Survivin inhibition induces human neural tumor cell death through caspase-independent and -dependent pathways.

Survivin inhibits apoptosis during development and carcinogenesis and is absent in differentiated cells. To determine whether survivin inhibition induces cell death in neural tumor cells, survivin antisense oligonucleotides (SAO) were administered to a human neuroblastoma (MSN) and an oligodendroglioma (TC620) resulting in a dose-dependent reduction in survivin protein. Although 74% of the SAO-treated MSN cells were trypan blue(+), PARP cleavage or activated caspase-3 was not observed. However nuclear translocation of AIF occurred and XIAP increased dramatically. Co-administration of z-Val-Ala-Asp(OMe)-fluoromethyl ketone (zVAD-fmk) with SAO did not inhibit cell death suggesting a caspase-independent mechanism of cell death. Propidium iodide (PI) staining revealed multiple large macronuclei with no apoptotic bodies supporting a role for survivin in cell division. By contrast, while 70% of the SAO-treated TC620 cells were trypan blue(+), PARP was cleaved, cells were TUNEL(+) and PI-staining revealed macronuclei and numerous apoptotic bodies. Co-treatment of the TC620 cells with SAO and zVAD-fmk blocked cell death. While no macronuclei or apoptotic bodies were observed there was a two-fold increase in metaphase cells. Our results suggest that survivin inhibition decreases the viability of human neural tumor cells and as a result of mitotic catastrophe, cell death can be initiated by either a classic apoptotic mechanism or a caspase-independent mechanism.

Binding of Fyn to MAP-2c through an SH3 binding domain. Regulation of the interaction by ERK2.

Microtubule-associated protein 2 (MAP-2) isoforms are developmentally expressed in the nervous system and contain a number of functional domains. Adjacent to the first repeat of the microtubule-binding domain is an RTPPKSP motif for binding SH3 domains. To identify SH3-containing proteins that interact with MAP-2, transfections, filter overlay assays, glutathione S-transferase (GST)-mediated binding assays, co-immunoprecipitations and enzyme-linked immunosorbent assays were performed. Transfections of MAP-2a, MAP-2b, and MAP-2c constructs into COS7 cells, followed by incubation of the cell lysates with SH3-GST fusion proteins, determined that the strongest interaction was between MAP-2c and the non-receptor tyrosine kinase Fyn; however, MAP-2b and MAP-2c also bound to Grb2. Co-immunoprecipitation of Fyn and MAP-2c from human fetal homogenates confirmed the interaction in vivo. MAP-2 synthetic peptides spanning the RTPPKSP motif bound to Fyn, and the interaction was regulated by phosphorylation. Co-transfections with MAP-2c and the extracellular signal-regulated kinase 2 (ERK2) demonstrated that MAP-2c is threonine/serine-phosphorylated on its RTPPKSP motif and that threonine phosphorylation abolished the MAP-2c/Fyn binding. Kinase assays and co-transfection of MAP-2c and Fyn confirmed that Fyn tyrosine kinase phosphorylates MAP-2c. Thus, the activation of signaling pathways may regulate cytoskeletal dynamics by altering the state of phosphorylation of MAP-2 by both ERK2 and Fyn kinase.

Novel microtubule-associated protein-2 isoform is expressed early in human oligodendrocyte maturation.

We have identified a developmentally regulated, oligodendrocyte-specific protein, designated microtubule-associated protein-2 expressing exon 13 (MAP-2+13), in the human central nervous system (CNS). Monoclonal antibodies directed against MAP-2+13 labeled oligodendrocytes in the white matter of human fetal spinal cord. Double-label immunofluorescence and confocal microscopy, and immunoelectron microscopy localized MAP-2+13 to the soma and extending processes of fetal oligodendrocytes, but not to the myelin sheath. The immunoreactivity was throughout the perikarya. Ultrastructural examination of the fetal myelin sheaths showed them to be thin and not fully compacted, indicating that myelination was in progress. There was no overlap in staining of GFAP+ astrocytes and MAP-2+13+ oligodendrocytes. MAP-2+13 was also expressed in intermediate filament-negative "radial glia" extending from the central canal to the subpial surface. In the mature CNS, MAP-2+13 also marked cells of oligodendroglial morphology, but these cells were rare. These finding demonstrate that in the human CNS, MAP-2+13 is a novel protein transiently expressed in cells of oligodendroglial lineage.

