bluuebunny/crossref_metadata_2025_split huggingface dataset:
Isolation and characterization of a variant of B16‐mouse melanoma resistant to MSH growth inhibition
Authors: Niles Richard M. , Logue Mary P. 
Published: May 2005

AbstractA variant of B‐16 F1 mouse melanoma was selected for its ability to survive and replicate in the presence of melanocyte‐stimulating hormone (MSH). Although the variant (MR‐4) was completely resistant to growth inhibition by MSH, cyclic AMP was still able to block cell replication. Tyrosinase activity in MR‐4 cells was considerably lower than in B‐16 F1 cells. MSH induced a twofold to three‐fold increase in tyrosinase activity in both cell types, but the absolute activity in MR‐4 remained significantly less than in the parental cells. MR‐4 cells were also found to have a markedly depressed cyclic AMP‐dependent protein kinase activity relative to B‐16 F1 cells. The protein kinase from both cell types was stimulated by cyclic AMP, but the level of MR‐4 kinase activity at maximal cyclic AMP concentrations remained considerably lower than B‐16 F1 kinase activity under the same conditions. In both cell types adenylate cyclase activity was markedly stimulated by MSH. When equal numbers of viable F1 and MR‐4 cells were injected subcutaneously into C57/B1 mice, the MR‐4 cells formed tumors earlier and killed the host sooner than the parental F1 cells. We conclude that the biochemical alteration which allows MR‐4 cells to replicate in the presence of MSH is a low level of tyrosinase activity, which in turn may be the result of low cyclic AMP‐dependent protein kinase activity.
Specific interaction of cytochalasins with muscle and platelet actin filaments in vitro
Authors: Howard Thomas H. , Lin Shin 
Published: May 2005

AbstractThe cytochalasins (CE, CD, CB and H2CB) inhibit numerous cellular processes which require the interaction of actin with other structural and contractile proteins. In this report we describe the effects of the cytochalasins on the viscosity and morphology of muscle and platelet actin. The cytochalasins decreased the viscosity of F‐actin solutions. The effect of H2CB, CB and CD on F‐actin viscosity was maximal at concentrations of 20–50μM and did not increase with time. In contrast, CE caused a progressive decrease in the viscosity of F‐actin solutions which was dependent upon the concentration of CE and the duration of incubation of the CE‐actin mixture. After two hours of incubation of drug‐actin mixtures, the relative effectiveness of the cytochalasins in reducing the viscosity of F‐actin was CE > CD > CB = H2CB. The effects of CD and CE were paralleled by morphologic changes in negatively stained actin filaments. The effects of the cytochalasins on the viscosity and morphology of muscle and platelet actin were the same whether the drugs were added before or after the polymerization of the protein.These studies show that the interaction of the cytochalasins with actin is highly specific. Because the relative potencies of these drugs for affecting motile processes and the relative affinities of the drugs for binding sites within a variety of cells are CE > CD > CB = H2CB, the effects of cytochalasins on actin described here may contribute to some of the biological effects of the drugs on motile processes.
Polypeptide subunits of dynein 1 from sea urchin sperm flagella
Authors: Bell Christopher W. , Fronk Earl , Gibbons I. R. 
Published: May 2005

AbstractA high‐resolution sodium dodecyl sulfate polyacrylamide gel electrophoresis system has been used to show the presence, in both whole sperm and isolated flagellar axonemes, of eight polypeptides migrating in the 300,000–350,000 molecular weight range characteristic of the heavy chains of dynein ATPase. Previously, only five such chains have been discernible. Extraction of isolated axonemes for 10 min at 4°C with a solution containing 0.6 M NaCl, pH 7, releases a mixture of particles that separate, in sucrose density gradient centrifugation, into a major peak, dynein 1 ATPase, sedimenting at 21 S and a minor peak at 12–14S. The polypeptide compositions of these two peaks are different. The dynein 1 peak, which contains most of the protein on the gradient, contains approximately equal quantities of two closely migrating heavy chains, with a small amount of a third, more slowly migrating chain; no other heavy chains appear in this peak. Two groups of smaller polypeptides (three intermediate chains, within the apparent molecular weight range 76,000–122,000 and four newly discovered light chains, within the apparent molecular weight range 14,000–24,000) cosediment with the 21 S peak. The heavy chain composition of the 12–14S peak is more complex, all eight heavy chains occurring in approximately the same ratios as occur in intact axonemes.
Fibrous projections from the core of a bacteriophage T7 procapsid
Authors: Serwer Philip 
Published: May 2005

