bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of phenylarsine oxide on fluid phase endocytosis: Further evidence for activation of the glucose transporter
Authors: Frost Susan C. , Lane M. Daniel , Gibbs E. Michael 
Published: February 2005

AbstractWe have shown previously that insulin stimulates fluid phase endocytosis in 3T3‐L1 adipocytes (Gibbs et al., 1986). Using [14C]sucrose as an endocytotic marker, we show here that phenylarsine oxide, a trivalent arsenical which binds neighboring dithiols, blocked not only insulin‐stimulated fluid phase endocytosis, but basal endocytosis as well. The K1 for this process was 6 μM in the presence or absence of insulin and the time required for inhibition was less than 2.5 min, the limit of detection in our assay system. These results can be compared with the inhibitory effect of phenylarsine oxide on insulin‐stimulated glucose transport. Although the K1 for insulin‐stimulated transport (7 μM) was similar to that for inhibition of endocytosis, basal glucose transport was not affected by the inhibitor. Further, when cells were prestimulated with insulin causing maximal stimulation of the glucose transport rate, phenylarsine oxide induced a time‐dependent reduction to the basal rate (t1/2 of 10 min), despite the fact that endocytosis was blocked immediately. This observation suggests that if the transporter is recycled by an exocytotic/endocytotic mechanism, it is distinct from fluid‐phase endocytosis/exocytosis, which is a vesicle‐mediated process, and provides further evidence that the transporter may undergo intrinsic activation/inactivation which does not require vesicle movement.
Differential effects of phorbol ester on the in vitro invasiveness of malignant and non‐malignant human fibroblast cells
Authors: Fridman Rafael , Lacal Juan Carlos , Reich Reuven , Bonfil Daniel R. , Ahn Chang‐Ho 
Published: February 2005

AbstractThe effect of the phorbol ester tumor promoter 12‐O‐tetradecanoylphorbol 13‐acetate (TPA) on cell invasion was studied using an in vitro assay for cell invasion through a reconstituted basement membrane matrix (Matrigel). TPA inhibited the invasiveness of malignant human fibrosarcoma HT1080 cells. In contrast, WI‐38 lung fibroblasts, which show a very low invasive capacity, were stimulated (3‐fold) to invade Matrigel after exposure to TPA for 48 hours. The inhibitory or stimulatory effects of TPA on cell invasion were correlated with a decrease or an increase in cell motility and collagenase IV activity, respectively. Synthetic diacylglycerols partially mimicked the inhibitory action of TPA on HT1080 cells but failed to stimulate WI‐38 cell invasion. Immunoblots demonstrated that in both cell lines the α and β isoforms of protein kinase C were equally down‐regulated after a 5 hour exposure to TPA despite the basal low level of protein kinase C polypeptide in the malignant cells. Thus, whereas in WI‐38 cells induction of an invasive behavior could be observed in the absence of protein kinase C, in the malignant cells disappearance of the kinase was associated with a non‐invasive phenotype.
Role of lipocortin I in the glucocorticoid induction of the terminal differentiation of a human squamous carcinoma
Authors: Violette S. M. , King I. , Browning J. L. , Pepinsky R. B. , Wallner B. P. , Sartorelli A. C. 
Published: February 2005

AbstractThe human squamous cell carcinoma SqC/Y1 undergoes spontaneous terminal differentiation in the confluent state. The degree of maturation was markedly increased by glucocorticoids and by both human recombinant and placental lipocortin I. Western analyses demonstrated cellular secretion of lipocortin into the medium. Glucocorticoid‐induced maturation was antagonized by a lipocortin l‐specific monoclonal antibody, by phospholipase A2 (PLA2), and by arachidonic acid. Induction of the differentiation of SqCC/Y1 cells by lipocortin I was prevented by arachidonic acid. The PLA2 inhibitor, dibromoacetophenone, caused an increase in envelope‐competent cells indicating that inhibition of PLA2 results in induction of differentiation. Epidermal growth factor prevented the induction of differentiation by both lipocortin I and by glucocorticoids. The nonsteroidal lipoxygenase/cyclo‐oxygenase inhibitor, phenidone, also increased SqCC/Y1 differentiation, suggesting that leukotrienes, thromboxanes, and/or prostaglandins may be involved in lipocortin‐mediated regulation of SqCC/Y1 maturation. The findings support a role for lipocortin I in mediating the effects of glucocorticoids on epidermal cell differentiation.
Effect of a continuously applied compressive pressure on mouse osteoblast‐like cells (MC3T3‐E1) in vitro
Authors: Ozawa Hiroyuki , Imamura Kazunobu , Abe Etsuko , Takahashi Naoyuki , Hiraide Takatoshi , Shibasaki Yoshinobu , Fukuhara Tatsuo , Suda Tatsuo 
Published: February 2005