A novel microtubule-associated protein-2 expressed in oligodendrocytes in multiple sclerosis lesions.

Elucidation of the mechanisms involved in the regeneration of oligodendrocytes and remyelination is a central issue in multiple sclerosis (MS) research. We recently identified a novel alternatively spliced, developmentally regulated oligodendrocyte-specific protein designated microtubule-associated protein-2+13 [microtubule-associated protein-2 expressing exon 13 (MAP-2+13)]. MAP-2+13 is expressed in human fetal oligodendrocytes during process extension and myelination but is minimally expressed in normal mature CNS. To test the hypothesis that MAP-2+13 is reexpressed in regenerating oligodendrocytes in MS lesions, we examined the brains of MS patients for the expression of this protein. By immunocytochemistry using a series of monoclonal antibodies specific for MAP-2+13, we determined that MAP-2+13 expression was up-regulated in all 31 lesions from 10 different MS brains. MAP-2+13 was expressed in regenerating oligodendrocytes associated with demyelinated lesions, with the highest counts found in regions of extensive remyelination. By electron microscopy, MAP-2+13 was localized to oligodendrocytes engaged in remyelination, evident by their process extension and association with thinly myelinated (remyelinated) and demyelinated axons. These results suggest a hitherto unsuspected role for this microtubule-associated protein in oligodendrocyte function during development and myelin repair.

Survey for CAG repeat polymorphisms in the human MAP-2 gene.

Microtubule-associated protein-2 (MAP-2) expression is altered in response to a number of physiological insults such as Alzheimer's disease, schizophrenia, stroke and AIDS-dementia. Changes include alteration in MAP-2 transcription, translation, and state of phosphorylation. Multiple MAP-2 transcripts exist within the nervous system and, as noted for a number of genes expressed in the central nervous system, MAP-2 contains a region of trinucleotide repeats located in exon 1 of the 5' untranslated region (5' UTR). Since expansion of CAG repeats are found in several neurodegenerative disorders, we analysed the CAG repeats in MAP-2 for polymorphisms in 31 controls, 35 chronic schizophrenics, and 20 with other neuropsychiatric illnesses. Genomic DNA samples from 86 individuals were used as templates in PCR amplifications with primers within exon 1. Sequencing of the PCR products, or short tandem repeat polymorphism (STRP) analysis, demonstrated consistency in the size of the CAG repeats. This study demonstrates that the seven copies of the CAG repeat located in the 5' UTR of the MAP-2 gene are highly conserved in the general population, and that there is no evidence for expansion of the CAG repeat.

Molecular and functional characteristics of MAP-2a: ability of MAP-2a versus MAP-2b to induce stable microtubules in COS cells.

Microtubule-associated protein-2 (MAP-2) is a prominent cytoskeletal protein in the mammalian nervous system. Two high-molecular-weight (HMW) MAP-2 isoforms, MAP-2a and MAP-2b, are developmentally regulated. MAP-2b is expressed through the life of the neuron, while MAP-2a expression coincides with the time of synaptic formation. MAP-2a and MAP-2b differ in size by approximately 10 kD. Attempts to differentiate MAP-2a from MAP-2b led to the identification of additional exons; exons 7A, 8, 13, and 16. The focus of the present study was to define the complete molecular composition of MAP-2a that was prerequisite for investigating the functional characteristic of the MAP-2a protein. Detailed examination of rat brain mRNA by Northern blot analysis and RT-PCR showed that MAP-2a contains only exon 8 in addition to the exons found in the MAP-2b transcript. Exons 7A, 13, and 16 are not present in the MAP-2a transcript. Antibody generated to exon 8 expressed protein, immunoprecipitated a HMW protein from adult rat brain that co-migrated with MAP-2a and was immunopositive with other MAP-2 antibodies. Comparative transfections of full-length MAP-2a and MAP-2b cDNA into COS-7 cells demonstrated that MAP-2a influenced the microtubule network differently than MAP-2b by inducing rapid and stable microtubule bundle formation even in the presence of nocodazole.

