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81.
Flemming S. Vassbotn Arne
stman Nina Langeland Holm Holmsen Bengt Westermark Carl-Henrik Heldin Monica Nistr 《Journal of cellular physiology》1994,158(2):381-389
Human glioblastoma cells (A172) were found to concomitantly express PDGF-BB and PDGF β-receptors. The receptors were constitutively autophosphorylated in the absence of exogenous ligand, suggesting the presence of an autocrine PDGF pathway. Neutralizing PDGF antibodies as well as suramin inhibited the autonomous PDGF receptor tyrosine kinase activity and resulted in up-regulation of receptor protein. The interruption of the autocrine loop by the PDGF antibodies reversed the transformed phenotype of the glioblastoma cell, as determined by (1) diminished DNA synthesis, (2) inhibition of tumor colony growth, and (3) reversion of the transformed morphology of the tumor cells. The PDGF antibodies showed no effect on the DNA synthesis of another glioblastoma cells line (U343MGa 31L) or on Ki-ras-transformed fibroblasts. The present study demonstrates an endogenously activated PDGF pathway in a spontaneous human glioblastoma cell line. Furthermore, we provide evidence that the autocrine PDGF pathway drives the transtormed phenotype of the tumor cells, a process that can be blocked by extracellular antagonists. © 1994 Wiley-Liss, Inc. 相似文献
82.
Biological Trace Element Research - The results of a research in progress at the Istituto di Fisica Generale Applicata—University of Milan—on natural and anthropogenic elements'... 相似文献
83.
84.
85.
Expression of the hepatitis delta virus large and small antigens in transgenic mice. 总被引:5,自引:3,他引:2
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S Guilhot S N Huang Y P Xia N La Monica M M Lai F V Chisari 《Journal of virology》1994,68(2):1052-1058
Simultaneous infection with hepatitis delta virus (HDV) and hepatitis B virus (HBV) in humans is often associated with severe viral liver disease including fulminant hepatitis. Since HBV is thought to be noncytopathic to the hepatocyte, the enhanced disease severity observed during dual infection has been attributed to either simultaneous immune responses against the two viruses or direct cytotoxic effects of HDV products on the hepatocyte or both. To examine these alternate possibilities, we produced transgenic mice that express the small and large delta antigens (HDAg) in hepatocyte nuclei at levels equal to those observed during natural HDV infection. No biological or histopathological evidence of liver disease was detectable during 18 months of observation, suggesting that neither the large nor small form of HDAg is directly cytopathic to the hepatocyte in vivo. 相似文献
86.
Abstract. The aim of our study was to investigate whether supernatant from lipopoly-saccharide-activated monocytes (monocyte-factor) and/or cytokines could enhance secretion of human monoclonal antibodies specific to HLA antigens produced by Epstein—Barr virus lymphoblastoid cell lines (EBV-LCLs). In a low cell density culture system, the monocyte-factor significantly stimulated cell growth of three monoclonal and two polyclonal EBV-LCLs while no enhancement of immunoglobulin production was observed. The enhancement of proliferation was completely neutralized by an antiserum to human IL-6 suggesting that IL-6 was required for the stimulation of growth of LCLs. The effect of cytokines on proliferation showed large variations among the cell lines, with IL-l β generally inducing the highest response. Of the cytokines tested, only IL-2 was able to enhance total immunoglobulin secretion due to the induction of a higher production of light chains. The specific anti-HLA activity was slightly increased by IL-10 although this cytokine had no effect on total immunoglobulin concentration or proliferation. 相似文献
87.
John C. Spurlino Angela M. Smallwood Dennis D. Carlton Tracey M. Banks Karen J. Vavra Jeffrey S. Johnson Ewell R. Cook Joseph Falvo Robert C. Wahl Tricia A. Pulvino John J. Wendoloski Douglas L. Smith 《Proteins》1994,19(2):98-109
The X-ray crystal structure of a 19 kDa active fragment of human fibroblast collagenase has been determined by the multiple isomorphous replacement method and refined at 1.56 Å resolution to an R-factor of 17.4%. The current structure includes a bound hydroxamate inhibitor, 88 waters and three metal atoms (two zincs and a calcium). The overall topology of the enzyme, comprised of a five stranded β-sheet and three α-helices, is similar to the thermolysin-like metalloproteinases. There are some important differences between the collagenase and thermolysin families of enzymes. The active site zinc ligands are all histidines (His-218, His-222, and His-228). The presence of a second zinc ion in a structural role is a unique feature of the matrix metalloproteinases. The binding properties of the active site cleft are more dependent on the main chain conformation of the enzyme (and substrate) compared with thermolysin. A mechanism of action for peptide cleavage similar to that of thermolysin is proposed for fibroblast collagenase. © 1994 Wiley-Liss, Inc. 相似文献
88.
