bluuebunny/crossref_metadata_2025_split huggingface dataset:
TGFβ1 Prevents the down‐regulation of type I procollagen, fibronectin, and TGFβ1 gene expression associated with 3T3‐L1 pre‐adipocyte differentiation
Authors: Bortell Rita , Owen Thomas A. , Ignotz Ronald , Stein Gary S. , Stein Janet L. 
Published: May 2005

AbstractPre‐adipocyte 3T3‐L1 cells, after an appropriate induction stimulus, proceed through a defined change in morphology as differentiation progresses. Transforming growth factor β1 (TGFβ1) is able to block the morphological and biochemical changes which occur with differentiation of these cells if given within 36–40 h of induction [Ignotz and Massague (1985): Proc Natl Acad Sci USA 82:8530–8534]. To begin to elucidate the role of the extracellular matrix in adipogenesis, as well as the mechanism whereby TGFβ1 inhibits differentiation, we examined the expression of two extracellular matrix genes, type I (α1) procollagen and fibronectin, as well as endogenous TGFβ1. Confluent cells were induced to differentiate by treatment with insulin, dexamethasone, and isobutylmethylxanthine in the presence or absence of TGFβ1. Following 6 days of treatment, the cells in the differentiated group acquired the rounded shape of mature adipocytes; the cytosol of these cells also contained numerous lipid‐filled vesicles, as demonstrated by oil red O staining. Cells treated with the differentiation compounds in the presence of TGFβ1 maintained the fibroblast‐like appearance of control cells and did not stain with oil red O. At the level of gene expression, both procollagen and fibronectin mRNAs were down‐regulated during differentiation of 3T3‐L1 cells. When cells from the control or differentiation groups were treated with TGFβ1, there was a 2–5‐fold induction of procollagen and fibronectin mRNAs throughout the 6‐day time course. No change in type I procollagen transcription was observed by nuclear run‐on analysis, suggesting that the increase in procollagen mRNA with TGFβ1 treatment was due to a post‐transcriptional process(es). However, both transcriptional and post‐transcriptional components were observed in the regulation of fibronectin gene expression by TGFβ1. In addition, TGFβ1 was found to positively regulate its own expression, as treatment of the cells with TGFβ1 enhanced endogenous TGFβ1 expression and prevented the small decrease in TGFβ1 mRNA levels which occurred early during the differentiation program. Thus, our data demonstrate that down‐regulation of type I procollagen, fibronectin, and TGFβ1 gene expression was prevented during TGFβ inhibition of 3T3‐L1 differentiation. Taken together, these data suggest that TGFβ may inhibit differentiation of 3T3‐L1 cells by maintaining the fibroblast‐like extracellular matrix, thus preventing the changes in cell shape that accompany differentiation.
Cell cycle arrest by prostaglandin A1 at the G1/S phase interface with up‐regulation of oncogenes in S‐49 cyc− cells
Authors: Hughes‐Fulford Millie 
Published: May 2005