AbstractBone metabolism is often affected by a variety of mechanical forces, but the cytological basis of their action is not known. In this study, we examined the effect of a continuously applied compressive pressure (CCP) on the growth and differentiation of clonal mouse osteoblast‐like cells (MC3T3‐E1) cultured in a specifically devised culture chamber. The gas phase of the chamber was maintained at a pressure of 2 atmospheres (atm) above ambient (3 atm total, 3.1 kg/cm2; 3.0 × 105 Pa) by continuously infusing a compressed mixed gas (O2: N2:CO2 = 7.0%:91.3%:1.7%). The pO2, pCO2, and pH in the culture medium at 37°C under 3 atm were maintained at the same levels as those under 1 atm. MC3T3‐E1 cells were cultured in α minimal essential medium containing 10% fetal bovine serum under either 3 atm in the CCP culture chamber or 1 atm in an ordinary CO2 incubator. Alkaline phosphatase activity, a marker of osteoblasts, was greatly suppressed by the CCP treatment. The inhibition of alkaline phosphatase activity was rapidly restored when the cells were transferred to an ordinary CO2, incubator under 1 atm, indicating that the inhibition of alkaline phosphatase activity by CCP is reversible. Cell growth was not altered under CCP. The CCP treatment greatly increased the production and secretion of prostaglandin E2(PGE2). Adding either conditioned medium from the CCP culture or exogenous PGE2 to the control culture under 1 atm suppressed alkaline phosphatase activity dose‐dependently. The CCP treatment also suppressed collagen synthesis and calcification. These results suggest that CCP causes the cells to produce and secrete PGE2 which, in turn, inhibits differentiation of osteoblasts and the concomitant calcification.
Expression and amplification of cloned rat liver tyrosine aminotransferase in nonhepatic cells
Authors: Kohli Kulwant K. , Stellwagen Robert H. 
Published: February 2005

AbstractA full‐length cDNA for the rat liver enzyme tyrosine aminotransferase has been used to construct mammalian expression vectors by recombinant DNA techniques. These vectors, which have employed either a simian virus 40 or a Rous sarcoma virus promoter, were transfected into a variety of nonhepatic mammalian cell lines in culture. Transient expression of tyrosine aminotransferase was readily observed after transfection into monkey COS cells and mouse L cells. Stable clones that express cloned tyrosine aminotransferase have been isolated from mouse L cells, hamster Wgla fibroblasts, and Chinese hamster ovary (CHO) cells. A vector capable of expressing both tyrosine aminotransferase and dihy‐drofolate reductase was stimulated to undergo amplification by treatment with methotrexate in a CHO cell line deficient in the latter enzyme. Levels of tyrosine aminotransferase as much as 50‐fold higher than typically seen in glucocorticoid‐induced hepatoma cells were achieved in some CHO clones by this technique. The tyrosine aminotransferase produced at these highly amplified levels appeared structurally normal and had no major harmful effects on the cells.
Glucocorticoid and thyroid hormones inhibit proliferation of serum‐free mouse embryo (SFME) cells
Authors: Loo Deryk , Rawson Cathleen , Schmitt Molly , Lindburg Katherine , Barnes David 
Published: February 2005

AbstractMouse embryo cells derived in a serum‐free medium formulation (SFME cells) do not exhibit growth crisis or chromosomal abnormalities and are nontumorigenic in vivo; these cells are also reversibly growth inhibited by serum or platelet‐free plasma (Loo et al.; Science, 236:200–202, 1987).A portion of the inhibitory activity of serum could be extracted by charcoal, a procedure that removes steroid and thyroid hormones. Both L‐3,5,3′‐triiodothyronine (T3) and hydrocortisone inhibited growth of SFME cells in a reversible manner. The inhibitory activity of serum also was partially removed by treatment with anion exchange resin in a procedure designed to deplete serum of thyroid hormone. However, the effect of serum on untransformed SFME cells could not be prevented by addition of the antiglucocorticoid RU38486, and ras‐transformed clones of SFME cells, which are capable of growing in serum‐containing medium, retained inhibitory responses to glucocorticoid and, with some clonal variability, to T3. These results suggest that glucocorticoid or thyroid hormones may contribute to the inhibitory activity of serum on SFME cells, but additional factors are also involved.
Alterations in electrophoretic mobility, diaphorase activity, and terminal differentiation induced in murine erythroleukemia lines by differentiating agents
Authors: Gascoyne Peter R. C. , Becker Frederick F. 
Published: February 2005