AbstractA cylindrical core previously demonstrated in a bacteriophage T7 procapsid (capsid I) has been further examined by electron microscopy. Fibrous extensions of the core have been observed; these fibers appear to connect the core to the capsid I envelope. After infection of a nonpermissive host with bacteriophage T7 amber mutant in any gene coding for a core protein, the resulting lysates contained more noncapsid assemblies of capsid envelope protien than did wild‐type lysates; these assemblies had a mass two to at least 500 times greater than the mass of capsid I. This suggests that the internal core and fibers assist the assembly of subunits in the envelope of capsid I.
Pyrenesulfonyl azide as a fluorescent label for the study of protein‐lipid boundaries of acetylcholine receptors in membranes
Authors: Gonzalez‐Ros J. M. , Calvo‐Fernandez P. , Šator V. , Martinez‐Carrion M. 
Published: May 2005

AbstractAcetylcholine receptor (AcChR) enriched membrane fragments from Torpedo californica electroplax were labeled by in situ photogenerated nitrenes from a hydrophobic fluorescent probe, pyrene‐1‐sulfonyl azide. Preferential photolabeling of membrane proteins, mainly AcChR, has been achieved and there is a pronounced exposure of the 48,000 and 55,000 molecular weight subunits of AcChR to the lipid environment of the membrane core.Covalent attachment of the photogenerated fluorescence probe does not perturb the α‐neurotoxins' binding properties of membrane‐bound AcChR or the desensitization kinetics induced by prolonged exposures to cholinergic agonists. Non‐covalent photoproducts can be conveniently removed from labeled membrane preparations by exchange into lipid vesicles prepared from electroplax membrane lipids. Fluorescence features of model pyrene sulfonyl amide derivatives, such as fine vibrational structure of emission spectra or fluorescence lifetimes, are highly sensitive to the solvent milieu. The covalently bound probe shows similar fluorescence properties in situ. PySA photoproducts have great potential to spectroscopically monitor neurotransmitter induced events on selected AcChR subunits exposed to the hydrophobic environment of membranes.
Effect of vanadate on gill cilia: Switching mechanism in ciliary beat
Authors: Wais‐Steider Jacobo , Satir Peter 
Published: May 2005

AbstractLateral (L) cilia of freshwater mussel (Margaritana margaritifera and Elliptio complanatus) gills can be arrested in one of two unique positions. When treated with 12.5 mM CaCl2 and 10−5 M A23187 they arrest in a “hands up” position, ie, pointing frontally. When treated with approximately 10 mM vanadate (V) they arrest in a “hands down” position, ie, pointing abfrontally. L‐cilia treated with 12.5 mM CaCl2 and 1 mM NaN3 also arrest in a “hands down” position; substitution of 20 mM KC1 and 1 mM NaN3 causes cilia to move rapidly and simultaneously to a “hands up” position.The observations suggest that there are two switching mechanisms for activation of active sliding in ciliary beat one at the end of the recovery stroke and the other at the end of the effective stroke; the first is inhibited by calcium and the second by vanadate or azide. This is consistent with a model of ciliary beating where microtubule doublet numbers 1, 2, 3, and 4 are active during the effective stroke while microtubule doublets numbers 6, 7, 8, and 9 are passive, and the converse occurs during the recovery stroke.
The errors in assembly of MuLV in interferon treated cells
Authors: Pitha Paula M. , Fernie Bruce , Maldarelli Frank , Wivel Nelson A. 
Published: May 2005

AbstractInterferon treatment of JLSV‐6 cells chronically infected with Rauscher MuLV leads to the formation of noninfectious particles (interferon virions) containing the structural proteins of env and gag genes as well as additional viral polypeptides. In the control virions the major glycoprotein detected is gp71, interferon virions contain in addition to gp71 and 85k dalton (gp85) glucosamine‐containing, fucose‐deficient glycoprotein which is recognized by antiserum to MuLV but not by the gp71 antiserum. The surface iodination of the intact virions indicates that both gp71 and gp85 are the major components of the external virions envelope. However, unlike the control virions in which gp71 associates with p15E (gp90), the gp71‐p15E complex was not detected in interferon virions. The analysis of the iodinated proteins of the disrupted interferon virions revealed the presence of 85k and 65k dalton polypeptides preciptable with antiserum against MuLV, which are not present in the control virions. The difference in the polypeptide pattern of virions produced in the presence of interferon does not seem to be a consequence of the slowdown in the synthesis of viral proteins or their processing in the interferon‐treated cells. Both the structural proteins of env and gag genes seem to be synthesized and processed at a comparable rate in the interferon‐treated and ‐untreated cells. These results indicate an alteration of virus assembly in the presence of interferon.
Structural and functional alterations in the surface of vascular endothelial cells associated with the formation of a confluent cell monolayer and with the withdrawal of fibroblast growth factor
Authors: Vlodavsky Israel , Gospodarowicz Denis 
Published: May 2005

