cell-death-associated-with-abnormal-mitosis-observed-confocal-imaging

Cell Death Associated with Abnormal Mitosis Observed by Confocal Imaging in Live Cancer Cells

Phenanthrene derivatives acting as potent PARP1 inhibitors prevented the bi-focal clustering of supernumerary centrosomes in multi-centrosomal human ...

Tel-Aviv University

Cells of most human cancers have supernumerary centrosomes. To enable an accurate chromosome segregation and cell division, these cells developed a yet unresolved molecular mechanism, clustering their extra centrosomes at two poles, thereby mimicking mitosis in normal cells. Failure of this bipolar centrosome clustering causes multipolar spindle structures and aberrant chromosomes segregation that prevent normal cell division and lead to 'mitotic catastrophe cell death'.

A phenanthrene derived PARP inhibitor is an extra-centrosomes de-clustering agent exclusively eradicating human cancer cells.

Spermatogenesis consists of spermatogonial proliferation, meiosis and spermatid differentiation. Laser scanning confocal microscopy (LSCM) may be used as an advanced analytical tool to follow spermatogenesis inside the seminiferous tubules without performing histological sections. For this purpose, separated seminiferous tubules are fixed in 0.5% paraformaldehyde, stained for DNA with propidium iodide and analyzed by LSCM. By producing longitudinal optical sections in the layer of spermatogonia, spermatocytes and spermatids, stage-specific changes in their structure may be followed within the tubules by LSCM. Longitudinal z-sections may be obtained to produce three-dimensional images of the seminiferous tubules. In addition, different proteins may be followed during spermatogenesis in a stage specific manner within the tubule by incubation of the fixed seminiferous tubules with appropriate antibodies. As an example of the spermatogenesis studies using described LSCM techniques, detailed examination of spermatogonia, spermatocytes and spermatids during golden hamster spermatogenesis is presented. LSCM analysis of c-kit and SC3 protein expression at different stages of hamster spermatogenesis is demonstrated.

Use of confocal microscopy for the study of spermatogenesis.

Hepatocyte growth factor/scatter factor (HGF/SF) binds to its tyrosine kinase receptor, Met, thereby stimulating diverse cellular responses. The multifunctional docking site in the C-terminal domain mediates the signal of phosphorylated Met receptors to multiple transducers. The tyrosine at position 1356 of the Met docking site is crucial for cell motility and morphogenesis.

In situ activation pattern of Met docking site following renal injury and hypertrophy.

The ATM protein kinase is a primary activator of the cellular response to DNA double-strand breaks (DSBs). In response to DSBs, ATM is activated and phosphorylates key players in various branches of the DNA damage response network. ATM deficiency causes the genetic disorder ataxia-telangiectasia (A-T), characterized by cerebellar degeneration, immunodeficiency, radiation sensitivity, chromosomal instability and cancer predisposition. The MRN complex, whose core contains the Mre11, Rad50 and Nbs1 proteins, is involved in the initial processing of DSBs. Hypomorphic mutations in the NBS1 and MRE11 genes lead to two other genomic instability disorders: the Nijmegen breakage syndrome (NBS) and A-T like disease (A-TLD), respectively. The order in which ATM and MRN act in the early phase of the DSB response is unclear. Here we show that functional MRN is required for ATM activation, and consequently for timely activation of ATM-mediated pathways. Collectively, these and previous results assign to components of the MRN complex roles upstream and downstream of ATM in the DNA damage response pathway and explain the clinical resemblance between A-T and A-TLD.

Requirement of the MRN complex for ATM activation by DNA damage.