AbstractOur previous studies have implied that prostaglandins inhibit cell growth independent of cAMP. Recent reports, however, have suggested that prostaglandin arrest of the cell cycle may be mediated through protein kinase A. In this report, in order to eliminate the role of c‐AMP in prostaglandin mediated cell cycle arrest, we use the‐49 lymphoma variant (cyc−) cells that lack adenylate cyclase activity. We demonstrate that dimethyl prostaglandin A1 (dmPGA1) inhibits DNA synthesis and cell growth in cyc− cells. DNA synthesis is inhibited 42% by dmPGA1 (50 μM) despite the fact that this cell line lacks cellular components needed for cAMP generation. The ability to decrease DNA synthesis depends upon the specific prostaglandin structure with the most effective form possessing the α,β unsaturated ketone ring. Dimethyl PGA1 is most effective in inhibiting DNA synthesis in cyc− cells, with prostaglandins PGE1 and PGB1 being less potent inhibitors of DNA synthesis. DmPGE2 caused a significant stimulation of DNA synthesis. S‐49 cyc‐ variant cells exposed to (30–50 μm) dmPGA1, arrested in the G1 phase of the cell cycle within 24 h. This growth arrest was reversed when the prostaglandin was removed from the cultured cells; growth resumed within hours showing that this treatment is not toxic. The S‐49 cyc− cells were chosen not only for their lack of adenylate cyclase activity, but also because their cell cycle has been extensively studied and time requirements for G1, S, G2, and M phases are known. Within hours after prostaglandin removal the cells resume active DNA synthesis, and cell number doubles within 15 h suggesting rapid entry into S‐phase DNA synthesis from the G1 cell cycle block. The S‐49 cyc− cells are known to have a G1/S boundary through M phase transition time of 14.8 h, making the location of the prostaglandin cell cycle arrest at or very near the G1/S interface. The oncogenes, c‐fos and c‐myc which are normally expressed during G1 in proliferating cells have a 2–3 fold enhanced expression in prostaglandin G1 arrested cells. These data using the S‐49 variants demonstrate that dmPGA1 inhibits DNA synthesis and arrests the cell cycle independent of cAMP‐mediated effects. The prostaglandin arrested cells maintain the gene expression of a G1 synchronous cell which suggests a unique molecular mechanism for prostaglandin action in arresting cell growth. These properties indicate that this compound may be an effective tool to study molecular mechanisms of regulation of the cell cycle.
Isolation of cDNA clones from an osteosarcoma‐ROS17/2.8 library by differential hybridization
Authors: Waye Mary M. Y. , Li Vincent K. C. 
Published: May 2005

AbstractWe have used differential hybridization to isolate and characterize two novel cDNAs expressed in chondrocytes and some osteoblastic cells. A rat osteosarcoma ROS17/2.8 cDNA library was screened and cDNA clones hybridizing strongly to radiolabeled porcine calvaria cDNA but weakly to a control radiolabeled cDNA were isolated. Two clones were obtained—p.6.1 and p.10.15. A radiolabeled probe of p10.15 was shown to hybridize specifically to a 2.3 Kb message RNA from a chondrogenic clonal cell population from rat calvaria‐RCJ 3.1C5.18, and the mRNA was downregulated by 1,25 (OH)2D3, which inhibits chondrogenesis in these cells. The other clone, p6.1, was found to hybridize to a 0.95 Kb message that is expressed in rat liver, kidney, lung, muscle, and brain, but not expressed in spleen and expressed only in low levels in thymus.
Cell attachment peptide of C‐reactive protein: critical amino acids and minimum length
Authors: Mullenix Michael C. , Kaumaya Pravin T. P. , Mortensen Richard F. 
Published: May 2005

AbstractHuman C‐reactive protein (CRP) is an acute phase blood component that accumulates at sites of tissue damage and necrosis and is degraded by neutrophils to biologically active peptides. A dodecapeptide composed of amino acids 27–38 of CRP mediates cell attachment in vitro. This peptide was designated the cell‐binding peptide (CB‐Pep) of CRP. Characterization of the interaction between fibroblasts and modified synthetic peptides with sequential deletions from either the N‐terminus or C‐terminus revealed that the minimal sequence for cell attachment or inhibition of cell attachment to the CB‐Pep was Phe‐Thr‐Val‐Cys‐Leu, which corresponds to residues 33–37 within each of the five 206 amino acid subunits of CRP. The pentapeptide by itself mediated cell attachment. Substitutions for each residue within the CB‐Pep indicated that the critical residues for activity were Phe‐33 and Thr‐34. This cell‐binding pentapeptide represents a recognition motif for cell adhesion not found in other proteins.
Histone gene transcription: A model for responsiveness to an integrated series of regulatory signals mediating cell cycle control and proliferation/differentiation interrelationships
Authors: Stein Gary S. , Stein Janet L. , van Wijnen André J. , Lian Jane B. 
Published: May 2005

