bluuebunny/crossref_metadata_2025_split huggingface dataset:
Functional and structural characteristics of EGF and its receptor and their relationship to transforming proteins
Authors: Stoscheck C. M. , King L. E. 
Published: December 2004

AbstractEpidermal growth factor (EGF) is a peptide which effects the growth and/or differentiated functions of many cell types. Several pieces of evidence indicate that EGF and its receptor may play a role in carcinogenesis. Functional and structural characteristics of EGF and its receptor and their relationship to transforming proteins are discussed. EGF has extensive homology with alpha‐transforming growth factor (alpha‐TGF), which may actually be an embryonic form of EGF. Nevertheless, both EGF and alpha‐TGF elicit transformation‐associated phenotypes in target cells under certain conditions.EGF effects are mediated by a receptor present on the plasma membrane. The EGF receptor is a highly complex protein having several functions in addition to binding EGF in a highly specific manner. One of these functions is to phosphorylate tyrosyl residues on certain proteins. This activity is similar to that expressed by the src family of oncogene‐encoded proteins. Besides sharing functional homology the EGF receptor also exhibits structural homology to several oncogene‐encoded proteins. The v‐erb‐B‐transforming protein has a striking extent of homology (95%) to the cytoplasmic portion of the EGF receptor. These data support the concept that some aspect of EGF‐stimulated metabolism is involved in cellular transformation.
Liver autophagy in the influenza B virus model of Reye's syndrome in mice
Authors: Woodfin Beulah M. , Davis Larry E. 
Published: December 2004

AbstractBiochemical evidence is presented for the autophagic destruction of liver mitochondria in the influenza B virus model of Reye's syndrome in mice. Separation of lysosomes and autophagic vacuoles from mitochondria was accomplished by prior treatment of the mice with Triton WR‐1339, resulting in uptake of detergent by these organelles (tritosomes), reducing their densities. The organelles were banded in a discontinuous sucrose gradient. Total protein in the heavy tritosomal fraction increased from 1–2% in controls to 7–8% in virus‐treated animals. Ornithine carbamoyl transferase (OCTase), a mitochondrial marker, increased from 2–3% (controls) to 11–15% (virus‐treated), and glucose‐6‐phosphatase, a marker for endoplasmic reticulum, increased from 1–2% (controls) to 8–10% (virus‐treated). β‐Galactosidase, a soluble enzyme in the lysosome, and OCTase also increase in the cell extract fraction following virus treatment, indicating that there was turnover of heavy lysosomal contents.
The receptor for urokinase‐plasminogen activator
Authors: Blasi Francesco , Stoppelli M. Patrizia , Cubellis M. Vittoria 
Published: December 2004

AbstractMany human cells and cell lines possess a specific receptor that binds urokinase plasminogen activator (uPA) with an affinity of about 10−10 M. Bound enzyme is not internalized, is slowly dissociated, and retains its enzymatic activity. The amino acid sequence of uPA responsible for receptor binding is located within the first 35 aminoterminal residues, ie, in the growth factor domain. Binding, however, is not competed for by other proteins that contain the growth factor domain (including epidermal growth factor). Cells that produce uPA secrete the pro‐uPA form, which subsequently binds to the receptor. A431 cells, in fact, have their receptors completely saturated with pro‐uPA. It is proposed that uPA:uPA‐receptor interaction plays a direct role in physiological and pathological processes that require cell migration.
Calcimedins: Purification and characterization from chicken gizzard and rat and bovine livers
Authors: Mathew J. K. , Krolak J. M. , Dedman J. R. 
Published: December 2004

AbstractA procedure for the simultaneous extraction and purification of four calcimedins from chicken gizzard, rat liver, and bovine liver is described. These proteins bind to hydrophobic resins in a calcium‐dependent manner similar to calmodulin and troponin C. The four calcimedins purified had molecular weights 67,000 (67K), 35,000 (35K), 33,000 (33K), and 30,000 (30K) as determined by SDS polyacrylamide gel electrophoresis. Their ability to bind calcium was demonstrated using the Hummel‐Dreyer method. Their tissue concentration ranged between 1–4 mg/ 100 g wet weight in the three tissues studied. During gel filtration, calcimedins 67K and 35K, had Rf (Ve‐Vo/Vt‐Vo) values of 0.46 and 0.74, respectively, indicating monomeric structure. However, the 33K and 30K calcimedins had Rf values of 0.26 (molecular weights > 90,000) suggesting that they occur as subunit complexes in their native state. Antibodies raised against the 67K and 35K calcimedins showed cross reactivity suggesting possible common origin. However, peptide mapping studies showed that they are independent proteins with considerable peptide homology. Antibodies to 30/33K calcimedins did not cross‐react with either 67K or 35K calcimedins. Moreover, their peptide maps were strikingly different from those of 67K and 35K calcimedins indicating that they are unique. At present, the regulatory function of this group of proteins is not clear. Indirect evidences support the possibility that they are involved in membrane associated events, such as endocytosis and secretion.
Fibrinolytic system of cultured endothelial cells: Regulation by plasminogen activator inhibitor
Authors: Loskutoff David J. , Ny Tor , Sawdey Michael , Lawrence Daniel 
Published: December 2004

