bluuebunny/crossref_metadata_2025_split huggingface dataset:
A new cGMP phosphodiesterase isolated from bovine platelets is substrate for cAMP‐ and cGMP‐dependent protein kinases: Evidence for a key role in the process of platelet activation
Authors: Robichon Alain 
Published: May 2005

AbstractThe biochemical differences among cGMP phosphodiesterases in platelets have not been thoroughly examined, primarily due to the lack of sufficient purified material. This report describes a simple method developed to isolate specific bovine platelet cGMP phosphodiesterase. This enzyme is cytosolic in its native form and was purified to an apparent homogeneity by ion‐exchange chromatography, affinity chromatography, and density gradient centrifugation. Cyclic GMP binds to a “pseudo‐site” when the catalytic site is deprived of Mg++. The affinity for cGMP at alkaline pH in presence of EDTA and IBMX (Kd = 60 nM) suggests that the removal of Mg++ by EDTA converts the catalytic site to a binding site. A ligand affinity chromatography was designed to take advantage of these features. The core enzyme has a molecular weight 190,000 composed of 2 subunits (MW 95,000) and has a specific activity of 2.5 μmol/min/mg. Moreover, this enzyme was phosphorylated by cAMP‐ and cGMP‐dependent protein kinases, suggesting that its activity could be indirectly regulated by cyclic nucleotides. Agents elevating cGMP and cAMP inhibit platelet activation by inhibiting protein kinase C and thrombin induced hydrolysis of phosphatidylinositol 4,5 diphosphate. The antiaggregating properties of some of these agents might therefore be attributed to the fact that they are inhibitors of phosphodiesterases.
Transcriptional regulation of basic fibroblast growth factor gene expression in capillary endothelial cells
Authors: Weich Herbert A. , Iberg Niggi , Klagsbrun Michael , Folkman Judah 
Published: May 2005

AbstractThe growth of capillary endothelial cells (BCE) is an important regulatory step in the formation of capillary blood vessels. In vivo, the proliferation of these cells is stringently controlled. In vitro they can be stimulated by polypeptide growth factors, such as acidic fibroblast growth factor (aFGF) and basic fibroblast growth factor (bFGF). Since bFGF is synthesized and stored by vascular endothelial cells, this mitogen may play an important role in an autocrine growth regulation during angiogenesis. Here, evidence is presented for induction of the mRNA of bFGF by bFGF itself. A similar increase of bFGF mRNA was observed in response to thrombin and after treatment with phorbol ester. These results suggest that an autocrine loop may exist that may serve to modulate the mitogenic response in BCE under various physiological conditions, (e.g., wound healing and new capillary formation).
Platelet release products modulate some aspects of polymorphonuclear leukocyte activation
Authors: Allegrezza‐Giulietti A. , Serretti R. , Beccerica E. , Muti S. , Ferretti G. , Cervini C. 
Published: May 2005

AbstractThe aim of this research was to evaluate in vitro interactions between platelets and polymorphonuclear leukocytes. The effects of supernatant from thrombin‐activated platelets and two platelet release products (adenosine triphosphate and beta‐thromboglobulin) were tested on the following features of polymorphonuclear leukocytes activation: opsonized zymosan and phorbol myristate acetate stimulated chemiluminescence, release of membrane bound calcium, NADPH‐oxidase activity, and membrane fluidity (fluorescent polarization). The results showed that the addition of platelet supernatant to polymorphonuclear leukocytes induces a significant activation of cells. On the other hand, after three hours of preincubation of polymorphonuclear leukocytes with platelet supernatant, a decreased response of polymorphonuclear leukocytes to stimulation with phorbol myristate acetate, a significant decrease in NADPH‐oxidase activity, and a lowered membrane fluidity were observed. Adenosine triphosphate modulated only opsonized zymosan stimulated chemiluminescence, with and without preincubation with polymorphonuclear leukocytes. Beta‐thromboglobulin caused a decrease of the chemiluminescent response of polymorphonuclear leukocytes, using both agonists, with and without preincubation with polymorphonuclear leukocytes. Moreover beta‐thromboglobulin only caused a decrease of the polymorphonuclear leukocytes membrane fluidity without preincubation with the cells. These results support the thesis that platelets have a “time‐related” modulating activity on polymorphonuclear leukocytes.
Nuclear structure and the three‐dimensional organization of DNA
Authors: Getzenberg Robert H. , Pienta Kenneth J. , Ward W. Steven , Coffey Donald S. 
Published: May 2005