Making sense of the multiple MAP-2 transcripts and their role in the neuron.

Microtubule-associated protein-2 (MAP-2) is a family of heat-stable, phosphoproteins expressed predominantly in the cell body and dendrites of neurons. Three major MAP-2 isoforms, (MAP-2a, MAP-2b, MAP-2c) are differentially expressed during the development of the nervous system and have an important role in microtubule dynamics. Several MAP-2 cDNA clones that correspond to the major MAP-2 transcripts and additional, novel MAP-2 transcripts expressed in the CNS and PNS have been characterized. The transcripts result from the alternative splicing of a single MAP-2 gene consisting of 20 exons. Studies are now being directed toward understanding the role of the multiple MAP-2 forms that contain novel exons in the nervous system. The expression, localization, and possible functions of the newly identified spliced forms are the focus of this review.

Distribution and subcellular localization of high-molecular-weight microtubule-associated protein-2 expressing exon 8 in brain and spinal cord.

The expression of high-molecular-weight (HMW) microtubule-associated protein-2 (MAP-2) expressing exon 8 (MAP-2 + 8) was examined by immunoblotting during rat brain development and in sections of human CNS. In rat brain, HMW MAP-2 + 8 expression was detected at embryonic day 21 and increased during postnatal development. In adult rats, HMW MAP-2 + 8 comigrated with MAP-2a. In human adult brain, HMW MAP-2 + 8 was expressed in select neuronal populations, including pyramidal neurons of layers III and V of the neocortex and parahippocampal cortex, pyramidal neurons in the endplate, CA2 and subiculum of the hippocampus, and the medium-sized neurons of the basal ganglia. In the cerebellum, a subpopulation of Golgi neurons in the internal granular cell layer and most Purkinje cells were also stained. In the spinal cord staining was observed in large neurons of the anterior horn. Staining was present in cell bodies and dendrites but not in axons. At the ultrastructural level, HMW MAP-2 + 8 immunoreactivity was observed on mitochondrial membranes and in postsynaptic densities (PSDs) of some asymmetric synapses in the midfrontal cortex and spinal cord. Immunoblots of proteins isolated from enriched mitochondrial and PSD fractions from adult human frontal lobe and rat brains confirmed the presence of HMW MAP-2 + 8. The presence of HMW MAP-2 + 8 in dendrites and in close proximity to PSDs supports a role in structural and functional attributes of select excitatory CNS synapses.

Expression of microtubule-associated protein-2a and other novel microtubule-associated protein-2 transcripts in human fetal spinal cord.

In human fetal spinal cord (HFSC), six additional microtubule-associated protein-2 (MAP-2) transcripts are generated by alternative splicing of two recently described exons, exon 8 and exon 13. The following three translated proteins are detected by western blot analysis: MAP-2b expressing exon 8 (MAP-2b + 8; MAP-2a), MAP-2b expressing exon 13 (MAP-2b + 13), and MAP-2c expressing exon 8 and exon 13 (MAP-2c + 8 + 13). The finding that MAP-2b + 8 is expressed in HFSC demonstrates for the first time the presence of MAP-2a in human fetal CNS. Immunocytochemical studies show that exon 8-specific antibody and exon 13-specific antibody stain independent and overlapping populations of neurons in the lumbar region of the HFSC. Antibody 13-immunopositive neurons have predominantly cytosolic staining, whereas in the antibody 8-immunoreactive neurons staining was observed in the cytosol, dendrites, and some synapses. The prenatal expression of MAP-2a, which has been used as a marker of synaptogenesis, not only demonstrates the presence of a mature MAP-2 isoform in HFSC, but suggests that MAP-2a is important during human fetal as well as postnatal synaptogenesis.

Genomic structure of human microtubule-associated protein 2 (MAP-2) and characterization of additional MAP-2 isoforms.