AbstractCultured bovine aortic endothelial cells have a relatively complex flbrinolytic system that is responsive to both the physiological state of the cell itself and to a variety of agents added to the culture medium. The flbrinolytic activity of these cells results from the production of both urokinase‐type and tissue‐type plasminogen activators and is regulated by an inhibitor capable of neutralizing their activities. The properties of these flbrinolytic components will be reviewed, and their respective roles in initiating and regulating the flbrinolytic activity of the cells will be summarized. A cDNA coding for the inhibitor has been isolated, and its sequence will be compared to that of other serine proteinase inhibitors.
Regulation of the ubiquitin‐mediated proteolytic pathway: Role of the substrate α‐NH2 group and of transfer RNA
Authors: Ciechanover Aaron 
Published: December 2004

AbstractDegradation of intracellular proteins via the ubiquitin pathway involves several steps. In the initial event, ubiquitin becomes covalently linked to the protein substrate in an ATP‐requiring reaction. Following ubiquitin conjugation, the protein moiety of the adduct is selectively degraded with the release of free and reusable ubiquitin. Ubiquitin modification of a variety of protein targets in the cell plays a role in basic cellular functions. Modification of core nucleosomal histones is probably involved in regulation of gene expression at the level of chromatin structure. Ubiquitin attachment to cell surface proteins may play roles in processes of cell‐cell interaction and adhesion, and conjugation of ubiquitin to other yet to be identified protein(s) could be involved in the progression of cells through the cell cycle. Despite the considerable progress that has been made in the elucidation of the mode of action and cellular roles of the ubiquitin pathway, many major problems remain unsolved. A problem f central importance is the specificity in the ubiquitin ligation system. Why are certain proteins conjugated and committed for degradation, whereas other proteins are not? A free α‐NH2 group is an important feature of the protein structure recognized by the ubiquitin conjugation system, and tRNA is required for the conjugation of ubiquitin to selective proteo‐lytic substrates and for their subsequent degradation. These findings can shed light on some of the features of a substrate that render it susceptile to ubiquitin‐mediated degradation.
Types I and IV collagenolytic and plasminogen activator activities in preovulatory ovarian follicles
Authors: Palotie Aarno , Salo Tuula , Vihko Kimmo K. , Peltonen Leena , Rajaniemi Hannu 
Published: December 2004

AbstractDuring ovulation, enzymatic degradation of the extracellular matrix occurs within and around the graafian follicles. In this study, the activities of several different proteolytic enzymes were measured in the culture media of follicles taken from pregnant mare serum gonadotropin (PMSG)‐primed immature rats. At 52 h after PMSG, the follicles were cultured for 2 to 15 h in media with or without human chorionic gonadotropin (hCG). Type I collagenase activity in hCG‐stimulated follicles gradually increased within 6 h to 3.3‐fold above that of the controls. Relatively pure populations of granulosa cells produced type I collagenase to a similar extent. Likewise, type IV collagenase increased 3.8‐fold by 6 h after exposure of the follicles to hCG. In contrast, plasminogen activator activity increased by 3.9‐fold at 2 h after hCG, but was negligible at 4, 6, and 15 h after incubation. These results suggest that plasminogen activator may activate both type I and type IV collagenase in hCG‐stimulated ovulatory follicles.
Heterologous regulation of EGF receptors in fibroblastic cells
Authors: Olashaw Nancy E. , Pledger W. J. 
Published: December 2004

