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S Cohen

Publications and source records attributed to S Cohen.

At least 703 records · Page 39Linked to original sources
PubMed1985

Internalization of functional epidermal growth factor:receptor/kinase complexes in A-431 cells.

We have isolated and partially purified an intracellular vesicle fraction from A-431 cells that contains both epidermal growth factor (EGF) and enzymatically active EGF:receptor/kinase. Exposure of intact A-431 cells to EGF leads to an accumulation of both EGF and kinase activity in this vesicle fraction. The accumulation is time- and temperature-dependent and is blocked by inhibitors of energy production. The EGF receptor in internalized vesicles is capable of autophosphorylation and, in the presence of Ca2+, of phosphorylation of the previously isolated 35-kDa protein (Fava, R. A., and Cohen, S. (1984) J. Biol. Chem. 259, 2636-2645). The demonstration of an EGF-induced increase in kinase activity of an internalized vesicle fraction lends credence to the hypothesis that EGF-induced endocytosis of the receptor is of physiological significance in the response of cells to this ligand. In addition, these results are consistent with the suggestion that the phosphorylation of the 35-kDa protein is associated with internalization of the EGF:receptor/kinase complex.

Carcinoma, Squamous Cell↗
PubMed1985

Epidermal growth factor stimulates the phosphorylation of the calcium-dependent 35,000-dalton substrate in intact A-431 cells.

We have previously reported the isolation of a 35-kDa protein from A-431 cells that, in the presence of Ca2+, is an excellent in vitro substrate for the epidermal growth factor (EGF) receptor/kinase present in membrane preparations (Fava, R. A., and Cohen, S. (1984) J. Biol. Chem. 259, 2636-2645). In this communication we demonstrate that the phosphorylation of the 35-kDa protein is markedly enhanced in intact, 32P-labeled, A-431 cells following exposure of the cells to EGF. The 35-kDa protein immunoprecipitated from cells treated with EGF is phosphorylated to a 20-120-fold greater extent than comparable preparations from control cells. Both phosphotyrosine and phosphoserine residues are detected in the protein after treatment of the cells with EGF. EGF-dependent phosphorylation of the 35-kDa protein is barely detected unless the intact cells are exposed to EGF for periods greater than 5 min. We suggest that endosomes containing internalized EGF X receptor/kinase complexes are primarily responsible for the observed phosphorylation of the 35-kDa protein in intact cells.

Animals↗
PubMed1985

Identification of residues in the nucleotide binding site of the epidermal growth factor receptor/kinase.

We have purified the epidermal growth factor receptor/kinase from A431 membrane vesicles which had been affinity labeled with the ATP analog, 5'-p-fluorosulfonylbenzoyl[8-14C]adenosine. The resulting purified, affinity labeled receptor/kinase preparation has been subjected to reduction and carboxymethylation followed by tryptic digestion. From this digest, we have isolated and sequenced the tryptic peptide containing the major site of labeling by the ATP analog. The sequence of this peptide is Ile-Pro-Val-Ala-Ile-X-Glu-Leu, where X corresponds to Lys 721 of the derived sequence of the EGF receptor/kinase.

Adenosine↗
PubMed1985

Bovine interferon alpha genes. Structure and expression.

The bovine genome contains a gene family of interferon-alpha s (bIFN-alpha) that consists of at least five distinct members. Four of the bIFN-alpha genes isolated show a high degree of homology (97% in the nucleotide sequence and 93% in amino acid sequence). The overall homology in amino acid sequence of bIFN-alpha to human, murine, and rat IFNs-alpha is approximately 60%. Yet there are amino acid clusters (positions 28-41 and 118-146) which are highly conserved throughout the mammalian evolution and in which the overall homology can be as high as 86%. Within the C terminus conserved cluster there is a sequence containing 9 amino acids completely conserved in 16 mammalian IFNs-alpha and of these, 7 are also shared with a similar domain in some bacterial toxins, implying a common functional role for these domains. One of the genes, IFN-alpha C, was expressed in Escherichia coli. The purified bacterial IFN (specific activity, 2 X 10(8) units/mg) exhibited antiviral activity on bovine cells but no detectable activity was demonstrated on human and simian cells.

Amino Acid Sequence↗
PubMed1985

Histamine-mediated acetylcholine release in the guinea-pig ileum.

