Biomedical subjects

Eva L Feldman

Publications and source records attributed to Eva L Feldman.

47 records · Page 3Linked to original sources

PubMed2002

N-Myc and Bcl-2 coexpression induces MMP-2 secretion and activation in human neuroblastoma cells.

Neuroblastoma is a peripheral nervous system tumor that accounts for 8-10% of all solid childhood tumors. N-Myc is the most reliable prognostic indicator for neuroblastoma. Bcl-2 is detected in 40-60% of primary neuroblastoma tumors and demonstrates anti-apoptotic action by conferring resistance to chemotherapy and radiation treatment. In neuroblastoma cell lines, the coexpression of N-Myc and Bcl-2 leads to increased tumorigenic properties. Matrix metalloproteinases (MMPs) are endopeptidases that degrade a wide range of basement membrane components, a process important for tumor invasion. This study investigates the effect of N-Myc and Bcl-2 on MMP expression and activation. MMP-2 expression and secretion are increased in SHEP neuroblastoma cells expressing Bcl-2 alone (SHEP/Bcl-2 cells) or both N-Myc and Bcl-2 (SHEP/N-Myc/Bcl-2 cells). MMP-2 activity is increased in the SHEP/N-Myc/Bcl-2 cells yet remains unchanged in SHEP/Bcl-2 cells. TIMP-2 expression is high in SHEP/Bcl-2 cells, which likely inhibits MMP-2 activity, and absent in SHEP/N-Myc/Bcl-2 cells, allowing MMP-2 activity. Invasion is increased in SHEP/N-Myc/Bcl-2 cells and prevented by the use of a pharmacologic MMP-2 inhibitor. These data imply that N-Myc and Bcl-2 cooperate to increase the expression, secretion, and activation of MMP-2, which likely leads to a more tumorigenic phenotype due to increased MMP-2 mediated invasion.

Blotting, Western↗

PubMed2002

Insulin-like growth factor I prevents mannitol-induced degradation of focal adhesion kinase and Akt.

In our laboratory, we are interested in hyperosmolarity-induced apoptosis in neuronal cells. We have shown that high concentrations of glucose or mannitol induce apoptotic cell death in dorsal root ganglia in culture and in SH-SY5Y and SH-EP human neuroblastoma cells. Focal adhesion kinase (FAK) is a cytoplasmic tyrosine kinase that has a critical role for transmitting integrin-mediated-signals. In this study, we report that hyperosmolar treatment mediates FAK dephosphorylation and cleavage, which is prevented by insulin-like growth factor I (IGF-I) treatment. Mannitol treatment of SH-EP cells transfected with vector (SH-EP/pSFFV) results in concentration- and time-dependent dephosphorylation and degradation of FAK. Dephosphorylation and degradation of FAK are tightly correlated with apoptotic morphological changes, including the disruption of actin stress fibers, the loss of focal adhesion sites, membrane blebbing, and cell detachment. Treatment of SH-EP/pSFFV cells with IGF-I or transfection of IGF-I receptor prevents these changes. Treatment of cells with pharmacologic inhibitors of the mitogen-activated protein kinase or phosphatidylinositol 3-kinase pathways does not affect mannitol-induced FAK dephosphorylation and degradation. However, phosphatidylinositol 3-kinase is necessary for IGF-I-mediated protection against FAK alteration. Mannitol treatment also results in the degradation of Akt. Mannitol induces the activation of caspases-3 and -9 in a time course similar to the dephosphorylation and degradation of FAK. Treatment of the cells with ZVAD, a general caspase inhibitor, blocks the mannitol-induced FAK and Akt degradation as well as cell detachment and apoptosis. These results suggest that one of the pathways of mannitol-mediated apoptosis is through the degradation of FAK and Akt and that IGF-I protects the cells from apoptosis by blocking the activation of caspases, which may be responsible for the loss of FAK and Akt.

Apoptosis↗

PubMed2002

Schwann cell caveolin-1 expression increases during myelination and decreases after axotomy.

The caveolins are a family of related proteins that form the structural framework of caveolae. They have been implicated in the regulation of signal transduction, cell cycle control, and cellular transport processes, particularly cholesterol trafficking. Caveolin-1 is expressed by a variety of cell types, including Schwann cells, although its expression is greatest in differentiated cell types, such as endothelial cells and adipocytes. In the present work, we characterize caveolin-1 expression both during rat sciatic nerve development and after axotomy. Schwann cells express little caveolin-1 on postnatal days 1 and 6. By P30, myelinating Schwann cells express caveolin-1, which is localized in the outer/abaxonal myelin membranes as well as intracellularly. After axotomy, Schwann cell caveolin-1 expression in the distal nerve stump decreases as Schwann cells revert to a premyelinating (p75-positive) phenotype; residual caveolin-1 within the nerve largely localizes to myelin debris and infiltrating macrophages. We speculate that caveolin-1 plays a role in the biology of myelinating Schwann cells.

