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Biomedical subjects

S Lev

Publications and source records attributed to S Lev.

At least 19 recordsLinked to original sources
PubMed2006

Lipid homoeostasis and Golgi secretory function.

The unique lipid composition of the Golgi membranes is critical for maintaining their structural and functional identity, and is regulated by local lipid metabolism, a variety of lipid-binding, -modifying, -sensing and -transfer proteins, and by selective lipid sorting mechanisms. A growing body of evidence suggests that certain lipids, such as phosphoinositides and diacylglycerol, regulate Golgi-mediated transport events. However, their exact role in this process, and the underlying mechanisms that maintain their critical levels in specific membrane domains of the Golgi apparatus, remain poorly understood. Nevertheless, recent advances have revealed key regulators of lipid homoeostasis in the Golgi complex and have demonstrated their role in Golgi secretory function.

Animals↗
PubMed2005

Close association between valvar heart disease and central nervous system manifestations in the antiphospholipid syndrome.

BACKGROUND: Heart valves lesions and central nervous system involvement are among the most common manifestations of the antiphospholipid syndrome (APS). OBJECTIVE: To evaluate possible interrelations between these manifestations in a large group of APS patients. METHODS: 284 APS patients were evaluated retrospectively, 159 of whom had primary APS. Cardiac-CNS associations were determined for the entire study population, and for subgroups of patients with primary APS or APS associated with systemic lupus erythematosus (SLE). RESULTS: Significant associations where found between cardiac vegetations and epilepsy (p < 0.02), and between cardiac valve thickening or dysfunction and migraine (p = 0.002). Borderline association was found between valvar vegetations and migraine (p = 0.09). A significant association was also found between all valvar lesions and stroke or transient ischaemic attacks. Subanalyses showed that patients with primary APS had significant associations between cardiac valve pathology and all CNS manifestations, while patients with APS associated with SLE had no such associations. CONCLUSIONS: The study suggests potential differences in biological behaviour between primary APS and APS associated with SLE. The presence of cardiac valve pathology may be a risk factor for several types of CNS involvement in PAPS.

Adolescent↗
PubMed2003

Prevalence and clinical correlations of antibodies against six beta2-glycoprotein-I-related peptides in the antiphospholipid syndrome.

Two-hundred ninety five patients with the antiphospholipid syndrome (APS) were studied for the presence of antibodies against six anti-beta2GPI-related peptides Abs. The prevalence of a wide spectrum of clinical and laboratory parameters of APS was evaluated in all patients, and correlated with the presence of each anti-beta2GPI peptide antibody. The rates of the various antipeptides Abs ranged from 18.0 to 63.7%. Altogether, 87.1% of the patients had antibody reactivity against at least one of the six beta2GPI-related peptides. A high degree of simultaneous reactivity against several beta2GPI-peptides was found. Positive and negative correlations were found between several antipeptides Abs and the rates of thrombosis and fetal loss. Our results point to a heterogeneous activity of antiphospholipid Abs in APS patients, directed, often concurrently, against various epitopes of the beta2GPI molecule. Evaluation of APS patients for the presence of specific antipeptides Abs may be of a value in predicting the risk for future thrombotic and obstetrical complication, as well as for specific therapeutic purposes.

Adolescent↗
PubMed2001

Calcium, protease activation, and cytoskeleton remodeling underlie growth cone formation and neuronal regeneration.

The cytoarchitecture, synaptic connectivity, and physiological properties of neurons are determined during their development by the interactions between the intrinsic properties of the neurons and signals provided by the microenvironment through which they grow. Many of these interactions are mediated and translated to specific growth patterns and connectivity by specialized compartments at the tips of the extending neurites: the growth cones (GCs). The mechanisms underlying GC formation at a specific time and location during development, regeneration, and some forms of learning processes, are therefore the subject of intense investigation. Using cultured Aplysia neurons we studied the cellular mechanisms that lead to the transformation of a differentiated axonal segment into a motile GC. We found that localized and transient elevation of the free intracellular calcium concentration ([Ca2+]i) to 200-300 microM induces GC formation in the form of a large lamellipodium that branches up into growing neurites. By using simultaneous on-line imaging of [Ca2+]i and of intraaxonal proteolytic activity, we found that the elevated [Ca2+]i activate proteases in the region in which a GC is formed. Inhibition of the calcium-activated proteases prior to the local elevation of the [Ca2+]i blocks the formation of GCs. Using retrospective immunofluorescent methods we imaged the proteolysis of the submembrane spectrin network, and the restructuring of the cytoskeleton at the site of GC formation. The restructuring of the actin and microtubule network leads to local accumulation of transported vesicles, which then fuse with the plasma membrane in support of the GC expansion.

