bluuebunny/crossref_metadata_2025 huggingface dataset:
Hepatic heparan sulphate proteoglycan and the recycling of transferrin
Authors: Hu Wei-Li , Regoeczi Erwin
Published: December 2009

Heparan sulphate proteoglycan, labelled with [35S]sulphate, was prepared from rat livers for studies of its interaction with purified rat transferrin. Affinity chromatography of the preparation on columns of immobilized differic transferrin and apotransferrin showed that the proteoglycan possessed affinity for both types of matrices at pH 7.3 and that this affinity significantly increased at pH 5.6. The glycosaminoglycan chains liberated from the proteoglycan by heparan sulphate lyase also bound to apotransferrin, albeit less strongly, whereas the deglycosylated core protein exhibited virtually no interaction with this matrix. In the presence of the proteoglycan at pH 5.6, the release of iron from the N-lobe of transferrin was accelerated. These observations suggest that heparan sulphate proteoglycan from the liver can mimick some of the known functions of bona fide transferrin receptors and, hence, interaction with the proteoglycan may provide an alternative nondegradative pathway for transferrin through hepatic cells.Key words: heparan sulphate proteoglycan, hepatic iron metabolism, receptor-mediated endocytosis, transferrin.
Cytochrome c and cytochrome c oxidase interactions: the effects of ionic strength and hydrostatic pressure studied with site-specific modifications of cytochrome c
Authors: Kornblatt Jack A. , Theodorakis Janice , Hoa Gaston Hui Bon , Margoliash Emmanuel
Published: December 2009

Seven cytochromes c, in which individual lysines have been modified to the propylthiobimane derivatives, have been prepared. These derivatives were also converted to the porphyrin cytochromes c by treatment with HF. The properties of both types of modified proteins were studied in their reactions with cytochrome c oxidase. The results show that lysines 25, 27, 60, 72, and 87 do not contribute a full charge to the binding interaction with the oxidase. These five residues, with the exception of the lysine-60 derivative, are on the front surface of the protein and contain the solvent-accessible edge of the heme prosthetic group. By contrast, lysines 8 and 13 at the top of the front surface do contribute a full charge to the binding interaction with the oxidase. The removal of the positive charge on any one lysine weakens the binding to cytochrome c oxidase by at least 1 kcal (1 cal = 4.1868 J). The presence of bimane at lysines 13 and 87 clearly forces the separation of the cytochrome c and oxidase, but this does not occur with the other complexes. The bimane-modified lysine-13 protein, and to a lesser extent that modified at lysine 8, show the interesting effect of enhanced complex formation with cytochrome c oxidase when subjected to pressure, possibly because of entrapment of water at the newly created interface of the complex. Our observations indicate that the two proteins of the cytochrome c – cytochrome oxidase complex have preferred, but not obligatory, spatial orientations and that interaction occurs without either protein losing significant portions of its hydration shell.Key words: cytochrome oxidase, cytochrome c, binding, hydrostatic pressure.
Metastasis-associated alterations in phospholipids and fatty acids of human prostatic adenocarcinoma cell lines
Authors: Dahiya Rajvir , Boyle Bryan , Goldberg Beth Carol , Yoon Wan-Hee , Konety Badrinath , Chen Katy , Yen Tien-Sze Benedict , Blumenfeld Walter , Narayan Perinchery
Published: December 2009

Metastatic variants of human prostatic adenocarcinoma cell lines (DU-145, LNCaP, and ND-1) were studied by using soft agar colony forming efficiency, nude mice tumorigenicity, in vitro invasion assay, and type IV collagenase assay. The DU-145 and ND-1 cell line snowed higher metastatic potential than LNCaP. Lipids from DU-145, ND-1, and LNCaP cells were extracted and analyzed by thin-layer chromatography and gas-liquid chromatography. The major lipids were phosphatidylcholine, phosphatidylethanolamine, sphingomyelin, fatty acids, and cholesterol. The sphingomyelin level was significantly higher in highly metastatic cells (DU-145 and ND-1) compared with the lower metastatic variant (LNCaP). The increase in the synthetic pathway and decrease in degradation pathway of sphingomyelin in microsomal fractions was sufficient to account for the measured increase in sphingomyelin in DU-145 cells compared with LNCaP cells. The major fatty acids of these lipids were palmitic (16:0), stearic (18:0), oelic (18:1), and arachidonic acid (20:4). The arachidonic acid level was significantly decreased in DU-145 and ND-1 compared with LNCaP cells. Electron microscopic studies showed no significant changes in the morphology of DU-145, ND-1, and LNCaP cells. The results of these investigations demonstrate for the first time that sphingomyelin and arachidonic acid contents are different in high and low metastatic variants of human prostatic adenocarcinoma cell lines.Key words: prostate cancer, metastasis, morphology, phospholipids, cytogenetic.
Proliferation is required for induction of terminal differentiation of Friend erythroleukemia cells
Authors: Spriggs Louaine L. , Hill Steven M. , Jeter Jr. James R.
Published: December 2009