AbstractHistone gene expression is restricted to the S‐phase of the cell cycle. Control is at multiple levels and is mediated by the integration of regulatory signals in response to cell cycle progression and the onset of differentiation. The H4 gene promoter is organized into a series of independent and overlapping regulatory elements which exhibit selective, phosphorylation‐dependent interactions with multiple transactivation factors. The three‐dimensional organization of the promoter and, in particular, its chromatin structure, nucleosome organization, and interactions with the nuclear matrix may contribute to interrelationships of activities at multiple promoter elements. Molecular mechanisms are discussed that may participate in the coordinate expression of S‐phase‐specific core and H1 histone genes, together with other genes functionally coupled with DNA replication.
How does the G protein, Gi2, transduce mitogenic signals?
Authors: Johnson Gary L. , Gardner Anne M. , Lange‐Carter Carol , Qian Nan‐Xin , Russell Marijane , Winitz Sim 
Published: May 2005

AbstractSerpentine receptors coupled to the heterotrimeric G protein, Gi2, are capable of stimulating DNA synthesis in a variety of cell types. A common feature of the Gi2‐coupled stimulation of DNA synthesis is the activation of the mitogen‐activated protein kinases (MAPKs). The regulation of MAPK activation by the Gi2‐coupled thrombin and acetylcholine muscarinic M2 receptors occurs by a sequential activation of a network of protein kinases. The MAPK kinase (MEK) which phosphorylates and activates MAPK is also activated by phosphorylation. MEK is phosphorylated and activated by either Raf or MEK kinase (MEKK). Thus, Raf and MEKK converge at MEK to regulate MAPK. Gi2‐coupled receptors are capable of activating MEK and MAPK by Raf‐dependent and Raf‐independent mechanisms. Pertussis toxin catalyzed ADP‐ribosylation of αi2 inhibits both the Raf‐dependent and‐independent pathways activated by Gi2‐coupled receptors. The Raf‐dependent pathway involves Ras activation, while the Raf‐independent activation of MEK and MAPK does not involve Ras. The Raf‐independent activation of MEK and MAPK most likely involves the activation of MEKK. The vertebrate MEKK is homologous to the Ste11 and Byr2 protein kinases in the yeast Saccharomyces cerevisiae and Schizosaccharomyces pombe, respectively. The yeast Ste11 and Byr2 protein kinases are involved in signal transduction cascades initiated by pheromone receptors having a 7 membrane spanning serpentine structure coupled to G proteins. MEKK appears to be conserved in the regulation of G protein‐coupled signal pathways in yeast and vertebrates. Raf represents a divergence in vertebrates from the yeast pheromone‐responsive protein kinase system. Defining MEKK and Raf as a divergence in the MAPK regulatory network provides a mechanism for differential regulation of this system by Gi2‐coupled receptors as well as other receptor systems, including the tyrosine kinases.
Effect of aluminum chloride on mitogenesis, mitosis, and cell cycle in human short‐term whole blood cultures: Lower concentrations enhance mitosis
Authors: Yao Xiu‐Lan , Jenkins Edmund C. , Wisniewski Henryk M. 
Published: May 2005