AbstractPlatelet‐derived growth factor (PDGF) increases the mitogenic activity of epidermal growth factor (EGF) in several cells lines, including BALB/C‐3T3. PDGF‐treated BALB/C‐3T3 cells manifest a reduced capacity to bind 125I‐labeled EGF due to a loss of high affinity EGF receptors. Cholera toxin potentiates the ability of PDGF to both decrease EGF binding and initiate mitogenesis. Whether PDGF increases EGF sensitivity via its effects on EGF receptors is not known and requires a more complete understanding of the mechanism by which PDGF decreases EGF binding.12‐0‐tetradecanoylphorbol 13‐acetate (TPA) also reduces EGF binding in BALB/C‐3T3 and other cells, presumably by activating protein kinase C and, consequently, inducing the phosphorylation of EGF receptors at threonine–654. PDGF indirectly activates protein kinase C, and EGF receptors in PDGF‐treated WI‐38 cells are phosphorylated at threonine‐654. Thus, the effects of PDGF on EGF binding may also be mediated by protein kinase C. We investigated this hypothesis by comparing the actions of PDGF and TPA on EGF binding in density‐arrested BALB/C‐3T3 cells.Both PDGF and TPA caused a rapid, transient, cycloheximide‐independent loss of 251‐EGF binding capacity. The actions of both agents were potentiated by cholera toxin. However, whereas TPA allowed EGF binding to recover, PDGF induced a secondary and cycloheximide‐dependent loss of binding capacity. Most importantly, PDGF effectively reduced binding in cells refractory to TPA and devoid of detectable protein kinase C activity. These findings indicate that PDGF decreases EGF binding by a mechanism that involves protein synthesis and is distinct from that of TPA.
Use of anti‐idiotypic antibodies as probes for the interaction of TSH subunits with its receptor
Authors: Briones‐Urbina Rosario , Islam M. N. , Ivanyi J. , Farid Nadir R. 
Published: December 2004

AbstractTSH is a heterodimeric glycoprotein hormone, whose dissociated subunits are without biological activity. This has precluded the assessment of the relative contribution of each subunit to hormone action. We have raised anti‐idiotypes to monoclonal antibodies specific, respectively, for the α and β hTSH subunits. The anti‐β anti‐idiotype inhibited l25I‐hTSH binding to the β subunit‐specific monoclonal quantitatively, whereas 125I‐hTSH binding to the α subunit‐specific monoclonal was not inhibited by anti‐α anti‐idiotypes, suggesting that only the former is an “internal image” anti‐idiotype. Neither of the two anti‐idiotypes nor equimolar mixtures thereof inhibited 125I‐bTSH binding to thyroid membranes, even though radiolabelled anti‐idiotypes showed saturable binding to thyroid plasma membrane which was inhibited 41–65% by bTSH. Each anti‐idiotype alone caused 9% inhibition (compared to 50% by NRIgG) of thyroid plasma membrane adenylate cyclase. Equimolar mixtures (125 μg/ml IgG of each anti‐idiotype) induced enzyme activity equivalent to 85% of that of 250 mU/ml of TSH. The TSH‐like action of the two anti‐idiotypes was also reflected in their capacity to increase (450% by 250 μg/ml IgG compared to normal rabbit IgG) the uptake of 131I into isolated thyrocytes and to promote the organization of such cells into follicular structures. At 250 μg/ml, anti‐β anti‐idiotype promoted the organization of small follicles and only at a concentration of 500 μg/ml did it enhance 131I uptake. Anti α idiotype was without effect in both assays. Lastly, mixture of anti‐idiotypes bound to the ∼ 197,000 Mr band (TSH holoreceptor) on protein blots of thyroid plasma membranes resolved on NaDSO4‐polyacrylamide gel electrophoresis under non‐reducing conditions. Individual anti‐idiotypes were without effect.The TSH α and β subunits apparently deliver two cooperative signals to the receptor and that specificity is associated with the β subunit, while the α subunit is important in enhancing receptor affinity for the heterodimer and in stablizing TSH‐receptor complex.
Crosslinking of DNA to nuclear lamina proteins by UV irradiation in vivo
Authors: Galcheva‐Gargova Z. , Dessev G. N. 
Published: December 2004

AbstractWe have been able to demonstrate that a fraction of DNA becomes crosslinked to nuclear lamina shells isolated from Ehrlich ascites tumour cells irradiated with UV light. Terminal labeling of short DNA fragments covalently attached to proteins reveals that DNA has become crosslinked to all three lamins and to a protein comigrating with vimentin.
Microtubule‐associated proteins present in different developmental stages ofDrosophila melanogaster
Authors: Wandosell Francisco , Avila Jesús 
Published: December 2004