We have determined that the gene for human microtubule-associated protein 2 (MAP-2) spans 19 exons, including 6 exons identified in this study, 1-4, 8, and 13; all six of these exons are transcribed. The alternative splicing of coding exons generates a greater diversity of MAP-2 transcripts and isoforms. The first three exons encode alternate 5' untranslated regions that can be spliced to additional untranslated sequences contained in exons 4 and 5. Exons 8 and 13 are transcribed in human fetal spinal cord, adult brain, MSN cells, and rat brain, and each exon maintains an open reading frame with both high and low molecular weight MAP-2 isoforms. Antibodies generated to synthetic peptides of exons 8 and 13 demonstrate that these exons are translated and MAP-2 isoforms containing these exons are generated.

Three unique 5' untranslated regions are spliced to common coding exons of high- and low-molecular-weight microtubule-associated protein-2.

Three unique 5' untranslated regions (UTRs) have been characterized for human microtubule-associated protein-2 (MAP-2) transcripts. All three UTRs shared a common 171-bp sequence adjacent to the MAP-2 coding region and then diverged upstream. The size of the unique upstream sequence was 281, 146, or 104 bp. PCR of genomic DNA demonstrated that the 5' UTRs span multiple exons. The unique region of the UTRs recognizes a 9.5- and a 6-kb MAP-2 transcript in poly(A)+ mRNA isolated from human MSN cells, and PCR analysis demonstrated that each unique UTR is contained in multiple high- and low-molecular-weight MAP-2 transcripts. Reverse transcription-PCR (RT-PCR) performed on MSN mRNA isolated from polysomes demonstrated that all three of the UTRs contained within multiple MAP-2 transcripts were associated with polysomes and hence translated. RT-PCR from human fetal spinal cord and adult brain mRNA demonstrated that all of the UTRs are expressed at these developmental time points.

Differential expression of exons 10 and 11 in normal tau and tau associated with paired helical filaments.

Antibodies were raised to two synthetic peptides with amino acid sequences encoded by a variable region of exons 10 and 11 of the tau gene. The affinity-purified antibodies, designated E-10 and E-11, were used to determine whether PHF-tau and normal tau differ in variants containing three or four repeats in the microtubule-binding domain, respectively. Normal adult human brain was shown by gel electrophoresis to contain six isoforms of tau. All of the isoforms reacted with E-11, whereas only four of them with slower electrophoretic mobility were recognized by E-10. Fetal brain tau was readily recognized by E-11 but reacted poorly with E-10. In PHF preparations, E-11 bound to all three polypeptides of PHF-tau of 68 kD, 64 kD, and 60 kD and reacted intensely with a material smearing from the top of the gel to about the 50-kD region. In contrast, E-10 only weakly recognized the two higher molecular weight PHF-tau polypeptides of 68 kD and 64 kD, as well as smeared material, and the binding was not affected by phosphatase treatment. Using recombinant tau with four repeats as a reference, the immunoreactivity of E-10 with PHF-tau was estimated to be approximately 5% of that of E-11. By comparison, the immunoreactivity of E-10 with four isoforms of normal tau was comparable to that of E-11. These results indicate that the ratio of three vs. four repeat variants in PHF-tau is higher than in normal tau and suggest that Alzheimer disease may be associated with the disproportional expression of fetal (or juvenile) forms of tau. Alternatively, the weak reactivity of PHF-tau with E-10 antibody could be due to post-translational modifications other than phosphorylation.

Human microtubule-associated protein-2c localizes to dendrites and axons in fetal spinal motor neurons.

Microtubule-associated protein-2 (MAP-2) functions to maintain neuronal morphology by promoting the assembly of microtubules. MAP-2c is an alternately spliced form of MAP-2, containing the first 151 amino acids of high-molecular-weight (HMW) MAP-2 joined to the last 321 amino acids, eliminating 1,352 amino acids specific to HMW MAP-2. A polyclonal antibody generated to the splice site of human MAP-2c was used to determine its cellular localization. The MAP-2c antiserum was depleted of any HMW MAP-2 reactivity by absorption with HMW MAP-2 fusion protein. Western blot analysis of human fetal spinal cord homogenates demonstrated that the antibody is specific for human MAP-2c. MAP-2c immunoreactivity was found in the perinuclear cytoplasm and processes of anterior motor neurons and large processes of the posterior column in sections from 22-24-week human fetal spinal cord. Double-label confocal microscopy was performed using the MAP-2c polyclonal antibody and either a HMW MAP-2 or a neurofilament protein (highly phosphorylated 160- and 200-kDa protein) monoclonal antibody to identify these processes as dendrites or axons, respectively. HMW MAP-2 and MAP-2c colocalized in cell bodies and dendrites of anterior motor neurons, demonstrating for the first time the presence of native MAP-2c within dendrites. In addition, immunoelectron microscopy showed MAP-2c associated with microtubules in dendrites of motor neurons. MAP-2c and the neurofilament proteins were found in axons of the dorsal and ventral roots. The presence of MAP-2c within axons and dendrites suggests that MAP-2c contributes to neuronal plasticity during human fetal development.