An octapeptide was previously described that protects neurons against a wide variety of insults directly and indirectly as a result of interactions (at femtomolar concentrations) with supporting glial cells. The current study set out to identify the octapeptide binding molecules so as to understand the high affinity mechanisms of cellular protection. Studies utilizing affinity chromatography of brain extracts identified tubulin, the brain major protein, as the octapeptide-binding ligand. Dot blot analysis with pure tubulin and the biotinylated octapeptide verified this finding. When added to cerebral cortical astrocytes, the octapeptide (10(-15)-10(-10) m) induced a rapid microtubule reorganization into distinct microtubular structures that were stained by monoclonal tubulin antibodies and visualized by confocal microscopy. Fluorescein-labeled octapeptide induced a similar change and was detected in the intracellular milieu, even when cells were incubated at 4 degrees C or at low pH. In a cell-free system, the octapeptide stimulated tubulin assembly into microtubules. Furthermore, treatment of astrocytes with zinc chloride resulted in microtubule disassembly and cell death that was protected by the octapeptide. In conclusion, the results suggest that the octapeptide crosses the plasma membrane and interacts directly with tubulin, the microtubule subunit, to induce microtubule reorganization and improved survival. Because microtubules are the key component of the neuronal and glial cytoskeleton that regulates cell division, differentiation, and protection, this finding may explain the breadth and efficiency of the cellular protective capacities of the octapeptide.

A femtomolar acting octapeptide interacts with tubulin and protects astrocytes against zinc intoxication.

Aspergillus fumigatus is an opportunistic pathogenic fungus that predominantly infects the respiratory system. Penetration of the lung alveolar epithelium is a key step in the infectious process. The cytoskeleton of alveolar epithelial cells forms the cellular basis for the formation of a physical barrier between the cells and their surroundings. This study focused on the distinct effects of A. fumigatus on the actin cytoskeleton of A549 lung pneumocytes. Of the 3 major classes of cytoskeletal fibers--actin microfilaments, microtubules, and intermediate filaments--only the actin cytoskeleton was found to undergo major structural changes in response to infection, including loss of actin stress fibers, formation of actin aggregates, disruption of focal adhesion sites, and cell blebbing. These changes could be specifically blocked in wild-type strains of A. fumigatus by the addition of antipain, a serine and cysteine protease inhibitor, and were not induced by an alkaline serine protease-deficient strain of A. fumigatus. Antipain also reduced, by approximately 50%, fungal-induced A549 cell detachment from the plates and reduction in viability. Our findings suggest that A. fumigatus breaches the alveolar epithelial cell barrier by secreting proteases that act together to disorganize the actin cytoskeleton and destroy cell attachment to the substrate by disrupting focal adhesions.

Involvement of secreted Aspergillus fumigatus proteases in disruption of the actin fiber cytoskeleton and loss of focal adhesion sites in infected A549 lung pneumocytes.

The protein kinase ATM (ataxia-telangiectasia mutated) activates the cellular response to double strand breaks (DSBs), a highly cytotoxic DNA lesion. ATM is activated by DSBs and in turn phosphorylates key players in numerous damage response pathways. ATM is missing or inactivated in the autosomal recessive disorder ataxia-telangiectasia (A-T), which is characterized by neuronal degeneration, immunodeficiency, genomic instability, radiation sensitivity, and cancer predisposition. The predominant symptom of A-T is a progressive loss of movement coordination due to ongoing degeneration of the cerebellar cortex and peripheral neuropathy. A major deficiency in understanding A-T is the lack of information on the role of ATM in neurons. It is unclear whether the ATM-mediated DSB response operates in these cells similarly to proliferating cells. Furthermore, ATM was reported to be cytoplasmic in neurons and suggested to function in these cells in capacities other than the DNA damage response. Recently we obtained genetic molecular evidence that the neuronal degeneration in A-T does result from defective DNA damage response. We therefore undertook to investigate this response in a model system of human neuron-like cells (NLCs) obtained by neuronal differentiation in culture. ATM was largely nuclear in NLCs, and their ATM-mediated responses to DSBs were similar to those of proliferating cells. Knocking down ATM did not interfere with neuronal differentiation but abolished ATM-mediated damage responses in NLCs. We concluded that nuclear ATM mediates the DSB response in NLCs similarly to in proliferating cells. Attempts to understand the neurodegeneration in A-T should be directed to investigating the DSB response in the nervous system.