Animals↗
PubMed2001

Molecular aspects of retinal degenerative diseases.

Retinal degeneration, either acquired or inherited, is a major cause of visual impairment and blindness in humans. Inherited retinal degeneration comprises a large group of diseases that result in the loss of photoreceptor cells. To date, 131 retinal disease loci have been identified, and 76 of the genes at these loci have been isolated (RetNet Web site). Several of these genes were first considered candidates because of their chromosomal localization or homology to genes involved in retinal degeneration in other organisms. In this review, I will discuss recent advances in the identification of genes that cause retinal degeneration, and I will describe the mechanisms of photoreceptor death and potential treatments for retinal degenerative diseases.

Animals↗
PubMed2000

Targeting of PYK2 to focal adhesions as a cellular mechanism for convergence between integrins and G protein-coupled receptor signaling cascades.

The non-receptor tyrosine kinase PYK2 appears to function at a point of convergence of integrins and certain G protein-coupled receptor (GPCR) signaling cascades. In this study, we provide evidence that translocation of PYK2 to focal adhesions is triggered both by cell adhesion to extracellular matrix proteins and by activation of the histamine GPCR. By using different mutants of PYK2 as green fluorescent fusion proteins, we show that the translocation of PYK2 to focal adhesions is not dependent on its catalytic activity but rather is mediated by its carboxyl-terminal domain. Translocation of PYK2 to focal adhesions was attributed to enhanced tyrosine phosphorylation of PYK2 and its association with the focal adhesion proteins paxillin and p130(Cas). Translocation of PYK2 to focal adhesions, as well as its tyrosine phosphorylation in response to histamine treatment, was abolished in the presence of protein kinase C inhibitors or cytochalasin D treatment, whereas activation of protein kinase C by phorbol ester resulted in focal adhesion targeting of PYK2 and its tyrosine phosphorylation in an integrin-clustering dependent manner. Overexpression of a wild-type PYK2 enhanced ERK activation in response to histamine, whereas a kinase-deficient mutant substantially inhibited this response. Furthermore, inhibition of PYK2 translocation to focal adhesions abolished ERK activation in response to histamine treatment. These results suggest that PYK2 apparently links between GPCRs and focal adhesion-dependent ERK activation and can provide the molecular basis underlying PYK2 function at a point of convergence between signaling pathways triggered by extracellular matrix proteins and certain GPCR agonists.

Cell Line↗
PubMed2000

Enhanced activity of a large conductance, calcium-sensitive K+ channel in the presence of Src tyrosine kinase.

Large conductance, calcium-sensitive K(+) channels (BK(Ca) channels) contribute to the control of membrane potential in a variety of tissues, including smooth muscle, where they act as the target effector for intracellular "calcium sparks" and the endothelium-derived vasodilator nitric oxide. Various signal transduction pathways, including protein phosphorylation can regulate the activity of BK(Ca) channels, along with many other membrane ion channels. In our study, we have examined the regulation of BK(Ca) channels by the cellular Src gene product (cSrc), a soluble tyrosine kinase that has been implicated in the regulation of both voltage- and ligand-gated ion channels. Using a heterologous expression system, we observed that co-expression of murine BK(Ca) channel and the human cSrc tyrosine kinase in HEK 293 cells led to a calcium-sensitive enhancement of BK(Ca) channel activity in excised membrane patches. In contrast, co-expression with a catalytically inactive cSrc mutant produced no change in BK(Ca) channel activity, demonstrating the requirement for a functional cSrc molecule. Furthermore, we observed that BK(Ca) channels underwent direct tyrosine phosphorylation in cells co-transfected with BK(Ca) channels and active cSrc but not in cells co-transfected with the kinase inactive form of the enzyme. A single Tyr to Phe substitution in the C-terminal half of the channel largely prevented this observed phosphorylation. Given that cSrc may become activated by receptor tyrosine kinases or G-protein-coupled receptors, these findings suggest that cSrc-dependent tyrosine phosphorylation of BK(Ca) channels in situ may represent a novel regulatory mechanism for altering membrane potential and calcium entry.

Animals↗
PubMed2000

Cerebral ischemia and seizures induce tyrosine phosphorylation of PYK2 in neurons and microglial cells.