Summary We have examined the 13C and 13C chemical shifts of a number of proteins and found that their values at the N-terminal end of a helix provide a good predictor for the presence of a capping box. A capping box consists of a hydrogen-bonded cycle of four amino acids in which the side chain of the N-cap residue forms a hydrogen bond with the backbone amide of the N3 residue, whose side chain in turn may accept a hydrogen bond from the amide of the N-cap residue. The N-cap residue exhibits characteristic values for its backbone torsion angles, with and clustering around 94±15° and 167±5°, respectively. This is manifested by a 1–2 ppm upfield shift of the 13C resonance and a 1–4 ppm downfield shift of the 13C resonance, relative to their random coil values, and is mainly associated with the unusually large value of . The residues following the N-cap residue exhibit downfield shifts of 1–3 ppm for the 13C resonances and small upfield shifts for the 13C ones, typical of an -helix. 相似文献
89.
Dipl. Geol. Jens Hefter Dipl. Geol. Volker Thiel Dr. Angela Jenisch Dr. Ursula Galling Dr. Stephan Kempe Dr. habil. Walter Michaelis 《Facies》1993,29(1):93-105
Summary Biomarker investigations were applied to the hydrocarbon fractions of three Recent (cyanobacterial mat, Lake Van microbialite
and Lake Satonda microbialite) and two Late Jurassic carbonate samples obtained from sponge bioherms. The relative concentrations
ofn-alkanes, monomethyl alkanes, acyclic isoprenoids, steroids and hopanoids in these samples are studied and their probable
biological precursors are discussed. Normal alkanes with carbon chain lengths ranging from C15 to C34 and monomethyl alkanes ranging from C17 to C21 with a varying methyl branching pattern are found. The major hydrocarbons are low molecular weight (LMW)n-alkanes (C15–C21) with a slight to strong predominance ofn-heptadecane (C17). High molecular weight (HMW)n-alkanes occur in low to moderate relative concentrations showing a preference of odd-carbon numbered compounds with a maximum
at C29. Within the acyclic isoprenoids, pristane, phytane/phytene, pentamethyl-eicosane, squalane and lycopane could be identified.
Polycyclic terpenoids of the sterane and/or hopane type are present in all carbonate samples. The carbon numbers of these
components range from 27 to 29 and 27 to 32, respectively. These organic compounds identified can be attributed to various
source organisms such as cyanobacteria, archaebacteria, algae and vascular plants. All hydrocarbon fractions of the samples
are characterized by moderate to high relative concentrations of compounds derived from cyanobacteria, signifying the role
of these organisms as contributors to the Recent as well as to the Late Jurassic carbonate deposits. 相似文献
90.
Valentina Bobyleva Nancy Kneer Monica Bellei Daniela Battelli Henry A. Lardy 《Journal of bioenergetics and biomembranes》1993,25(3):313-321
Dehydroepiandrosterone (DHEA) treatment of rats decreases gain of body weight without affecting food intake; simultaneously, the activities of liver malic enzyme and cytosolic glycerol-3-P dehydrogenase are increased. In the present study experiments were conducted to test the possibility that DHEA enhances thermogenesis and decreases metabolic efficiency via trans-hydrogenation of cytosolic NADPH into mitochondrial FADH2 with a consequent loss of energy as heat. The following results provide evidence which supports the proposed hypothesis: (a) the activities of cytosolic enzymes involved in NADPH production (malic enzyme, cytosolic isocitrate dehydrogenase, and aconitase) are increased after DHEA treatment; (b) cytosolic glycerol-3-P dehydrogenase may use both NAD+ and NADP+ as coenzymes; (c) activities of both cytosolic and mitochondrial forms of glycerol-3-P dehydrogenase are increased by DHEA treatment; (d) cytosol obtained from DHEA-treated rats synthesizes more glycerol-3-P during incubation with fructose-1,6-P2 (used as source of dihydroxyacetone phosphate) and NADP+; the addition of citratein vitro further increases this difference; (e) mitochondria prepared from DHEA-treated rats more rapidly consume glycerol-3-P added exogenously or formed endogenously in the cytosol in the presence of fructose-1,6-P2 and NADP+. 相似文献