AbstractThe organization of DNA within the nucleus has been demonstrated to be both cell and tissue specific and is arranged in a non‐random fashion in both sperm and somatic cells. Nuclear structure has a pivotal role in this three‐dimensional organization of DNA and RNA and contributes as well to forming fixed organizing sites for nuclear functions, such as DNA replication, transcription, and RNA processing. In sperm, DNA is also organized in a specific fashion by the nuclear matrix, and DNA‐protamine interactions. Within somatic cells, the nuclear matrix provides a three‐dimensional framework for the tissue specific regulation of genes by directed interaction with transcriptional activators. This differential organization of the DNA by the nuclear matrix, in a tissue specific manner, contributes to tissue specific gene expression. The nuclear matrix is the first link from the DNA to the entire tissue matrix system and provides a direct structural linkage to the cytomatrix and extracellular matrix. In summary, the tissue matrix serves as a dynamic structural framework for the cell which interacts to organize and process spatial and temporal information to coordinate cellular functions and gene expression. The tissue matrix provides a structural system for integrating form and function.
Binding of glucocorticoid receptors to model DNA response elements
Authors: Benore‐Parsons Marilee , Liebman Jeffrey , Wennogle Lawrence P. 
Published: May 2005

AbstractDNA sequences were synthesized that contained the consensus 15‐base pair glucocorticoid receptor binding site linked to flanking sequences of various lengths. Binding of these synthetic oligomers to glucocorticoid receptor, employing a reconstituted binding system with purified components, indicated that a minimal size of approximately 45 base pairs was necessary to bind the receptor optimally. Sequences containing multiple receptor binding sites competed more effectively for binding. These findings are consistent with recent demonstrations that multiple control elements act synergistically to affect transcriptional control by glucocorticoids and confirm that regions flanking the consensus GRE binding site are instrumental in optimizing binding interactions.
The NH2‐terminal α subunit attenuator domain confers regulation of G protein activation by βγ complexes
Authors: Dhanasekaran N. , Osawa Shoji , Johnson Gary L. 
Published: May 2005

AbstractGs and Gi, respectively, activate and inhibit the enzyme adenylyl cyclase. Regulation of adenylyl cyclase by the heterotrimeric Gs and Gi proteins requires the dissociation of GDP and binding of GTP to the αs or αi subunit. The βγ subunit complex of Gs and Gi functions, in part, to inhibit GDP dissociation and α subunit activation by GTP. Multiple β and γ polypeptides are expressed in different cell types, but the functional significance for this heterogeneity is unclear. The βγ complex from retinal rod outer segments (βγt) has been shown to discriminate between αi and αs subunits (Helman et al: Eur J Biochem 169:431–439, 1987). βγt efficiently interacts with αi‐like G protein subunits, but poorly recognizes the αs subunit. βγt was, therefore, used to define regions of the αi subunit polypeptide that conferred selective regulation compared to the αs polypeptide. A series of α subunit chimeras having NH2‐terminal αi and COOH‐terminal αs sequences were characterized for their regulation by βγt, measured by the kinetics of GTPγS activation of adenylyl cyclase. A 122 amino acid NH2‐terminal region of the αi polypeptide encoded within an αi/αs chimera was sufficient for βγt to discriminate the chimera from αs. A shorter 54 amino acid αi sequence substituted for the corresponding NH2‐terminal region of αs was insufficient to support the αi‐like interaction with βγt. The findings are consistent with our previous observation (Osawa et al: Cell 63:697–706, 1990) that a region in the NH2‐terminal moiety functions as an attenuator domain controlling GDP dissociation and GTP activation of the α subunit polypeptide and that the attenuator domain is involved in functional recognition and regulation by βγ complexes.
Desensitization of the insulin‐secreting beta cell
Authors: Grodsky Gerold M. , Bolaffi Janice L. 
Published: May 2005