AbstractThe electrophoretic mobilities (EPMs) and semiquinone reductase activities of two clones of Friend murine erythroleukemia (MEL) cells were investigated as a function of treatment with the inducing agents dimethylsulfoxide (DMSO) and hexamethylene bisacetamide (HMBA) As reported previously by others, the inducible clone DS19 lost its ability to grow in soft agar and expressed hemoglobin as judged by benzidine/H2O2 staining after 96 hours of treatment with 1% DMSO or 4 mM HMBA. In addition, its EPM fell by 14%, its semiquinone reductase activity by 40%, and its mean diameter by 10%. The second clone, R1, retained its ability to grow in soft agar and lacked hemoglobin expression after treatment with HMBA and DMSO, characterizing it as noninducible. However, R1 did demonstrate alterations in EPM, semiquinone reductase activity, and cell diameter that closely paralleled those found in DS19. Such responses were not seen in three non‐MEL cell lines exposed to HMBA or DMSO, suggesting that clone R1 responded to these inducing agents in a cell‐line specific manner but that its ability to complete the sequences necessary for differentiation may be blocked at an unknown point distal to the block characteristic of untreated cells. The data show that while a reduction in EPM, semiquinone reductase activity, and cell diameter accompany induced differentiation in MEL cells, such changes can occur in the absence of a commitment to terminal differentiation.
c‐fos Reduces growth factor requirements for mitogenic stimulation of L6 rat myoblasts
Authors: Rahm Magnus , Sejersen Thomas 
Published: February 2005

AbstractAddition of fetal calf serum (FCS) to serum‐deprived L6J1 rat myoblasts increases fos‐like immunoreactivity. The nuclear immunoreactivity reached a maximum 2 h after serum addition. Effects of the c‐fos protein on myoblast proliferation were analyzed in L6J1 rat myoblasts transfected with the murine c‐fos gene under control of a metallothionein promoter. L6J1 myoblasts with elevated expression of transfected c‐fos reached higher cell densities than neo transfected control myoblasts when approaching a stationary phase in normal culture conditions (5% FCS). The differences in cell densities were even more pronounced at low serum concentrations (0.5% FCS). c‐fos transfected cells also had a faster growth rate than did control cells in serum‐free medium supplemented with calcium chloride, lithium chloride, sodium selenite, hydrocortisone, and insulin. The cell morphology of c‐fos transfected L6J1 myoblasts was not affected compared to control myoblasts.These results suggest that c‐fos protein expression in L6J1 myoblasts is activated by serum and that mitogenic stimulation of L6J1 myoblasts is facilitated by the presence of elevated amounts of c‐fos protein.
Na+/H+ antiporter is the primary proton transport system used by osteoclasts during bone resorption
Authors: Hall Tony J. , Chambers Timothy J. 
Published: February 2005

AbstractWe have examined the effects of inhibitors of proton transport systems on osteoclastic bone resorption using an in vitro bone slice assay, where osteoclasts (OCs) are free from the influence of other bone cells. Amiloride (AM) and dimethyl‐amiloride (DMA), inhibitors of the Na+ /H+ antiporter, were potent inhibitors of bone resorption (IC50 ∼ 9 and 0.7 μM for AM and DMA, respectively). Omeprazole (OM), a potent inhibitor of parietal cell K+ /H+ ‐ATPase, was a poor inhibitor of OC bone resorption (IC50 ∼ 100 μM). These results strongly suggest that the Na+ /H+ antiporter is the primary proton system used by OCs during bone resorption.
Epidermal growth factor and bombesin differ strikingly in the induction of early responses in Swiss 3T3 cells
Authors: Bierman Arjo J. , Koenderman Leo , Tool Anton J. , Siegfried W. De Laat 
Published: February 2005

