bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dual effects of glucagon and cyclic amp on dna synthesis in cultured rat hepatocytes: Stimulatory regulation in early G1 and inhibition shortly before the s phase entry
Authors: Thoresen G. Hege , Sand Tor‐Erik , Refsnes Magne , Dajani Olav F. , Guren Tormod K. , Gladhaug Ivar P. , Killi Anne , Christoffersen Thoralf 
Published: February 2005

AbstractAlthough several lines of evidence implicate cyclic AMP in the humoral control of liver growth, its precise role is still not clear. To explore further the role of cyclic AMP in hepatocyte proliferation, we have examined the effects of glucagon and other cyclic AMP‐elevating agents on the DNA synthesis in primary cultures of adult rat hepatocytes, with particular focus on the temporal aspects. The cells were cultured in a serum‐free, defined medium and treated with epidermal growth factor (EGF), insulin, and dexamethasone. Exposure of the hepatocytes to low concentrations (10 pM‐1 nM) of glucagon in the early stages of culturing (usually within 6 h from plating) enhanced the initial rate of S phase entry without affecting the lag time from the plating to the onset of DNA synthesis, whereas higher concentrations inhibited it. In contrast, glucagon addition at later stages (24–45 h after plating) produced only the inhibition. Thus, if glucagon was added at a time when there was a continuous EGF/insulin‐induced recruitment of cells to S phase, the rate of G1‐S transition was markedly decreased within 1–3 h. This inhibitory effect occurred at low glucagon concentrations (ID50 < 1 nM) and was mimicked by cholera toxin, forskolin, isobutyl methylxanthine, and 8‐bromo cyclic AMP. The results indicate that cyclic AMP has dual effects on hepatocyte proliferation with a stimulatory modulation early in the prereplicative period (Go or early G1), and a marked inhibition exerted immediately before the transition from G1 to S phase.
Comparison of bone and parathyroid hormone as stimulators of osteoclast development and activity in calvarial cell cultures from normal and osteopetrotic (mi/mi) mice
Authors: Graves Leland , Jilka Robert L. 
Published: February 2005

AbstractOsteoclast development was studied in cell cultures prepared from calvaria of neonatal osteopetrotic (mi/mi) mice or their normal littermates, using tartrate‐resistant acid phosphatase (TRAPase), as an osteoclast marker. In cultures from normal mice, treatment with 10 nM PTH for 4–5 days stimulated the formation of osteoclasts. However in cultures from mi/mi mice, this response was only 7% ± 5% that of normal mice and they were significantly smaller than osteoclasts of normal mice. Mineralized bone particles elicited osteoclast development in cultures from both normal and mi/mi mice, and osteoclast size was identical for both genotypes. Seventy‐eight to 96% of the TRAPase‐positive cells bound 125 I‐CT, as demonstrated by autoradiography. 125I‐CT binding characteristics were identical in cultures from both genotypes treated with bone particles, exhibiting a Kd of 3.3–3.6 × 10−10 M. Addition of PTH stimulated 45Ca release from the added bone particles only in the case of cultures prepared from normal mice, and CT inhibited this response. Cells from normal mice were capable of excavating bone from the surface of smooth cortical bone wafers, but such excavations were rarely seen in the case of calvarial cells from mi/mi mice. Thus, PTH‐driven differentiation of osteoclasts is arrested in calvarial cell cultures from mi/mi mice, but mi/mi preosteoclasts retain the ability to express certain osteoclast markers in response to bone derived signals. We hypothesize that the lack of activity of mi/mi osteoclasts is due to the failure of mi/mi preosteoclasts to respond appropriately to resorptive agents, or to cytokines elicited by these agents.
Sarcolectin and interferon in the regulation of cell growth
Authors: Chany‐fournier Françoise , Jiang Pan Hong , Chany Charles 
Published: February 2005