AbstractIn human diabetes, inherent impaired insulin secretion can be exacerbated by desensitization of the β cell by chronic hyperglycemia. Interest in this phenomenon has generated extensive studies in genetic or experimentally induced diabetes in animals and in fully in vitro systems, with often conflicting results. In general, although chronic glucose causes decreased β‐cell response to this carbohydrate, basal response and response to alternate stimulating agents are enhanced. Glucose‐stimulated insulin synthesis can be increased or decreased depending on the system studied. Using a two‐compartment β‐cell model of phasic insulin secretion, a unifying hypothesis is described which can explain some of the apparent conflicting data. This hypothesis suggests that glucose‐desensitization is caused by an impairment in stimulation of a hypothetical potentiator singularly responsible for: (1) some of the characteristic phases of insulin secretion; (2) basal release; (3) potentiation of non‐glucose stimulators; and (4) apparent “recovery” from desensitization. Review of some of the pathways that regulate insulin secretion suggest that phosphoinositol metabolism and protein kinase‐C production are regulated similarly to the theoretical potentiator and their impairment is a major contributor to glucose desensitization in the β cell.
Tissue‐Specific regulation of glucokinase gene expression
Authors: Magnuson Mark A. 
Published: May 2005

AbstractGlucokinase contributes to the maintenance of blood glucose homeostasis by catalyzing the high Km phosphorylation of glucose in the liver and the pancreatic β cell, the only two tissues known to express this enzyme. Molecular biological studies of the glucokinase gene and its products have advanced our understanding of how this gene is differentially regulated in the liver and β cell. The production of an active glucokinase isoform is determined by both transcriptional and post‐transcriptional events. Two different promoter regions that are widely separated in a single glucokinase gene are used to produce glucokinase mRNAs in the liver, pancreatic β cell, and pituitary. The different transcription control regions are tissue‐specific in their expression and are differentially regulated. In liver, glucokinase gene expression is regulated by insulin and cAMP, whereas in the β cell it is regulated by glucose. The upstream glucokinase promoter region, which gives rise to the glucokinase mRNA in pituitary and pancreas, is structurally and functionally different from the downstream promoter region, which gives rise to the glucokinase mRNA in liver. The use of distinct promoter regions in a single glucokinase gene enables a different set of transcription factors to be utilized in the liver and islet, thus allowing a functionally similar gene product to be regulated in a manner consistent with the different functions of these two tissues. In addition, the splicing of the glucokinase pre‐mRNA is regulated in a tissue‐specific manner and can affect the activity of the gene product. This is most apparent in the pituitary where an alternately spliced glucokinase mRNA is produced that does not encode a functional enzyme due to an introduced frameshift.
Butanol‐extractable and detergent‐solubilized cell surface components from murine large cell lymphoma cells associated with adhesion to organ microvessel endothelial cells
Authors: Tressler Robert J. , Nicolson Garth L. 
Published: May 2005

AbstractMetastatic variant cell lines of the murine RAW117 large cell lymphoma were used to study the cell surface components involved in syngeneic tumor cell/microvessel endothelial cell interactions. Poorly liver‐metastatic parental RAW 117‐P cell line adhered to murine hepatic sinusoidal endothelial cell monolayers at significantly lower rates than the liver‐selected, highly liver‐metastatic RAW117‐H10 line and both cell lines were poorly adherent to lung microvessel and bovine aorta endothelial cells. Viable, 2% 1‐butanol‐treated RAW117‐H10 tumor cells formed fewer liver tumor nodules in experimental metastasis assays than untreated H10 cells and were significantly less adherent to murine hepatic sinusoidal endothelial cell monolayers. When 2% 1‐butanol extracts of metabolically labeled or CHAPS detergent Iysates of cell surface‐labeled tumor cells were analyzed for their ability to bind to fixed microvessel endothelial cell monolayers, quantitative differences were found in the extractable tumor cell surface components that bound to the different organ‐derived microvessel endothelial cells. Cell surface components (1‐butanol extractable), of Mr ∼ 85,000–90,000 and ∼ 37,000–40,000 bound to hepatic sinusoidal endothelial cell monolayers to a greater extent than to murine lung microvessel endothelial or bovine aortic endothelial cell monolayers, Whereas tumor cell surface components of Mr ∼ 45,000, ∼ 33,000, and ∼ 25,000 bound similarly to endothelial cells regardless of origin. The results suggest but do not prove that tumor cell/endothelial cell adhesion involves multiple tumor cell surface components, some of which commonly bind to various endothelial cells and others for which binding may be dictated by the tissue origin and type of endothelial cell. Particular RAW117 butanol‐extractable cell membrane components were associated with tumor cell‐endothelial cell adhesion, and these components could be responsible, in part, for the preferential adhesion of RAW117 cells to liver sinusoidal endothelial cells and metastasis to liver.
Rapid induction of competence formation is PDGF‐isoform specific
Authors: Coats Steven R. , Olson J. E. , Pledger W. J. 
Published: May 2005