The isometric contraction induced by histamine in guinea-pig ileum longitudinal muscle was biphasic in Krebs ([Ca]: 3.36 mM) but monophasic in Tyrode solution ([Ca]: 1.80 mM). The late phase (histamine: 20-400 nM) was common to the two solutions but the early phase (histamine: 2-20 nM) was observed only in Krebs solution. This early phase could be blocked with atropine (0.01-0.2 microM), morphine (0.1, 1 microM), adenosine (5, 20 microM) and tetrodotoxin (0.3 microM) without affecting the late phase. Washout of morphine or adenosine was fast. Neostigmine (100 nM) greatly potentiated the effect of histamine (4 nM) in the early phase, the muscle undergoing almost maximum contraction but also reversible desensitization to doses of histamine less than or equal to 20 nM for as long as 40 min after washout. Beyond this concentration, the preparation responded to increasing doses of histamine as observed in the late phase. It is concluded that low concentrations of histamine that have no observable direct effect on muscle contractility release acetylcholine in the presence of [Ca] 3.36 mM, the early phase being entirely due to release of endogenous acetylcholine.

Acetylcholine↗
PubMed1985

Binding of hematoporphyrin derivative to membranes. Expression of porphyrin heterogeneity and effects of cholesterol studied in large unilamellar liposomes.

The binding of hematoporphyrin derivative to membrane was studied at the molecular level, employing fluorimetric techniques and using liposomes (large unilamellar) to model biological membranes. Two specific issues were probed: (a) the effect of increasing the porphyrin-liposome incubation period (37 degrees C, neutral pH, in the dark) from 2 h up to 24 h, with liposomes composed of PC or PC/cholesterol 7:3 (molar ratio); (b) the effects of membrane lipid composition, in terms of mol% cholesterol in PC/cholesterol liposomes, on the porphyrin-membrane binding equilibrium, for a long incubation period (16 h). The data were processed and found to be in good agreement with the following proposed model: With time (t greater than 2 h), the porphyrin fractions into three components, two of them binding to membrane with high and low affinities, respectively, the time effect reaching a plateau at 16 h. Linkage was observed between the slow process and changes in the available pools of each fraction. At sufficiently long incubations, the magnitude of each of the two binding fractions was found to be (roughly) 30%, independent of the membrane lipid composition. On the other hand, the magnitude of the binding constants was found to depend on the lipid composition, that of the high-affinity fraction decreasing from 9000 M-1 for 0% cholesterol, to 3000 M-1 for 40% cholesterol, then increasing back to 5000 M-1 upon further increase in cholesterol (to 50% mol) and that of the low-affinity fraction going from 1000 M-1, to 100 M-1, to 300 M-1 for similar lipid compositions. The origin of the time effect, in terms of porphyrin-specific processes, and the biological relevance of the present findings are discussed.

Cholesterol↗
PubMed1985

Beta-adrenergic activity and conformation of the antihypertensive specific alpha 2-agonist drug, guanabenz.

In recent research a new series of specific drugs, one of which is guanabenz (GBZ, 2,6(dichlorobenzyliden)-aminoguanidine) has been introduced into the clinical treatment of centrally mediated hypertension. Guanabenz (GBZ) is considered to be among the most specific alpha 2-adrenergic agonists, acting similarly to clonidine by decreasing the sympathetic outflow from the brain to the peripheral circulatory system. In the present report we show that GBZ displays a significant affinity for beta-adrenoceptors. In displacement studies of the iodinated beta-antagonist [125I]cyanopindolol (CYP) from turkey erythrocyte membranes, the dissociation constant of GBZ was 3.8 microM. Inhibition of the (-) epinephrine induced adenylate cyclase activity by GBZ is competitive, with an apparent dissociation constant of 30 microM. A similar value was obtained by studies of GBZ's effect on the (-) epinephrine-induced [3H]cAMP accumulation in intact turkey erythrocytes. In view of its unexpected affinity for beta-adrenoceptors, we examined the three-dimensional structure of crystalline GBZ. In these studies substantial differences between clonidine and GBZ were observed, despite their strong structural resemblance. These dissimilarities (angle of rotation phi = 39.7 degrees as compared to 76 degrees in clonidine, and the rotational restriction of clonidine as compared to the greater mobility in rotation of GBZ) could explain the difference of specificity between these two compounds.

Adenylyl Cyclases↗
PubMed1985

Chemical modification of the Na+/H+ exchanger of thymic lymphocytes. Inhibition by N-ethylmaleimide.

A Na+/H+ exchanger is involved in the regulation of cytoplasmic pH and cellular volume in a variety of cells. Little is known about the molecular nature of this exchanger. The purpose of this study was to survey a variety of group-specific covalent reagents as potential inhibitors of the exchanger. Na+/H+ countertransport activity was assayed as the amiloride-sensitive rate of Na+-induced alkalinization in acid-loaded lymphocytes, or as the rate of swelling in cells suspended in sodium propionate medium. Activity was not affected by proteinases or by carboxyl-group and amino-group specific reagents. A significant inhibition was produced by diethylpyrocarbonate, a histidine-specific reagent and by N-ethylmaleimide, a sulfhydryl group reagent. A similarly reactive but nonpermeating sulfhydryl agent, glutathione-maleimide, failed to inhibit Na+-H+ exchange. Moreover, the reaction with N-ethylmaleimide was sensitive to changes in the cytoplasmic pH. The data suggest that the chemically reactive groups of the Na+/H+ exchanger of lymphocytes have limited exposure to the extracellular medium but that an internally located sulfhydryl group is critical for the cation-exchange activity.

