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Biomedical subjects

A Shalev

Publications and source records attributed to A Shalev.

At least 19 recordsLinked to original sources
PubMed2001

Saccharomyces cerevisiae protein Pci8p and human protein eIF3e/Int-6 interact with the eIF3 core complex by binding to cognate eIF3b subunits.

Mammalian, plant, and Schizosaccharomyces pombe eukaryotic initiation factor-3 (eIF3) contains a protein homologous to the product of int-6 (eIF3e), a frequent integration site of mouse mammary tumor viruses. By contrast, Saccharomyces cerevisiae does not encode a protein closely related to eIF3e/Int-6. Here, we characterize a novel S. cerevisiae protein (Pci8p, Yil071cp) that contains a PCI (proteasome-COP9 signalosome-eIF3) domain conserved in eIF3e/Int-6. We show that both Pci8p and human eIF3e/Int-6 expressed in budding yeast interact with the yeast eIF3 complex in vivo and in vitro by binding to a discrete segment of its eIF3b subunit Prt1p and that human eIF3e/Int-6 interacts with the human eIF3b segment homologous to the Pci8p-binding site of yeast Prt1p. These results refine our understanding of subunit interactions in the eIF3 complex and suggest structural similarity between human eIF3e/Int-6 and yeast Pci8p. However, deletion of PCI8 had no discernible effect on cell growth or translation initiation as judged by polysome analysis, suggesting that Pci8p is not required for the essential function of eIF3 in translation initiation. Motivated by the involvement of Int-6 in transcriptional control, we investigated the effects of deleting PCI8 on the total mRNA expression profile by oligonucleotide microarray analysis and found reduced mRNA levels for a subset of heat shock proteins in the pci8Delta mutant. We discuss possible dual functions of Pci8p and Int-6 in transcriptional and translational control.

Binding Sites↗
PubMed2001

Multiple roles for the C-terminal domain of eIF5 in translation initiation complex assembly and GTPase activation.

eIF5 stimulates the GTPase activity of eIF2 bound to Met-tRNA(i)(Met), and its C-terminal domain (eIF5-CTD) bridges interaction between eIF2 and eIF3/eIF1 in a multifactor complex containing Met-tRNA(i)(Met). The tif5-7A mutation in eIF5-CTD, which destabilizes the multifactor complex in vivo, reduced the binding of Met-tRNA(i)(Met) and mRNA to 40S subunits in vitro. Interestingly, eIF5-CTD bound simultaneously to the eIF4G subunit of the cap-binding complex and the NIP1 subunit of eIF3. These interactions may enhance association of eIF4G with eIF3 to promote mRNA binding to the ribosome. In vivo, tif5-7A eliminated eIF5 as a stable component of the pre-initiation complex and led to accumulation of 48S complexes containing eIF2; thus, conversion of 48S to 80S complexes is the rate-limiting defect in this mutant. We propose that eIF5-CTD stimulates binding of Met-tRNA(i)(Met) and mRNA to 40S subunits through interactions with eIF2, eIF3 and eIF4G; however, its most important function is to anchor eIF5 to other components of the 48S complex in a manner required to couple GTP hydrolysis to AUG recognition during the scanning phase of initiation.

Codon, Initiator↗
PubMed2000

A multifactor complex of eukaryotic initiation factors, eIF1, eIF2, eIF3, eIF5, and initiator tRNA(Met) is an important translation initiation intermediate in vivo.

Translation initiation factor 2 (eIF2) bound to GTP transfers the initiator methionyl tRNA to the 40S ribosomal subunit. The eIF5 stimulates GTP hydrolysis by the eIF2/GTP/Met-tRNA(i)(Met) ternary complex on base-pairing between Met-tRNA(i)(Met) and the start codon. The eIF2, eIF5, and eIF1 all have been implicated in stringent selection of AUG as the start codon. The eIF3 binds to the 40S ribosome and promotes recruitment of the ternary complex; however, physical contact between eIF3 and eIF2 has not been observed. We show that yeast eIF5 can bridge interaction in vitro between eIF3 and eIF2 by binding simultaneously to the amino terminus of eIF3 subunit NIP1 and the amino-terminal half of eIF2beta, dependent on a conserved bipartite motif in the carboxyl terminus of eIF5. Additionally, the amino terminus of NIP1 can bind concurrently to eIF5 and eIF1. These findings suggest the occurrence of an eIF3/eIF1/eIF5/eIF2 multifactor complex, which was observed in cell extracts free of 40S ribosomes and found to contain stoichiometric amounts of tRNA(i)(Met). The multifactor complex was disrupted by the tif5-7A mutation in the bipartite motif of eIF5. Importantly, the tif5-7A mutant is temperature sensitive and displayed a substantial reduction in translation initiation at the restrictive temperature. We propose that the multifactor complex is an important intermediate in translation initiation in vivo.