AbstractAluminum, the third most common element in the earth's crust (second to oxygen and silicon) and recently suspected by some investigators to be implicated in Alzheimer disease etiology, has been studied in relation to its effect on mitogenesis, mitosis, and cell cycle. We have observed that 2–4 mM concentrations of AlCl3 have decreased the number of cells that undergo mitogenesis (PHA‐induced blast transformation) and mitosis in human short term whole blood cultures. We have also shown that the rate of the cell cycle was slowed down, i.e., cell cycle time was increased in the presence of AlCl3. Also, we have demonstrated a reversible effect on aluminum‐induced reduced mitotic index in long‐term EBV‐transformed lymphoblastoid cultures. Although safeguards such as limiting aluminum serum concentrations have been recommended to protect individuals undergoing dialysis, it should be realized that concentration accumulations of aluminum may increase over chronic exposures. Accordingly, if the number of cells stimulated by PHA is reduced in the presence of AlCl3, there may be a reduction of immune competence, since the degree of PHA stimulation has been used as an indicator of immune response. Similar reductions in mitotic index could affect every tissue involved with cell division. Although it may not be the same for higher concentrations, from our results, we have also shown that decreased mitotic rates were reversible in long‐term EBV‐transformed lymphoblastoid cultures.Increased numbers of mitoses were observed in human short‐term whole blood cultures that were exposed to 2 μM concentrations of aluminum chloride. The concentration is close to those found in normal human serum and within the “safeguard” range recommended for dialysis patients. A similar trend for aluminum sulfate was also observed, while preliminary results for three other aluminum species, lactate, citrate, and maltol, were also reported. Although previous reports have indicated a positive effect of aluminum on mitosis in vitro or in vivo, this is the first such report involving human material.It is clear that higher concentrations of aluminum chloride at 2.0–4.0 mM reversibly inhibit mitosis while more dilute concentrations of 1–2 μM, closer to those found in normal serum, enhance mitosis. The present results, as well as those in the literature, suggest that aluminum may be an essential element in cellular processes for optimal growth, development, and health maintenance. Future research will further test this hypothesis.
ras‐p21 Activates phospholipase D and A2, but not phospholipase C or PKC, in Xenopus laevis Oocytes
Authors: Carnero Amancio , Dolfi Fabrizio , Lacal Juan Carlos 
Published: May 2005

AbstractXenopus laevis oocytes are a powerful tool for the characterization of signal transduction pathways leading to the induction of DNA synthesis. Since activation of PLA2, PLC, or PLD has been postulated as a mediator of ras function, we have used the oocyte system to study the putative functional relationship between ras‐p21 and these phospholipases. A rapid generation of PA and DAG was observed after ras‐p21 microinjection, suggesting the activation of both PLC and PLD enzymes. However, production of DAG was sensitive to inhibition of the PA‐hydrolase by propranolol, indicating that PLD is the enzyme responsible for the generation of both PA and DAG. Microinjection of PLD or ras‐p21 induced the late production of lysophosphatidylcholine on a p42MAPK‐dependent manner, an indication of the activation of a PLA2. Inhibition of this enzyme by quinacrine does not inhibit PLD‐ or ras‐induced GVBD, suggesting that PLA2 activation is not needed for ras or PLD function. Contrary to 3T3 fibroblasts, where ras‐p21 is functionally dependent for its mitogenic activity on TPA‐ and staurosporine‐sensitive PKC isoforms, in Xenopus oocytes, induction of GVBD by ras‐p21 was independent of PKC, while PLC‐induced GVBD was sensitive to PKC inhibition. Thus, our results demonstrate the activation of PLD and PLA2 by ras‐p21 proteins, while no effect on PLC was observed.
Effect of prostaglandin F2α on Ca2+ influx in osteoblast‐like cells: Function of tyrosine kinase
Authors: Suzuki Atsushi , Kozawa Osamu , Saito Hidehiko , Oiso Yutaka 
Published: May 2005