AbstractSarcolectin is an endolectin present in a great variety of conjunctival tissues (muscles, cartilage, sarcomas), but also in brain or placental extracts of vertebrates, including primates. When purified to electrophoretical homogeneity as a 65‐kd protein, it agglutinates cells and has an affinity for simple sugars. In addition, it is able to inhibit the synthesis of interferon (IFN)‐dependent secondary proteins and to restore cells to their status ad primum. The biological effect of Poly(I). Poly(C)‐induced feedback interferon is inhibited by the addition of sarcolectins, which also abolishes cellular refractoriness to repeated IFN induction. Similarly, sequential association of, first, Poly(I). Poly(C); 4–5 h later, sarcolectin restores the full capacity of both to promote cell growth, unrestrained by IFN. Indeed, the secondary proteins which are in the process of being synthesized are inhibited. In a great variety of animal cells, sarcolectin can also initiate growth after it has been blocked by IFN. This is not an all‐or‐none effect, but a balance may be struck by IFN and sarcolectin, depending on their respective concentrations and specific activity. We propose that the coordination of these cellular functions of Poly(I).Poly(C), IFN, and sarcolectin takes place in the form of a triangular growth‐regulatory cycle and postulate that they thus maintain a balance during differentiated normal tissue development.
Interaction of Epidermal growth factor receptors with the cytoskeleton is related to receptor clustering
Authors: van Belzen Nico , Spaargaren Marcel , Verkleij Arie J. , Boonstra Johannes 
Published: February 2005

AbstractRecently it has been established that cytoskeleton‐associated epidermal growth factor (EGF) receptors are predominantly of the high‐affinity class and that EGF induces a recruitment of low‐affinity receptors to the cytoskeleton. The nature of this EGF‐induced receptor‐cytoskeleton interaction, however, is still unknown. Therefore, we have studied the association of mutated EGF receptors with the cytoskeleton. Receptor deletion mutants lacking almost all intracellular amino acid residues displayed no interaction with the cytoskeleton, demonstrating that the cytoplasmic receptor domain is involved in this interaction. Further analysis revealed that receptor‐cytoskeleton interaction is independent of receptor kinase activity and the C‐terminal 126 amino acid residues, which include the autophosphorylation sites. Furthermore, it is shown that the high‐affinity receptor subclass is not essential for association of low‐affinity receptors to the cytoskeleton. EGF receptor‐cytoskeleton interaction was increased, however, by treatment with sphingomyelinase, an enzyme known to induce membrane protein clustering, indicating that EGF receptor clustering may cause the association to the cytoskeleton.
TGF‐β inhibits the platelet‐derived growth factor‐induced formation of inositol trisphosphate in MG‐63 human osteosarcoma cells
Authors: Pontbriant Candace M. , Chen Jan‐Kan , Orlando Joseph A. 
Published: February 2005

AbstractEpidermal growth factor (EGF), platelet‐derived growth factor (PDGF), and heparin‐binding growth factor‐1 (HBGF‐1) stimulated the proliferation of a variant of the human osteosarcoma cell line, MG‐63‐LS = low serum. Transforming growth factor beta (TGF‐β) completely inhibited cell growth in basal medium supplemented with 2% fetal calf serum (FCS), blocked PDGF‐ and EGF‐stimulated cell proliferation, and modulated that of HBGF‐1. PDGF, but not EGF or HBGF‐1, activated the inositol trisphosphate/diacylglycerol (IP3/DAG) second message system in a dose‐dependent manner. EGF inhibited phosphoinositol lipid turnover and HBGF‐1 and TGF‐β stimulated phosphatidylinositol hydrolysis to produce inositol phosphate (IP) but not IP3. Preincubation of quiescent cells with TGF‐β for 30–40 minutes prior to the addition of PDGF resulted in an inhibition of PDGF‐induced production of IP3. This suggested that TGF‐β was an indirect inhibitor and blocked PDGF‐stimulated cell growth in part by interfering with the generation of the second messenger, IP3.
Tumor necrosis factor enhances the neutrophil‐dependent increase in endothelial permeability
Authors: Gibbs Lester S. , Lai Linda , Malik Asrar B. 
Published: February 2005