AbstractPlatelet‐derived growth factor (PDGF) stimulates the expression of a number of genes associated with entry of quiescent Balb/c‐3T3 fibroblasts into the cell cycle. We determined that two of these genes, c‐myc and c‐fos, are induced equivalently in medium supplemented with platelet‐poor plasma (PPP) and either PDGF‐BB or PDGF‐AA. The rate at which fibroblasts entered S phase was also similar in PDGF‐BB– and AA–treated cells as was the expression of the late G1 gene, thymidine kinase (TK). However, PDGF‐AA must be present for a period of 16 h to stimulate the proliferation of 90% of the cells, whereas PDGF‐BB was required for only 4 h. Exposure of cells to PDGF‐AA for 4 h, a time during which maximum expression of c‐fos and c‐myc occurred, only induced 20% of the cells in a quiescent population to enter the cell cycle. Therefore, PDGF‐AA–mediated expression of the immediate early genes c‐fos and c‐myc may be necessary but is not sufficient to rapidly stimulate density‐arrested Balb/c‐3T3 fibroblasts into the competent state. Thus, these data suggest that PDGF‐AA and PDGF‐BB initiate traverse of the cell cycle by distinct mechanisms.
Pima Indians as a model to study the genetics of NIDDM
Authors: Bogardus Clifton , Lillioja Stephen 
Published: May 2005

AbstractMore than half the Pima Indians over 35 years of age have non‐insulin dependent diabetes mellitus (NIDDM). They have been the focus of prospective epidemiologic and metabolic studies for over two decades and the data collected during these studies are now providing invaluable in efforts to find genetic markers for NIDDM in humans. The Pima Indian model of this disease affords two major advantages. The population is genetically homogeneous compared to Caucasian populations, and therefore the causes of NIDDM are less heterogeneous, simplifying genetic linkage studies. Equally important, based on results from metabolic studies, two pre‐diabetic phenotypes have been identified in the Pimas: insulin resistance and a low metabolic rate. Use of these phenotypes in genetic linkage analyses should greatly improve chances of finding genetic markers for NIDDM since these phenotypes may be more closely related to the putative abnormal gene products, and actual disease genes, than is the hyperglycemia of the fully developed phenotype of NIDDM.
Apoptosis and DNA fragmentation precede TNF‐induced cytolysis in U937 cells
Authors: Wright Susan C. , Kumar Poornima , Tam Albert W. , Shen Naiping , Varma Madhu , Larrick James W. 
Published: May 2005

AbstractThe hypothesis that activation of apoptosis and DNA fragmentation is involved in TNF‐mediated cytolysis of U937 tumor cells was investigated. Morphological, biochemical, and kinetic criteria established that TNF activates apoptosis as opposed to necrosis. Within 2–3 h of exposure to TNF, U937 underwent the morphological alterations characteristic of apoptosis. This was accompanied by cleavage of DNA into multiples of nucleosome size fragments. Both of these events occurred 1–2 h prior to cell death as defined by trypan blue exclusion of 51Cr release. DNA fragmentation was not a non‐specific result of cell death since U937 cells lysed under hypotonic conditions did not release DNA fragments. The percentage of cells undergoing apoptosis depended on the concentration of TNF and was augmented by the addition of cycloheximide. A TNF‐resistant variant derived from U937 did not undergo apoptosis in response to TNF, even in the presence of cycloheximide. Furthermore, TNF could still activate NFkB in this variant, suggesting that this pathway is not involved in TNF‐mediated cytotoxicity. Two agents known to inhibit TNF‐mediated cytotoxicity, ZnSo4, and 3‐aminobenzamide, were shown to inhibit TNF‐induced apoptosis. Taken altogether, these data support the hypothesis that activation of apoptosis is at least one essential step in the TNF lytic pathway in the U937 model system.
Ligand‐induced formation of the leukotriene B4 receptor‐G protein complex of human polymorphonuclear leukocytes
Authors: Sherman Jeffrey W. , Mendelson Michelle A. , Boggs John M. , Koo Catherine H. , Goetzl Edward J. 
Published: May 2005

