bluuebunny/crossref_metadata_2025_split huggingface dataset:
The requirements for ionized calcium and magnesium in lymphocyte proliferation
Authors: Abboud C. N. , Scully S. P. , Lichtman A. H. , Brennan J. K. , Segel G. B. 
Published: February 2005

AbstractThe extracellular ionized calcium and magnesium requirements for lectin‐induced lymphocyte DNA synthesis were measured in a serum‐free system. The use of this system permitted measurements of the ionized calcium and magnesium concentrations with ion‐selective electrodes. Maximal DNA synthesis was observed at 270 μ ionized calcium and at 100 μ ionized magnesium in phytohemagglutinin‐treated lymphocytes. Lymphocyte DNA synthesis was much more sensitive to reduction of external ionized calcium than to reduction of ionized magnesium. In calcium‐free medium (ionized calcium 25 μM), DNA synthesis was reduced by 90%, but in magnesium‐free medium (ionized magnesium concentration 7 μM) DNA synthesis was reduced by only 30%. Fifty percent of DNA synthesis stimulated by phytohemagglutinin (PHA) and concanavalin A (Con A) was observed at external ionized calcium concentrations of 97 and 43 μM, respectively. When lymphocytes were stimulated with PHA and the external calcium was chelated with EGTA, 50% inhibition of DNA synthesis was observed at 98 μM ionized calcium. This value agreed well with the free calcium required for PHA activation of DNA synthesis (97 μM). Cytoplasmic calcium, measured with the fluorescent probe Quin 2, increased following lectin exposure if the extracellular ionized calcium concentration was greater than 80 μM. No increase in cytoplasmic calcium could be detected in lectin‐treated lymphocytes below 80 μM extracellular ionized calcium, although substantial DNA synthesis was sustained.
Amino acid analogs while inducing heat shock proteins sensitize CHO cells to thermal damage
Authors: Li Gloria C. , Laszlo Andrei 
Published: February 2005

AbstractAmino acid analogs have been shown to induce heat shock proteins (HSPs). We have examined the effect of these analogs on the thermal sensitivity of Chinese hamster fibroblasts (HA‐1) and their stable heat‐resistant variants. We found that exposure of HA‐1 cells and their heat‐resistant variants to canavanine or L‐azetidine‐2‐carboxylic acid cause enhanced synthesis of the three major mammalian HSPs (molecular weight 70,000, 87,000, and 110,000 kd). Although the synthesis of HSPs was increased, the analogs did not induce thermotolerance, a transient ability to protect cells from thermal damage. On the contrary, the analog treatment increased the thermal sensitivity of HA‐1 cells, but not of the heat‐resistant strains, when these cells were exposed subsequently to elevated temperatures. Our tentative explanation for these findings is that the incorporation of amino acid analogs into HSPs or other cellular proteins sensitizes HA‐1 cells to heat. The heat‐resistant strains contain higher levels of constitutive HSPs. The additional functional HSPs in the heat‐resistant variants may protect these cells from thermal stress. The presence of some newly synthesized analog‐substituted, perhaps nonfunctional, HSPs need not affect this thermal protection.
Differential responsiveness of cultured suckling and adult rat hepatocytes to growth‐promoting factors: Entry into s phase and mitosis
Authors: Baribault Hélène , Leroux‐Nicollet Isabelle , Marceau Normand 
Published: February 2005

AbstractThe capacity of suckling and adult rat hepatocytes in culture to enter into S phase and mitosis in response to EGF, insulin, and glucagon was measured. Both cell types were isolated in high yield and purity and cultured in the absence of serum under identical conditions. At the time of isolation, suckling rat hepatocytes were all diploid and in the G1 phase of the cell cycle. Adult rat hepatocytes constituted a population of mixed ploidy level, as shown by flow cytometry. Upon stimulation, both suckling and adult rate hepatocytes entered S phase after a minimum lag period of 24 h. For suckling rat hepatocytes EGF was required, but its stimulating action was dependent on insulin and/or glucagon. In contrast, adult rat hepatocytes entered into S phase in response to EGF alone; insulin and glucagon did not significantly potentiate its effect. Under optimal hormonal stimulation for entry into S phase a large proportion of suckling rat hepatocytes underwent mitosis, whereas only a few mitoses were observed in the case of adult rat hepatocytes. Therefore, there is a differential response of suckling and adult rat hepatocytes to growth factors which correlates with ploidy level, and this difference may be associated with the degree of maturation.
Cyclic AMP‐independent processes mediate Kirsten sarcoma virus‐induced changes in collagen production and other properties of cultured cells
Authors: Majmudar Gopa , Peterkofsky Beverly 
Published: February 2005