AbstractVascular endothelial cells cultured in the presence of fibroblast growth factor (FGF) devide actively when seeded at low or clonal cell densities and upon reachin confluence adopt a morphologic appearance and differentiated properties similar to those of the vascular endothelium in vovi. In this review, we present some of our recent observations regarding the characteristics (both structural and functional) of these endothelial cells and the role of FGF in controlling their proliferation and normal differentation. At confluence the endothelial cells from a monolayer of closely apposed and nondividing cell that have a nonthrombogenic apical surface and can no longer internalize bound ligands such as low‐density lipoprotein (LDL). The adoption of these properties is correlated and possibly causally related to changes in the cell surface such as the appearance of a 60,000 molecular weight protein (CSP‐60); the disappearance of fibronectin from the apical cell surface and its concomitant accumulation in the basal lamina; and a restriction of the lateral mobility of various cell surface receptor sites. In contrast, endothelial cells that are maintained in the absence of FGF undergo within three passages alterations that are incompatible with their in vivo morphologic apperarance and physiologic beharior. They grow at confluence on top of each other and hence can no longer adopt both the structural (CSP‐60, cell surface polarity) and functional (barrier function, nonthrombogenicity) attributes of differentiated endothelial cell. Since these characteristics can be reacquired in response to readdition of FGF, in addition to being a mitogen FGF may also be involved in controlling the differentitation and phenotypic expression of the vascular endothelium.
Polyoma T (tumor) antigen species in abortively and stably transformed cells
Authors: Benjamin Thomas L. , Schaffhausen Brian S. , Silver Jonathan E. 
Published: May 2005

AbstractStable neoplastic transformation of cells by polyoma virus requires the participation of two viral genes, designated ts‐a and hr‐t. The effects of mutations in these two genes on the patterns of T‐antigen synthesis during productive infection have been previously described: ts‐ a mutants are affected in the “large” (100K) nuclear T antigen, and hr‐t mutants are affected in the “middle” (36K, 56K, 63K) and “small” (22K) T agtigens. The latter are associated predominantly with the plasma membrane (56K) and cytosol fractions, rrespectively.Here we examine the expression of the various forms of polyoma T antigen in nonproductive infection (abortive transformation) as well as in stably transformed cell lines of different species. The results on abortive transformation are essentially the same as those described above for productive infection. In stably transformed cells, the middle and small T antigens are seen to various extents. The large T antigen, however, is often absent or present below the level of detection. Clones lacking the large T antigen are found most often among mouse transformants, but are also seen among rat transformants. Retention of the 100K species in transformed cells therefore appears to be, at least in part, an inverse function of the level of permissivity of the host toward productive viral infection. These findings indicate that the induction of the transformed phenotype in both abortively and stably transformed cells generally does not require the large T antigen, but rather the products of the hr‐t gene.
Biosynthesis and maturation of cellular membrane glycoproteins
Authors: Hunt Lawrence A. 
Published: May 2005

AbstractThe biosynthesis and the processing of asparagine‐linked oligosaccharides of cellular membrane glycoproteins were examined in monolayer cultures of BHK21 cells and human diploid fibroblasts after pulse‐and pulse‐chase labeling with [2‐3H] mannose. After pronase digestion, radiolabeled glycopeptides were characterized by high‐resolution gel filtration, with or without additional digestion with various exoglycosidases and endoglycosidases. Pulse‐labeled glycoproteins contained a relatively homogenous population of neutral oligosaccharides (major species: Man9GlcNAc2ASN). The vast majority of these asparagine‐linked oligosaccharides was smaller than the major fraction of lipid‐linked oligosaccharides from the cell and was apparently devoid of terminal glucose. After pulse‐chase or long labeling periods, a significant fraction of the large oligomannosyl cores was processed by removal of mannose units and addition of branch sugars (NeuNAc‐Gal‐GlcNAc), resulting in complex acidic structures containing three and possibly five mannoses. In addition, some of the large oligomannosyl cores were processed by the removal of only several mannoses, resulting in a mixture of neutral structures with 5–9 mannoses. This oligomannosyl core heterogeneity in both neutral and acidic oligosaccharides linked to asparagine in cellular membrane glycoproteins was analogous to the heterogeneity reported for the oligosaccharides of avian RNA tumor virus glycoproteins (Hunt LA, Wright SE, Etchison JR, Summers DF: J Virol 29:336, 1979).
Regulation of dome formation in differentiated epithelial cell cultures
Authors: Lever Julia E. 
Published: May 2005

