摘要:

AbstractSomatic cell hybrids between either normal human fibroblasts, phenotypically normal mouse fibroblasts or mouse peritoneal macrophages and HT1080 human diploid fibrosarcoma cells were studied for their ability to form tumors in nude mice. The results of this study indicate that tumorigenic behavior is expressed as a dominant trait in both human‐human and mouse‐human hybrid ce

ISSN:0021-9541    

DOI:10.1002/jcp.1040990302

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

年代:1979

数据来源: WILEY

摘要:

AbstractThe ability to synthesize inosinetriphosphate was demonstrated in blood cells as well as in a variety of tissue extracts in spite of the presence of ITP pyrophosphohydrolase. At the expense of having sub‐optimal conditions, an assay system was selected that completely repressed the hydrolyzing enzyme, thus permitting the accumulation of ITP.In an attempt to define the biosynthetic pathway of ITP, and since guanylate kinase has been implicated in the formation of ITP, the rate of synthesis of ITP and GTP in cell extracts was compared.The comparison of the specific activities of the [14C]‐labeled hypoxanthine and guanine moieties of the inosine and guanosine phosphates formed during incubation with [8‐14C]‐inosine and [8‐14C]‐guanosine respectively, revealed striking differences in the relative rates of isotope incorporation. Tentative mechanisms are proposed to explain these differences.The data obtained thus far does not discard the possibility that ITP may be formed by stepwise phosphorylation and (or) by direct pyrophosphoryla

ISSN:0021-9541    

DOI:10.1002/jcp.1040990303

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

年代:1979

数据来源: WILEY

摘要:

AbstractA preliminary investigation was carried out to determine how conditional lethal mutants affected in particular aminoacyl‐tRNA synthetases may be used to study the role of tRNA charging levels in protein synthesis. The relationship between rate of protein synthesis and level of histidyl‐tRNA in wild‐type cultured Chinese hamster ovary cells was determined using the analogue histidinol to inhibit histidyl‐tRNA synthetase activity. This response was compared with that obtained using a mutant strain with a defective histidyl‐tRNA synthetase that phenotypically shows decreased rates of protein synthesis at reduced concentrations of histidine in the growth medium. The approach used was based on measuring the histidyl‐tRNA levels in live cells. The percentage charging was estimated by comparing [14C]histidine incorporated into alkali‐labile material in paired samples, one of which was treated with cycloheximide, five minutes before terminating during the incubation, to produce maximal aminoacylation. Wild‐type cells under histidinol inhibition exhibited a sensitive, sigmoidal relationship between the level of histidyl‐tRNA and the rate of protein synthesis. A decrease in the relative percentage of acylated tRNAHisfrom 46% to 35% elicited a large reduction in the rate of protein synthesis from 90% to 30% relative to untreated cells. An unpredicted result was that the relationship between protein synthesis and histidyl‐tRNA in the mutant was essentially linear. High acylation values for tRNAHiswere associated with rates of protein synthesis that were not nearly as high as in wild‐type cells. These findings suggest that the charging levels of tRNAHisisoacceptors could play a regulatory role in determining the rate of protein synthesis under conditions of histidine starvation in normal cells. The mutant appears to be a potentially useful system for studying the pivotal role of tRNA charging in protein synthesis, assuming that the altered response in the mutant is caused by i

ISSN:0021-9541    

DOI:10.1002/jcp.1040990304

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

年代:1979

数据来源: WILEY

摘要:

AbstractThe effect of insulin on hexose transport in cultured human skin fibroblasts.Studies were carried out on cultures of human skin fibroblasts to explore the effect of insulin on hexose transport in serum‐starved monolayers. Insulin (100 mU/ml) stimulated 2‐deoxy‐D‐glucose transport (30% above control values) after 30 minutes exposure time, the response being similar up to four hours exposure to insulin. In several experiments (n = 22) employing three cell strains, insulin (100 mU/ml) exposure led to variable stimulation of 2‐deoxy‐D‐glucose transport (an average of 37% above control values, with a range of 0 = 120%). The insulin‐induced stimulation of 2‐deoxy‐D‐glucose transport showed a dose dependency with increasing amounts of insulin, the response being maximal at an insulin concentration of 100 mU/ml. Kinetic analysis of 2‐deoxy‐D‐glucose transport showed that insulin addition resulted in a slight change in the transport Km(3.13 to 4.06 mM) and a 1.8‐fold increase in the transport Vmax(17.6 nanomoles/mg protein/min to 32.1 nanomoles/mg protein/min). Insulin also stimulated the transport of 3‐0‐methyl‐D‐glucose while the hexokinase activity of the cells was not affected. Further, this insulin‐induced stimulation of sugar transport was not blocked by cycloheximide. The results indicate that insulin stimulated the stereospecific carrier‐mediated of hexose tra

ISSN:0021-9541    

DOI:10.1002/jcp.1040990305

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

年代:1979

数据来源: WILEY

摘要:

AbstractIt is demonstrated here that cells in a suspension culture of an established mammalian cell line release non‐dialyzable factors into their growth medium. These factors are capable of promoting the adhesion and spreading of these cells on a generally non‐attachable substratum and also promote spreading on an adhering substrate. Evidence in presented which demonstrates that the spreading promotion activity of the conditioned medium is dependent on the cell density of the culture from which it was derived. Dilution of the conditioned medium results in a proportionate dilution of the spreading promotion activity. The results clearly demonstrate that the production of this spreading promotion factor is continued even in the absence of cell to substrate attachm