The nonreceptor tyrosine kinase PYK2 represents a stress-sensitive mediator of c-Jun N-terminal kinase and p38 mitogen-activated protein kinase (MAPK) signaling pathways in many cell types. In the present study, we assessed the tyrosine phosphorylation of PYK2 under normal and pathological conditions in the CNS. We generated a polyclonal antibody that selectively recognizes tyrosine-phosphorylated PYK2 at its major autophosphorylation site. By using this antibody, we demonstrate that the phosphorylation profile of PYK2 after focal cerebral ischemia is biphasic. The first phase occurs within 1 hr, when most of the phospho-PYK2 immunoreactivity was observed in cortical neurons, whereas 24-72 hr after ischemia, a striking induction of phospho-PYK2 immunoreactivity was evident in microglia around the necrotic infarcted area. Double-immunostaining analysis using both anti-phospho-PYK2 antibody and antibody against the double-phosphorylated active form of p38MAPK revealed that the two phosphorylated protein kinases exhibit strikingly similar distribution patterns after ischemia. A short time after ischemia, phosphorylation of p38MAPK was evident in the cortical neurons as demonstrated by both immunohistochemistry and immunoblotting analysis, whereas 24-72 hr after ischemia, phospho-p38MAPK was found in activated microglia and colocalized with phospho-PYK2. In contrast to cortical neurons, basal phospho-PYK2 immunoreactivity was observed in hippocampal pyramidal neurons, which was markedly decreased after kainate acid-induced status epilepticus. However, 24 hr after the epileptic onset, a pronounced upregulation of PYK2 and phospho-PYK2 immunoreactivities was evident in microglial cells, as demonstrated by double-immunostaining with the microglial marker OX42. These results provide, for the first time, in situ localization of tyrosine-phosphorylated PYK2 in neuronal stress pathways in the adult rat brain and are consistent with the role of PYK2 as an upstream regulator of p38MAPK signaling cascades in response to stress signals.

Animals↗
PubMed2000

Imaging of cystic lesions.

Cystic neck masses are varied in their histology and embryogenesis. Because neural, vascular, and lipomatous lesions may all appear cystic, a multimodality imaging approach can help identify these potential mimics. Developmental neck cysts include thyroglossal duct, thymic, and branchial cleft cysts, and teratomatous lesions or lymphangiomas. Although laryngoceles are acquired lesions, congenital anomalies (e.g., abnormally long saccules) may play a role in their formation. Lesion location is at least as important a determinant as morphology in formulating the differential diagnosis of a cystic neck mass. Midline cystic lesions are most commonly thyroglossal duct cysts, although dermoid tumors are also frequently midline. Squamous cell carcinoma metastatic to anterior triangle lymph nodes (Fig. 17), and cystic, necrotic schwanommas, can mimic the typical appearance of an infected second branchial cleft cyst. Posterior triangle lymphadenopathy and lipomatous lesions may resemble cystic hygromas. Cystic-appearing masses in the carotid space include neurogenic tumors, vascular thromboses, and carotid chain lymphadenopathy. Neural-based lesions typically occur posterolateral to the carotid artery. Necrotic lymphadenopathy may be suggested by lesion multiplicity, or by the presence of ancillary features, such as systemic symptoms, or the existence of a primary tumor. It must be emphasized that the primary role of the radiologist in head and neck imaging is to help stage disease and guide surgery. Despite clinical and radiographic analysis, the diagnosis of many lesions ultimately depends on image-guided or excisional biopsy.

Branchioma↗
PubMed1999

A mitogen-activated protein kinase of the corn leaf pathogen Cochliobolus heterostrophus is involved in conidiation, appressorium formation, and pathogenicity: diverse roles for mitogen-activated protein kinase homologs in foliar pathogens.

Fungal pathogens perceive and respond to molecules from the plant, triggering pathogenic development. Transduction of these signals may use heterotrimeric G proteins, and it is thought that protein phosphorylation cascades are also important. We have isolated a mitogen-activated protein kinase homolog from the corn pathogen Cochliobolus heterostrophus to test its role as a component of the transduction pathways. The new gene, CHK1, has a deduced amino acid sequence 90% identical to Pmk1 of the rice blast fungus Magnaporthe grisea and 59% identical to Fus3 of Saccharomyces cerevisiae. A series of chk1 deletion mutants has poorly developed aerial hyphae, autolysis, and no conidia. No pseudothecia are formed when a cross between two Deltachk1 mutants is attempted. The ability of Deltachk1 mutants to infect corn plants is reduced severely. The growth pattern of hyphae on a glass surface is strikingly altered from that of the wild type, forming coils or loops, but no appressoria. This set of phenotypes overlaps only partially with that of pmk1 mutants, the homologous gene of the rice blast fungus. In particular, sexual and asexual sporulation both require Chk1 function in Cochliobolus heterostrophus, in contrast to Pmk1, but perhaps more similar to yeast, where Fus3 transmits the mating signal. Chk1 is required for efficient colonization of leaf tissue, which can be compared with filamentous invasive growth of yeast, modulated through another closely related mitogen-activated protein kinase, Kss1. Ubiquitous signaling elements thus are used in diverse ways in different plant pathogens, perhaps the result of coevolution of the transducers and their targets.