The relationship between cell proliferation and differentiation has long been a source of controversy. Stimulation of normal erythroid maturation results in a finite number of cell divisions accompanied by a concomitant accumulation of hemoglobin. Friend erythroleukemia cells treated with hexamethylene bisacetamide differentiate in a similar manner, while agents such as hemin apparently induce differentiation without limiting cell proliferation. Aphidicolin, an inhibitor of DNA synthesis, has been reported to induce differentiation in the absence of cell proliferation. Using these three chemicals we have investigated the relationship between cell proliferation and erythrocytic maturation by exposing Friend erythroleukemia cells to either hexamethylene bisacetamide (5 mM), hemin (100 μM), or aphidicolin 1.2 μM) and examining the effects on cell growth, morphology, and hemoglobin production. Proliferation in the presence of hexamethylene bisacetamide is limited to four to five rounds of cell division, while hemin has no inhibitory effect. Hexamethylene bisacetamide initiates the complete erythrocytic maturation program, including cellular structural changes and hemoglobin synthesis. Hemin stimulates only globin gene transcription, not differentiation. Aphidicolin inhibits cell growth within 24 h, but does not induce differentiation. Furthermore, inhibition of proliferation by aphidicolin prevents subsequent hexamethylene bisacetamide induced differentiation. These results indicate that at least one round of cell division is required for initiation of erythrocytic differentiation.Key words: proliferation, erythrocytic differentiation, hexamethylene bisacetamide, hemin, aphidicolin.
Effect of diethyl pyrocarbonate modification on spectral and steady-state kinetic properties of bovine heart cytochrome oxidase
Authors: Doran John D. , Hill Bruce C.
Published: December 2009

The histidine-specific reagent diethyl pyrocarbonate has been used to chemically modify bovine heart cytochrome oxidase. Thirty-two of sixty-seven histidine residues of cytochrome oxidase are accessible to modification by diethyl pyrocarbonate. Effects on the Soret and α bands of the heme spectrum indicate disturbance in the environment of one or both of the heme groups. However, diethyl pyrocarbonate modification does not alter the 830-nm absorbance band, suggesting that the environment of CuA is unchanged. Maximal modification of cytochrome oxidase by diethyl pyrocarbonate results in loss of 85–90% of the steay-state electron transfer activity, which can be reversed by hydroxylamine treatment. However, modification of the first 20 histidines does not alter either activity or the heme spectrum, but only when 32 residues have been modified are the activity and heme spectral changes complete. The steady-state kinetic profile of fully modified oxidase is monophasic; the phase corresponding to tight cytochrome c binding and low turnover is retained, whereas the high turnover phase is abolished. Proteoliposomes incorporated with modified oxidase have a 65% lower respiratory control ratio and 40% lower proton pumping stoichiometry than liposomes containing unmodified oxidase. These results are discussed in terms of a redox-linked proton pumping model for energy coupling via cytochrome oxidase.Key words: cytochrome oxidase, histidine modification, electron transfer, proton pumping, diethyl pyrocarbonate.
Effects of nonenzymatic glycation of subfragment-1 of myosin on interactions with actin
Authors: Brown Michael R. , Knull Harvey R.
Published: December 2009

Nonenzymatic bonding of reducing sugars to subfragment-1 of myosin (S-1) resulted in a reduction in actin-activated S-1 ATPase activity. Fructose caused a greater reduction than glucose. The Km for binding of actin to S-1 was significantly increased with sugar derivatization. In addition, sugar derivatization lowered the ability of S-1 to promote polymerization of G-actin. Western blot analysis demonstrated that glucose was nonenzymatically incorporated into the 50 and 20 kilodalton (kDa) fragments of S-1 with preponderance in the 20-kDa fragment. The reduced affinity of derivatized myosin for actin is indicated by the increased Km, the reduced ability to stimulate actin polymerization, and the positive Western blot reaction in the 20-kDa fragment.Key words: myosin, actin, S-1, glycation, polymerization.
Purification and characterization of a 32-kDa protein that localizes to the sea urchin extraembryonic matrix, the hyaline layer
Authors: Robinson John J.
Published: December 2009

We have purified a 32 kilodalton (kDa) protein that localized with isolated, intact hyaline layers prepared from 1-h-old embryos. The protein appeared not to bind calcium and was not quantitatively released from 1-h-old embryos in the absence of Ca2+ and Mg2+. Using polyclonal antiserum prepared against the 32-kDa protein, the antigen was detected throughout embryonic development. By the hatched blastula stage of development, the 32-kDa protein was replaced by a species of slightly smaller molecular mass. Quantitative determination indicated that the 32-kDa protein accounted for approximately 6% of the total protein present in the sea urchin egg. This result is suggestive of a structural role for the 32-kDa protein that is required throughout embryonic development, although perhaps in a modified form from the hatched blastula stage on.Key words: sea urchin, embryo, hyaline layer, component.
Effects of cholesterol on viability and (n – 6) fatty acid metabolism in cultured human monocyte-like cells (U937)
Authors: Howie Andrew , Huang Yung-Sheng , Horrobin David F.
Published: December 2009