AbstractPrevious studies suggested that the decreased collagen production observed in Kirsten sarcoma virus (Ki‐MSV)‐transformed BALB 3T3 cells could be reversed by treating cells with Bt2cAMP. We examined the relationship between intracellular cAMP, collagen production, and other properties in NRK and BALB 3T3 cells transformed by Ki‐MSV. Two 3T3 transformants (Ki‐3T3‐234 and Ki‐3T3Cl1) had lower cAMP levels than nontransformed cells. The level in a temperature‐sensitive transformant, tsKi‐3T3‐714, was similar to the level in its parent, 3T3‐714, and when it was shifted to a temperature nonpermissive for transformation (40°C), intracellular cAMP did not increase although the growth and morphological properties were normal. The relative rate of collagen production also increased to the normal level. These results indicate that transformation‐induced changes were regulated independently of cAMP. Further observations supported this conclusion. Intracellular cAMP in a flat revertant of Ki‐3T3Cl1 was lower, rather than higher, than in the transformant, although the relative rate of collagen production was higher. Treatment of Ki‐3T3‐234 and tsKi‐3T3‐714 with cholera toxin plus isobutylmethylxanthine increased intracellular cAMP concentrations to 2–20 times the level in untreated cells, levels much higher than in nontransformed 3T3. In spite of this, collagen production was not increased by these agents in tsKi‐3T3‐714 and it was only partially restored in Ki‐3T3‐234 relative to the level in the nontransformed cells. In contrast, these agents inhibited growth on a substratum or in soft agar and produced a flattened morphology in both lines. Similarly, collagen production in transformed NRK cells (K‐NRK) was only 3% of normal but treatment with Bt2cAMP or cholera toxin plus isobutylmethylxanthine increased production to only one‐third the normal level while increasing cAMP to four times the normal level. We conclude that in Ki‐MSV‐transformed BALB 3T3 cells, changes in cAMP may be secondary effects and not related to maintenance of the transformed phenotype. The high levels of cAMP induced by exogenous agents may act on similar targets as those affected by transformation, but reversal of the transformed phenotype by these agents probably occurs by a different mechanism than that originally used to impose the changes.
Hormonal regulation of the system a amino acid transport adaptive response mechanism in a kidney epithelial cell line (MDCK)
Authors: Boerner Paula , Saier Milton H. 
Published: February 2005

AbstractWhen mamalian cells are starved for amino acids, the activity of the A amino acid transport system increases, a phenomenon called adaptive regulation. We have examined the effects of those factors which support Madin‐Darby canine kidney (MDCK) cell growth in a defined medium on the derepression of System A activity. Of the five factors which supported MDCK cell growth, insulin was found to be an absolute requirement for derepression. In contrast, PGE1 was a negative controlling factor for the transport system. Growth of MDCK cells in the absence of PGE1 resulted in elevated System A activity which derepressed poorly upon amino acid starvation. Kinetic analysis of α‐(methylamino) isobutyric acid (mAIB) uptake as a function of substrate concentration showed that the elevated A activity observed when cells were grown in the absence of PGE1 was kinetically similar to the activity induced by starvation for amino acids. Transport of mAIB by amino‐acid‐fed cells grown in the presence of PGE1 was characterized by a linear Eadie‐Hofstee graph and by a relatively low Vmax. Transport by cells starved for amino acids or by cells grown in the absence of PGE1 was characterized by biphasic kinetics for mAIB transport and by elevated Vmax values. An influence of growth factors on the inactivation of derepressed A activity was also observed. In the presence of cycloheximide the rate of loss of A activity in amino‐acid‐starved cells was 1/4–1/2 that of amino‐acid‐fed cells. Insulin slowed inactivation in the absence of most amino acids in a protein‐synthesis‐independent manner, but insulin did not influence the more rapid inactivation observed in amino‐acid‐fed cells. These results indicate that the level of System A activity observed in response to regulation by amino acids represents a balance between carrier synthesis and inactivation, which can be positively or negatively influenced by growth factors.
Synthesis of extracellular matrix glycoproteins by cultured microvascular endothelial cells isolated from the dermis of neonatal and adult skin
Authors: Kramer R. H. , Fuh G. M. , Bensch K. G. , Karasek M. A. 
Published: February 2005