AbstractWe examined the effect of tumor necrosis factor α (TNFα) on the increase in pulmonary microvascular endothelial monolayer permeability induced by activated neutrophils (PMN). Layering of PMN onto endothelial monolayers followed by activation of PMN with phorbol 12‐myristate 13‐acetate (PMA) increased125I‐albumin clearance rate across the monolayers. Pretreatment of endothelial monolayers for 6 hr with TNFα(200 U/ml) potentiated the PMN‐dependent increase in endothelial permeability, whereas 1 hr or 6 hr pretreatment of endothelial monolayers with 200 U/ml and 100 U/ml, respectively, TNFαdid not enhance the reponse. Adherence of PMN to the endothelial cells was increased at 1 and 6 hr after TNFα(200 U/ml) treatment, but the adherence reponse was markedly greater following 6 hr of TNFα. The TNFαtreatment of endothelial cells did not enhance neutrophil activation responses to PMA. Pretmeatment of PMN with IB4, a MAb to the CD18 integrin, the common β subunit of the adhesion proteins LFA‐1, Mac‐1, and p150,95 of PMN, reduced the increases in PMN adherence and the endothelial monolayer permeability induced by the 6 hr TNFα treatment. In contrast, pretreatment of PMN with OKM‐1, a MAb to the CD11b epitope (‐subunit), had no effect on the adherence and the potentiation of the increase in permeability. The potentiation of the PMN‐dependent permeability increase and enhanced endothelial adhesivity at 6 hr after TNFαpriming of endothelial cells was dependent on protein synthesis. The results indicate that protein synthesis‐dependent expression of an endothelial ligand for CD18 and resultant endothelial hyperadhesiveness potentiates the PMN‐mediated increase in endothelial permeability after TNFαactivation of endothelial cells. The priming of endothelial cells by TNFαmay be a critical step in the mediation of endothelial injury.
Effects of hypertonic and sodium‐free medium on transport of a membrane glycoprotein along the secretory pathway in cultured mammalian cells
Authors: Docherty Pamela A. , Snider Martin D. 
Published: February 2005

AbstractIncubation of cultured cells in hypertonic medium and sodium‐free medium have been shown to block transport at two different stages along the endocytic pathway. To determine the effects of these treatments on the exocytic pathway, we studied the transport of the membrane glycoprotein of vesicular stomatitis virus (VSV‐G) in cells infected with tsO45 mutant virus. This mutant synthesizes a VSV‐G that accumulates in the endoplasmic reticulum (ER) when cells are incubated at 39.5°C. In addition, VSV‐G accumulates in the post‐ER pre‐Golgi compartment when cells are incubated at 15°C and in the trans‐Golgi network (TGN) when cells are incubated at 18°C. Upon transfer of cells to 32°C in control medium, VSV‐G exits each of these compartments and is transported to the cell surface. Incubation in sodium‐free medium at 32°C did not block transport from any of these three compartments. In contrast, incubation in hypertonic medium blocked export from the ER, transport from the pre‐Golgi compartment to the Golgi complex, and transport from the TGN to the cell surface. Our results, in combination with previous studies, suggest that hypertonic medium blocks at least five distinct transport steps: the three exocytic steps described here, endocytosis from the cell surface, and transport of cell surface proteins into the Golgi complex. This raises the possibility that vesicular transport in different parts of the cell shares common elements that are inhibited by this treatment.
Homocysteine export from cells cultured in the presence of physiological or superfluous levels of methionine: Methionine loading of non‐transformed, transformed, proliferating, and quiescent cells in culture
Authors: Christensen Benedicte , Refsum Helga , Vintermyr Olav , Ueland Per Magne 
Published: February 2005

AbstractDetermination of the transient increase in plasma homocysteine following administration of excess methionine is an established procedure for the diagnosis of defects in homocysteine metabolism in patients. This so‐called methionine loading test has been used for 25 years, but the knowledge of the response of various cell types to excess methionine is limited. In the present paper we investigated homocysteine export from various cell types cultured in the presence of increasing concentrations (15–1,000 μM) of methionine. For comparison of homocysteine export, the export rates per million cells were plotted versus cell density for proliferating cells, and versus time for quiescent cells. The homocysteine export from growing cells was greatest during early to mid‐exponential growth phase, and then decreased as a function of cell density. The export rate was higher from phytohemagglutinin‐stimulated than non‐stimulated lymphocytes, and higher from proliferating than from quiescent fibroblasts. The hepatocytes showed highest export rate among the cell types investigated. The enhancement of homocysteine export by excess methionine ranged from no stimulation to marked enhancement, depending on cell type investigated, and three different response patterns could be distinguished: (1) quiescent fibroblasts and growing murine lymphoma cell showed no significant increase in homocysteine export following methionine loading; export from human lymphocytes was only slightly enhanced in the presence of excess methionine; (2) the homocysteine export from proliferating hepatoma cells and benign and transformed fibroblasts was stimulated three to eightfold by increasing the methionine concentration in the medium from 15 to 1,000 μM; and (3) the response to methionine loading was particularly increased (about 15‐fold) in non‐transformed primary hepatocytes in stationary culture. The results outline a potentially useful procedure for the comparison of homocysteine export during cell growth in the presence of various concentrations of methionine. The results are discussed in relation to the special feature of homocysteine metabolism in various cell types and tissues including liver, and to the possible source of plasma homocysteine following methionine loading in vivo.
Epidermal growth factor treatment of A431 cells alters the binding capacity and electrophoretic mobility of the cytoskeletally associated epidermal growth factor receptor
Authors: Roy Linda M. , Gittinger Cynthia K. , Landreth Gary E. 
Published: February 2005