Effects of supplementation of growth-promoting cholesterol on metabolism of the cytotoxic (n – 6) polyunsaturated fatty acids in cultured human monocyte-like cells (U937) have been examined. U937 cells were incubated in 5% delipidated fetal bovine serum containing 0 or 38.7 μM cholesterol. The rate of uptake and the distribution of metabolites of (n – 6) fatty acids (such as 18:2(n – 6), 18:3(n – 6), and20:3(n – 6), and20:4(n – 6)) were examined by adding radiolabelled fatty acid at a level of 1 μg/mL (3.3 μM for 20-carbon fatty acids and 3.6 μM for 18-carbon fatty acids). For assessing the cytotoxicity, (n – 6) fatty acids were added to medium at a concentration of 5 μg/mL (16.4 μM for 20-carbon fatty acids and 17.9 μM for 18-carbon fatty acids). Cholesterol supplementation suppressed the uptake of all (n – 6) fatty acids and reduced the cytotoxic effects of 18:2(n – 6), 20:3(n – 6), and 20:4(n – 6), but not 18:3(n – 6). In addition, cholesterol supplementation increased peroxide production and metabolism of (n – 6) fatty acids in U937 cells. Thus, the differential suppressive effect of cholesterol on the cytotoxicity of different fatty acids could not be attributed to an inhibitory effect on fatty acid Δ6- and Δ5-desaturation, or to an antioxidant effect on peroxide formation.Key words: (n – 6) fatty acid metabolism, cytotoxicity, peroxides.
Enhancement of differentiation of cultured adipogenic cells (TA1) by pertussis toxin
Authors: Shinohara Osamu , Murata Yoh-Ichi , Shimizu Makoto
Published: December 2009

Differentiation of adipocytes is controlled by a variety of hormones and growth factors. To investigate the possible role of GTP-binding proteins (G proteins) in the process of adipose conversion, we studied the effect of pertussis toxin on differentiation of the fibroblast/adipocyte cell line (TA1). Pertussis toxin potentiated dexamethasone- and indomethacin-induced adipocyte differentiation in a time- and dose-dependent fashion. Addition of dibutyryl cAMP or forskolin inhibited adipose conversion, indicating that an abolishment of inhibitory control of adenylate cyclase is not responsible for the action of pertussis toxin. The B oligomer of the toxin did not mimic the effect of the holotoxin. Pertussis toxin catalyzed ADP-ribosylation of 40 000 molecular mass protein of the membrane fraction was dose-dependently inhibited by the pretreatment of the cells with the toxin. These results indicate the possible involvement of pertussis toxin-sensitive G proteins in adipogenesis.Key words: adipose tissue, pertussis toxin, GTP-binding protein.
In vitro transfer of N,N′-diacetylchitobiose to glycoproteins in rat liver nuclei
Authors: Frot—Coutaz Jacques , Degiuli Agnès , Martel Marie-Bénédicte , Létoublon Robert
Published: December 2009

This work demonstrates that (N-acetyl[14C]glucosamine)2 is transferred from dolichyl pyrophosphate – (N-acetyl[14C]glucosamine)2 to endogenous nuclear glycoproteins. The (N-acetyl[l4C]gIucosamine)2 moiety is N-linked, since it can be released from the tryptic glycopeptides by N-glycosidase F and by hydrazinolysis, but not by β-elimination. The biological significance of this direct transfer of N, N′-diacetylchitobiose to nuclear proteins remains to be elucidated.Key words: nucleus, nuclear glycoproteins, nuclear N-acetylglucosaminyltransferase, N,N′ -diacetylchitobiose.
Effect of methylation inhibitors on gene expression in HL-60 cells
Authors: Duerre John A. , Buttz Harris R. , Ackerman Julie J.
Published: December 2009

The methylation inhibitors Neplanocin A (Nep A), 3′-deazaadenosine (dzAdo), and 3-deaza(±)aristeromycin (Dari) were tested for their effect on the expression of histone H2B, actin, and the protooncogenes c-myc, and v-fos. Nep A and Dari bind to the S-adenosylhomocysteine hydrolase resulting in the accumulation of S-adenosylhomocysteine, while dzAdo served as a substrate for the enzyme. With dzAdo, inordinant amounts of 3-deazaadenosylhomocysteine (dzAdoHcy) accumulated in the cell, provided L-homocysteine (Hey) was present. When added at sublethal concentrations, the methylation inhibitors had little or no effect on c-myc, v-fos, histone H2B, or actin expression, nor did any significant number of the drug-treated cells demonstrate myeloid characteristics. However, growth and gene expression were markedly inhibited upon the addition of Hey and dzAdo. One of the earliest effects of dzAdoHcy on HL-60 cells was the disappearance of c-myc mRNA. Within 1 h of the addition of dzAdo and Hey, only trace amounts of c-myc mRNA were detectable. After 4–5 h v-fos, histone H2B, and actin mRNAs also decreased to about 40% of control levels. Differences in the stability of preexisting mRNAs would appear to account for these results. Within 1 h following the addition of dzAdo and Hey, the synthesis of rRNA and mRNA were completely blocked as measured by the incorporation of [3H]uridine.Key words: methylation inhibitors, 3-deazaadenosine, c-myc, HL-60 cells, gene expression, RNA.
A downstream sequence of the rpL32 promoter competes with the glucocorticoid responsive element for a protein factor
Authors: Yoganathan Thillainathan , Sells Bruce H.
Published: December 2009

The murine ribosomal protein (rp) L32 gene contains essential promoter sequences located both upstream and downstream of the cap site. A combination of gel mobility shift, UV cross-linking, and cell-free transcription assays were used to analyze the interaction of factors binding to a downstream element (located at position +25 to +37). The rpL32 downstream element identified polypeptides (transcription factors) ranging in size from 45 to 25 kilodaltons (kDa). Four base pair changes in the wild-type sequence of the downstream element eliminated binding. An oligonucleotide containing the glucocorticoid responsive element sequence competed specifically for the 45-kDa protein in both the gel mobility shift assay and in the UV cross-linking studies. Our data also indicate that the downstream binding factors contribute to cell-free transcription of the rpL32 gene.Key words: ribosomal protein L32, transcription factor, glucocorticoid response element.
Immunological characterization of neutral cholesteryl ester hydrolase from rat liver cytosol
Authors: Ghosh Shobha , Grogan W. McLean
Published: December 2009