Amino Acid Sequence↗
PubMed1999

Identification of a novel family of targets of PYK2 related to Drosophila retinal degeneration B (rdgB) protein.

The protein tyrosine kinase PYK2 has been implicated in signaling pathways activated by G-protein-coupled receptors, intracellular calcium, and stress signals. Here we describe the molecular cloning and characterization of a novel family of PYK2-binding proteins designated Nirs (PYK2 N-terminal domain-interacting receptors). The three Nir proteins (Nir1, Nir2, and Nir3) bind to the amino-terminal domain of PYK2 via a conserved sequence motif located in the carboxy terminus. The primary structures of Nirs reveal six putative transmembrane domains, a region homologous to phosphatidylinositol (PI) transfer protein, and an acidic domain. The Nir proteins are the human homologues of the Drosophila retinal degeneration B protein (rdgB), a protein implicated in the visual transduction pathway in flies. We demonstrate that Nirs are calcium-binding proteins that exhibit PI transfer activity in vivo. Activation of PYK2 by agents that elevate intracellular calcium or by phorbol ester induce tyrosine phosphorylation of Nirs. Moreover, PYK2 and Nirs exhibit similar expression patterns in several regions of the brain and retina. In addition, PYK2-Nir complexes are detected in lysates prepared from cultured cells or from brain tissues. Finally, the Nir1-encoding gene is located at human chromosome 17p13.1, in proximity to a locus responsible for several human retinal diseases. We propose that the Nir and rdgB proteins represent a new family of evolutionarily conserved PYK2-binding proteins that play a role in the control of calcium and phosphoinositide metabolism downstream of G-protein-coupled receptors.

Amino Acid Sequence↗
PubMed1998

Relationship of maternal and general self-acceptance to pre- and postpartum affective experience.

Forty-nine married primiparous Israeli women responded to W. W. K. Zung's (1965) Self-Rating Depression Scale, N. M. Bradburn's (1969) Affect Balance Scale, and measures of general and maternal self-acceptance during the last trimester of pregnancy and again 6 to 8 weeks following childbirth. There was a significant decrease in depression from pre- to postpartum for the total group. Women high in general self-acceptance were less depressed and displayed less negative affect than those low in general self-acceptance. There were no corresponding differences between the high and low maternal self-acceptance groups. Both pre- and postpartum women tended to rate themselves significantly higher for maternal self-acceptance than for general self-acceptance.

Adult↗
PubMed1997

Tyrosine phosphorylation of Pyk2 is selectively regulated by Fyn during TCR signaling.

The Src family protein tyrosine kinases (PTKs), Lck and Fyn, are coexpressed in T cells and perform crucial functions involved in the initiation of T cell antigen receptor (TCR) signal transduction. However, the mechanisms by which Lck and Fyn regulate TCR signaling are still not completely understood. One important question is whether Lck and Fyn have specific targets or only provide functional redundancy during TCR signaling. We have previously shown that Lck plays a major role in the tyrosine phosphorylation of the TCR-zeta chain and the ZAP-70 PTK. In an effort to identify the targets that are specifically regulated by Fyn, we have studied the tyrosine phosphorylation of Pyk2, a recently discovered new member of the focal adhesion kinase family PTK. We demonstrated that Pyk2 was rapidly tyrosine phosphorylated following TCR stimulation. TCR-induced tyrosine phosphorylation of Pyk2 was selectively dependent on Fyn but not Lck. Moreover, in heterologous COS-7 cells, coexpression of Pyk2 with Fyn but not Lck resulted in substantial increases in Pyk2 tyrosine phosphorylation. The selective regulation of Pyk2 tyrosine phosphorylation by Fyn in vivo correlated with the preferential phosphorylation of Pyk2 by Fyn in vitro. Our results demonstrate that Pyk2 is a specific target regulated by Fyn during TCR signaling.