AbstractSwiss 3T3 cells express receptors for both the polypeptide epidermal growth factor (EGF) and the tetradecapeptide bombesin and respond mitogenically to these substances. These cells thus provide a system to analyze potential signal transduction pathways involved in mitogenic stimulation. Here we have determined and compared the early ionic responses elicited by EGF and bombesin and their relation to diacylglycerol (DG) and inositolphosphate (InsPn) production. Whereas EGF fails to cause any significant change in intracellular Ca2+ bombesin effectively induces prompt and transient Ca2+ mobilization from intracellular stores. Further support of the idea that these receptors utilize distinct signalling pathways comes from the measurements of cytoplasmic pH (pHi). As in most target cells, EGF induces a delayed (1 min) but sustained intracellular alkalinization that reaches a new steady state after ∼︁10 min. Bombesin, in contrast, elicits a biphasic response; within seconds, a rapid but transient rise in pHi is observed, followed by a further slower sustained alkalinization. Inhibition of the Na+/H+ exchanger prevents both EGF as well as bombesin‐induced alkalinization. However, under these conditions, bombesin evokes a rapid and sustained acidification related to the Ca2+ response. Apparently, bombesin initiates a Ca2+ ‐dependent acidifying process immediately after binding of the hormone to its receptor. Furthermore, we could demonstrate that the bombesin‐induced alkalinization depends on protein kinase C activation whereas the EGF response does not. Determination of the total DG and InsPn accumulation revealed that EGF is ineffective in stimulating phospholipase C‐mediated production of these second messengers. In contrast, bombesin causes a rapid DG and InsPn production coinciding with the Ca2+ response and the first phase of the rise in pHi followed by a slower DG accumulation coinciding with the second alkalinization phase. Our results show that in Swiss 3T3 cells the bombesin receptor activates the hydrolysis of inositol lipids as a mechanism of signal transduction, which consequently causes changes in Ca2+i and pHi. Clearly, the EGF receptor utilizes different pathways to evoke mitogenisis and stimulates Na+/H+ exchange independently of DG production and protein kinase C activation.
Heparin and acidic fibroblast growth factor interact to decrease prostacyclin synthesis in human endothelial cells by affecting both prostaglandin H synthase and prostacyclin synthase
Authors: Weksler Babette B. 
Published: February 2005

AbstractProstaglandin production by cultured human endothelial cells varies with growth conditions. We observed a marked diminution in both spontaneous and inducible production of prostacyclin (PGI2) by human umbilical vein and saphenous vein endothelial cells when they were cultured in the presence of the heparin‐binding growth factor, acidic fibroblast growth factor (aFGF) and heparin, compared with PGI2 production during culture in medium lacking these factors. Decreased PGI2 production was related to duration of exposure of the cells to aFGF and heparin and depended on the concentration of both substances. Heparin (1—100 μg/ml) strongly potentiated the effects of aFGF but had a limited and variable effect alone. The decrease in PGI2 production correlated with a reduction in the cellular content of immunoreactive prostaglandin H synthase and prostacyclin synthase. Arachidonate deacylation was not decreased. In addition, the eicosanoid profile of endothelial cells was changed by exposure to aFGF and heparin. These studies indicate that heparin acts as a modulator of prostaglandin synthesis in endothelial cells through its interaction with aFGF, mediated by alterations in two key enzymes in the arachidonate metabolic pathway.
Effect of K+ channel‐blockers on sugar uptake by isolated chicken enterocytes
Authors: Montero M. C. , Calonge M. L. , Bolufer J. , Ilundáin A. 
Published: February 2005

AbstractThe effects of Ba2+, quinine, verapamil, and Ca2+‐free saline solutions on sugar active transport have been investigated in isolated chicken enterocytes. Ba2+, quinine, and verapamil, which have been shown to inhibit Ca2+‐activated K+ channels, decreased basal and theophylline‐dependent 3‐O‐methylglucose (3‐O‐MG) accumulation. Ca2+‐free conditions reduced 3‐O‐MG uptake in the‐ophylline‐treated enterocytes, but it had no effect in control cells. On the other hand, the uptake of a non‐actively transported sugar, 2‐deoxyglucose (2‐DOG), by control or theophylline‐treated cells was not modified by the presence of verapamil or by Ca2+‐removal. 3‐O‐MG increased ouabain‐sensitive Na+‐efflux, but had no effect on either K+ efflux or K+ uptake. However, in the presence of Ba2+, K+ uptake was stimulated by 3‐O‐MG, and this increase was prevented by ouabain. All these findings are discussed in terms of the role that K+ permeability may play in cellular homeostasis during sugar active transport.
Internalization of the fibronectin receptor is a constitutive process
Authors: Sczekan Melanie M. , Juliano R. L. 
Published: February 2005