Rabbit polyclonal antibodies were raised against rat liver bile salt-independent neutral cholesteryl ester hydrolase (CEH) and used for subcellular localization and immunological comparison with isoforms from other tissues. Antibodies exhibited a high degree of specificity for the liver CEH through all stages of purification and neutralized 70–80% of the activity of liver cytosolic CEH. They exhibited various levels of cross-reactivity with cytosolic proteins from other tissues, but reacted weakly with pancreatic and intestinal proteins and did not inhibit pancreatic CEH. Cytosol contained 78% of total cellular CEH activity and 75% of CEH immunoreactive protein. Washed microsomes contained 3% of CEH activity and 5% of CEH protein.Key words: cholesteryl esterase, polyclonal antibodies, rat liver, subcellular distribution.
Nuclear matrix proteins bind very tightly to specific regions of the chicken histone H5 gene
Authors: Sun Jian-Min , Hendzel Michael J. , Davie James R.
Published: December 2009

The nuclear matrix is operationally defined as the structure remaining after nuclease-digested nuclei are extracted with high concentrations of salt. The nuclear matrix is thought to have a role in organizing higher order chromatin into loop domains. We determined whether specific regions of the histone H5 gene were very tightly bound to protein of erythrocyte and liver nuclear matrices in vitro. We demonstrate that DNA fragments spanning sequences 5′ to the promoter and the 3′ enhancer region of the histone H5 gene, but not DNA fragments spanning the promoter, were very tightly bound to protein of nuclear matrices of erythrocytes and liver. The nuclear matrix consists of internal nuclear matrix and nuclear pore–lamina complex. Recently, we demonstrated that histone deacetylase could be used as a marker enzyme of the internal nuclear matrix. We demonstrate that nuclear pore–lamina complex preparations that were depleted of histone deacetylase activity, and thus of internal nuclear matrix, retained the protein that bound very tightly to the β-globin and histone H5 enhancers. These results provide evidence that specific regions of the histone H5 gene are very tightly bound to nuclear pore–lamina complex protein.Key words: histone H5 gene, DNA organization, nuclear matrix
The origin of the cancer cell: oncogeny reverses phylogeny
Authors: Johnston Randal N. , Pai S. Balakrishna , Pai Rekha B.
Published: December 2009

The formulation in 1874 of the biogenetic law by Ernst Haeckel as "ontogeny recapitulates phylogeny" emphasized the structural similarities detected in metazoans between their developmental and ancestral forms. More recently, many workers have independently commented on the similarities observed between the behaviours displayed by dedifferentiated cancer cells and their embryonic precursors. This review will explore a possible linkage between these disparate observations and will suggest that cancer cells behave in ways that are reminiscent of primitive eukaryotic cells. In particular, we suggest that the acquisition of a multicellular level of organization during early metazoan evolution required a critical and difficult change in growth strategy as germ line and somatic cells became distinct. Whereas unicellular free living eukaryotes follow a simple strategy of rapid division as long as conditions permit, the elaboration of powerful growth inhibitory pathways must have been necessary in primitive multicellular organisms to enable some but not all sister cells to stop dividing, even under conditions of nutrient abundance. This limitation on cellular growth would then have permitted the appearance of tissues and organs with differentiated characteristics, ultimately enabling the enhanced survival of the meiotic lineage. Cancer cells might therefore be considered to represent, with their loss of tumor suppressor inhibitory activity and elevation of oncogene stimulatory activity, a reversion to a more primitive evolutionary state capable of indeterminate growth at the expense of the host. By this analogy, the growth phenotypes displayed by cancer cells, embryonic cells, and free-living eukaryotes are fundamentally similar.Key words: phylogeny, oncogenesis, evolution, oncogene, antioncogene.
How to make a blastocyst
Authors: Watson Andrew J. , Kidder Gerald M. , Schultz Gilbert A.
Published: December 2009

Several of the new reproductive technologies have been cultivated from our current understanding of the genetic programming and cellular processes that are involved in the major morphogenetic events of mammalian preimplantation development. Research directed at characterizing the patterns of gene expression during early development has shown that the embryo is initially under maternal control and later superseded by new transcriptional activity provided by the activation of the embryonic genome. Several embryonic transcripts encoding (i) growth factors, (ii) cell junctions, (iii) plasma membrane ion transporters, and (iv) cell adhesion molecules have been identified as contributing directly to the progression of the embryo through the preimplantation interval of development. In this brief review, we have outlined the patterns of expression and the integral roles that these gene families play in the morphogenetic events of compaction and cavitation. Research of this type has greatly facilitated our understanding of the control processes that underlie preimplantation development and represent but one area of this exciting and vigorous field of research.Key words: Na,K-ATPase, cavitation, compaction, preimplantation development, embryonic transcription.
Regulation of the G2-mitosis transition
Authors: Feilotter Harriet , Lingner Carol , Rowley Roy , Young Paul G.
Published: December 2009