AbstractThe epidermal growth factor (EGF) receptor interacts with structural elements of A431 cells and remains associated with the cytoskeleton following extraction with nonionic detergents. Extraction of cells with 0.15% Triton X‐100 resulted in detection of only approximately 40% of the EGF binding sites on the cytoskeleton. If the cells were exposed to EGF prior to extraction, approximately twofold higher levels of low‐affinity EGF binding sites were detected. The difference in number of EGF binding sites was not a consequence of differences in numbers of EGF receptors associated with the cytoskeleton; equal amounts of 35S‐labeled receptor were immunoprecipitated from the cytoskeletons of both control and EGF‐treated cells. The effect of EGF pretreatment on binding activity was coincident with a change in the mobility of the receptor from a doublet of Mr ∼ 160–180 kDa to a single sharp band at 180 kDa. The alteration in receptor mobility was not a simple consequence of receptor phosphorylation in that the alteration was not reversed by alkaline phosphatase treatment, nor was the shift produced by treatment of the cells with phorbol ester. The two EGF receptor species demonstrated differential susceptibility to V8 proteinase digestion. The EGF‐induced 180 kDa species was preferentially digested by the proteinase relative to the 160 kDa species, indicating that EGF binding results in a conformational change in the receptor. The EGF‐mediated preservation of binding activity and altered conformation may be related to receptor oligomerization.
Programmed cell death (apoptosis) is induced rapidly and with positive cooperativity by activation of cyclic adenosine monophosphate‐kinase I in a myeloid leukemia cell line
Authors: Lanotte M. , Riviere J. B. , Hermouet S. , Houge G. , Vintermyr O. K. , Gjertsen B. T. , Døskeland S. O. 
Published: February 2005

AbstractProgrammed death (apoptosis) of the rat myelocytic leukemic cell line IPC‐81 was triggered by cyclic adenosine monophosphate (cAMP) analogs or by agents (cholera toxin, prostaglandins) increasing the endogenous cAMP level. The induction of cell death by cholera toxin was preceded by increased activation of cAMP‐kinase. Cell lysis started already 5 hr after cAMP challenge and was preceded by internucleosomal DNA fragmentation and morphological changes characteristic of apoptosis. The cell suicide could be prevented by inhibitors of macromolecular synthesis. cAMP analogs induced cell death in a positively cooperative manner (apparent Hill coefficient of 2.9), indicating that triggering of the apoptotic process was under stringent control. There was a strong synergism between cAMP analogs complementing each other in the activation of cAMP‐dependent protein kinase I (cAKI). No such synergism was noted for analogs complementing each other in the activation of cAKII. It is concluded that apoptosis can be induced solely by activation of cAKI. The IPC‐81 cells expressed about four times more cAKI than cAKII. The expression of cAK subunits, on the protein and mRNA levels, was only minimally affected by cholera toxin treatment.
Role of intracellular‐free calcium in the cornified envelope formation of keratinocytes: Differences in the mode of action of extracellular calcium and 1,25 dihydroxyvitamin D3
Authors: Pillai Sreekumar , Bikle Daniel D. 
Published: February 2005