AbstractWe previously reported that pertussis toxin–sensitive GTP‐binding protein is involved in prostaglandin F2α (PGF2α)‐induced phosphoinositide (PI) hydrolysis in osteoblast‐like MC3T3‐E1 cells [Miwa et al. (1990): Biochem Biophys Res Commun 171:1229–1235]. In the present study, we investigated the mechanism of PGF2α‐induced Ca2+ influx in MC3T3‐E1 cells. PGF2α‐induced formation of total inositol phosphates (IPs) was markedly reduced by the depletion of extracellular Ca2+ with EGTA. On the other hand, the depletion of extracellular Ca2+ had little effect on PGF2α‐induced inositol 1,4,5‐trisphosphate formation. PGF2α stimulated 45Ca2+ influx dose dependently, attaining a maximum effect at 10 nM. Dose of PGF2α above 10 nM caused less than maximal stimulation. Genistein, an inhibitor of protein tyrosine kinase, which by itself had little effect on 45Ca2+ influx, significantly suppressed the PGF2α‐induced 45Ca2+ influx in a dose‐dependent manner in the range between 1 μg/ml and 0.1 mg/ml. Sodium orthovanadate, an inhibitor of protein tyrosine phosphatases, enhanced the PGF2α‐induced 45Ca2+ influx. Genistein also suppressed the PGF2α‐induced total IPs formation dose dependently in the range between 1 μg/ml and 0.1 mg/ml. However, it had little effect on the PGF2α‐induced inositol 1,4,5‐trisphosphate formation. The pretreatment with pertussis toxin had little effect on the PGF2α‐induced 45Ca2+ influx. These results strongly suggest that PGF2α stimulates Ca2+ mobilization from extracellular space and PI hydrolysis via independent pathways in osteoblast‐like cells, and the PGF2α‐induced Ca2+ influx is regulated by protein tyrosine kinase, resulting in the promotion of PI hydrolysis.
Coupling of cell structure to cell metabolism and function
Authors: Pienta Kenneth J. , Hoover Carol N. 
Published: May 2005

AbstractThe fact that cells make directed decisions regarding how to use energy, i.e., where to direct intracellular particles or where to move, suggests that energy can be, and is, harnessed in specific ways. It is now well established that the chemical reactions of the cell do not occur in nonorganized soup, but rather in the context of ordered structure. The physical components that make up this ordered structure of the cell are part of the tissue matrix, which consists of the dynamic linkages between the skeletal networks of the nucleus (the nuclear matrix), the cytoplasm (the cytoskeleton), and the extracellular environment (the extracellular matrix). To understand gene function and how the energy of the cell is directed towards accomplishing the tasks directed by DNA (gene expression), a further understanding of how cell structure is tied to cellular energy and function is required. We propose that the structural components of the cell harness cellular energy to direct cell functions by providing a dynamic bridge between thermodynamics and gene expression. © 1994 Wiley‐Liss, Inc.
Naturally occurring ether‐linked phosphatidylcholine activates phosphatidylinositol 3‐kinase and stimulates cell growth
Authors: Misra Siniti , Ghosh Amitabha , Varticovski Lyuba 
Published: May 2005

AbstractPhosphatidylcholine (PC) from marine invertebrates is enriched in ether‐linked forms. PCs from ray fish, Dasyatis sp., and bivalve, Macoma birmanica, used in the present study, contain 65% and 75% (w/w of total PC) of ether‐linked forms, respectively. Ether‐linked PCs also occur in mammalian membranes. Agonist‐mediated hydrolysis of PC generates second messengers which participate in cellular responses. In this study, we tested whether PCs from marine invertebrates directly affect mammalian cell growth and activity of phosphatidylinositol (PI‐3‐kinase). PI‐3‐kinase participates in mitogenesis initiated by a variety of growth factors. PI‐3‐kinase converts polyphosphoinositides to 3′ phosphorylated isomers and these products accumulate in response to mitogenic stimuli. Whether cell membrane lipids regulate PI‐3‐kinase activity is not known. The marine animal–derived PCs and dioleoyl DAG (dioleoylglycerol) stimulated growth of murine pre‐B lymphocytes, whereas chicken PC (egg lecithin) inhibited growth of these cells. Egg lecithin is also a potent inhibitor of PI‐3‐kinase activity in vitro. We studied the effect of PCs and DAG on PI‐3‐kinase activity. Unlike egg lecithin, marine animal PCs enhanced PI‐3‐kinase activity. We investigated the effect of lipids on PI‐3‐kinase substrate utilization. PCs enriched in ether‐linked species increased utilization of substrates by PI‐3‐kinase. PCs purified from marine organisms also contain a substantially higher percentage of the cis‐unsaturated fatty acids, especially of the − ω3 series (25% and 30% of total fatty acids for Dasyatis sp. and Macoma birmanica, respectively), as compared to vertebrate sources. In spite of differences in fatty acid composition, marine PCs and dioleoyl DAG showed similar effects on cell growth and PI‐3‐kinase activity. These findings indicate that ether‐linked phospholipids activate PI‐3‐kinase and may participate in mitogenic responses. © 1994 Wiley‐Liss, Inc.
Role of the retinoblastoma protein in cell cycle arrest mediated by a novel cell surface proliferation inhibitor
Authors: Enebo Daniel J. , Fattaey Heideh K. , Moos Philip J. , Johnson Terry C. 
Published: May 2005