Animals↗
PubMed1997

Tumour necrosis factor alpha binding to human and mouse trophoblast.

Tumour necrosis factor alpha (TNF-alpha) is a cytokine with pleiotropic effects, modulating cell growth, differentiation, and synthesis of various substances. Recent demonstration of TNF-alpha mRNA and protein in the uteroplacental unit suggests that this cytokine may be involved in the development of the embryo. To determine whether the embryo itself binds TNF-alpha, mouse blastocyst outgrowths and human first trimester villous trophoblast were analysed for TNF-alpha binding. Our experiments revealed that binding of TNF-alpha could be specifically detected on the trophectoderm of the outgrowing mouse embryos. They also show a complete disappearance of the colony-stimulating factor 1 (CSF-1) receptor that occurs shortly after the binding of TNF-alpha by the trophectoderm. In human first trimester villous trophoblast, TNF-alpha binding was found to be predominantly detectable on the syncytiotrophoblast and to a lesser extent on the cytotrophoblastic cells. Binding was not observed on adjacent embryonic or maternal cells. Our results further support the idea that TNF-alpha as well as other cytokines may modulate early embryonic development and implantation.

Animals↗
PubMed1997

Functional analysis of third ventriculostomy patency with phase-contrast MRI velocity measurements.

Our purpose was to explore the utility of cine phase-contrast MRI velocity measurements in determining the functional status of third ventriculostomies, and to correlate the quantitative velocity data with clinical follow-up. We examined six patients with third ventriculostomies and 12 normal subjects by phase-contrast MRI. The maximum craniocaudal to maximum caudocranial velocity range was measured at regions of interest near the third ventricular floor, and in cerebrospinal fluid anterior to the upper pons and spinal cord on midline sagittal images. Ratios of the velocities of both the third ventricle and prepontine space to the space anterior to the spinal cord were obtained. The velocities near the third ventricular floor and in the pontine cistern were significantly higher in patients than in normal subjects, but the velocity anterior to the spinal cord was similar between the groups. The velocity ratios, used to normalize individual differences, were also higher in patients than in controls. Two patients had lower velocity ratios than their fellows at the third ventricular floor and in the pontine cistern; one required a shunt 11 months later, while in the other, who had a third ventricular/thalamic tumor, the lower values probably reflect distortion of the third ventricular floor. We conclude that phase-contrast MR velocity measurements, specifically the velocity ratio between the high pontine cistern and the space anterior to the spinal cord, can help determine the functional status of third ventriculostomies.

Adolescent↗
PubMed1996

A role for Pyk2 and Src in linking G-protein-coupled receptors with MAP kinase activation.

The mechanisms by which mitogenic G-protein-coupled receptors activate the MAP kinase signalling pathway are poorly understood. Candidate protein tyrosine kinases that link G-protein-coupled receptors with MAP kinase include Src family kinases, the epidermal growth factor receptor, Lyn and Syk. Here we show that lysophosphatidic acid (LPA) and bradykinin induce tyrosine phosphorylation of Pyk2 and complex formation between Pyk2 and activated Src. Moreover, tyrosine phosphorylation of Pyk2 leads to binding of the SH2 domain of Src to tyrosine 402 of Pyk2 and activation of Src. Transient overexpression of a dominant interfering mutant of Pyk2 or the protein tyrosine kinase Csk reduces LPA- or bradykinin-induced activation of MAP kinase. LPA- or bradykinin-induced MAP kinase activation was also inhibited by overexpression of dominant interfering mutants of Grb2 and Sos. We propose that Pyk2 acts with Src to link Gi- and Gq-coupled receptors with Grb2 and Sos to activate the MAP kinase signalling pathway in PC12 cells.

Animals↗
PubMed1996

Activation of Pyk2 by stress signals and coupling with JNK signaling pathway.

The c-Jun amino-terminal kinase (JNK) is activated by various heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptors, inflammatory cytokines, and stress signals. Yet, upstream mediators that link extracellular signals with the JNK signaling pathway are currently unknown. The tyrosine kinase Pyk2 was activated by tumor necrosis factor alpha, by ultraviolet irradiation, and by changes in osmolarity. Overexpression of Pyk2 led to activation of JNK, and a dominant-negative mutant of Pyk2 interfered with ultraviolet light- or osmotic shock-induced activation of JNK. Pyk2 represents a cell type-specific, stress-sensitive mediator of the JNK signaling pathway.

Animals↗