AbstractRat mammary (Rama 25) and dog kidney (MDCK) epithelial cell cultures formed ‘domes’ of cells due to fluid accumulation in focal regions between the culture dish and the cell monolayer. Addition of ouabain caused collapse of domes, suggesting that transport functions were required for maintenance of domes.Dome formation in both epithelial cell lines was stimulated by a broad spectrum of known inducers of erythroid differentiation in Friend erythroleukemia cells. Among these inducers were: (1) polar solvents such as dimethylsulfoxide, dimethylformamide, and hexamethylene bisacetamide; (2) purines such as hypoxanthine, inosine, and adenosine; (3) low‐molecular‐weight fatty acids such as n‐butyrate; and (4) conditions expected to elevate levels of cyclic AMP. In the latter group were activators of adenylate cyclase such as cholera toxin and prostaglandin E1; cyclic AMP phosphodiesterase inhibitors such as theophylline and 1‐methyl‐3‐isobutylxanthine; and analogs of cyclic AMP.Induction of domes occurred 15–30 h after addition of inducer to the culture medium. Induction by chemicals was serum‐dependent and required protein synthesis but not DNA synthesis. Induced dome formation was reversible after removal of inducer, requiring the contiuous presence of inducer. Reversal was also observed after either removal of serum or addition of inhibitors of protein synthesis.These results suggest the hypothesis that domes arise in these epithelial cultures by a process that is similar to cell differentiation and is influenced by cyclic AMP.
Scanning electron microscopy of differentiated liver cells transformed in vitro by chemical carcinogens
Authors: Borek Carmia 
Published: May 2005

AbstractA scanning electron microscopy study was carried out on differentiated liver cells transformed in vitro by three chemical carcinogens into cells that give rise to carcinomas. The results indicate that the transformed cells grow as a rule in tightly adherent monolayers but differ in topography. There is a tendency toward heterogeneity in cell shape compared to the normal and on the whole toward a larger number of surface microvilli in the malignant cell population. However, both in sparse and confluent cultures the topographic differences are often not striking enough to unequivocally distinguish single neoplastic cells from the normal.
Protein‐RNA interactions during TMV assembly
Authors: Holmes K. C. 
Published: May 2005

AbstractA review of the structural studies of tobacco mosaic virus (TMV) is given. TMV is essentially a flat helical microcrystal with 16 1/3 subunits per turn. A single strand of RNA runs along the helix and is deeply embedded in the protein. The virus particles form oriented gels from which high‐resolution X‐ray fiber diffraction data can be obtained. This may be interpreted by the use of six heavy‐atom derivatives to give an electron density map at 0.4 nm resolution from which the RNA configuration and the form of the inner part of the protein subunit may be determined. In addition, the protein subunits form a stable 17‐fold two‐layered disk which is involved in virus assembly and which crystallizes. By the use of noncrystallographic symmetry and a single heavy‐atom derivative, it has been possible to solve the structure of the double disk to 0.28 nm resolution. In this structure one sees that an important structural role is played by four alpha‐helices, one of which (the LR helix) appears to form the main binding site for the RNA. The main components of the binding site appear to be hydrophobic interactions with the bases, hydrogen bonds between aspartate groups and the sugars, and arginine salt bridges to the phosphate groups. The binding site is between two turns of the virus helix or between the turns of the double disk. In the disk, the region proximal to the RNA binding site is in a random coil until the RNA binds, whereupon the 24 residues involved build a well‐defined structure, thereby encapsulating the RNA.
β‐Bungarotoxin binding sites (acetylcholine receptors) in denervated mammalian sarcolemma
Authors: Tipnis Ulka R. , Malhotra Sudarshan K. 
Published: May 2005