AbstractWe examined the synthesis of extracellular matrix macromolecules by human microvascular endothelial cells isolated from the dermis of neonatal (foreskin) and adult (abdominal) skin. Electron microscopy showed that both cell types produced an extracellular matrix that was strictly localized to the subendothelial space. The subendothelial matrices were initially deposited as a single discontinuous layer of filamentous, electron‐dense material that progressively became multilayered. Biosynthetic studies indicated that 2–4% of the newly synthesized protein was deposited in the subendothelial matrices by both cell types. Approximately 15–20% of the radiolabeled protein was secreted into the culture medium, and the remainder was confined to the cellular compartment. Biochemical and immunochemical analyses demonstrated the extracellular secretion of type IV collagen, laminin, fibronectin, and thrombospondin by the newborn and adult cells. Whereas type IV collagen was the predominant constituent of the matrix, fibronectin was secreted into the medium, with only small amounts being deposited in the matrix. Thrombospondin was a major constituent of the matrix produced by the newborn foreskin cells but was virtually absent in the matrix elaborated by the adult cells. However, both cell types did release comparable amounts of thrombospondin into their medium. Immunoperoxidase staining for type IV collagen revealed a fibrillar network in the subendothelial matrices produced by both adult and neonatal cells. In contrast, thrombospondin, which was detected only in the matrix of newborn cells, exhibited a spotty and granular staining pattern. The results indicate that the extracellular matrices synthesized by cultured human microvascular endothelial cells isolated from anatomically distinct sites and different stages of development and age are similar in ultrastructure but differ in their macromolecular composition.
The effects of taxol, a microtubule‐stabilizing drug, on steroidogenic cells
Authors: Rainey W. E. , Kramer R. E. , Mason J. I. , Shay J. W. 
Published: February 2005

AbstractThe effects of taxol on steroid production and microtubule polymerization were examined using Y‐1 adrenocortical tumor cells, MLTC‐1 Leydig tumor cells, and primary cultures of bovine adrenocortical cells. Taxol inhibited the following steroidogenic processes within the Y‐1 and MLTC‐1 cells: (1) hormonal increase of steroid production, (2) dibutyryl cyclic AMP‐increased steroid production, and (3) hormone‐stimulated pregnenolone production. The inhibitory action of taxol was concentration dependent and also resulted in an increase in cytoplasmic microtubules. In addition, the inhibitory action of taxol on hormone‐stimulated steroid production was reversible. Taxol appeared to inhibit cholesterol movement to the mitochondrial site of cholesterol side‐chain cleavage enzyme but did not affect overall protein synthesis. Interestingly, taxol did not affect hormone‐stimulated steroid production in bovine adrenocortical cells. This lack of inhibition may correspond to the ultrastructural observation that microtubule bundling after taxol treatment was observed in the tumor cells but not in similarly treated bovine adrenal cells. With this conflicting information between cell types, a direct relationship between taxol treatment and inhibition of steroid production has not been established. However, these results suggest that taxol alters the rate of transport of cholesterol to the cholesterol side‐chain cleavage enzyme within the steroidogenic tumor cells.
Stochastic branching model for hemopoietic progenitor cell differentiation
Authors: Kurnit David M. , Matthysse Steven , Papayannopoulou Thalia , Stamatoyannopoulos George 
Published: February 2005

AbstractWe present algebraic expressions describing the predictions of a stochastic branching model for differentiation of hemopoietic progenitor cells. The model assumes that there is a fixed probability, p (0 ⩽ p ⩽ 1), that commitment to a differentiative event occurs per progenitor cell division for each daughter cell. The model describes properties of in vitro hemopoietic cell differentiation including the population structure at the time the first progenitor cell becomes committed, the number of committed progenitor cells engendered by a single progenitor cell, and the probability of eventual commitment of all daughter cells derived from a single progenitor or stem cell. Application of the model to experimental data obtained from erythroid cultures suggests that the observed data can be explained by the stochastic branching model alone without making the deterministic assumption that there is a differentiative hierarchy in the lineage of the progenitors of erythropoiesis (BFU‐E). The qualitative and quantitative aspects of the proposed stochastic model are discussed in conjunction with other analogous stochastic branching models.
Pseudomonas aeruginosa cytotoxin stimulates prostacyclin production in cultured pulmonary artery endothelial cells: Membrane attack and calcium influx
Authors: Suttorp Norbert , Seeger Werner , Uhl Jürgen , Lutz Frieder , Roka Ladislaus 
Published: February 2005