AbstractThe components of the polymorphonuclear leukocyte (PMNL) receptor for leukotriene B4 (LTB4) were examined by Sephacryl S‐300 exclusion chromatography of PMNL membrane proteins, which were solubilized before and after the binding of [3H] LTB4. When the PMNL membranes were solubilized in 3‐[(3‐cholamidopropyl)‐dimethylammonio]‐1‐propanesulfonate (CHAPS) and filtered on Sephacryl S‐300 prior to addition of [3H] LTB4, the binding activity was associated with a 65 kD protein. In contrast, the radioactivity of [3H] LTB4 bound to PMNL membranes prior to solubilization was recovered predominately with a 140 kD protein. When PMNL membranes had been pretreated with pertussis toxin, but not cholera toxin, before the addition of LTB4 and subsequent solubilization, radioactivity was recovered predominately with the 65 kD protein. The addition of guanylylimidodiphosphate (GMP‐PNP), a nonhydrolyzable derivative of guanosine triphosphate (GTP), to PMNL membrane receptors bearing [3H] LTB4 either prior to or after CHAPS solubilization reduced the yield of the 140 kD presumed LTB4 receptor protein‐G protein complex. That the maximum specific binding of [35S] guanosine‐5′‐0‐3‐thiotriphosphate (GTP‐gammaS) to LTB4‐binding proteins in the Sephacryl S‐300 effluent corresponded to the 140 kD protein supported the presence of a G protein in the LTB4 receptor complex.
Dihydropyridine calcium antagonist modulates cholesterol metabolism and eicosanoid biosynthesis in vascular cells
Authors: Nicholson Andrew C. , Etingin Orli R. , Pomerantz Kenneth B. , Summers Barbara D. , Friday Karen , Wolff Andrew A. , Hajjar David P. 
Published: May 2005

AbstractRecent clinical studies have shown that calcium channel blockers can retard and possibly reduce the angiographic progression of coronary artery disease. Calcium channel blockers also inhibit dietary‐induced atherosclerosis in animal models of this disease. In this study, we delineate potential cellular and molecular mechanisms by which nicardipine, a dihydropyridine calcium antagonist, may alter lipoprotein and cholesterol trafficking, affect the regulatory signal transduction pathways involved in accelerating cholesteryl ester (CE) catabolism in vascular smooth muscle cells, and modulate cell‐cell interactions of vascular and inflammatory cells. We demonstrate in arterial smooth muscle cells that nicardipine increases (1) LDL binding, uptake, and degradation, (2) RNA transcript levels for the LDL receptor, (3) CE catabolic activity, (4) PGI2 release, and (5) RNA transcript levels for cyclooxygenase. Furthermore, nicardipine blocked cytokine‐induced monocyte adhesion to endothelial cells and smooth muscle cells. Taken together, these findings support the hypothesis that nicardipine may function as an anti‐atherosclerotic agent by promoting CE catabolism and cholesterol clearance and by reducing monocyte adhesion to the activated endothelium.
Vitamin D hydroxylases
Authors: Henry Helen L. 
Published: May 2005

AbstractThere are three mixed function oxidases which catalyze hydroxylations of vitamin D and its derivatives. These include the hepatic mitochondrial or microsomal vitamin D3‐25‐hydroxylase and the two renal mitochondrial enzymes which further hydroxylate 25‐hydroxyvitamin‐D3 (25‐OH‐D3) to form 24R,25‐dihydroxyvitamin D3 (24,25(OH)2D3) and 1,25‐dihydroxyvitamin D3 [1,25(OH)2D3], the primary steroid hormonal derivative of vitamin D3. All three enzymes are cytochrome P450 dependent. The two renal mitochondrial enzymes are regulated, usually in a reciprocal fashion. The intracellular signalling systems involved in this regulation include 1,25(OH)2D3 itself and both protein kinases A and C. Recent progress has been made in the purification and cloning of the vitamin D3‐25‐hydroxylase and the 25‐OH‐D3‐24‐hydroxylase. When the 25‐OH‐D3‐1‐hydroxylase is purified and cloned, efforts which have thus far been frustrated by its low abundance, fertile new ground for the study of the regulation of vitamin D metabolism at the molecular level will be opened up.
Rapid actions of vitamin D compounds
Authors: de Boland Ana R. , Nemere Ilka 
Published: May 2005

AbstractThe rapid actions of vitamin D compounds are surveyed in a variety of target tissues, including intestine, muscle, bone, hepatocytes, fibroblasts, HL‐60 cells, kidney, mammary gland, and parathyroid. Evidence for non‐nuclear receptors vs. membranophilic effects is discussed, followed by a consideration of signal transduction mechanisms including steroid hormone activated Ca2+ channels, phospholipid metabolism, protein kinases, and the role of G‐proteins.