AbstractThe nonsynaptic sarcolemma of denervated skeletal muscle of rat shows an abundance of ∼15 nm intramembranous particles on the P face. These particles are either singly distributed or are in clusters, and they are essentially lacking from the comparable freeze‐fractures of the innervated sarcolemma. Autoradiographic studies using 125I‐α‐bungarotoxin (BGT) on 1 μ‐thick sections, and freeze‐etch studies using ferritin‐α‐BGT conjugates on membrane fractions, show that the distribution of the label corresponds to the distribution of the 15‐nm particles in the nonsynaptic sarcolemma. On the basis of these results and existing physiologic and biochemical data, it is suggested that the 15‐nm intramembranous particles are components of the α‐BGT binding sites, ie, acetylcholine (Ach) receptors, in the nonsynaptic sarcolemma of denervated muscle and that the two types of distributions represent two spatial manifestations of Ach receptor molecules. The significance of these findings in relation to synapse formation in denervated muscle is discussed.
Alteration of human breast tumor cell membrane functions by chromosome‐mediated gene transfer
Authors: Muneer Razia S. , Gray Peter N. 
Published: May 2005

AbstractBOT‐2 cells (human breast tumor origin) have an impaired ability to utilize exogenous thymidine. Previous studies revealed this deficiency to be the permeation event rather than phosphorylation, since the cells have active thymidine kinase. Chromosome‐mediated gene transfer was used to transfer genetic information in the form of metaphase chromosomes, from HeLa‐65 cells to the BOT‐2 cells, correcting the permease deficiency. Poly‐L‐ornithine or lipochromes were used for facilitation of chromosome uptake. After selection on HAT medium, transferant clones were isolated at a frequency of 4 X 10−5 and 1 X 10−5, respectively. Transferants MGP‐1 and MGL‐1 are stable after 18 months and have been characterized on the bases of purine and pyrimidine nucleoside uptake, relative thymidine kinase activities, alkaline phosphatase activities, and hydrocortisone‐induced alkaline phosphatase activity. MGP‐1 demonstrates positive thymidine uptake and incorporates radiolabeled thymidine into DNA. MGL‐1 remains thymidine transport‐deficient and survives on HAT by increasing endogenous dihydrofolate reductase activity. Alkaline phosphatase activity in MGL‐1 is similar to HeLa‐65, 2% of that in BOT‐2, and in addition, is inducible 25‐30‐fold by 3 μM hydrocortisone. We have separated, genetically, a thymidine permease function from phosphorylation in cells of human origin and have transferred genetic information for the regulation of alkaline phosphatase.
Tumor‐associated antigenic differences between the primary and the descendant metastatic tumor cell populations
Authors: Gorelik Eliezer , Fogel Mina , Segal Shraga , Feldman Michael 
Published: May 2005

AbstractThe existence of antigenic differences between cell populations in the local growth of the 3LL tumor (L‐3LL) and its lung metastases (M‐3LL) was studied. Normal C57BL/6 spleen cells sensitized in vitro for 5 days against L‐3LL monolayers lysed preferentially L‐3LL targets but not M‐3LL tumor cell targets. Conversely, anti‐M‐3LL‐sensitized lymphocytes killed M‐3LL targets more efficiently than they killed L‐3LL targets. Furthermore, spleen cells from mice bearing subcutaneous L‐3LL tumors were significantly more cytotoxic to L‐3LL targets than to M‐3LL targets and vice versa. M‐3LL cells were found also to be more resistant in vitro and in vivo to natural killer cells than were L‐3LL tumor cells. M‐3LL cells were more resistant than L‐3LL cells to hybrid resistant mechanisms when they were inoculated into F1 (C3Heb X C57BL/6) or F1 (BALB/c X C57BL/6) mice. Anti‐M‐3LL lymphocytes generated both in vitro and in vivo, but not anti‐L‐3LL lymphocytes, admixed with L‐3LL or M‐3LL tumor cells and inoculated into footpads of syngeneic recipients suppressed the development of lung metastases. These results suggest that metastatic cells are indeed phenotypic variants of the local growing tumor cell populations. Presumably, these variants are selected for their capacity to home to and grow in the lungs, and for their resistance to specific immune effects initially evoked against the local tumor and to nonspecific natural killer cells. These data may prove to be of importance with respect to any rational approach to the problem of immunotherapy.