Aging↗

PubMed2002

Control of cell survival by IGF signaling pathways.

The insulin-like growth factor system efficiently signals to cells to grow, differentiate, and survive. One central player in the prevention of cell death is the IGF-I receptor. Transduction of signals through this receptor leads to multiple series of intracellular phosphorylation events and the activation of several signaling pathways. Mechanisms of IGF system signaling that prevent cell death continue to be identified, suggesting that cells have alternative ways to avert death signals in addition to primary protective pathways. This review describes current knowledge of the mechanisms utilized by the IGF system to promote cell survival.

Animals↗

PubMed2002

Signaling mechanisms that regulate actin-based motility processes in the nervous system.

Actin-based motility is critical for nervous system development. Both the migration of neurons and the extension of neurites require organized actin polymerization to push the cell membrane forward. Numerous extracellular stimulants of motility and axon guidance cues regulate actin-based motility through the rho GTPases (rho, rac, and cdc42). The rho GTPases reorganize the actin cytoskeleton, leading to stress fiber, filopodium, or lamellipodium formation. The activity of the rho GTPases is regulated by a variety of proteins that either stimulate GTP uptake (activation) or hydrolysis (inactivation). These proteins potentially link extracellular signals to the activation state of rho GTPases. Effectors downstream of the rho GTPases that directly influence actin polymerization have been identified and are involved in neurite development. The Arp2/3 complex nucleates the formation of new actin branches that extend the membrane forward. Ena/VASP proteins can cause the formation of longer actin filaments, characteristic of growth cone actin morphology, by preventing the capping of barbed ends. Actin-depolymerizing factor (ADF)/cofilin depolymerizes and severs actin branches in older parts of the actin meshwork, freeing monomers to be re-incorporated into actively growing filaments. The signaling mechanisms by which extracellular cues that guide axons to their targets lead to direct effects on actin filament dynamics are becoming better understood.

Actins↗

PubMed2002

High glucose-induced oxidative stress and mitochondrial dysfunction in neurons.

The current study examines the association between glucose induction of reactive oxygen species (ROS), mitochondrial (Mt) depolarization, and programmed cell death in primary neurons. In primary dorsal root ganglion (DRG) neurons, 45 mM glucose rapidly induces a peak rise in ROS corresponding to a 50% increase in mean Mt size at 6 h (P<0.001). This is coupled with loss of regulation of the Mt membrane potential (Mt membrane hyperpolarization, followed by depolarization, MMD), partial depletion of ATP, and activation of caspase-3 and -9. Glucose-induced activation of ROS, MMD, and caspase-3 and -9 activation is inhibited by myxothiazole and thenoyltrifluoroacetone (P<0.001), which inhibit specific components of the Mt electron transfer chain. Similarly, MMD and caspase-3 activation are inhibited by 100 microM bongkrekic acid (an inhibitor of the adenosine nucleotide translocase ANT). These results indicate that mild increases in glucose induce ROS and Mt swelling that precedes neuronal apoptosis. Glucotoxicity is blocked by inhibiting ROS induction, MMD, or caspase cleavage by specific inhibitors of electron transfer, or by stabilizing the ANT.

Adenosine Diphosphate↗

PubMed2002

Update on diabetic neuropathy.

PURPOSE OF REVIEW: This review will focus on recent advances in the field of diabetic neuropathy, with an emphasis on distal symmetric sensory and sensorimotor polyneuropathy. Some new information in the areas of diabetic amyotrophy and diabetic autonomic neuropathy will also be reviewed. RECENT FINDINGS: The pathogenesis of diabetic neuropathy is multifactorial. There is increasing evidence to link abnormalities in the polyol pathway to the pathogenesis of diabetic neuropathy. In addition, there appear to be abnormalities of nerve regeneration and of sodium and calcium channels. Aldose reductase inhibitors have shown promise in animal models for reversing neuropathy if started early and used for a sufficient time, but those used to date in human trials are probably not of sufficient potency. Neurotrophic factors and vascular endothelial growth factor both also show promise. Specific recommendations and pathways for diabetic foot care have been devised. Lamotrigine and bupropion represent new treatments for neuropathic pain. The role of impaired glucose tolerance is being explored as it relates to polyneuropathy. SUMMARY: An increasing understanding of the pathogenetic mechanisms holds out promise for the effective treatment of diabetic neuropathy. The early detection of abnormal glucose metabolism is particularly important, as treatments will probably be most effective if administered early in the course of the neuropathy, when abnormalities of peripheral nerves are more likely to be reversible.

Diabetic Foot↗

PubMed2002

Neuronal survival following remote adenovirus gene delivery.