Binding Sites↗
PubMed1999

Childhood imaginary companionship and mental health in adolescence.

An imaginary companion (IC) is a frequently encountered childhood fantasy, invisible to anyone but the child, who may be named, addressed or played with. Whether the presence of an IC is a normal developmental feature has not been determined. We examined psychometric measures and the presence/absence of childhood IC in a sample of 850 mentally healthy adolescents. 17.6% of our subjects, more often females, reported having had such a companion. Subjects who reported having had an IC in childhood exhibited higher levels of distress and emotional discontrol, displayed prolonged transitional object attachment and immature modes of coping with stress. Thus, although childhood imaginary companionship is not indicative of psychopathology, it may denote a vulnerability for adolescent perturbation and difficulty in coping with emotionally laden situations.

Adaptation, Psychological↗
PubMed1999

Predictors of chronic post-traumatic stress disorder. A prospective study.

BACKGROUND: Most individuals who, shortly after trauma, express symptoms of post-traumatic stress disorder (PTSD) recover within one year of their traumatic experiences. In contrast, those who remain ill for one year rarely recover completely. The early identification of the latter is, therefore, very important. AIMS: To prospectively evaluate predictors of PTSD at four months and one year. METHOD: We followed 236 trauma survivors recruited from admissions to a general hospital's emergency room for four months, at which point 41 (17.4%) met diagnostic criteria for PTSD. Twenty-three of these individuals, and 39 individuals without PTSD at four months, were assessed again at one year. RESULTS: Depressive symptoms were the best predictors of PTSD at both time points. Intrusive symptoms and peri-traumatic dissociation were better at predicting four-month PTSD than one-year PTSD. CONCLUSIONS: The occurrence of depression during the months that follow a traumatic event is an important mediator of chronicity in PTSD.

Adult↗
PubMed1998

[Chylothorax as the initial manifestation of malignant Hodgkin lymphoma].

A 22 year-old man complaining of slight thoracic pain, was found to have a right pleural effusion in his chest X-ray. The pleural aspiration yielded chylous fluid and radiological examination and biopsy of a mediastinal mass led to the diagnosis of Hodgkin's disease of the nodular sclerosis type with supra- and radiologically infradiaphragmatic disease and a pathological fracture of the sternum. After complete initial aspiration of the pleural effusion the chylothorax did not recur following initiation of a combination chemotherapy, and a clear regression of the lymphoma was found after the first 3 cycles. This case provides an example of an oligosymptomatic, right sided chylothorax as the first manifestation of Hodgkin's disease in a young immuno-competent patient.

Adult↗
PubMed1998

A novel one-step, highly sensitive fluorometric assay to evaluate cell-mediated cytotoxicity.

In this study, a fluorometric method using alamarBlue has been developed for detecting cell-mediated cytotoxicity in vitro. AlamarBlue is a non-toxic metabolic indicator of viable cells that becomes fluorescent upon mitochondrial reduction. Specific lysis of targets by effector cells is quantified by comparing the total number of viable cells in wells containing effector and targets together, with wells where target and effector cells were separately seeded. Cell-mediated cytotoxic activity by alloreactive T cells and natural killer cells has been detected using a novel application of the alamarBlue technique. The assay that we have developed to detect cell-mediated cytotoxicity is extremely sensitive and specific and requires a significant lower number of effector cells than the standard 51Cr assay. Since alamarBlue reagent is non-toxic to cells and the assay can be performed under sterile conditions, effector cells may be recovered at the end for further analysis or cell expansion, if desired. Direct comparison of cell-mediated cytotoxicity measured by the alamarBlue method with the standard 51Cr release assay revealed that the former method is as specific and more sensitive than the conventional assay. Moreover, very small inter and intra-assay variations have been observed for alamarBlue cytotoxicity assays. In conclusion, this study shows that the alamarBlue assay is an extremely sensitive, economical, simple and non-toxic procedure to evaluate cell-mediated cytotoxicity that yields accurate results using a limited number of effector cells. Furthermore, since this assay is a one-step procedure, and does not involve any risk for the personnel, it may be useful to analyze automatically cell-mediated cytotoxicity in a large number of samples.