Localization of specific epitopes on human microtubule-associated protein 2.

Microtubule-associated protein 2 (MAP-2) is an abundant neuronal cytoskeletal protein that binds to tubulin and stabilizes microtubules. Using fusion protein constructs we have defined the epitopes of 10 monoclonal antibodies (mAbs) to discrete regions of human MAP-2. Proteins were expressed in pATH vectors. After electrophoresis, immunoblotting was performed. By western blot analysis five of the mAbs (AP-14, AP-20, AP-21, AP-23, and AP-25) share epitopes with only the high molecular weight isoforms (MAP-2a, MAP-2b); two of the mAbs (AP-18 and tau 46) recognize MAP-2a, MAP-2b, and MAP-2c. Although AP-18 immunoreactivity was detected within heat-stable protein homogenates isolated from a human neuroblastoma cell line MSN, fusion protein constructs encompassing human MAP-2 were negative, suggesting that the AP-18 epitope is phosphorylated. Furthermore, AP-18 immunoreactivity was lost after alkaline phosphatase treatment of heat-stable protein preparations from MSN cells. Four of the mAbs (322, 636, 635, and 39) recognize epitopes located within amino acids 169-219 of human MAP-2. AP-21 maps to a region between amino acids 553 and 645. AP-23 maps between amino acids 645 and 993, whereas AP-20, AP-14, and AP-25 map between amino acids 995 and 1332. Expression of the region of MAP-2 between amino acids 1787 and 1824 was positive to tau 46.

Cytoskeletal alterations in human fetal astrocytes induced by interleukin-1 beta.

Previous studies in this and other laboratories have shown that interleukin-1 beta (IL-1 beta) is a selective and potent activator of human astrocytes with respect to induction of cytokines and hematopoietic growth factors. To study the effect of recombinant human IL-1 beta (rhIL-1 beta) on astrocyte morphology, glial fibrillary acidic protein (GFAP) and vimentin expression, and actin organization, we conducted a systematic survey using dissociated human fetal astrocyte cultures. Within hours of stimulation with IL-1 beta, the majority of astrocytes converted from flat, polygonal cells to small, contracted, highly branched cells. This change in morphology was more striking when serum was eliminated from the medium. Complete dissolution of filamentous actin occurred simultaneously with the change in cell shape, as demonstrated by fluorescein-phalloidin binding. These "activated" astrocytes displayed intense GFAP and vimentin immunoreactivity in the small perikarya and processes. In contrast, the large, flat astrocytes in control cultures showed diffuse pale immunoreactivity for GFAP and vimentin. To quantify the changes in GFAP and vimentin content with IL-1 beta stimulation, densitometric analyses of northern and western blots were performed. Northern blot analysis of IL-1 beta-stimulated astrocytes revealed a transient, marked decrease in steady-state levels of mRNA for GFAP, vimentin, and microtubule-associated protein 4. The decrease in mRNA levels was evident by 4-8 h and fell to the lowest level at 16-24 h (80-98% decrease by densitometry) with partial recovery by 72 h. By immunoblotting, a significant decrease in both GFAP and vimentin protein content was observed after IL-1 beta stimulation. Furthermore, metabolic labeling studies revealed an almost total loss of GFAP synthesis following stimulation with IL-1 beta for 16 h. These observations are consistent with the idea that increases in immunoreactivity were related to factors such as redistribution of epitope, rather than increases in total protein content. We hypothesize that in IL-1 beta-stimulated astrocytes, synthesis of other proteins, e.g., inflammatory cytokines, occurs at the expense of structural proteins and that the decrease in content of cytoskeletal proteins may reflect an "activated" state of astrocytes.

