摘要:

AbstractWhen CHO cells are incubated under conditions of extreme amino acid starvation, effected by withdrawal of an amino acid from the medium together with genetic or chemical interference with the activity of the corresponding aminoacyl‐tRNA synthetase, there is a rapid and profound decline in the functional capacity of the protein synthetic machinery. The effect was observed for all amino acids tested including leucine, asparagine, histidine, methionine and glutamine. This decline in protein synthetic potential appears to be due to a progressive permanent inactivation of the specific aminoacyl‐tRNA synthetase concerned, as shown by a decline in the amount of cellular, specific aminoacyl‐tRNA and a decline in the cell‐free enzyme activity, measured after reversal of the starvation conditions. When cells are left for more than several hours under these starvation conditions, they shrink in size, lose viability and eventually disintegrate, with anomalous rapidity. We suggest that the progressive loss of protein synthetic capacity of the cells is the prime cause of these subsequent events.If the starvation conditions are reversed before cell death, regeneration of the protein synthetic potential occurs rapidly but requires protein synthesis itself, implying the existence of strong control mechanisms for cellular aminoacyl‐tRNA synthetase a

ISSN:0021-9541    

DOI:10.1002/jcp.1040950202

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

年代:1978

数据来源: WILEY

摘要:

AbstractRat liver epithelial cells in culture (WIRL‐3C) have the enzymes that synthesize serine from 3‐phosphoglyceric acid. Both phosphoglyceric acid dehydrogenase (PGAD) and serine‐phosphate (serine‐P) forming activities fluctuate with time after subculture and are higher in growing than confluent cells. This activity pattern was not common for other dehydrogenases in WIRL‐3C cells, nor was it common for PGAD activity in other cultured cells. At time of sub‐culture, cells are removed from spent medium, treated with trypsin, and fed fresh medium. None of these parameters causes the rise in activity; in contrast, reduction in cell density and the accompanying stimulation of growth do. PGAD activity decreases when growth is slowed either as the cells progress to the end of the culture cycle, when cells are treated with dexamethasone‐phosphate (Dx‐P) or dibutyryl cyclic AMP (cAMP) and theophylline or when the serum concentration of the medium is reduced to 0.2%. Under these conditions, decreased PGAD activity is paralleled by a decline in growth and DNA accumulation. PGAD activity in WIRL‐3C cells is regulated in a manner closely resembling what has been observed previously in rat liver from the whole animal. The possible use of this system in studying regulation of gene expression in mammalian c

ISSN:0021-9541    

DOI:10.1002/jcp.1040950203

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

年代:1978

数据来源: WILEY

摘要:

AbstractThe separation of L1210 cells with columns of Con A‐derivatized nylon was investigated. Most of the cells bound to the column irreversibly. The binding was lectin‐specific. Cells were pulse labeled with3H‐thymidine and applied to Con A columns. Those cells not binding the columns were enriched in incorporated thymidine compared to the unseparated population. Data is presented which suggests that a small, synchronized fraction of cells synthesizing DNA at a high rate is reduced in Con A‐nylon affinity. It is proposed that L1210 cell DNA synthesis is not uniform in rate and that changes in this rate are related to changes in the ability of cells to bind Con

ISSN:0021-9541    

DOI:10.1002/jcp.1040950204

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

年代:1978

数据来源: WILEY

摘要:

AbstractClone B559 mouse melanoma cells are highly tumorigenic and produce plasminogen activator. Cells of clone C3471, a line obtained by continued growth of B559 cells in medium containing 5‐bromodeoxyuridine (1 μg/ml), have no plasminogen activator and are non‐tumorigenic. When B559 cells are co‐cultivated with C3471 cells, the ability of B559 cells to activate plasminogen is suppressed. Under these conditions cell fusion occurs. Lack of expression of plasminogen activators is not a consequence of cell fusion, inhibition of cell division or release of soluble inhibitors of either plasminogen activators or plasmin. No inhibitors of plasminogen activators could be demonstrated in association with subcellular fractions of C3471 cells or with the C‐type viral particles released from C3471 cells. Close contact between cells of the two lines is shown to be essential for suppression of plasminogen ac

ISSN:0021-9541    

DOI:10.1002/jcp.1040950205

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

年代:1978

数据来源: WILEY

摘要:

AbstractMouse melanoma clones B559 and B78 are highly tumorigenic when injected into C57BL/6J mice. Tumor formation by these cells is suppressed when they are mixed with nonmalignant bromodeoxyuridine‐grown clone C3471 before injection. C3471 cells suppress tumor formation only in immunocompetent hosts; mixtures of B559 and C3471 cells or C3471 cells alone form tumors in antithymocyte serum (ATS)‐treated mice. Explants of C3471 tumors grown in ATS‐treated mice form tumors in immunocompetent mice, most of which regress. Inability of C3471 or mixtures of C3471 with malignant cells to grow in normal mice, as contrasted with ability to grow in immunosuppressed mice, indicates that host response is involved. Both tumorigenic clones have high plasminogen activator activity, whereas nontumorigenic clone C3471 has none. Mixture of either tumorigenic clone with C3471 cells decreases plasminogen activator in vitro. C3471 tumor explants from ATS‐treated mice initially express plasminogen activator, but lose the capacity to express this activity upon prolonged cultivation in vitro. Explants from B559 tumors retain plasminogen activator in long term culture. Close physical contact between C3471 and B559 cells appears essential both for inhibition of plasminogen activator expression by B559 cells in vitro, and for tumor suppression in vivo. These findings suggest that production of plasminogen activators by tumor cells may play an important role in suppressing the host's immune response locally to an inoculum of syngeneic tumo

