摘要:

AbstractProperties of the cells (TE‐CFU) that give rise within four to six days to transient endogenous erythropoietic spleen colonies in irradiated mice have been investigated. The results obtained indicate that (1) erythropoietic maturation within such colonies is highly erythropoietin‐dependent, (2) the population size of TE‐CFU is not erythropoietin‐dependent, (3) initial exposure to a high dose of erythropoietin followed by continuing exposure to lower doses is required for maximal efficiency of colony formation by TE‐CFU, (4) successful transplantation of TE‐CFU has not been achieved, but they appear among the progeny of transplanted hemopoietic cells, (5) TE‐CFU are defective in mice of genotype W/Wv. These findings are consistent with the view that the TE‐CFU assay detects a class of early erythropoietin‐sensitive progenitor cells committed to erythropoietic differentiation, rather than “abortive” colony formation by p

ISSN:0021-9541    

DOI:10.1002/jcp.1040860102

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

年代:1975

数据来源: WILEY

摘要:

AbstractIn the presence of complete growth media (Eagle's MEM), human diploid WI‐38 cells have a low level of glutamine synthetase activity. The activity could be increased by depriving the cells of exogenous glutamine; addition of hydrocortisone to either glutamine‐deficient or complete medium had no effect on the activity of the enzyme. Cell growth ceased under conditions that enhanced glutamine synthetase activity, and hydrocortisone could not reverse this inhibit

ISSN:0021-9541    

DOI:10.1002/jcp.1040860103

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

年代:1975

数据来源: WILEY

摘要:

AbstractVero M3cells, a line derived from the kidney of an African Green Monkey, display certain alterations in their protein synthetic apparatus as a function of time during a growth cycle. (Growth cycle here refers to exponential growth of unsynchronized cells in culture and their subsequent passage into the stationary phase.) The capacity of cytoplasmic extracts of these cells to promote endogeneous mRNA‐mediated polypeptide synthesis or poly U‐mediated polyphenylalanine synthesis declines from the second day after the initiation of the growth cycle. The ribosome sedimentation profile indicates that after the second day of growth a decrease also occurs in the total amount of ribosomes per cell, and that a shift occurs from predominantly polyribosome structures to predominantly subunits and monoribosomes structures. The activity of the translation factor, elongation factor 1, also progressively decreases after the second day of growth. Furthermore, when crude factor preparations from cells in the second day of growth (Exponential phase) and from cells in the fifth day of growth (Stationary phase) are compared for leucyl‐tRNA synthetase and prolyl‐tRNA synthetase activities, it is found that the extracts from fifth‐day cells have significantly less activity. The activity of another enzyme, acid phosphatase, remains relatively unaffected as a function of time during the cell growth cycle. When HeLa S3plating cells are grown under the same conditions, they do not display the same

ISSN:0021-9541    

DOI:10.1002/jcp.1040860104

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

年代:1975

数据来源: WILEY

摘要:

AbstractFollicular fluid aspirated from large cow follicles inhibits endogenous, DNA‐dependent RNA polymerase activity in Yoshida ascites cells. The inhibitory component of follicular fluid is probably a protein and appears to affect specifically the activity of the nucleoplasmic polymerase I

ISSN:0021-9541    

DOI:10.1002/jcp.1040860105

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

年代:1975

数据来源: WILEY

摘要:

AbstractSerum starvation of growing and nongrowing (density‐inhibited) mouse 3T3 cells resulted in decreased phosphorylation of 2‐deoxy‐D‐glucose. while the time course of transport of this sugar remained unchanged. Serum starvation of SV40 transformed 3T3 cells (SV101) and spontaneously transformed 3T6 cells did not alter either the time course of transport, or phosphorylation of the sugar. Treatment of SV101 cells with 10−4M dibutyryl adenosine cyclic 3′:5′ monophosphate and 10−3M theophylline did not restore the capacity to regulate 2‐deoxy‐D‐glucose phosphorylation when these cells were serum deprived. We conclude that serum factors are involved in the modulation of phosphorylation of 2‐deoxy‐D‐glucose in 3T3 cells rather than its transport. This regulation is operative both in growing as well as nongrowing 3T3 cells. In contrast, transformed cells do not respond to this regulation of 2‐de

ISSN:0021-9541    

DOI:10.1002/jcp.1040860106

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

年代:1975

数据来源: WILEY

摘要:

AbstractSerum, elevated pH, excess Zn++, 9,10 dimethyl‐1,2 dibenzanthracene (DMBA) and insulin accelerate the progress of growth‐inhibited chick embryo cells into the S‐period of DNA synthesis. A comparative study was made of their capacity to elicit other cellular responses within two hours after their application. All the agents studied stimulated the uptake of the glucose analogue 2‐deoxy‐D‐glucose (2‐dGlc). Elevated pH elicited a more striking increase than the other agents in the uptake of the amino acid analogue α‐amino isobutyric acid (AIB). The application of subtoxic concentrations of Zn++or DMBA did not stimulate the uptake of uridine by cells nor its incorporation into RNA when tested at 2 hours. However, it was found that the stimulation of uridine utilization did occur but was delayed several hours. Similarly, the accelerated onset of DNA synthesis was also delayed for several hours by these agents. Insulin acted like serum in stimulating the utilization of 2‐dGlc, AIB and uridine. Serum and DMBA were particularly effective in stimulating the utilization of choline. It was concluded that the utilization of 2‐dGlc, uridine and thymidine are affected similarly by all the agents, but that there may be differential effects in the utilization of AIB and choline.The inhibition of RNA synthesis by actinomycin D did not prevent the relative stimulation of 2‐dGlc, AIB and choline utilization by serum and pH treatment. The inhibition of protein synthesis by cycloheximide did not prevent the relative stimulation of 2‐dGlc and choline utilization by serum and pH treatment. It partially blocked the increased uptake of AIB and had erratic effects on the utilization of uridine. It was concluded that neither RNA nor protein synthesis is required for some, if not all, the early responses to growth stimuli measured here. The inhibited cell appears to be a poised system which carries out a programmed array of reactions characteristic of the cell type following perturbation by a variety of unrelated agents. In vivo specificity is provided by the physiological reagents available (i.e., hormones) and their capacity to interact w

ISSN:0021-9541    

DOI:10.1002/jcp.1040860107

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe alkali cation content of HeLa cells is independent of culture density and of whether the cells are grown in suspension or attached to the culture vessel. With a cell doubling time of 28 hours, the cell K content turns over approximately once per hour. Following partial blockade of the alkali‐cation transport system with ouabain, two distinct but interrelated mechanisms operate in the cellular response: (a) an increase in intracellular Na stimulates the pump so that the short‐term alteration in electrolyte composition is less than would be expected from the fraction of pump sites inhibited, and (b) there is a cyclo‐heximide‐sensitive recovery in transport capacity reflecting a restoration of functional transport sites to their normal density on the cell surface. Experimental manipulations that mimic the effect of ouabain lead to a stimulation of transport, but they do not result in an increase in the number of ouabain‐binding sites on the surface. The data are consistent with a four‐to‐six‐hour turnover of transport sites at the surface, but there is no evidence for a specific induction of the transport system within this short‐ter

ISSN:0021-9541    

DOI:10.1002/jcp.1040860108

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

年代:1975

数据来源: WILEY

摘要:

AbstractWhen resting confluent monolayers of WI‐38 fibroblasts are trypsinized and replated at a lower density they are stimulated to proliferate again with an interval of 18 hours between replating and the onset of DNA synthesis. Trypsinization of resting cells causes a 40% loss of nuclear proteins as well as of cytoplasmic proteins. The amount of nuclear proteins remains low for the first six hours after the cells have been replated and then it increases rapidly, reaching the same level of non‐trypsinized resting cells by ten hours after plating. The proteins that are lost from the nucleus immediately after trypsinization are chromatin‐associated proteins and most of them are non‐histone chromosomal proteins, although a modest loss of histones cannot be ruled out. The loss of non‐histone chromosomal proteins from cells that have been trypsinized causes changes in the structure of chromatin that can be detected by circular dichroism and by viscosity measurements. These results show that cell trypsinization causes an extensive loss of proteins from chromatin and that the loss is restored only several hours after the cells have been replated at a lowe

ISSN:0021-9541    

DOI:10.1002/jcp.1040860109

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe effect of exogenously administered cyclic AMP derivatives and of endogenously elevated cyclic AMP levels on the spontaneous fusion of skeletal muscle myoblasts has been investigated. Contrary to earlier reports, cAMP does not appear to have a direct inhibitory effect on the fusion of an established line (L8) of rat myoblasts. Similarly, cAMP did not block the fusion of primary chick myoblasts. However, fusion of the rat myoblasts was prevented when the cAMP induced inhibition of growth prevented the cells from reaching the “critical” cell density necessary for fus

ISSN:0021-9541    

DOI:10.1002/jcp.1040860110

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

年代:1975

数据来源: WILEY

摘要:

AbstractIn human diploid cell strains, the substitution of galactose for glucose as the sole hexose in the medium had no measurable effect on the specific activity of the cell protein for any of the three enzymes of the Leloir pathway. These enzymes are galactokinase, α‐D‐galactose‐1‐phosphate:UDP glucose uridylyl transferase and UDP galactose 4‐epimerase. A cell strain from a patient with galactosemia had no detectable activity for the transferase. The substitution of galactose for glucose in the medium of these cells (which has been shown to cause the cells to accumulate galactose‐1‐phosphate) also failed to affect cellular activity for the three enzymes. Similarly, the three activities failed to respond to the substitution of galactose for glucose in cultures of a rat hepatoma line. Cells of this line have been shown by others to perform a number of the tissue‐specific functions of liver.The failure of galactose to stimulate increased cellular activity for the three enzymes represents a striking difference between the behavior of these enzymes in human diploid cell strains and their be

ISSN:0021-9541    

DOI:10.1002/jcp.1040860111

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

年代:1975

数据来源: WILEY