The cell cycle is regulated by pathways composed of a dependent series of steps, by timers, and by checkpoint controls which ensure the completion of one event before the initiation of another. This review focusses on the regulation of the initiation of mitosis, with particular emphasis on the regulation of p34cdc2 activity at this point in the cell cycle. The review draws on data from various organisms, but strongly emphasizes the genetic framework as seen in the fission yeast Schizosaccharomyces pombe and the biology and biochemistry of maturation promoting factor in frog oocytes. An attempt is made to include all known genes and proteins where a link can be made to the initiation event. The nutritional size control and its major known controlling elements, the wee1/mik1 protein kinases, and cdc25 protein tyrosine phosphatase are considered in detail along with their regulation. In addition, the checkpoint control pathways which mediate G2 delay in response to failure of DNA replication or DNA damage are examined.Key words: cell cycle, mitosis, Schizosaccharomyces pombe, cdc2, p34.
Multiple antigens recognized by anti-c-myc antibodies in human cells and Xenopus oocytes
Authors: Gibson A. W. , Ye R. , Johnston R. N. , Browder L. W.
Published: December 2009

We have investigated the localization, solubility, serum regulation, and phosphorylation of MYC antigens from Colo 320 cells, a human transformed cell line with an amplified c-myc gene, and from Xenopus oocytes, which express high levels of c-myc mRNA. Although MYC proteins are often reported to range from 60 to 68 kilodaltons, our panel of anti-MYC monoclonal antibodies recognized a number of higher and lower molecular mass antigens, in addition to proteins within this range. Based upon various criteria, including cross-recognition by several anti-MYC antibodies, we suggest that some of these antigens are bona fide MYC family proteins. Our results, as well as those of others reported previously, suggest that several MYC antigens may be simultaneously present in cells. The apparent diversity among members of the MYC family of antigens raises the possibility of multiple cellular functions and regulatory roles for these proteins.Key words: MYC, antibodies, Colo 320, Xenopus, immunoprecipitation, immunoblotting, oncoproteins.
Molecular analysis of different allelic variants of wild-type human p53
Authors: Moreau France , Matlashewski Greg
Published: December 2009

The p53 tumour suppressor gene is intensively studied because mutations in this gene are the most common genetic alteration so far identified in human cancer. Considerable emphasis has thus been placed on characterizing the biological differences between mutant and wild-type p53 protein. This has led to the realization that in cultured cells, mutant p53 behaves like an oncogene, whereas wild-type p53 is a tumour suppressor gene. The p53 protein is also a target for the tumour virus oncogene products SV40 large T, adenovirus E1B, and human papillomavirus type 16 E6, which are all capable of forming complexes to the p53 protein. Although p53 represents an extremely important cellular regulatory molecule which is well conserved, there exists two allelic variants of wild-type human p53 that differ both in primary and confirmational structure. One variant contains an arginine at amino acid 72 (p53Arg), whereas the other form contains a proline at this residue (p53Pro). The possible implications for more than one allelic variant of wild-type human p53 in the general population is unknown. The present study was undertaken to compare some of the biological features of the different wild-type p53 variants. We present data demonstrating that there was a post-transcriptional selection against accumulation of both variants of wild-type human p53 in 3T3-A31 cells, arguing that both forms are proliferation inhibitory in these cells. Both variants of human p53 were stabilized by SV40 large T, but did not displace mouse p53 from SV40 large T. Neither allelic variant of human p53 was able to reduce significantly SV40-mediated anchorage-independent growth of 3T3-A31 cells. Taken together, these data suggest that although there are structurally different variants of wild-type human p53, there is no difference in the biological activity of these molecules at the level of the biological assays performed here.Key words: human p53, large T, transformation, oncogenes, tumour suppressor.
Purification and partial characterization of thiol protease inhibitors from embryos of the brine shrimp Artemia
Authors: Warner Alden H. , Sonnenfeld-Karcz Margaret J.
Published: December 2009

Thiol protease inhibitor (TPI) proteins in embryos of the brine shrimp Artemia were purified to apparent homogeneity and several of their properties were studied. Four protein fractions containing thiol protease inhibitor activity were obtained by high performance liquid chromatography of Artemia embryo proteins on a C-18 reverse-phase column and these were designated as TPI-1a, -1b, -2, and -3. Acrylamide gel electrophoresis showed that TPI-1a and TPI-1b each consisted of two bands of 11.8 and 13.6 kilodaltons (kDa), while TPI-2 and TPI-3 consisted of only one band of 12.5 kDa. Isoelectric focusing experiments demonstrated that TPI-3 contained one band at pH 5.3, while both TPI-1b and TPI-2 yielded bands at pH 5.2 and 5.3. TPI-1a did not yield any major bands. Amino acid composition analyses of the Artemia TPI proteins showed them to be remarkably similar to one another. All were rich in valine and aspartic and glutamic acids, and devoid of cysteine. Partial trypsin digestion of TPI-1b, TPI-2, and TPI-3 yielded several peptides with identical mobilities on a reverse-phase column and several other peptides with different mobilities, suggesting that the multiple forms of Artemia TPIs may have originated from the same parental protein. N-terminal amino acid sequence analyses of TPI-3 suggest that Artemia TPI proteins are members of the type I cystatin family of protease inhibitors.Key words: thiol protease inhibitors, protease regulation, embryos, Artemia, development.
Isolation and characterization of a cDNA encoding a synaptonemal complex protein
Authors: Chen Qianfa , Pearlman Ronald E. , Moens Peter B.
Published: December 2009