Animals↗
PubMed1998

Effects of glucagon-like peptide 1 (7-36 amide) on glucose kinetics during somatostatin-induced suppression of insulin secretion in healthy men.

Glucagon-like peptide 1 (GLP-1) is known to stimulate insulin secretion and biosynthesis, but has also been shown to decrease insulin requirements in type 1 diabetic subjects suggesting insulin-independent effects. To assess whether GLP-1 exerts also direct effects on whole-body glucose metabolism, 6,6-D2-glucose kinetics were measured in 8 healthy volunteers receiving once GLP-1, once saline during hyperglycemic glucose clamping, while somatostatin with replacement amounts of insulin, glucagon and growth hormone was infused. Even though endogenous insulin secretion could not be blocked completely (increased plasma concentrations of C-peptide and proinsulin), somatostatin infusion resulted in stable insulin and glucagon plasma levels in both protocols (GLP-1 vs. placebo: NS). After 3 h of GLP-1 infusion, peripheral glucose disappearance significantly increased compared to placebo (p < 0.03) despite of somatostatin-induced suppression of insulin and glucagon secretion. Thus, GLP-1 infusion seems to have direct stimulatory effects on peripheral glucose metabolism in man.

Adult↗
PubMed1997

Psychophysiologic parameters of traumatic stress disorder in rats.

Nonhabituation of the acoustic startle response is used to identify rat subjects with altered alarm responses subsequent to trauma exposure. Subjects (n = 31) were exposed to 30 minutes of intermittent tail shock on 2 days followed by exposure to the apparatus on the third day. Twenty-nine percent of traumatized rats developed nonhabituation of startle over the subsequent 3 weeks of testing. No control rats developed nonhabituation of startle reactions over a similar time period. These data suggest that this system represents a more accurate representation of clinical PTSD than do other animal models.

Animals↗
PubMed1997

Absence of short-term effects of glucagon-like peptide-1 and of hyperglycemia on plasma leptin levels in man.

In rodents, leptin and the incretin glucagon-like peptide-1 (7-36) amide (GLP-1) affect feeding at least in part via interaction with hypothalamic neuropeptide Y (NPY), suggesting that cross talk may exist between GLP-1 and the ob gene product. Besides insulin, acute hyperglycemia has recently been shown to induce ob gene expression. To address the question of whether leptin plasma levels in humans are affected by GLP-1 infusion and/or hyperglycemia, eight healthy volunteers were studied during euglycemia and hyperglycemic clamping with or without GLP-1 administration while insulin levels were kept constant by somatostatin infusion. Under all conditions, leptin plasma levels remained unchanged, demonstrating that in humans leptin plasma concentrations are affected neither by short-term peripheral GLP-1 infusion nor by hyperglycemia, which suggests that postprandial GLP-1 release and hyperglycemia do not modulate secretion of the ob gene product.

Adult↗
PubMed1997

Effects of glucagon-like peptide 1 (7-36 amide) on whole-body protein metabolism in healthy man.

The incretin glucagon-like peptide 1 (GLP-1) shows glucose-dependent insulinotropic activity and may exert anabolic effects. Whole-body protein metabolism was assessed by measuring [1-13C]-leucine kinetics in 13 healthy volunteers during hyperglycaemic clamping with or without pancreatic clamping (somatostatin infusion) in order to differentiate between insulin-mediated and direct GLP-1 effects. During intact pancreatic secretion leucine flux and leucine oxidation rate as parameters of whole-body protein breakdown decreased markedly after 180 min of synthetic GLP-1 infusion (GLP-1 vs. placebo: P < 0.003). Indirect calorimetry showed an increase in energy expenditure and CO2 production during GLP-1 administration (P < 0.0005). Plasma insulin increased after 3h of GLP-1 infusion to 1486 +/- 145 pmol L(-1) vs. 185 +/- 12 pmol L(-1) for saline (P < 0.0001). When plasma insulin levels were kept constant (GLP-1 vs. saline, NS) during pancreatic clamping, GLP-1 effects on both protein metabolism and energy expenditure were abolished. Thus, GLP-1 infusion in man exerts protein anticatabolic and thermic effects, which are mediated by GLP-1-induced stimulation of insulin secretion.

Adult↗