AbstractMicrotubule‐associated proteins (MAPs) have been isolated from different development stages ofDrosophila melanogasterand characterized by their association to tubulin, but not to tubulin lacking its 4‐kD carboxy terminal region (S‐tubulin), and by their ability to promote tubulin polymerization. Following these criteria some peptides of Mr 255, 205, and 180 kD were identified as MAPs.By means of immunological analogy we have identified a peptide related to mammalian brain MAP known as tau factor.
Developmentally regulated primary glucocorticoid hormone induction of chick retinal glutamine synthetase mRNA
Authors: Patejunas Gerald , Young Anthony P. 
Published: December 2004

AbstractWe have characterized the glucocorticoid hormone induction of glutamine synthetase mRNA in embryonic chick retinal organ cultures by quantitative dot hybridization using a cDNA clone derived from chick retinal RNA. Hydrocortisone (Kapp = 3–4 nM) and dexamethasone (Kapp = 1–2 nM) produce an approximate 30‐fold increase in glutamine synthetase mRNA after incubation of organ cultures derived from embryonic day 12 retinae with either hormone for 3 hr. Progesterone is a poor inducer. The glucocorticoid‐mediated rise is rapid (t½ = 2–3 hr) and occurs in the presence of either of the protein synthesis inhibitors cycloheximide or puromycin, indicating that the induction is a primary or direct response to the hormone. However, the magnitude of the hormonal response observed in culture increases markedly during retinal development. These observations, coupled with the previously reported absence of a hormonal induction in embryonic liver, raise the possibility of a synergistic mechanism, involving tissue‐specific regulatory molecules in addition to the glucocorticoid hormone receptor, to explain the retinal‐specific primary glucocorticoid hormone induction of glutamine synthetase mRNA.
Regulation of inositol phospholipid and inositol phosphate metabolism in chemoattractant‐activated human polymorphonuclear leukocytes
Authors: Dillon Susan B. , Murray John J. , Uhing Ronald J. , Snyderman Ralph 
Published: December 2004

AbstractBinding of chemoattractants to specific cell surface receptors on polymorphonu‐clear leukocytes (PMNs) initiates a series of biochemical responses leading to cellular activation. A critical early biochemical event in chemoattractant (CTX) receptor‐mediated signal transduction is the phosphodiesteric cleavage of plasma membrane phosphatidylinositol 4,5‐bisphosphate (PIP2), with concomitant production of the calcium mobilizing inositol‐1,4,5‐trisphosphate (IP3) isomer, and the protein kinase C activator, 1,2‐diacylglycerol (DAG). The following lines of experimental evidence collectively suggest that CTX receptors are coupled to phospholipase C via a guanine nucleotide binding (G) protein. Receptor‐mediated hydrolysis of PIP2 in PMN plasma membrane preparations requires both fMet‐Leu‐Phe and GTP, and incubation of intact PMNs with pertussis toxin (which ADP ribosylates and inactivates some G proteins) eliminates the ability of fMet‐Leu‐Phe plus GTP to promote PIP2 breakdown in isolated plasma membranes. Studies with both PMN paniculate fractions and with partially purified fMet‐Leu‐Phe receptor preparations indicate that guanine nucleotides regulate CTX receptor affinity. Finally, fMet‐Leu‐Phe stimulates high‐affinity binding of GTPγS to PMN membranes as well as GTPase activity. A Ga subunit has been identified in phagocyte membranes which is different from other Ga subunits on the basis of molecular weight and differential sensitivity to ribosylation by bacterial toxins. Thus, a novel G protein may be involved in coupling CTX receptors to phospholipase C. Studies in intact and sonicated PMNs demonstrate that metabolism of 1,4,5‐IP3 proceeds via two distinct pathways: (1) sequential dephosphorylation to 1,4‐IP2, 4‐IP1 and inositol, or (2) ATP‐dependent conversion to inositol 1,3,4,5‐tetrakisphosphate (IP4) followed by sequential dephosphorylation to 1,3,4‐IP3, 3,4‐IP2, 3‐IP1 and inositol. Receptor‐mediated hydrolysis of PIP2 occurs at ambient intracellular Ca2+ levels; but metabolism of 1,4,5‐IP3 via the IP4 pathway requires elevated cytosolic Ca2+ levels associated with cellular activation. Thus,the two pathways for 1,4,5‐IP3 metabolism may serve different metabolic functions. Additionally, inositol phosphate production appears to be controlled by protein kinase C, as phorbol myristate acetate (PMA) abrogates PIP2 hydrolysis by interfering with the ability ofthe activated G protein to stimulate phospholipase C. This implies a physiologic mechanism for terminating biologic responses via protein kinase C mediated feedback inhibition of PIP2 hydrolysis.
Lipid polarity and sorting in epithelial cells
Authors: van Meer Gerrit , Simons Kai 
Published: December 2004