AbstractThe effects of highly purified Pseudomonas aeruginosa cytotoxin were investigated on cultured pulmonary artery endothelial cells. This toxin dose‐dependently (7.5–60 μg/ml) and time‐dependently (20–75 minutes) stimulated the release of radiolabeled arachidonic acid and metabolites and the synthesis of prostacyclin in the absence of overt cell damage (no enhanced lactate dehydrogenase [LDH] release). Preincubation of the toxin with neutralizing antibodies abolished the effect. The toxin response on endothelial cells required extracellular calcium but not magnesium and was accompanied by a calcium influx. Interference with intracellular calcium function by TMB 8 or with (calcium)‐calmodulin function by trifluoperazine and W7 dose‐dependently reduced the cytotoxin mediated synthesis of prostacyclin. Calcium channel blockers (nimodipine, diltiazem, verapamil, D 888), however, were ineffective in this system. Following addition of cytotoxin to endothelial cells, an increased passive permeability for small marker molecules (potassium, 45calcium, 3H‐sucrose), but not for large ones (3H‐inulin, 3H‐dextran, LDH) was noted, suggesting that cytotoxin creates discrete hydrophilic transmembrane lesions of about 0.5‐1.5 nm in diameter. These data are compatible with the notion that Pseudomonas aeruginosa cytotoxin triggers the arachidonic acid pathway in cultured pulmonary artery endothelial cells by calcium influx and suggest that this calcium influx may proceed through toxin created transmembrane lesions.
A comparison of protein synthetic patterns of MDCK cells grown in serum and hormonally defined serum‐free medium
Authors: Jefferson Douglas M. , Yang Chia‐Ping H. , Cobb Melanie H. , Scott Walter N. 
Published: February 2005

AbstractThe development of hormonally defined serum‐free media (HDM) for the culture of mammalian cells has allowed the study of specific cellular functions in a totally defined environment. Recently, several reports have indicated that there are differences in the basic cellular physiology of cells cultured in HDM when compared to cells cultured by the more traditional method of using serum‐supplemented culture media (SM). We report here that there are significant changes in the protein synthetic pattern in MDCK cells grown in HDM. There were no changes exhibited during the first passage in HDM, but following 10 passages in HDM there was an increased isotope ratio of (1) plasma membrane proteins with molecular weights of 12,000, 36,000 and 68,000 and (2) endoplasmic reticulum proteins with molecular weights of 12,000 and 37,000. Additionally, the incorporation of methionine and uridine were significantly increased in cells cultured in HDM for 10 passages. At present, we believe that these changes in the protein synthetic patterns are due at least partially to increased protein synthesis as indicated by monosome/polysome ratios. Therefore, though the use of HDM offers a completely defined system for studying cellular function, results obtained using HDM must be interpreted with caution when comparing them to previous studies that have used SM.
Identification of a PDGF‐like mitoattractant produced by NIH/3T3 cells after transformation with SV40
Authors: Bleiberg Ilan , Harvey Anita K. , Smale Georgeann , Grotendorst Gary R. 
Published: February 2005

AbstractIt has previously been shown that fibroblastic cells transformed by SV40 exhibit a reduced requirement for PDGF for growth. In addition, NIH/3T3 cells lose both their chemotactic response to PDGF and specific cell surface binding of PDGF after transformation with SV40. We have now examined whether the SV40 transformed NH/3T3 cells are producing a factor which acts similarly to PDGF. Our studies indicate that NIH/3T3 cells transformed with SV 40 produce a factor which shares many biological properties with PDGF. We were unable to detect this activity in conditioned media from non‐transformed NIH/3T3 cells. The SV40/NIH/3T3 derived factor appears to possess both chemotactic and mitogenic activity for connective tissue cells but not endothelial or epithelial cells. Furthermore, in preliminary studies, this activity competes with 125I‐PDGF for binding to smooth muscle cells. The biochemical properties of the SV40/NIH/3T3 derived factor are different from those of PDGF. The SV40 activity appears to reside in a heat labile acidic protein (pI < 7.0) of MW < 30,000 whereas PDGF is a heat stable basic protein (pI9.8) of 30,000 MW. Production of this factor may play a role in the decreased serum requirement for cell replication exhibited by SV40‐transformed NIH/3T3 cells by supplying the cells with their own PDGF‐like growth factor.
Superinduction by cycloheximide of mitogen‐induced secreted proteins produced by Balb/c 3T3 cells
Authors: Hamilton Richard T. , Nilsen‐Hamilton Marit , Adams Greg 
Published: February 2005