OBJECT: Virus-mediated central nervous system gene delivery is a promising means of treating traumatized tissue or degenerative diseases. In the present study, the authors examined gene expression and neuronal survival in the spinal cord after sciatic nerve administration of an adenovirus vector expressing a LacZ reporter gene. METHODS: The time course of adenovirus gene expression, DNA fragmentation, and neuronal density were quantified in rat lumbar spinal cord by staining for beta-galactosidase (beta-Gal), terminal deoxynucleotidyl transferase, and cresyl violet after microinjection of either saline or the reporter virus into rat sciatic nerve. The expression of beta-Gal following remote vector delivery peaked at 7 days and declined thereafter but was not accompanied by neuronal cell death, as measured by DNA fragmentation. No significant difference in spinal motor neuron density was detected between virus-treated and control rats at any time point examined. Although the spinal cords removed from rats treated with cyclosporine prior to adenovirus injection contained substantially more neurons staining for beta-Gal at 7 days (67% of total neurons), the decay in the number of stained neurons was not paralleled by a decline in motor neuron density. CONCLUSIONS: The authors conclude that remote gene expression is suppressed by a noncytolytic process.

Adenoviridae↗

PubMedDate not supplied

Degradation and dephosphorylation of focal adhesion kinase during okadaic acid-induced apoptosis in human neuroblastoma cells.

Focal adhesion kinase (FAK) prevents apoptosis in many cell types. We have reported that tyrosine residues in FAK are dephosphorylated and FAK is degraded during mannitol-induced apoptosis in human neuroblastoma cells. Several studies suggest that FAK dephosphorylation and degradation are separate events. The current study defines the relationship between FAK dephosphorylation and degradation in neuroblastoma cells using okadaic acid (OA). OA, a serine phosphatase inhibitor, promotes serine/threonine phosphorylation, which in turn blocks tyrosine phosphorylation. OA induced focal adhesion loss, actin cytoskeleton disorganization, and cellular detachment, which corresponded to a loss of FAK Tyr397 phosphorylation. These changes preceded caspase-3 activation, Akt and MAP kinase activity loss, protein ubiquitination, and cellular apoptosis. Insulin-like growth factor-I prevented mannitol-induced, but not OA-induced, substrate detachment and FAK Tyr397 dephosphorylation, and the effects of OA on FAK Tyr397 phosphorylation were irreversible. The proteolytic degradation of FAK is temporally distinct from its tyrosine dephosphorylation, occurring when apoptotic pathways are already initiated and during a generalized destruction of signaling proteins. Therefore, agents resulting in the dephosphorylation of FAK may be beneficial for therapeutic treatment, irrespective of FAK protein levels, as this may result in apoptosis, which cannot be prevented by growth factor signaling.

Apoptosis↗

PubMedDate not supplied

Cell culture modeling to test therapies against hyperglycemia-mediated oxidative stress and injury.

The concept that oxidative stress is a key mediator of nerve injury in diabetes has led us to design therapies that target oxidative stress mechanisms. Using an in vitro model of glucose-treated dorsal root ganglion (DRG) neurons in culture, we can examine both free radical generation, using fluorimetric probes for reactive oxygen species, and cell death via the TUNEL assay. The cell culture system is scaled down to a 96-well plate format, and so is well suited to high-throughput screening. In the present study, we test the ability of three drugs, nicotinamide, allopurinol, and alpha-lipoic acid, alone and in combination to prevent DRG neuron oxidative stress and cell death. This combination of drugs is currently in clinical trial in type 1 diabetic patients. We demonstrate independent effects on oxidative stress and neuronal survival for the three drugs, and neuronal protection using the three drugs in combination. The data strengthen the rationale for the current clinical trial. In addition, we describe an effective tool for rapid preclinical testing of novel therapies against diabetic neuropathy.

Animals↗

PubMedDate not supplied

Integrin expression regulates neuroblastoma attachment and migration.

Neuroblastoma (NBL) is the most common malignant disease of infancy, and children with bone metastasis have a mortality rate greater than 90%. Two major classes of proteins, integrins and growth factors, regulate the metastatic process. We have previously shown that tumorigenic NBL cells express higher levels of the type I insulin-like growth factor receptor (IGF-IR) and that beta1 integrin expression is inversely proportional to tumorigenic potential in NBL. In the current study, we analyze the effect of beta1 integrin and IGF-IR on NBL cell attachment and migration. Nontumorigenic S-cells express high levels of beta1 integrin, whereas tumorigenic N-cells express little beta1 integrin. Alterations in beta1 integrin are due to regulation at the protein level, as translation is decreased in N-type cells. Moreover, inhibition of protein synthesis shows that beta1 integrin is degraded more slowly in S-type cells (SHEP) than in N-type cells (SH-SY5Y and IMR32). Inhibition of alpha5beta1 integrin prevents SHEP (but not SH-SY5Y or IMR32) cell attachment to fibronectin and increases SHEP cell migration. Increases in IGF-IR decrease beta1 integrin expression, and enhance SHEP cell migration, potentially through increased expression of alphavbeta3. These data suggest that specific classes of integrins in concert with IGF-IR regulate NBL attachment and migration.

Cell Adhesion↗