AbstractUsing a monoclonal antibody specific for the hamster fibronectin receptor (FnR), we have demonstrated that a portion of the CHO cell FnR population is constitutively endocytosed. Three independent techniques were used to study the internalization: (1) after saturation binding of an anti‐FnR antibody (PB1) to cells at 4°C, internalization was initiated by warming to 37°C, and then acid/salt elution of membrane‐bound ligand was used to quantitate the internalized 125I‐PB1; (2) cell vesicular traffic was pharmacologically disrupted with monensin or chloroquine, and the subsequent reduction of the cell surface pool of FnR was monitored; and (3) selective immunoprecipitation was used to separate surface and internalized 125I‐labeled FnR. These experiments indicate that about 30% of the cell surface FnR is endocytosed with a t1/2 of 7 min and that this internalization occurs regardless of the ligation state of the receptor. Other observations indicate that the larger fraction of the cell surface FnR pool (70—75%) is apparently shed from the cell upon ligation with antibody at 37°C. This process occurs much more slowly than receptor internalization and leads to an overall reduction in the amount of cell surface FnR. Our results suggest physically or chemically distinct populations of FnR, one of which is unavailable for internalization and recycling.
Tumor necrosis factor‐alpha induces vitamin D‐1‐hydroxylase activity in normal human alveolar macrophages
Authors: Pryke A. M. , Duggan C. , White C. P. , Posen S. , Mason R. S. 
Published: February 2005

AbstractThe induction of 1‐hydroxylase in alveolar macrophages by tumor necrosis factor‐alpha (TNF) was examined in view of recent evidence suggesting that local production of 1,25‐(OH)2D3 may play a role in the regulation of immune functions. Incubation of pulmonary alveolar macrophages from normal human subjects with recombinant TNF caused a 2‐ to 10‐fold increase in 25‐hydroxyvitamin D3‐1‐hydroxylase activity. The dose‐response curve was linear over the range 0.05—5.0 IU/ml, and no further increase was seen at higher concentrations. The increase in 1‐hydroxylase activity was present after 12 h and reached a maximum after 3 days. The effect of TNF was inhibited in a dose‐dependent manner by the presence of 1,25(OH)2D3 (10−10−10−8 M) in the incubation media for 5 days but was unaffected by 10−9 M 1,25(OH)2D3 after 12 h. The enhancement of macrophage 1‐hydroxylase activity by TNF was comparable to that induced by gamma interferon (IFN) but the effects of maximal doses of both agents were not additive. The presence of antibody to TNF resulted in a 76% inhibition of TNF‐induced 1‐hydroxylase but had no significant effect on IFN‐induced 1‐hydroxylase activity.
Metabolic basis for differential glutamine requirements of human leukemia cell lines
Authors: Kitoh Toshiyuki , Kubota Masaru , Takimoto Tetsuya , Hashimoto Hisako , Shimizu Tsunehiro , Sano Hirohiko , Akiyama Yuichi , Mikawa Haruki 
Published: February 2005

AbstractWe compared the ability of human leukemia cell lines of various origins to grow in glutamine‐deficient media. The growth of B lymphoblastoid cell lines, including promyelocytic HL‐60, is highly dependent on glutamine, whereas T‐cell lines are able to proliferate in glutamine‐free media. Such glutamine dependency has a good inverse correlation with the activity of glutamine synthetase. Moreover, glutamine synthetase can be induced in glutamine‐deficient media, especially in glutamine‐independent cells. In HL‐60 cells, glutamine deprivation results in the decrease of both ATP and dATP levels. The addition of adenine to the culture medium abolishes these changes without restoring cell growth, indicating that the effects of glutamine deprivation on cell growth cannot be fully explained by the perturbation of adenine nucleotide pools.
Distinct genomic copy number in mitochondria of different mammalian organs
Authors: Veltri Karen L. , Espiritu Myrna , Singh Gurmit 
Published: February 2005

AbstractThis study shows that mitochondria in liver, kidney, heart, and brain of the mouse have a distinct mitochondrial density. It also demonstrates that the mtDNA copy number per mitochondrion is organ‐specific. A reliable method of determining mitochondrial density per organ is by stereological analysis of tissue sections while mtDNA quantitation is by the use of radiolabelled mtDNA probe. This is the first study in which a comprehensive examination of mitochondrial density and quantitation of mitochondrial genomes in mouse organs have been done. In summary the variability is not only in mitochondrial density but also in genomic copy number in mitochondria of various tissues.