Nuclear ataxia-telangiectasia mutated (ATM) mediates the cellular response to DNA double strand breaks in human neuron-like cells.

Mitotic cell death (MCD) is a prominent but poorly defined form of death that stems from aberrant mitosis. One of the early steps in MCD is premature mitosis and uneven chromatin condensation (UCC). The mechanism underlying this phenomenon is currently unknown. In this study, we show that DNA damage in cells with a compromised p53-mediated G2/M checkpoint triggers the unscheduled activation of cyclin-dependent kinase 1 (Cdk1), activation and chromatin loading of the condensin I complex, and UCC followed by the appearance of multimicronucleated cells, which is evidence of MCD. We demonstrate that these processes engage some of the players of normal mitotic chromatin packaging but not those that drive the apoptotic chromatin condensation. Our findings establish a link between the induction of DNA damage and mitotic abnormalities (UCC) through the unscheduled activation of Cdk1 and recruitment of condensin I. These results demonstrate a clear distinction between the mechanisms that drive MCD-associated and apoptosis-related chromatin condensation and provide mechanistic insights and new readouts for a major cell death process in treated tumors.

Condensin I recruitment and uneven chromatin condensation precede mitotic cell death in response to DNA damage.

The p53 tumor suppressor plays a major role in maintaining genomic stability. Its activation and stabilization in response to double strand breaks (DSBs) in DNA are regulated primarily by the ATM protein kinase. ATM mediates several posttranslational modifications on p53 itself, as well as phosphorylation of p53's essential inhibitors, Hdm2 and Hdmx. Recently we showed that ATM- and Hdm2-dependent ubiquitination and subsequent degradation of Hdmx following DSB induction are mediated by phosphorylation of Hdmx on S403, S367, and S342, with S403 being targeted directly by ATM. Here we show that S367 phosphorylation is mediated by the Chk2 protein kinase, a downstream kinase of ATM. This phosphorylation, which is important for subsequent Hdmx ubiquitination and degradation, creates a binding site for 14-3-3 proteins which controls nuclear accumulation of Hdmx following DSBs. Phosphorylation of S342 also contributed to optimal 14-3-3 interaction and nuclear accumulation of Hdmx, but phosphorylation of S403 did not. Our data indicate that binding of a 14-3-3 dimer and subsequent nuclear accumulation are essential steps toward degradation of p53's inhibitor, Hdmx, in response to DNA damage. These results demonstrate a sophisticated control by ATM of a target protein, Hdmx, which itself is one of several ATM targets in the ATM-p53 axis of the DNA damage response.

Differential roles of ATM- and Chk2-mediated phosphorylations of Hdmx in response to DNA damage.

Ataxia-telangiectasia (A-T) is a multi-system genomic instability syndrome that is caused by loss or inactivation of the ATM protein kinase. ATM is largely nuclear in proliferating cells, and activates an extensive network of pathways in response to double strand breaks (DSBs) in the DNA by phosphorylating key proteins in these pathways. The prominent symptom of A-T is neuronal degeneration, making the elucidation of ATM's functions in neurons essential to understanding the disease. It has been suggested that ATM is cytoplasmic in neurons and functions in processes that are not associated with the DNA damage response. Recently we showed that in human neuron-like cells obtained by in vitro differentiation of neuroblastomas, ATM was largely nuclear and mediated the DSB response as in proliferating cells. We have now extended these studies to two additional model systems: neurons derived from human embryonic stem cells, and cortical neurons derived from neural stem cells. The results substantiate the notion that ATM is nuclear in human neurons and mediates the DSB response, the same as it does in proliferating cells. We present here unique and powerful model systems to further study the ATM-mediated network in neurons.

ATM-mediated response to DNA double strand breaks in human neurons derived from stem cells.