A gene encoding a 65-kilodalton antigen of the rat synaptonemal complex, SC65, has been cloned by screening rat testis λgt11 and λZAPII cDNA expression libraries using polyclonal antibodies against rat synaptonemal complex proteins. The longest open reading frame, initiating at an ATG codon in the cDNA, encodes a protein of 431 amino acids, with a relative molecular mass of 50 000. Immunological analysis locates the SC65 gene product on the synaptonemal complex between the pairing faces of the parallel aligned cores of homologous chromosomes in spermatocytes. Of the rat tissues examined, the SC65 gene is transcribed in testis, brain, and heart at similar levels, and in the liver at a much lower level. The DNA sequence extending about 80 base pairs downstream of the translation termination codon has 93% similarity to the identifier sequence present in the rat genome in 1 × 105 – 1.5 × 105 copies and in cDNA clones of precursors of brain-specific mRNAs. The amino acid sequence encoded by the SC65 gene contains an acidic region in the C-terminal domain of the protein, potential glycosylation sites, and at least one possible phosphorylation site. The protein shows no overall similarity to proteins of known function, nor is there similarity to protein sequences present in GenBank or EMBL data bases.Key words: meiosis, synaptonemal complex, antibody, rat testis cDNA library, molecular cloning.
Transcription factor activity during cellular aging of human diploid fibroblasts
Authors: Riabowol Karl T.
Published: December 2009

Human diploid fibroblasts display a limited proliferative life span in vitro, which is directly correlated to the age of the donor from which the cells were explanted. In an effort to identify molecular events that may underlie the loss of proliferative potential in aging fibroblasts, we have determined, at the protein level, the abundance of several cell-cycle-regulated proteins and the activity of the two major members of the activator protein-1 (AP-1) DNA binding complex. We find that cyclin A and p34cdc2 expression is decreased by two- to four-fold in old fibroblasts, but that Fos expression and binding activity are reduced by as much as 95% in old, as opposed to young cells, despite equivalent amounts of p105Rb and Jun proteins being expressed. We have further determined that the composition of the protein complex which binds a consensus (-TGACTCA-) AP-1 site changes dramatically during in vitro aging. Since we have shown previously that AP-1 activity is required for progression through the cell cycle, we propose that the quantitative and qualitative changes seen in AP-1 may play a direct role in the gradual loss of proliferative ability seen as cells approach senescence.Key words: cellular aging, Fos, transcription factors.
Pharmacological doses of insulin equalize insulin receptor phosphotyrosine content but not tyrosine kinase activity in plasmalemmal and endosomal membranes
Authors: Burgess James W. , Bevan A. Paul , Bergeron John J. M. , Posner Barry I.
Published: December 2009

Following insulin administration to intact rats, the insulin receptor kinase activity of subsequently isolated cell fractions was significantly augmented. Of interest was the observation that the endosomal insulin receptor tyrosine kinase displayed four- to six-fold greater autophosphorylation activity than that of plasma membrane. Surprisingly, the endosomal insulin receptor tyrosine kinase displayed a decrease in β-subunit phosphotyrosine content compared with that seen in the plasma membrane. These observations prompted the suggestion that insulin receptor tyrosine kinase phosphotyrosine dephosphorylation mediated by an endosome-specific phosphotyrosine phosphatase(s) yields activation of the endosomal insulin receptor tyrosine kinase. In a previous study we examined the effect of subsaturating doses of injected insulin. In this work we evaluated insulin receptor tyrosine kinase activity and phosphotyrosine content in plasma membrane and endosomes after a receptor-saturating pharmacological dose of insulin (150 μg/100 g body weight). At this dose the phosphotyrosine content per receptor was reduced compared with that seen earlier at insulin doses of 1.5 and 15 μg/100 g body weight. Endosomal insulin receptor tyrosine kinase was greater than that seen at the lower nonsaturating insulin doses. Furthermore, endosomal insulin receptor tyrosine kinase activity exceeded that of the plasma membrane, despite retaining about the same phosphotyrosine content per receptor. These data are consistent with the view that insulin receptor tyrosine kinase activity may be regulated by a particular pattern of phosphotyrosine content on the β-subunit wherein both activating and inhibitory phosphotyrosine residues play a role.Key words: insulin receptor tyrosine kinase, autophosphorylation, endosomes, plasma membrane, phosphotyrosine phosphatases.
Zygote giant cell differentiation in Dictyostelium discoideum: biochemical markers of specific stages of sexual development
Authors: Browning Darren D. , Lewis Keith E. , O'Day Danton H.
Published: December 2009

Sexual development in Dictyostelium discoideum has many unique features making it an attractive eukaryotic model system for the study of biomembrane fusion and intercellular communication. The work presented here provides primary biochemical evidence for two distinct phases during early sexual development that appear to be defined by calcium-dependent gamete cell fusion. In addition, we introduce a novel procedure for the enrichment of zygote giant cells and use this method to define certain wheat-germ agglutinin binding glycoproteins which are specifically located in zygote giant cells and others which are markers for surrounding amoebae in the second phase of development. In addition, a G protein which is present in high amounts early in development is unique to giant cells in the second phase, suggesting a role in phagocytosis. Finally, alkaline phosphatase activity was found to mark the first phase of sexual development, suggesting a role in cell fusion. This contrasts with the patterns of α-mannosidase and β-glucosidase activity that increase late in the second developmental phase, where they likely function in endocyte digestion during the cytophagic period. The developmental significance of these findings is discussed.Key words: zygote giant cell differentiation, Ca2+, glycoproteins, GTP-binding proteins, alkaline phosphatase, glycosidase, cell fusion.
Cytoplasmic membrane transplants in early Xenopus embryos indicate cell-cycle-specific effects
Authors: Paiement Jacques , Dominguez J. Manuel , Messier Paul-Emil
Published: December 2009