Antisense MAP-2 oligonucleotides induce changes in microtubule assembly and neuritic elongation in pre-existing neurites of rat cortical neurons.

Microtubule-associated protein 2 (MAP-2) is an abundant component of the cytoskeleton present in dendrites and cell bodies of neurons of the CNS. To examine the biological function of MAP-2, two MAP-2 antisense (AS) oligonucleotides complementary to the 5' region of the rat MAP-2 cDNA were added to rat primary embryonic day 17-18 (E17-18) cultured cortical neurons 24 h after plating and neurite outgrowth and morphology studied. The treatment of primary cortical cultures with either of the two MAP-2 AS oligonucleotides resulted in decreased MAP-2 and reduction in the number of neuritic processes relative to the control or MAP-2 sense-treated cultures. By immunostaining and light microscopy the AS-treated neurons appeared smaller, more rounded, and less intensely stained for MAP-2 than the untreated or the MAP-2 sense-treated cultures. By electron microscopy disorganized microtubules and a reduction in the number of microtubules within neurites of the AS-treated cultures were observed. We conclude that MAP-2 continues to be required for microtubule spacing and stability within neurites once they have formed.

Characterization of the transcripts encoding two isoforms of human microtubule-associated protein-2 (MAP-2).

Through the isolation of a series of overlapping clones from human fetal and adult cDNA libraries, we have generated the complete cDNA sequences encoding human high- and low-molecular-weight microtubule-associated protein-2 (MAP-2) which have strong sequence homology with rodent MAP-2.

Okadaic acid induces early changes in microtubule-associated protein 2 and tau phosphorylation prior to neurodegeneration in cultured cortical neurons.

Microtubules and their associated proteins play a prominent role in many physiological and morphological aspects of brain function. Abnormal deposition of the microtubule-associated proteins (MAPs), MAP2 and tau, is a prominent aspect of Alzheimer's disease. MAP2 and tau are heat-stable phosphoproteins subject to high rates of phosphorylation/dephosphorylation. The phosphorylation state of these proteins modulates their affinity for tubulin and thereby affects the structure of the neuronal cytoskeleton. The dinoflagellate toxin okadaic acid is a potent and specific inhibitor of protein phosphatases 1 and 2A. In cultured rat cortical neurons and a human neuroblastoma cell line (MSN), okadaic acid induces increased phosphorylation of MAP2 and tau concomitant with early changes in the neuronal cytoskeleton and ultimately leads to cell death. These results suggest that the diminished rate of MAP2 and tau dephosphorylation affects the stability of the neuronal cytoskeleton. The effect of okadaic acid was not restricted to neurons. Astrocytes stained with antibodies to glial fibrillary acidic protein (GFAP) showed increased GFAP staining and changes in astrocyte morphology from a flat shape to a stellate appearance with long processes.

CSF-1 expression is upregulated in astrocyte cultures by IL-1 and TNF and affects microglial proliferation and morphology in organotypic cultures.

Astrocytes produce factors that control the growth and differentiation of many cell types within the CNS as well as play a role in the generation of the immune response. The extent to which these two functions interact has received less attention. We now report that astrocyte cultures established from rat brain endogenously express mRNA and low levels of secreted biologically active protein for the monocyte growth and differentiation factor colony stimulating factor-1 (CSF-1). Exposure of astrocytes to interleukin-1 (IL-1) and/or tumor necrosis factor (TNF) upregulated the expression of CSF-1 mRNA and protein. Following treatment with 100 U/ml of TNF, IL-1, or TNF+IL-1, maximum CSF-1 mRNA expression was observed at 3 hr. In the presence of IL-1 an increase in biologically active CSF-1 was detected in the astrocyte conditioned medium at 6 hr. These data indicate that the expression of CSF-1 by astrocytes can be modulated by exposure to the cytokines IL-1 and TNF. To determine whether CSF-1 provides a mitogenic signal for microglia during development, mouse spinal cord organotypic cultures were exposed to recombinant mouse CSF-1 (rmCSF-1), resulting in proliferation of microglia by 7 days and an increase in the number of ramified microglia over ameboid microglia by 14 days.