Animals↗
PubMed1985

Retinal hemorrhages in the newborn following labor induced by oxytocin or dinoprostone.

We examined the fundi of 100 newborns following labor induced by intravenous oxytocin or by oral dinoprostone. Retinal hemorrhage was observed in 40% of neonates in the dinoprostone treatment group, as compared with 28% in the oxytocin treatment group. The accumulation of prostaglandins in the fetal circulation may be responsible for the hemorrhages, which clear spontaneously once the noxious agent is metabolized. Other organ systems must be carefully examined in the neonate to detect other possible untoward effects.

Dinoprostone↗
PubMed1985

Dependence of solute solubility parameters on solvent polarity.

In nonpolar solvents a solute may self-associate through polar interactions, exposing its nonpolar surface to a solvent with a low solubility parameter, delta 1. In polar solvents a solute is solvated, presumably, by the polar groups of the solvent. This "chameleonic" effect results in different solubility parameters for a solute, depending on the polarity of the solvent. This report presents data for solute solubility parameters in solvents of variable polarity and gives suggestions for dealing with the chameleonic effect associated with solute-solvent interaction.

Benzoates↗
PubMed1985

Ascending myelopathy after chemotherapy for central nervous system acute lymphoblastic leukemia: correlation with cerebrospinal fluid myelin basic protein.

Ascending myelopathy developed in a previously irradiated 10-year-old boy after intraventricular methotrexate and cytosine arabinoside were given for central nervous system relapse of acute lymphoblastic leukemia. The course was fatal in 10 weeks. Cerebrospinal fluid myelin basic protein levels, indicating a demyelinative process, rose prior to the onset of clinical symptoms and remained at very high levels until death. Myelin basic protein may be useful as a predictor of chemotherapy-associated neurotoxicity.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1985

Increased colonic motility during exposure to a stressful situation.

Colonic smooth muscle spike potentials and contractility were recorded during the periods of stress by a bipolar electrode-perfused catheter apparatus placed in the rectosigmoid colon. Healthy subjects and patients with the irritable colon syndrome (ICS) were exposed to three standardized stressful conditions: (1) ice-water immersion, (2) Stroop stimulus differentiation test, and (3) ball sorting. In healthy controls, colonic motility increased after the first exposure to ice-water immersion (P less than 0.05), Stroop test (P less than 0.05), or ball sorting. Respiratory frequency also increased after exposure to the stressful stimuli. However, repeat exposures to the stress tests did not stimulate colonic motility. An increase in colonic motility occurred in patients with the irritable colon syndrome pretreated with a placebo after exposure to ice water (P less than 0.05), Stroop Test, or ball sorting (P less than 0.05). However, after exposure to the stressful situations patients pretreated with chlordiazepoxide had a diminished increase in colonic motility or in respiratory frequency. These studies suggest: (1) in healthy controls habituation reduces the stress-related increase in colonic motility, and (2) in patients with the irritable colon syndrome, chlordiazepoxide decreases the stress-related increase in colonic motility.

Action Potentials↗
PubMed1985

Lipolysis: pitfalls and problems in a series of 1,246 procedures.

In a large series of lipolysis procedures, followed for 2 years, there have been no serious major and few minor complications. Selection of patients is important and for the best results patients should be under 30 years of age. Many areas of lipodystrophy may be dealt with at one session in most cases. However, postoperative circulatory control, especially during the first 24 hours, is very important and always requires vigilance to avoid the tendency to hypotension. Early local problems include tenderness, bruising, and swelling, and the management of these is discussed. Later complications include skin flaccidity, dimpling, and localized areas of pigmentation and hypesthesia. The prevention and management of all these sequelae and others are discussed.

Adipose Tissue↗
PubMed1985

The production of regulatory cytokines for thymocyte proliferation by murine thymic epithelium in vitro.