Fragments of rough endoplasmic reticulum or Golgi complex isolated from normal adult rat liver homogenates were injected into one cell of cleaving two-cell Xenopus laevis embryos and the effects on development were monitored during early cleavage by morphological analysis. Scanning electron microscopy revealed the formation of large cells on the injected side of the embryos. Such large cells were not present in controls and thus were considered to have been formed as a consequence of delayed cleavage. Delay of cleavage was obtained with as little as 1 ng of membrane protein giving a ratio of membrane protein to embryo protein of 1:105. Cytological observations of microinjected embryos confirmed the occurrence of delayed cytokinesis and suggested that nuclear division became asynchronous. Since rough microsomes from proliferating tissues (i.e., livers with primary tumors and livers undergoing regeneration) showed little or no effect on cytokinesis after microinjection into early embryos, we conclude that cytoplasmic membranes may exhibit cell-cycle-specific properties important for normal development.Key words: rough endoplasmic reticulum and Golgi membranes, hepatectomy, hepatocellular carcinoma, cell cycle, membrane transplants, Xenopus embryos, cleavage arrest.
Apolipoprotein synthesis and secretion in Hep G2 cells: effects of monensin and cycloheximide
Authors: Hahn Susan E. , Parkes Joel G. , Goldberg David M.
Published: December 2009

Hep G2 cells were used to study the relationship between apolipoprotein synthesis and secretion, as revealed by their interaction with agents modulating these processes. Cycloheximide inhibited the secretion of both apolipoproteins (apo) AI and B, but the reduction in apo AI secretion was evident at earlier times. Monensin also inhibited secretion of apo AI and apo B, but only apo AI accumulated intracellularly. Pulse–chase studies showed that, at concentrations of monensin that had no effect on total protein synthesis, apo B synthesis was specifically inhibited. Triacylglycerol synthesis was inhibited to the same extent as apo B synthesis, but this preceded the latter inhibition and unlike apo B there was an accumulation of intracellular triglyceride. These results suggest that distinctive mechanisms modulate the synthesis and secretion of apo AI and apo B, and that apo B synthesis can be specifically inhibited by mechanisms that initially block triglyceride production.Key words: apolipoprotein, cycloheximide, monensin, Hep G2 cells.
Induction and intracellular localization of the 80-kilodalton heat-shock protein of Neurospora crassa
Authors: Roychowdhury H. S. , MacAlister T. J. , Costerton J. W. , Kapoor M.
Published: December 2009

The most abundant heat-shock protein of Neurospora crassa is a multimeric glycoprotein of 80-kilodaltons (i.e., HSP80), induced strongly by hyperthermia and at a lower level by sodium arsenite, ethanol, and carbon source depletion. Immunoelectron microscopy, using indirect immunogold labelling demonstrated that HSP80 was undetectable in mycelium cultured at the normal growth temperature of 28 °C, but it appeared rapidly following the commencement of heat-shock treatment at 48 °C. HSP80, visualized by the gold label, was observed almost exclusively in the cytoplasm, exhibiting a uniform distribution. Association of this protein with cellular membranes and (or) targeting to a particular subcellular compartment or organelle was not apparent.Key words: 80-kilodalton heat-shock protein, Neurospora, intracellular location, immunoelectron microscopy.
Dephosphorylation of the retinoblastoma protein during differentiation of HL60 cells
Authors: Whyte Peter , Eisenman Robert N.
Published: December 2009

Immunoprecipitated retinoblastoma protein from HL60 cells migrated as a series of bands during electrophoresis. The heterogeneity appeared to be generated by phosphorylation of the retinoblastoma protein. Treatment of the cells with the phorbol ester, tetradecanoyl phorbol acetate (TPA), resulted in both a loss of the heterogeneity of the pRB species and a significant decrease in the level of pRB phosphorylation. These changes accompanied differentiation of the HL60 cells into macrophages. Treatment of the cells with dibutyryl cAMP also resulted in dephosphorylation of pRB as well as cell cycle arrest, although no recognizable differentiation occurred. These results are consistent with a model in which TPA and dibutyryl cAMP dependent pathways can activate pRB by altering its phosphorylation.Key words: retinoblastoma, cell cycle, differentiation, leukemia.
Characterization of the in vitro hepatocyte model for toxicological evaluation: repeated growth stimulation and glutathione response
Authors: Guillemette Josée , Marion Michel , Denizeau Francine , Fournier Michel , Brousseau Pauline
Published: December 2009

