摘要:

AbstractNormal human serum or plasma was studied for the presence of inhibitors of cell proliferation by assaying inhibition of incorporation of labeled thymidine into acid‐insoluble fraction using human FL cells. Lipoprotein fraction obtained by gel filtration through Sepharose 4B and by KBr density gradient centrifugation was found to play a major part of the inhibitory activity of the serum. It was also shown that the inhibitory activity resides in low‐density lipoprotein (LDL). The addition of the lipoprotein fraction to growing FL cells caused an early decrease in the transport of uridine and thymidine across the membrane. This change in the permeability of membrane was followed by the preferential inhibition of DNA synthesis and a reduction in the percentage of mitotic cells in the cell population. The inhibition of the growth was reversible and was observed in various types of cells irrespective of spec

ISSN:0021-9541    

DOI:10.1002/jcp.1041130102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1982

数据来源: WILEY

摘要:

AbstractTrypsinized cells from embryonic chick neural retina redistributed concanavalin A receptors to patches and caps. Between 12 and 16 days of development, the ability to redistribute concanavalin A receptors declined. This restriction in mobility of the receptors was accompanied by changes in susceptibility to the capping‐inhibitory drugs colchicine and cytochalasin

ISSN:0021-9541    

DOI:10.1002/jcp.1041130103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1982

数据来源: WILEY

摘要:

AbstractThree structurally related anticancer drugs, mithramycin, chromomycin A3, and olivomycin, showed large unexpected differences (up to more than 1000 fold) in their toxicity towards cultured cells from various species (human, Chinese hamster, Syrian hamster, and mouse). Among the cell types examined, human cells (both a diploid fibroblast cell strain and HeLa cells) were maximally sensitive to all these drugs, followed by the Syrian hamster kidney cells (BHK 21). The mouse (LMTK−cells) and Chinese hamster (CHO) cells, which were more resistant, showed interesting differences in their sensitivity towards these drugs. For example, whereas the mouse cells were more resistant to mithramycin than CHO cells, the sensitivity pattern was reversed for both chromomycin A3and olivomycin. In cell extracts derived from human, mouse, and Chinese hamster cells RNA synthesis, which is the cellular target of these drugs, showed identical sensitivity to both mithramycin and chromomycin A3, indicating that the species specific differences in the toxicity to these drugs are at the level of cellular entry of these compounds. Based on the structures of these glycosidic antibiotics and their patterns of toxicity, it is suggested that the intracellular transport of these drugs involves specific interactions between the sugar residues on these compounds and some type of cell surface receptor(s), which differ among different cell types. Some implications of these results for toxicity studies are discusse

ISSN:0021-9541    

DOI:10.1002/jcp.1041130104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1982

数据来源: WILEY

摘要:

AbstractThe carbohydrate components of some glycoproteins of hamster cells differ as a function of their growth on various substrates; glass, plastic, or plastic coated with collagen. This observation is interpreted as an effect of the environment on cellular structure at the molecular level. The basis of the change and its possible significance are discussed.

ISSN:0021-9541    

DOI:10.1002/jcp.1041130105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1982

数据来源: WILEY

摘要:

AbstractIsolated rat liver hepatocytes exhibited a twofold to threefold increase in both specific cytochrome oxidase activity and heme a concentration during their first 24 h in monolayer culture. Other mitochondrial respiratory enzyme activity did not increase over this same period. Decreasing the oxygen content of the gas phase to 5% of ambient eliminated the stimulation in heme a content without having an effect on cell protein synthesis or viability. These results indicate that oxygen concentration can effect the level of cytochrome oxidase (heme a) in these differentiated cells. The effect of oxygen may be on the translation or assembly of subunits, synthesis of heme, or incorporation of heme into holoenzyme. Oxygen stimulation of cytochrome oxidase content was not accompanied by increased incorporation of pulsed radiolabelled methionine into immunoprecipitated holoenzyme subunits. Moreover, chloramphenicol, a translation inhibitor of three mitochondrially synthesized cytochrome oxidase subunits, did not diminish the increase in heme a seen over the first 24 h of culture. These latter results suggest that the increasing enzyme content is not due to stimulated translation.

ISSN:0021-9541    

DOI:10.1002/jcp.1041130106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1982

数据来源: WILEY

摘要:

AbstractNerve growth factor (NGF) is required for the growth and development of sensory and sympathetic neurons. Incubation of chick dorsal root ganglionic cells without NGF resulted in a decrease of active (Na+, K+‐pump‐mediated) K+influx over a period of several hours. Addition of NGF to NGF‐deprived cells caused (1) a return of the active K+influx to the values occurring in cells continuously exposed to NGF, preceded by (2) a very rapid, but transient overstimulation of the Na+, K+‐pump‐mediated K+influx. Restoration of normal Na+, K+‐pump activity occurred at NGF concentrations of 1 biological unit/ml or greater, whereas the NGF concentration in the 1–100 biological unit/ml range affected the rapidity with which the pump restoration took place. The transient pump behavior was only observed in NGF‐deprived cells and could not be elicited in NGF‐supported steady‐state cells or in cells having already received delayed NGF once. This transient Na+, K+‐pump behavior was exclusively displayed in conjunction with a high intracellular Na+concentration. Decreasing the external Na+concentration below 70 mM reduced the hyperstimulation response to NGF, until at 10 mM Na+the delayed presentation of NGF caused no overshoot at all. The effect of NGF on the Na+, K+‐pump was specific for the NGF molecule and could not be mim

ISSN:0021-9541    

DOI:10.1002/jcp.1041130107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1982

数据来源: WILEY

摘要:

AbstractCholera toxin via its ability to increase intracellular cyclic AMP levels can induce drastic changes in cell morphology. This report describes a temperature sensitive mutant of chemically transformed rat liver epithelial cells which only display cell shape alterations in response to cholera toxin at the permissive temperature. Shift up‐shift down experiments indicate that the change in the response occurs fairly rapidly, i.e., within 2 hours at the new temperature. The behavior of the temperature sensitive cells at the nonpermissive temperature mimics that of the untransformed rat liver epithelial cells (i.e., no morphological change in response to cholera toxin) while at the permissive temperature the positive cell shape change is identical to that exhibited by chemically transformed rat liver epithelial cells. The temperature sensitive response to cholera toxin is not a function of cyclic AMP production, since the amount of cyclic AMP found as a function of either time or concentration of cholera toxin is quite similar in cells treated at either temperatur

ISSN:0021-9541    

DOI:10.1002/jcp.1041130108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1982

数据来源: WILEY

摘要:

AbstractExpression of the cell surface receptor for the serum glycoprotein transferrin has been correlated with cellular proliferation in normal lymphocytes undergoing mitogen or antigen induced proliferative responses. In the present study, the expression of transferrin receptor in Concanavalin A stimulated rat lymphocytes or Gross virus transformed lymphoma cells has been examined with respect to the following questions: (1) is expression of receptor activity related to blastogenesis or to the subsequent IL‐2 dependent DNA synthetic activity, and (2) is transferrin receptor expression regulated in similar fashion in both normal and malignant lymphoblasts? Scatchard analysis of saturation binding data illustrated that binding site number increased and subsequently decreased during the response while the receptor affinity for transferrin remained constant. These findings were confirmed by SDS‐polyacrylamide gel electrophoretic analysis of radiolabeled cell surface proteins which specifically interact with transferrin. Examination of nonproliferating normal lymphoblasts (96 hr post Con A stimulation) compared with the same population of cells stimulated to reinitiate DNA synthesis with a partially purified preparation of Interleukin 2 (IL‐2) showed that transferrin receptor expression was tightly linked to the IL‐2 dependent stimulation of DNA replication. This coordinate regulation of receptor expression was markedly less stringent in retrovirus transformed thymic lymphom

ISSN:0021-9541    

DOI:10.1002/jcp.1041130109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1982

数据来源: WILEY

摘要:

AbstractRetinoic acid reduces the growth rate of mouse S91 melanoma cells in culture and increases the proportion of cells in the G1phase of the cell cycle. Because of the integral role protein synthesis has been shown to play in growth control we studied the effect of retinoic acid on the protein synthesis machinery with a cell‐free system developed from the melanoma cells. This system was capable of translating endogenous mRNA, exogenous globin mRNA, and the synthetic template poly(U). Of the above activities of the protein synthesis system only the translation of endogenous mRNA was reduced significantly in the cell‐free system prepared from retinoic acid‐treated cells. Analyses of the amount and function of RNA revealed that treatment with retinoic acid leads to reductions in total RNA content, in the proportion of ribosomes in polysomes, in the amount of poly(A)RNA, and in the amount of polysome‐associated mRNA. All these effects of retinoic acid contribute to the decrease in protein synthesis activity of treated cells. Two‐dimensional electrophoresis anlaysis of L‐[35S]methionine‐labeled proteins produced by untreated and treated cells revealed only a few quantitative differences. We suggest that retinoic acid‐induced suppression of protein synthesis activity may be the cause for gr

ISSN:0021-9541    

DOI:10.1002/jcp.1041130110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1982

数据来源: WILEY

摘要:

AbstractThe mechanism of stimulation of amino acid transport system A caused by amino acid deprivation in L6 cells was investigated. In cells loaded with α‐aminoisobutyric acid (AIB), amino acid deprivation increased the rate of proline uptake only after the intracellular [AIB] dropped below 7 mM. Efflux of proline was not sensitive to the presence of proline in the outer medium (with or without external Na+), suggesting that efflux through system A (and possibly uptake) is not susceptible to transinhibition. Transport (stimulated uptake) into amino acid‐deprived cells and that into amino acid‐supplemented cells differed in several chemical properties: (1) In the former group, transport was higher at lower pH values than in the latter, and the optimum pH values were 7.5 and 7.8, respectively. (2) Unlike proline uptake in supplemented cells, uptake in deprived cells was inhibited by 50% with N‐ethylmaleimide (1 mM) or by 50 μM p‐chloromercuribenzoate (PCMBS). Inhibition by PCMBS was not due to collapse of the Na+gradient. The mercurial inhibited only the deprivation‐inducedstimulationof transport, bringing the rate of proline uptake to the “basal” uptake level observed in amino acid‐supplemented cells. Proline uptake was not stimulated by a second deprivation following treatment with PCMBS and a supplementation‐deprivation cycle. However, in untreated cells, or by reversing mercaptide formation with dithiotreitol, the second deprivation stimulated transport. Deprivation at 4°C did not elicit stimulation of proline uptake. Cycloheximide prevented the stimulation and decreased the rate of proline uptake in deprived cells more efficiently than in supplemented cells. Actinomycin D prevented stimulation when added at the onset of deprivation. The above data indicate that stimulation of transport by deprivation is protein synthesis‐dependent and that the stimulated transport had chemical properties distinct from the “basal” transport in supplemented cells. The evidence presented is consistent with a model of activation of a finite pool of transporters upon deprivation, the chemical characteristics of which differ from those of

ISSN:0021-9541    

DOI:10.1002/jcp.1041130111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1982

数据来源: WILEY