in vitro. We have recently described that OSM inhibits growth and changes cell morphology of human glioma cell lines. Although leukemia inhibitory factor (LIF) receptor components are also expressed by these cells, the response to LIF was significantly weaker compared to OSM. We have therefore analyzed the signal transduction pathways induced by these cytokines. While OSM induces a number of strong tyrosine phosphorylations, including Janus tyrosine kinases (Jak) and the signal transducer and activator of transcription (Stat) proteins, LIF induces only minor tyrosine phosphorylation of Tyk2 and Stat3. Specific activation of the tyrosine phosphatase SHP-2 as well as the mitogen-activated kinase 2 (MAPK2) was found in glioma cells upon OSM treatment. MAPK2 turns out to be a crucial mediator of the OSM effect in glioma cells since inhibition of MAPK activity by the Mek1 inhibitor PD98059 blocks the OSM-induced inhibition of DNA synthesis by about 70%.

Growth inhibition of newly established human glioma cell lines by leukemia inhibitory factor

We have established three new cell lines deriving from malignant human gliomas. The cell lines were described in terms of both morphology and growth characteristics. Most cells in all three cell lines expressed the neuroepithelial marker protein GFAP. In terms of growth characteristics, the cells showed only slight differences. The cell lines showed no expression of the neural form of the c-src gene, pp60c-srcN, but did express the ubiquitous form, pp60c-src. The established glioma cell lines were also examined for expression of members of the neuropoietic cytokine family, CNTF and LIF, and their respective receptor components CNTFRalpha, LIFRbeta and gp130. With the exception of CNTFRalpha both the ligands and their receptor components were expressed in similar amounts in all three cell lines. The presence of ligand and receptor prompted us to study the effects of exogenously supplied factors on the growth of the glioma cell lines. Whereas LIF induced a high c-fos expression, only low c-fos induction was observed upon CNTF treatment. Accordingly, CNTF did not have any noticeable effects on glioma cell growth in culture, while LIF mediated an inhibiting effect on the growth of the three glioma cell lines in culture.

Inhibition of growth and induction of differentiation of glioma cell lines by oncostatin M (OSM)

The neuropoietic cytokines of the interleukin-6 family are a group of structurally and functionally related polypeptides. We studied the effect of the multifunctional neuropoietic cytokines, including oncostatin M (OSM), leukemia inhibitory factor (LIF) and interleukin-6 (IL-6), on anaplastic glioma cell lines. Growth and morphology of the glioma cell lines were affected differently. While IL-6 and LIF exerted no or only small minor morphological changes and growth retardation, OSM induced a marked change in morphology and a strong suppression of growth. OSM treated cells were characterized by enlargement and the formation of multiple, thin processes thus resembling mature cultured astrocytes. The growth inhibitory effects were dose dependent with a maximum exerted by addition of 50 ng/ml OSM. The inhibition of DNA synthesis by OSM could be abolished by antibodies blocking either the activity of OSM or the OSM-receptor component, gp130.

[Molecular biology and genetics of hereditary motor and sensory neuropathies]

Hereditary neuropathies (HMSN) are among the most common genetic diseases in neurology. Various mutations in different genes are known which lead to the most frequent hereditary neuropathies. These mutations concern proteins of the myelin of the peripheral nervous system, as well as a gap-junction protein expressed in peripheral nerves. The molecular mechanisms leading from gene mutation to disease phenotypes are not fully understood. Nowadays, we are able to use DNA analysis for symptomatic, presymptomatic, and prenatal screening. The latter is of questionable value because of the variability in disease severity and outcome. Deeper insights into the molecular pathophysiology will, however, yield new therapeutic strategies in individual patients.