The nuclear protein PARP-1 [poly(ADP-ribose) polymerase-1] is activated in cardiomyocytes exposed to hypoxia causing DNA breaks. Unlike this stress-induced PARP-1 activation, our results provide evidence for Ca(2+)-induced PARP-1 activation in contracting newborn cardiomyocytes treated with growth factors and hormones that increased their contraction rate, induced intracellular Ca(2+) mobilization and its rhythmical and transient translocation into the nucleus. Furthermore, activated PARP-1 up-regulated the activity of phosphorylated ERK (extracellular-signal-regulated kinase) in the nucleus, promoting expression of the Elk1 target gene c-fos. Up-regulation of the transcription factor c-Fos/GATA-4 promoted ANF (atrial natriuretic factor) expression. Given that expression of ANF is known to be implicated in morphological changes, growth and development of cardiomyocytes, these results outline a PARP-1-dependent signal transduction mechanism that links contraction rate and Ca(2+) mobilization with the expression of genes underlying morphological changes in cardiomyocytes.

Ca2+-induced PARP-1 activation and ANF expression are coupled events in cardiomyocytes.

The use of artificial, prepatterned neuronal networks in vitro is a promising approach for studying the development and dynamics of small neural systems in order to understand the basic functionality of neurons and later on of the brain. The present work presents a high fidelity and robust procedure for controlling neuronal growth on substrates such as silicon wafers and glass, enabling us to obtain mature and durable neural networks of individual cells at designed geometries. It offers several advantages compared to other related techniques that have been reported in recent years mainly because of its high yield and reproducibility. The procedure is based on surface chemistry that allows the formation of functional, tailormade neural architectures with a micrometer high-resolution partition, that has the ability to promote or repel cells attachment. The main achievements of this work are deemed to be the creation of a large scale neuronal network at low density down to individual cells, that develop intact typical neurites and synapses without any glia-supportive cells straight from the plating stage and with a relatively long term survival rate, up to 4 weeks. An important application of this method is its use on 3D nanopillars and 3D nanowire-device arrays, enabling not only the cell bodies, but also their neurites to be positioned directly on electrical devices and grow with registration to the recording elements underneath.

Highly Ordered Large-Scale Neuronal Networks of Individual Cells - Toward Single Cell to 3D Nanowire Intracellular Interfaces.

The cerebellum is exquisitely sensitive to deficiencies in the cellular response to specific DNA lesions. Genetic disorders caused by such deficiencies involve relentless, progressive cerebellar atrophy with striking loss of Purkinje and granule neurons. The reason for the extreme sensitivity of these cells to defective response to certain DNA lesions is unclear. This is particularly true for ataxia-telangiectasia (A-T) - a genomic instability syndrome whose major symptom is cerebellar atrophy. It is important to understand whether the DNA damage response in the cerebellum, particularly in Purkinje neurons, has special characteristics that stem from the unique features of these cells. Murine cerebellar organotypic cultures provide a valuable experimental system for this purpose since they retain the tissue organization for several weeks in culture and appear to provide the delicate Purkinje neurons with a physiological environment close to that in vivo. We have optimized this system and are using it to examine the Atm-mediated DNA damage response (DDR) in the cerebellum, with special emphasis on Purkinje cells. Our results to date, which indicate special chromatin organization in Purkinje cells that affects certain pathways of the DDR, demonstrate the usefulness of cerebellar organotypic cultures for addressing the above questions.

Leonid Mittelman

Imaging Unit,
Sackler Faculty of Medicine,
Imaging Unit, Sackler Faculty of Medicine

Tel-Aviv University

Cell Death Associated with Abnormal Mitosis Observed by Confocal Imaging in Live Cancer Cells

Leonid Mittelman

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Tel-Aviv University

Cell Death Associated with Abnormal Mitosis Observed by Confocal Imaging in Live Cancer Cells

Imaging Unit,
Sackler Faculty of Medicine,
Imaging Unit, Sackler Faculty of Medicine