ISSN:0021-9541    

DOI:10.1002/jcp.1040990306

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

年代:1979

数据来源: WILEY

摘要:

AbstractThe effect of the presence of nerve extracts on the development of tetrodotoxin (TTX)‐sensitive sodium channels in cultures of dissociated embryonic chick skeletal muscle cells was examined by measuring the maximum rate of rise of TTX‐sensitive spike potential. The addition of the nerve extract prepared from brain or spinal cord of chick embryos to the culture medium caused an increase in the channel density. Extracts of non‐neural tissues, i.e., lung, kidney, and muscle, were ineffective Liver extract, however, produced an effect similar to the nerve extracts. These resutls suggest that the TTX‐sensitive sodium channels in the muscle cell membrane are regulated by a diffusible chemical substance independently of innervation, and that this substance resides in neural tissues, and perhaps also i

ISSN:0021-9541    

DOI:10.1002/jcp.1040990307

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

年代:1979

数据来源: WILEY

摘要:

AbstractGlucocorticoids induce several phenotypic changes in rat hepatoma cells in tissue culture, including the inhibition of plasminogen activator activity. Variant cell lines resistant to dexamethasone inhibtion of plasminogen activator activity have been isolated using an agar‐fibrin overlay technique to identify colonies with fibrinolytic (plasminogen activator) activity. The variants are resistant to concentrations of dexamethasone 1,000 times that necessary to completely inhibit plasminogen activator activity in wild‐type cells. The variant phenotype has been inherited in a stable manner for more than 300 generations in continuous culture in the absence of dexamethasone. These variants are unique in that the resistance is not secondary to defective or absent glucocorticoid receptors but is due to a lesion specific for regulation of plasminogen activator. Fluctuation analyses support the hypothesis that resistance to dexamethasone arises randomly and is not induced by dexamethasone. Because HTC cells are heteroploid and karyotypically highly variable, variants are thought to arise primarily by chromosomal segregation events. These variants provide a valuable tool for studying the mechanism of hormonal regulation of plasminogen activator as well as the role of proteases in hormonal regulation of membrane functi

ISSN:0021-9541    

DOI:10.1002/jcp.1040990308

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

年代:1979

数据来源: WILEY

摘要:

AbstractHuman diploid skin fibroblasts derived from normal individuals and those with the testicular feminization syndrome (TFM) have been shown to be killed to the same degree by dihydrotestosterone in spite of the absence of high affinity cellular androgen receptors in the TFM fibroblasts. Furthermore, several different normal fibroblast strains from various anatomical sites all showed similar amounts of androgen‐induced cytotoxicity even though their respective receptor contents differed by as much as ten‐fold. These results suggest that steroid‐induced cytotoxicity in human fibroblasts in not correlated with receptor content, unlike murine lymphoid cells in which the receptor content has been shown to be closely related to their ability to survive hormone exp

ISSN:0021-9541    

DOI:10.1002/jcp.1040990309

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

年代:1979

数据来源: WILEY

摘要:

AbstractAutophosphorylation of 3T3 cells, utilizing endogenous membrane protein kinase, can be detected by incubating the cells with μgM32P‐ATP. The phosphorylation activity of growing cells is two to four‐fold greater than quiescent ones. In this study, the increased phosphorylation activity of serum‐stimulated cells was examined. Phosphorylation, measured at times after serum stimulation of quiescent cultures, was found to increase in early G1and to reach a maximum prior to DNA synthesis. This increase in stimulated cells was dependent on RNA and protein synthesis but not on DNA synthesis. The increased activity decayed quickly (half‐life approximately 2–3 hours) in the presence of cycloheximide, while the basal activity in quiescent cells was relatively unchanged. Insulin, prostaglandin E1or prostaglandin F2α were also found to bring about the same increase in phosphorylation as serum, although in contrast with serum they caused only a small percentage of the culture to synthesize DNA. The results suggest that enhanced phosphorylation activity is a G1event. It does not depend on subsequent DNA synthesis. Phosphorylation may be one of the biochemical steps in G1, necessary but not sufficient for cells to move i

ISSN:0021-9541    

DOI:10.1002/jcp.1040990310

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

年代:1979

数据来源: WILEY

摘要:

AbstractMitotic HeLa cells (M cells) synthesize protein at about 25% of the rate of S phase cells. This decrease in protein synthesis is due to a reduction in the rate of initiation. However, extracts prepared from M cells are almost as active in protein synthesis as S cell extracts. Both cell extracts are quite active in in vitro initiation of protein synthesis. Moreover, two steps in initiation, binding of Met‐tRNAfto 40S ribosomal subunits and binding of mRNA to ribosomes, show similar activity in both extracts. The difference in protein synthesizing activity observed in vivo is largely eliminated in the preparation of cell‐free systems. The ribosomes of M cells contain small mot wt RNA, which inhibits protein synthesis in vitro. This RNA, which has possibly a nuclear origin, may be a cause of the reduction in the rate of protein synthesis in M ce

ISSN:0021-9541    

DOI:10.1002/jcp.1040990311

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

年代:1979

数据来源: WILEY