Tyrosine 785 is a major determinant of Trk--substrate interaction

Interaction of the nerve growth factor (NGF) receptor/Trk with cellular substrates was investigated by transient co-overexpression in human 293 fibroblasts using ET-R, a chimeric receptor consisting of the epidermal growth factor receptor (EGF-R) extracellular ligand binding domain and the Trk transmembrane and intracellular signal-generating sequences. The chimera was fully functional, and associated with and phosphorylated phospholipase C gamma (PLC gamma), ras GTPase-activating protein (GAP) and the non-catalytic subunit of phosphatidylinositol-3'-kinase, p85, in a ligand-dependent manner. Deletion of 15 C-terminal amino acids, including tyrosine 785 (Y-785) abrogated receptor and substrate phosphorylation activities. Mutation of Y-785 to phenylalanine somewhat impaired receptor phosphorylation activity, which was reflected in reduced GAP and p85 phosphorylation. In contrast, ET-YF phosphorylation of PLC gamma was significantly reduced, while the high affinity association potential with this substrate was abrogated by this point mutation in vitro and in intact cells. Furthermore, a tyrosine-phosphorylated synthetic C-terminal peptide competitively inhibited Trk cytoplasmic domain association with PLC gamma. Thus, the short C-terminal tail appears to be a crucial structural element of the Trk cytoplasmic domain, and phosphorylated Y-785 is a major and selective interaction site for PLC gamma.

Sequence, expression and mutational analysis of BAF1, a transcriptional activator and ARS1-binding protein of the yeast Saccharomyces cerevisiae

We report the cloning and sequence analysis of the yeast BAF1 gene which encodes an abundant protein previously shown to act as a transcription activator in the YPT1-TUB2 intergene region. As predicted from the DNA sequence, the highly hydrophilic BAf1 protein is 731 amino acids long and has a molecular mass of 81 748 daltons. The protein product of the cloned BAF1 gene produced in Escherichia coli is able to form specific complexes with DNA fragments containing the conserved element TCN7ACG. The protein binds also to the ABF1-binding site of the B-domain of ARS1, entertaining the possibility that BAF1 and ABF1 are identical proteins. Extensive deletion studies identified the N-terminal two thirds of the Baf1 protein to be required for specific DNA binding. Amino acid substitutions point to the N-terminal sequence CysX7HisX3HisX4CysX4Cys to form an atypical metal-binding 'finger' structure. Disruption of the BAF1 gene is lethal. The existence of five potential Baf1-protein binding sites in the 5' region of the gene suggests the involvement of the Baf1 protein in transcription regulation of its own gene.

Isolation and DNA-binding characteristics of a protein involved in transcription activation of two divergently transcribed, essential yeast genes

We have identified a protein, BAF1, which has two oppositely oriented, partially overlapping binding sites within a symmetrical sequence located midway between and upstream of the divergently transcribed YPT1 and TUB2 genes of the yeast Saccharomyces cerevisiae. The 120 kd BAF1 protein was purified to near homogeneity and used to delineate the two binding sites and to identify apparent protein contact sites by the missing contact technique, methylation interference and by site-directed mutagenesis. The BAF1-recognition sequence contains a conserved TCN7ACG element recently identified at autonomously replicating sequences (ARS) and in the 5' and 3' flanking region of other yeast genes. The symmetrical sequence of the YPT1/TUB2 intergene region seems not to be involved in DNA replication but activates transcription in an orientation-independent fashion.

Impairment of yeast pre-mRNA splicing by potential secondary structure-forming sequences near the conserved branchpoint sequence

The absolutely conserved TACTAAC box within introns of RNA polymerase II-transcribed genes of the yeast Saccharomyces cerevisiae serves an indispensable role in lariat formation. We show in this report that rather short palindromic sequences inserted into the yeast actin gene intron immediately 3' to the TACTAAC box block the second but not the first splicing step. In contrast, a palindromic sequence inserted some 23 bp 3' of the TACTAAC box did not affect correct and efficient splicing. The data suggest that hairpin structures that might form adjacent to the branchsite sequence interfere with some necessary alteration of the spliceosome required for 3' intron cleavage and exon ligation.