ISSN:0021-9541    

DOI:10.1002/jcp.1040950206

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

年代:1978

数据来源: WILEY

摘要:

AbstractRates of uptake of glucose (measured with3H‐2‐deoxy‐d‐glucose), galactose, and leucine increase after exposure of chick embryo cells to increasing concentrations of Na+over the range 100 to 200 mM. Uptake of nucleosides was unaffected by [Na+] over this range. Prior exposure of cells was required for the [Na+] effect on uptake. Changes were measureable within two hours after changing [Na+], and although the capacity for deoxyglucose uptake remained constant thereafter, the capacity for leucine uptake continued to change during the next few hours. Inhibition of protein synthesis by cycloheximide, or of RNA synthesis by Actinomycin D, failed to prevent these uptake changes. Analysis of the kinetics of uptake showed that only the Km for uptake of deoxyglucose or leucine was affected by [Na+]; the maximum V for each compound remained the same. Effects of [Na+] could be distinguished from the increased capacity for glucose uptake induced by glucose starvation.Incorporation of both radioactive uridine into RNA, and radioactive thymidine into DNA, were affected by [Na+], but the differences were not correlated with uptake of other metabolites. No differences in countable mitoses were apparent, although the growth of chick embryo cells increased slightly with increasing [Na+].Changes in uptake due to differing [Na+] also were observed in mammalian (rat NRK) cells. However, no effects of [Na+] on rates of cell growth or saturation density were observed with thes

ISSN:0021-9541    

DOI:10.1002/jcp.1040950207

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

年代:1978

数据来源: WILEY

摘要:

AbstractEarlier work showed that thrombin stimulates proliferation of human fibroblasts in serumfree medium. This work demonstrates (1) that thrombin has to be present during most or all of the G1 period to ensure maximal DNA synthesis, (2) that DNA synthesis increases about three hours later after thrombin than after serum treatment, (3) that both thrombin and serum activate transport of uridine, D‐2‐deoxy‐glucose and putrescine, (4) that thrombin is able to increase3H‐thymidine incorporation also in SV40 transformed human fibroblasts, in HeLa cells and in two continuous monkey cel

ISSN:0021-9541    

DOI:10.1002/jcp.1040950208

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

年代:1978

数据来源: WILEY

摘要:

AbstractEpidermal growth factor (EGF) is a mitogen for Swiss 3T3 cells. Short incubation periods with physiological concentrations of EGF induced increased binding of Swiss 3T3 cells to Con A‐coated nylon fibers. This effect was not induced in an EGF non‐responsive 3T3 variant, in the transformed murine XC cells or in Swiss SV3T3 cells. The increase in Con A fiber‐binding seems to be specific for EGF, since it was not observed in response to insulin, prostaglandin F2α or a higher serum concentration, which also initiate cell division of confluent quiescent 3T3 cells.EGF also reduced Con A‐mediated hemadsorption to 3T3, but had no effect on hemadsorption by the EGF non‐responsive 3T3 variant. There was no change in the number of Con A‐receptors on 3T3 cells after EGF treatment. Binding to WGA‐coated fibers and WGA‐mediated hemadsorption were not effected by preinc

ISSN:0021-9541    

DOI:10.1002/jcp.1040950209

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

年代:1978

数据来源: WILEY

摘要:

AbstractIn order to further investigate the connection between transport and growth control, 3T3 cells, SV40 transformed 3T3 cells (SV101), and three revertant cell lines derived from SV101 which have regained certain manifestations of growth control were used. Transport rates of 2‐aminoisobutyric acid and 3‐0‐methyl‐D‐glucose were measured in sparse, confluent, serum‐starved, and serum‐stimulated cultures.As shown before, cessation of 3T3 cell growth in G0under conditions of confluence or serum deprivation was associated with reduced rates of transport for both compounds, whereas the density and serum dependence of growth and transport was largely eliminated in SV101. The density revertant F1SV101, which has regained density regulation of growth similar to 3T3 cells, has also regained density regulation of transport. Neither growth nor transport were serum dependent. The serum revertants AγSV7 and LsSV6 have regained both density and serum regulation of growth, but not according to the original mechanism of 3T3 cells of entry into a G0state. Transport was high under conditions of confluence or serum deprivation. Thus for these cells rates of transport were not reduced simply as a consequence of slower cell growth nor were low transport rates responsible for growth arrest. The data are consistent with the possibility that growth arrest specifically in the G0state could shut off a number of cellular activities, inclu

ISSN:0021-9541    

DOI:10.1002/jcp.1040950210

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

年代:1978

数据来源: WILEY

摘要:

AbstractThe relationship between differentiation of murine erythroleukemia cells (MEL) induced by DMSO and the cell division cycle has been analyzed. We demonstrate that incubation in the presence of DMSO increases the length of the G1 phase of the cell cycle. A method of synchronization of MEL cells by unit gravity sedimentation has been developed and characterized. Using this method, a series of synchronized cell populations covering the entire cell division cycle can be generated simultaneously. Cells synchronized by this technique were challenged with DMSO and analyzed for kinetics of commitment to the differentiation program. Our results indicate that populations of cells in G1 or G2 at the time of addition of inducer give rise to a greater proportion of committed cells than an unfractionated population, while cells in S phase result in a lower percentage of committed cells than the unfractionated population when cultured in DMSO.

ISSN:0021-9541    

DOI:10.1002/jcp.1040950211

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

年代:1978

数据来源: WILEY