AbstractWe describe here some of the characteristics of the regulation of a group of secretory proteins whose secreted levels rise within 2–4 h of adding fibroblast growth factor (FGF), epidermal growth factor (EGF), or serum to quiescent Balb/c 3T3 cells. The levels of these secretory proteins are regulated similarly to the interferons. When cycloheximide is present during the induction period, the amounts of [35S]methionine incorporated into five of these proteins that we have called “superinducible proteins” (SIPs) is increased 2–5 fold. Superinduction of the SIPs is seen also in response to polyribol‐polyriboC, the classical inducer of interferons. None of the SIPs, however, are immunoprecipitated by anti‐β‐interferon antibody. Induction and superinduction of the SIPs is inhibited by actinomycin D. Superinduction occurs at concentrations of cycloheximide that inhibit protein synthesis by at least 85%. The SIPs are not major intracellular proteins; they are barely detectible in cellular peptide growth factor to stimulate DNA synthesis; EGF, FGF, and serum induce the SIPs, whereas insulin does not, and insulin alone weakly stimulates DNA synthesis in these cells. Because FGF, EGF, and serum cause the SIPs to be produced at concentrations of cycloheximide that inhibite 85% of bulk protein and DNA synthesis, it follows that the SIPs are produced directly from the action of the growth factor and not as a consequence of increased growth. Although probably not interferons, in analogy to the lymphokines, the SIPs could be a set of autocrine or paracrine factors that rapidly convey the growth of differentiation signal between cells.
The differentiation of avian skeletal muscle in culture: Changes in responsiveness of adenylyl cyclase to prostaglandin E1 and adrenergic agonists
Authors: Curtis David H. , Zalin Rosalind J. 
Published: February 2005

AbstractThe responsiveness of adenylyl cyclase during avian myogenesis in vitro has been examined. Measurements of cyclic AMP generation in intact cells revealed that the precursor myoblast is highly responsive to prostaglandin E1 (11‐fold maximum stimulation): whereas its response to isoproterenol is much smaller (2‐fold). From the onset of terminal differentiation, responsiveness to the β‐adrenergic agonist increases progressively, reaching a 5.5‐fold maximum response by 96 hr of culture. In contrast, there is little change in the cell population's responsiveness to prostaglandin E1. The rise in catecholamine responsiveness is consistent with previously reported increases in β‐receptors accompanying differentiation. DL‐propanolol blocks the response of myoblasts and myotubes to 10−6 M isoproterenol with the same half maximal inhibition value of 1 × 10−8 mol. The results also suggest a change in the adrenergic character of the receptors and/or coupling to adenylyl cyclase as myoblasts differentiate. First the α‐adrenergic antagonist phentolamine (10−7−10−4 mol) inhibits the myoblast's response but enhances that of the myotube. Second, the potency ratios for the responses to isoproterenol, epinephrine, and norepinephrine shift from 1.1:1.0:1.0 in the myoblast to 3.3:2.1:1.0 in the myotube. The findings are discussed with reference to (1) the role of prostaglandins in the positive control of muscle differentiation and (2) the changes in the catecholamine‐responsive adenylyl cyclase system as an aspect of the expression of the muscle phenotype.
Changes in self‐renewal potential of human leukemic cells (K562): A bidirectional stochastic process
Authors: von Melchner Harald , Höffken Klaus 
Published: February 2005

AbstractDaughter cells arising from a single cell division in the leukemic cell line K562 have equivalent self‐renewal potential with respect to their ability to form clones in semisolid medium. However, individual cells isolated from these clones in sequence have vastly different abilities in their self‐renewal potentials. Thus, cells originating from a clone with any particular self‐renewal potential exhibit the full range of self‐renewal potentials–‐from highly renewing to none renewing, cells. These results show that self‐renewal potential in the K562 cell line is a random, reversible and partially noninherited characteristic. It is suggested that the stochastic variability of the intraclonal self‐renewal potential of K562 progeny cells either reflects the initial expression of a differentiation program or the expression of the predeterministic portion of the normal myelopoietic differentiation pathway.