Two separate cultures of pure, morphologically distinct thymic epithelial cells have been generated and maintained in culture for one year (A.C. Nieburgs et al., Cell. Immunol. 90, 439-450, 1985). Supernatants from one of these cell lines, TECs, were examined for functional activity on thymocytes in vitro. These supernatants contained three distinct intercellular mediators, each capable of modulating thymocyte responses to T-cell mitogens. Enhancement of thymocyte proliferation to suboptimal doses of mitogen was associated with a factor that eluted in the 97,000-Da region on molecular sieve chromatography and was functionally and physicochemically distinct from interleukin-1 and interleukin-2 (IL-1 and IL-2). Suppression of the thymocyte response to optimal doses of mitogen was mediated by a 1000- to 5000-Da factor. These two intercellular components have different susceptibilities to heat treatments and are trypsin insensitive. In addition, thymic epithelial cells produced significantly high levels of prostaglandin E2 (PGE2) which also suppressed thymocyte responses to mitogen, but only at high doses of supernatant. These epithelial cell-derived enhancing and inhibitory effects on thymocytes could play a role in regulating intrathymic events.

Animals↗
PubMed1985

In vitro growth and maintenance of two morphologically distinct populations of thymic epithelial cells.

Cultures of thymic epithelial cells were generated and maintained in valine-free minimum essential medium (MEM) supplemented with 690 mg/liter of D-valine. These cultures have been maintained for 1 year through multiple passages by trypsinization of 60-70% confluent monolayers. Large and small epithelial cells were present in early cultures. They were separated into two stable subpopulations based on (1) their differential growth rates and (2) their differential adherence to the culture substratum. These morphologically distinct cell populations, TECS and TECL, were 100% keratin positive and contained cells with desmosomes and tonofilaments, all characteristics of epithelial cells. Esterase analysis of both cell populations revealed a 1 and 9% esterase-positive cell population in cultures of keratin-positive small (TECS) and large (TECL) cells, respectively. The percentages of esterase-positive cells corresponded to the 2 and 10% populations of TECS and TECL, respectively, that contained both desmosomes and phagolysosomes. These results establish conditions for the long-term propagation of pure thymic epithelial cells. Such cultures can be used to study the functional interactions between epithelial cells and lymphoid cells. Morphologic and histochemical analyses have identified subsets of these cells which may prove to have differential effects on thymocyte proliferative and developmental processes.

Animals↗
PubMed1985

Desensitization. V: Suppression of MIF production by lymphokine-activated macrophages.

The systemic injection of high doses of antigen into a previously immunized animal results in a state of transient anergy with respect to cell-mediated immune reactions. This phenomenon is known as desensitization. We have previously shown that desensitization is a multistage process. The initial 24-hr period is characterized by excessive lymphokine production with a failure to express delayed hypersensitivity reactions due to abolition of local chemotactic gradients. Subsequent stages of desensitization involve failure of lymphokine production in vivo. The results presented here demonstrate that lymphocytes obtained from immunized and desensitized animals later than 24 hr after desensitization are markedly suppressed in their ability to produce MIF. In addition, it was found that lymphokine-activated macrophages can suppress in vitro MIF production by lymphocytes from immune, nondesensitized animals. In vitro and in vivo activation of macrophages were equally effective. Thus, it is likely that at least one mechanism for the inhibition of lymphokine production in the post-24-hr period of desensitization, involves activation of a population of suppressor macrophages by lymphokines produced during the initial 24-hr period.

Animals↗
PubMed1985

Role of the diaphragm in the genesis of lower esophageal sphincter pressure in the cat.

To determine the role of the diaphragm in the genesis of the high-pressure zone at the lower esophageal sphincter (LES) we studied the effect of diaphragmatic contraction on lower esophageal sphincter pressure in 10 anesthetized adult cats. Despite anchoring the pressure recording assembly within the LES to prevent axial movement of the sphincter during respiration relative to the pressure recording ports, there was an average oscillation in LES pressure of 17.4 +/- 5.5 mmHg, the frequency of which was the same as the respiratory rate. Peak LES pressure occurred at end-inspiration corresponding with peak diaphragmatic electromyogram. During periods of central apnea induced by manual hyperventilation there was absence of both diaphragmatic electromyogram and the oscillations in LES pressure. Lower esophageal sphincter pressure during apnea was equal to end-expiratory pressure during spontaneous respiration. Following complete neuromuscular blockade with pancuronium, artificial respiration with increasing tidal volumes resulted in increasing oscillations in pressure. However, the magnitude of the pressure oscillation even at tidal volumes four times normal was always significantly below that observed during spontaneous eupnic respiration. Furthermore, progressive augmentation of diaphragmatic electromyogram activity by breathing 5% CO2 in air revealed a linear correlation between the magnitude of the respiratory-induced pressure oscillations of the LES and peak integrated diaphragmatic electromyogram in individual animals. It is concluded, therefore, that (a) intrinsic LES tone is best approximated by end-expiratory pressure during spontaneous respiration, (b) the respiratory-induced oscillations in LES pressure are primarily the result of active diaphragmatic contraction, and (c) the level of diaphragmatic electrical activity directly influences the magnitude of the pressure oscillation.

Analysis of Variance↗