AbstractExtracellular calcium (Cao) and the steroid hormone 1,25(OH)2D, induce the differentiation of human epidermal cells in culture. Recent studies suggest that increases in intracellular free calcium (Cai) levels may be an initial signal that triggers keratinocyte differentiation. In the present study, we evaluated cornified envelope formation, the terminal event during keratinocyte differentiation, and correlated it with changes in the Cai levels during differentiation of keratinocytes in culture induced by Cao or 1,25(OH)2D, Keratinocytes were grown in different Cao concentrations (0.1 or 1.2 mM) or in the presence of 1,25(OH)2D OCT'1 to 10−7 M, and the Cai levels were measured using the fluorescent probe lndo‐1. Our results suggest that the induction of cornified envelope formation is associated with an increase in Cai level during calcium‐induced differentiation. Cao and the calcium ionophore ionomycin acutely increased Cai and cornified envelope formation. In contrast, the effect of 1,25(OH)2D on increasing Cai levels and stimulating cornified envelope formation was long‐term, requiring days of treatment with 1,25(OH)2D. Our data are consistent with other recent studies and support the hypothesis that Cao regulates keratinocyte differentiation primarily by acutely increasingtheirCai levels. The roleofcalcium in the mechanism ofaction of 1,25(OH)2D keratinocyte differentiation is less clear. The increase in Cai of keratinocytes during 1,25(OH)2D induced differentiation may be essential for or subsequent to its prodifferentiation effects.
Role of growth factors in the contraction and maintenance of collagen lattices made with arterial smooth muscle cells
Authors: Chen Jan‐Kan , Haimes Howard B. , Weinberg Crispin B. 
Published: February 2005

AbstractThe contraction of collagen lattices made with arterial smooth muscle cells was studied in medium MCDB 107 without serum or supplemented with 1% fetal bovine serum, plus insulin, transferrin, and low‐density lipoprotein. Under these conditions, smooth muscle cell mitogens including HBGF‐1 (aFGF), PDGF, and EGF stimulated contraction. Stimulation by HBGF‐1 was more profound than with other factors tested. HBGF‐1 stimulation of lattice contraction was blocked by protein synthesis inhibitors, but not by inhibitors of DNA synthesis. Histological observations indicated that HBGF‐1 also enhanced the maintenance of healthy cells in the lattice. Taken together, these observations suggest that HBGF‐1 stimulates lattice contraction, not by a mitogenic effect, but by stimulating synthesis of specific cellular proteins. Since the greatest effects of HBGF‐1 on lattice contraction were seen during the first 72 h following casting, the effects on maintenance of cell viability are probably less important in promoting lattice contraction.
Effects of prostaglandin E2 and F2α on cytoplasmic pH in a clonal osteoblast‐like cell line, MOB 3–4
Authors: Kawase Tomoyuki , Orikasa Michiaki , Suzuki Akitoshi 
Published: February 2005

AbstractProstaglandin E2 (PGE2, 5 ng/ml to 5 μg/ml) induced a dose‐dependent increase in cAMP accumulation, inositol phosphates (IPs) accumulation, and cytoplasmic free Ca2+ ([Ca2+]i) in a clonal osteoblast‐like cell line, MOB 3–4. In contrast, prostaglandin F2α (PGF2α, 5 ng/ml to 5 μg/ml) stimulated increases in IPs accumulation and [Ca2+]i without stimulating an increase in cAMP accumulation. Both PGE2 (>0.5 μg/ml) and PGF2α (≥0.5 μg/ml) increased cytoplasmic pH (pHi) from approximately 7.15 to 7.35 in BCECF‐loaded cells. A tumor promotor, phorbol 12‐myristate 13‐acetate (PMA, 0.1–100 nM) also increased pHi without effect on phosphoinositide hydrolysis. Both PGE2‐(5 μg/ml) and PMA‐ (100 nM) induced cytoplasmic alkalinization was inhibited by removal of extracellular Na+, or by pretreatment of the cells with amiloride (0.5 mM), an inhibitor of Na+/H+ exchange, or H‐7 (100 μM), a nonspecific inhibitor of protein kinase C. Thus, MOB 3–4 cells appeared to possess PGE2 receptors and PGF2α receptors: the former are coupled to adenylate cyclase and phospholipase C, and the latter are predominantly coupled to phospholipase C. Also the cells appeared to possess an amiloride‐sensitive Na+/H+ exchange activity, which increases pHi in response to PGE2 and PGF2α, as well as to PMA. Long‐term (48 hr) exposure of the cells to PGE2 at a high concentration (5 μg/ml), but not to PGF2α and PMA, decreased DNA synthesis in the serum‐deficient medium. Thus, cytoplasmic alkalinization appeared insufficient for cell replication. At least in MOB 3–4 cells, the inhibitory effect of PGE2 on DNA synthesis may be due to the cAMP messenger system.