AbstractApical and basolateral membrane domains of epithelial cell plasma membranes possess unique lipid compositions. The tight junction, the structure separating the two domains, forms a diffusion barrier for membrane components and thereby prevents intermixing of the two sets of lipids. The barrier apparently resides in the outer, exoplasmic leaflet of the plasma membrane bilayer. First data are now available on the generation of these differences in Madin‐Darby canine kidney (MDCK) cells, grown on filter supports. Experiments in which fluorescent precursors of apical lipids were introduced into the cell have demonstrated that upon biosynthesis apical lipids are sorted from basolateral lipids in an intracellular compartment. In this paper we present a model for the sorting process, the central point of which is that the two sets of lipids laterally segregate into microdomains that bud to form vesicles delivering the lipids to the apical and the basolateral plasma membrane domains, respectively.
Characterization of yeast clathrin and anticlathrin heavy‐chain monoclonal antibodies
Authors: Lemmon Sandra K. , Lemmon Vance P. , Jones Elizabeth W. 
Published: December 2004

AbstractClathrin‐coated vesicles (CVs) were isolated from Saccharomyces cerevisiae by using procedures developed by Mueller and Branton [17]. Triskelions were purified from this material by extraction of CVs to release clathrin and by subsequent fractionation on Sepharose CL‐4B. Triskelions were composed of ∼ 180,000 Mr heavy chains and a single light‐chain type of ∼ 38,000 Mr and were able to undergo self‐assembly into polyhedral cages. Trypsin digestion of such reassembled cages showed a peptide pattern very similar to that obtained for mammalian clathrin with two fragments of 125,000 and 110,000 Mr, which represent the major portion of the heavy‐chain arm, and a polypeptide of ∼ 43,000 Mr, which is the presumptive terminal domain.Eight monoclonal antibodies reacting with yeast clathrin heavy chains were produced. All eight bind to the major portion of the heavy‐chain arm, and none bind to the terminal domain fragment. Peptide digestion experiments also indicated that at least three major regions on the arm are recognized by these antibodies. These will be useful in further structural and functional studies of clathrin from yeast.
Correlation of immunomodulatory and therapeutic activities of interferon and interferon inducers in metastatic disease
Authors: Black Paul L. , Phillips Hamblin , Tribble Henry R. , Pennington Robin , Schneider Mark , Talmadge James E. 
Published: December 2004

AbstractThe mechanism of therapeutic activity of recombinant murine interferon‐gamma (rMu IFN‐γ) and the IFN inducer polyinosinic‐polycytidylic acid solubilized with poly‐L‐lysine in carboxy methyl cellulose (pICLC) in treating metastatic disease was investigated by comparing effector cell augmentation with therapeutic activity in mice bearing experimental lung metastases (B16‐BL6 melanoma). Effector cell functions in spleen, peripheral blood, and lung (the organ with tumor) were tested after 1 and 3 weeks of rMu IFN‐γ or pICLC administration (intravenous, three times a week). In these studies, natural killer (NK), lymphokine‐activated killer (LAK), cytolytic T lymphocytes (CTL) (against specific and nonspecific targets), and macrophage tumoricidal and tumoristatic activities were measured. rM IFN‐γ and pICLC had therapeutic activity and immunomodulatory activity in most assays of immune function examined. Specific CTL activity of pulmonary parenchymal mononuclear cells (PPMC), but not in splenocytes or peripheral blood lymphocytes (PBL), during week 3 and not during week 1, correlated with the therapeutic activity of rMu IFN‐γ and of pICLC. Macrophage tumoricidal activity in PPMC, but not in alveolar macrophages, also correlated with the therapeutic activity of rMu IFN‐γ, but the opposite was true for the therapeutic activity of pICLC. NK activity of PPMC, but not of splenocytes or PBL, during week 1 correlated with the therapeutic activity of pICLC; in contrast, NK activity at any site did not correlate with the therapeutic activity of rMu IFN‐γ. LAK activity at any site did not correlate with the therapeutic activity of either agent.