Hepatocytes in culture represent a useful model for investigating the effects of toxic agents on liver cells. However, further development of this model is hampered by the difficulty in promoting cell proliferation over prolonged periods and the lack of knowledge about the biochemical status of the cells relevant to the toxic response under proliferation conditions. In an effort to overcome these limitations, this work focused on the establishment of conditions to ameliorate the promotion of hepatocyte proliferation in vitro. It also examined the effects of growth stimuli on the levels of glutathione (GSH), a highly significant parameter influencing the resistance against toxic agents. In addition, albumin secretion was monitored as an indicator of liver-specific functions. Two modified L-15 media were developed: medium A for supporting cell differentiation, and medium B for promotion of proliferation. Collagen and Matrigel were used as substrata. In medium A, the time course of GSH levels was comparable for both substrata, with an initial increase followed by a plateau and then by a progressive decrease from the second to the fourth week. Hepatocytes cultured on collagen and sequentially exposed to medium B (containing epidermal growth factor ± norepinephrine) and medium A, showed repeated responsiveness to stimulation of DNA synthesis. Moreover, for cultures on collagen, a higher GSH content was observed in parallel with DNA synthesis stimulation, while albumin secretion was diminished. Although cells on Matrigel were refractory to DNA synthesis stimulation, GSH levels were still increased upon exposure to the growth factors, while under these conditions, albumin synthesis remained unaltered. These results show the possibility of expanding growth stimulus applications in hepatocyte cultures when it is of interest in cell pathology studies, such as those involving the effects of long-term exposure to xenobiotics, especially carcinogens. The results also suggest that hepatocytes subjected to a growth stimulus may have better protection against toxic injury.Key words: hepatocyte, glutathione, growth factors, long-term culture, collagen.
Purification and characterization of rat epididymal neutral β-galactosidase and its changes during in vivo development
Authors: Dutta Pratima , Majumder Gopal C.
Published: December 2009

A neutral β-D-galactosidase has been partially purified from rat epididymis and characterized. The enzyme having molecular mass of approximately 50 kilodaltons has been purified 400-fold by using calcium phosphate gel adsorption, DEAE-cellulose chromatography, Sephadex G-100 gel filtration, and concanavalin A - agarose affinity chromatography. Although the neutral enzyme binds to the concanavalin A affinity column, the activity could be eluted with α-methyl mannoside only if the buffer contained salt (NaCl) at a concentration as high as 0.3 M. The enzyme was of cytosolic origin, since 90% of the total enzymic activity of the tissue homogenate was recovered in the soluble fraction of these cells. The neutral β-galactosidase was not dependent on metal ions for its activity and it had a pH optimum of 7.0. Zn2+, p-chloromercuribenzoate, Hg2+, and Pb2+ served as potent inhibitors of the enzyme. There was a marked increase (approximately fourfold) in the specific activity of the neutral β-galactosidase during sexual maturity of epididymis in vivo.Key words: neutral β-galactosidase, rat epididymal, cytosolic, developmental, sexual maturity.
In vivo phosphorylation of liver glycogen synthase. Effect of glucose and glucagon treatment of liver cells on the distribution of the [32P] phosphate
Authors: Tan Agnes W. H. , Nuttall Frank Q.
Published: December 2009

Glycogen synthase was phosphorylated in vivo by perfusing rat liver or incubating liver cells with [32P]phosphate. It was then isolated by immunoprecipitation and subjected to exhaustive tryptic proteolysis. The trypsin-derived [32P]phosphopeptides were separated by high pressure liquid chromatography (HPLC). Incubation of in vivo phosphorylated synthase with endogenous synthase phosphatase to convert synthase D to synthase R resulted in removal of phosphate from all of the labeled phosphopeptides. In prelabeled liver cells treated with glucagon or glucose, the activities of synthase and phosphorylase changed in the direction expected. The total labeling in the immunoprecipitated synthase was found to be increased to 126% and decreased to 67% of the control with glucagon and glucose treatment, respectively. When the HPLC [32P]phosphopeptide profile of synthase from glucagon-treated animals was compared with that of controls, there were only minor differences in the two profiles. All the peaks were present and the proportion of labeling in each remained similar. There also was only a modest change in the [32P]phosphopeptide profile with glucose treatment when compared with that of controls. These results indicate that regulation of synthase activity in the hepatocyte involves changes in phosphorylation at multiple sites. Indeed, in 32P-labeled liver cells, all of the labeled sites appeared to be involved.Key words: glycogen synthase, liver, phosphorylation state, glucose treatment, glucagon treatment.
Inhibition of glucose-6-phosphate phosphohydrolase by 3-mercaptopicolinate and two analogs is metabolically directive
Authors: Bode Ann M. , Foster James D. , Nordlie Robert C.
Published: December 2009

3-Mercaptopicolinae (3-MP) blocks gluconeogenesis from lactate, pyruvate, alanine, and other substrates through its inhibition of phosphoenolpyruvate carboxykinase. Nevertheless, we observed increased glycogenesis, net glucose uptake, and glucose-6-P levels in livers perfused with glucose in the presence of 3-MP. In perfusions with 20 mM dihydroxyacetone, increased glycogenesis and decreased glucose production were observed with 3-MP. These metabolic effects suggested additional site(s) of action of 3-MP. Further studies showed that 3-MP inhibits glucose-6-P phosphohydrolase activity of intact liver microsomes. Several compounds with structural similarities to 3-MP (2-mercaptonicotinic acid, picolinic acid, cysteine, reduced glutathione, nicotinic acid, quinolinic acid, tryptophan, and pyridine) were tested for their effect on glucose-6-P phosphohydrolase activity. Two of these compounds, 2-mercaptonicotinic acid and picolinic acid, were found to inhibit. In perfusions including 7.5 mM fructose, the addition of 3-MP, 2-mercaptonicotinic acid, or picolinic acid increased glycogenesis, decreased glucose production, and increased hepatic glucose-6-P concentrations. These observations indicate that the inhibition of glucose-6-P phosphohydrolase may play a role in enhanced glycogenesis from glucose, dihydroxyacetone, and fructose in isolated livers from 48-h fasted rats perfused with 3-MP or certain sulfhydryl-containing and sulfhydryl-devoid analogs.Key words: glucogenesis, 3-mercaptopicolinate, glucose-6-P phosphohydrolase.