AbstractA novel cell regulatory sialoglycopeptide (CeReS‐18), purified from the cell surface of bovine cerebral cortex cells has been shown to be a potent and reversible inhibitor of proliferation of a wide array of fibroblasts as well as epithelial‐like cells and nontransformed and transformed cells. To investigate the possible mechanisms by which CeReS‐18 exerts its inhibitory action, the effect of the inhibitor on the posttranslational regulation of the retinoblastoma susceptibility gene product (RB), a tumor suppressor gene, has been examined. It is shown that CeReS‐18 mediated cell cycle arrest of both human diploid fibroblasts (HSBP) and mouse fibroblasts (Swiss 3T3) results in the maintenance of the RB protein in the hypophosphorylated state, consistent with a late G1 arrest site. Although their normal nontransformed counterparts are sensitive to cell cycle arrest mediated by CeReS‐18, cell lines lacking a functional RB protein, through either genetic mutation or DNA tumor virus oncoprotein interaction, are less sensitive. The refractory nature of these cells is shown to be independent of specific surface receptors for the inhibitor, and another tumor suppressor gene (p53) does not appear to be involved in the CeReS‐18 inhibition of cell proliferation. The requirement for a functional RB protein product, in order for CeReS‐18 to mediate cell cycle arrest, is discussed in light of regulatory events associated with density‐dependent growth inhibition. © 1994 Wiley‐Liss, Inc.
Signal peptide hydrophobicity is finely tailored for function
Authors: Rusch Sharyn L. , Chen Huanfeng , Izard Jennifer W. , Kendall Debra A. 
Published: May 2005

AbstractIn order to titrate the dependence of individual steps in protein transport on signal peptide hydrophobicity, we have examined a series of mutants which involve replacement of the hydrophobic core segment of the Escherichia coli alkaline phosphatase signal peptide. The core regions vary in composition from 10:0 to 0:10 in the ratio of alanine to leucine residues. Thus, a nonfunctional polyalanine‐containing signal peptide is titrated with the more hydrophobic residue, leucine. Analysis of this series identified a midpoint for rapid precursor processing between alanine to leucine ratios of 6:4 and 5:5 [Doud et al. (1993): Biochemistry 32:1251–1256]. Examination of precursors that are processed more slowly indicates a lower limit of signal peptide hydrophobicity that permits membrane association and translocation. Analysis of precursors that are processed rapidly defines an intermediate range of hydrophobicity that is optimum; above this level precursors become insensitive to transport inhibitors such as sodium azide and carbonyl cyanide 3‐chlorophenylhydrazone (CCCP) in parallel with substantial inhibition of β‐lactamase processing. Our data indicate that there is a surprisingly narrow range of signal peptide hydrophobicity which both supports transport of the protein to which it is attached and which does not have such a high affinity for the transport pathway that it disrupts the appropriate balance of other secreted proteins. © 1994 Wiley‐Liss, Inc.