摘要:

AbstractNormal rat hepatocytes have been fused with highly differentiated rat hepatoma cells. Some of the hybrids express a physiologically significant level of activity of the urea cycle enzyme ornithine carbamoyltransferase (OCT), a liver‐specific function not found in the hepatoma cells. These hybrids have 10% of the adult rat liver OCT specific activity, incorporate3H‐ornithine into protein arginine, and can be selectively grown in arginine‐free medium supplemented with ornithine. Somatic cell hybridization of normal differentiated cells with highly differentiated neoplastic cells of the same tissue type may be useful as a general method for obtaining permanent cell lines with new tissue‐specific phe

ISSN:0021-9541    

DOI:10.1002/jcp.1041000302

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

年代:1979

数据来源: WILEY

摘要:

AbstractProstaglandin generation by human peripheral blood mononuclear cells is enhanced during co‐culture with human thyroid cells. The objective of the present study was to determine the influence of various sera on this process.Human thyroid adenoma cell monolayers were cultured with normal human peripheral blood mononuclear cells for three days in the presence of a variety of sera, or serum fractions. Prostaglandin E (PGE) in the medium was measured by bioassay or by radioimmunoassay. Significantly more PGE was generated in cultures containing fetal calf serum than in those containing human serum. This difference was not abolished by dialysis of the human serum. When the 50% (NH4)2SO4precipitate of the serum was used, PGE generation was similar to that in fetal calf serum, indicating the presence of an inhibitory factor in human serum. The degree of this inhibitory activity was similar in autologous and heterologous human serum, as well as in normal subjects and patients with Graves' disease. Gel filtration and ion‐exchange chomatography of human serum showed the inhibitor to co‐migrate with albumin. Evidence presented suggests that the inhibitor is not albumin itself but is, instead, a factor tightly bound to albumin. Inhibitory activity was also found in rabbit, goat, rat and cow serum.Prostaglandins are potent modulators of immune‐cell function. These data indicate that this process may be modulated by a factor in mammalian serum. The relative absence of this factor in fetal serum may have important implications in regard to the profound changes which occur in the immune system afte

ISSN:0021-9541    

DOI:10.1002/jcp.1041000303

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

年代:1979

数据来源: WILEY

摘要:

AbstractThis report strongly suggests that two compartments inTetrahymena thermophilacontain peptidase activity: the cytoplasm and the outer cell surface.Determinations of amino acid concentrations in the extracellular medium upon incubation of cells with peptides suggest that the surface‐bound peptidase activity hydrolyses di‐ and tri‐phenylalanine equally fast on a molar basis.Growth experiments designed to characterize the in vivo peptidase specificities showed that bothT. thermophilaandT. pyriformiscan use L‐leucyl‐L‐leucine, but not L‐leucyl‐D‐leucine as a leucine donor. These results are independent of whether the cells form foo

ISSN:0021-9541    

DOI:10.1002/jcp.1041000304

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

年代:1979

数据来源: WILEY

摘要:

AbstractStimulation of Balb/c‐3T3 cell growth by TPA requires factors found in serum. We examined the interaction between TPA and serum growth factors in the stimulation of cell growth. The number of cells synthesizing DNA (incorporating3H‐thymidine) within 24 to 30 hours after the addition of TPA and the growth factors to density‐inhibited Balb/c‐3T3 cultures in serum‐free medium was determined by autoradiography. With no additions or with TPA (30‐300 ng/ml) alone, only 3‐7% of cells synthesized DNA. However, TPA synergistically promoted DNA synthesis in combination with each of the defined serum growth fractions, platelet derived growth factor and platelet poor plasma. TPA also synergistically promoted DNA synthesis in combination with purified growth factors including fibroblast growth factor, insulin (10−6‐10−5M), and epidermal growth factor. In all conditions, TPA enhancement of DNA synthesis also resulted in an increase in cell number. Because TPA synergistically enhanced the activity of each growth factor tested, it did not act identically to any of

ISSN:0021-9541    

DOI:10.1002/jcp.1041000305

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

年代:1979

数据来源: WILEY

摘要:

AbstractThe metachromatic fluorochrome acridine orange was used to differentially stain DNA and RNA in Chinese hamster ovary (CHO) cells and in mitogen‐stimulated human lymphocytes during their progression through the cell cycle. Green and red fluorescence of individual cells, representing cellular DNA and RNA, respectively, was measured by flow cytometry.CHO cells were synchronized by selective detachment at mitosis. Their rate of progression through G1and subsequently through S phase correlated with the content of stainable RNA. The mean duration of the G1phase was 5.2 hours for cells with high RNA content (highest 25 percentile population) and 8.1 hours for cells with low RNA (lowest 25 percentile). The duration of S phase was 5.9 and 7.5 hours for high‐ and low‐RNA, 25 percentile subpopulations, respectively.Lymphocytes synchronized at the G1/S boundary by hydroxyurea or 5‐fluorodeoxyuridine showed extremely high intecellular variation with respect to content of stainable RNA. After release from the block they traversed S phase at rates linearly proportional to the content of stainable RNA. The duration of S phase was five hours for cells with high RNA‐, six to nine hours for cells with moderate RNA‐ and up to 27 hours for cells with minimal RNA‐content.The data suggest that the rate of progression the cell cycle of individual cells within a population may be correlated with the number of ribos

ISSN:0021-9541    

DOI:10.1002/jcp.1041000306

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

年代:1979

数据来源: WILEY

摘要:

AbstractWe have recently found that aphidicolin, a tetracyclic diterpene‐tetraol produced by several fungi, blocks DNA synthesis of sea urchin embryos by interfering with the activity of DNA polymerase α. These cells fail to proliferate in the presence of aphidicolin.In continuation of these studies, we determined the drug‐sensitive stage in the first cell cycle of the sea urchinClypeaster japonicusembryo.In continuous exposure to aphidicolin (2 μg/ml) from five minutes after fertilization, mitotic division of the embryo was completely suppressed. Embryos were exposed to the drug at progressively later intervals and their capability for cytokinesis was examined. Evidence was thereby obtained that aphidicolin acts at the S‐period to inhibit DNA synthesis resulting in developmental arrest of the

ISSN:0021-9541    

DOI:10.1002/jcp.1041000307

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

年代:1979

数据来源: WILEY

摘要:

AbstractTreatment of embryonic chick heart fibroblast cultures with 0.2Murea reversibly increases cellular overlap. The increase in cellular overlapping over that in control cultures may be quantitated by the overlap ratio (R), the ratio of the number of superimposed nuclei observed, to the number expected to occur when cells are assumed to be distributed randomly over the culture substratum (R = observed/expected overlaps). Reversal of the urea‐induced increase in R is blocked by 0.2 μg/ml cycloheximide. In the presence of cycloheximide, normal (low) overlap ratios are restored to urea‐treated cultures by adding non‐dialyzable material recovered by washing fibroblast monolayers with serum‐free medium. The overlap ratio assay revealed no effect of supernatant material added either to urea‐treated cultures in the continued presence of urea, or to untreated cultures. Although unfiltered supernatants were shown by SDS‐polyacrylamide gel electrophoresis to contain fibronectin (CSP; LETS; MWappar.= 220,000 d) and smaller proteins, the ability to reverse the urea‐induced increase in overlap ratio was present in Diaflo and Millipore filtrates of culture supernatants in which fibronectin was greatly depleted or absent. In contrast, purified fibronectin preparations failed to lower urea‐induced increases in overlap‐ratio. Partially purified, biologically active supernatants, prepared from14C‐leucine or125I‐labeled cultures, contained several macromolecules smaller than fibronectin that were labeled by both radioisotopes. In particular, one band (MWappar.= 58‐60,000 d) was present in polyacrylamide gels of active supernatant and also depleted in gels of homogenates from urea‐treated cultures. These results indicate that external macromolecules other than fibronectin are synthesized by culture fibroblasts and can affect cell social beha

ISSN:0021-9541    

DOI:10.1002/jcp.1041000308

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

年代:1979

数据来源: WILEY

摘要:

AbstractStimulation of postconfluent Swiss 3T3 cells in serum‐free medium with 4.3 mM Ca2+results in marked increases in both released and cell‐associated plasminogen activator (PA). Increased release of PA commenced approximately 10 to 12 hours post‐stimulation and continued to increase steadily until 48 hours at which time the stimulated cells (4.3 mM Ca2+) released approximately 14 times more PA than control cells (1.8 mM Ca2+). Sr2+, like Ca2+, also stimulates PA synthesis/release either in the presence or in the absence of 1.8 mM Ca2+whereas an excess of Mg2+inhibits Ca2+stimulation. Supranormal [Pi] in the medium stimulates PA synthesis/release in the presence of 1.8 mM Ca2+. Further, optimal stimulation by 4.3 mM Ca2+requires a normal level of Pi (1.0 mM). Elevation of medium [Ca2+] or [Pi]results in an enhanced uptake of Ca2+. The facts that cycloheximide treatment completely abolishes the Ca2+stimulatory effect and that an increase in cell associated PA precedes release indicate that PA release is coupled to synthesis of new PA. Ca2+stimulation of PA synthesis/release also requires continuous energy production and RNA as well as protein synthesis. A hypothesis is proposed to explain the relationship between stimulation of PA production and its enhanced release from cells stimulated by elevated [Ca2+] or [Pi]in the media. The possibility that PA release may be an example of the phenomenon of membrane shedding as opposed to secretion is disc

ISSN:0021-9541    

DOI:10.1002/jcp.1041000309

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

年代:1979

数据来源: WILEY

摘要:

AbstractThe addition of a chemical inducer, such as dimethylsulfoxide (DMSO), to cultures of mouse Friend erythroleukemic cells results in the induction of a number of late erythroid events, including the accumulation of globin mRNA, the induction of hemoglobin synthesis, the appearance of erythrocyte membrane antigens (EMA), and the cessation of cell division. The experiments presented in this study demonstrate that heme is necessary but not sufficient for the loss of proliferative capacity associated with DMSO‐induced Friend cell differentiation, whereas the accumulation of globin mRNA and EMA can occur in the absence of heme synthesis or heme itself. These conclusions were reached by selectively inhibiting heme synthesis in DMSO‐treated cells in two independent ways: (i) Inducible cells were treated with 3‐amino‐1,2,4‐triazole (AT), a drug which inhibits the induction of heme synthesis in Friend cells in a dose‐dependent manner. Treatment of inducible Friend cells with 1.5% DMSO for five days caused the plating efficiency in methyl cellulose to decrease to 1% of that in untreated cultures. However, treatment of the cells with DMSO plus AT almost totally prevented this decrease in plating efficiency. The addition of exogenous hemin, which alone had no significant effect on plating efficiency, largely reversed the effect of AT in DMSO‐treated cells, reducing the plating efficiency to below 5%. In contrast to the marked effects of AT on the proliferative capacity of differentiating Friend cells, the levels of globin mRNA and EMA were only partially decreased in cells treated with DMSO plus AT, compared to cells treated with DMSO alone. (ii) The relationship between heme synthesis, terminal cell division, and the induction of globin mRNA was investigated further through the use of non‐inducible Friend cell variant clones. One such non‐inducible clone, M18, appears to be a phenotypic analog of inducible cells treated with DMSO plus AT. Clone M18 did not accumulate heme or hemoglobin, as detected by benzidine staining, nor lose its proliferative capacity in response to DMSO. However, globin mRNA was induced by DMSO in this clone. Treatment of clone M18 with DMSO plus hemin overcame the block in hemoglobin accumulation suggesting that M18 has a defect in the induction of heme biosynthesis. In addition, exposure of M18 cells to DMSO plus hemin caused a gradual decrease in plating efficiency which was not due to non‐specific toxicity. Prior incubation of M18 cells in DMSO for three to five days was necessary before hemin caused a rapid loss of proliferative capacity. Thus, these results, in agreement with the AT studies on inducible Friend cells and previous studies on the induction of EMA in clone M18, indicate that there may be both heme‐dependent and heme‐independent events in the program of Frie

ISSN:0021-9541    

DOI:10.1002/jcp.1041000310

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

年代:1979

数据来源: WILEY

摘要:

AbstractBinding of either low density lipoprotein (LDL) or Concanavalin A (ConA) to actively growing vascular endothelial cells is associated with a redistribution of the appropriate cell surface receptor sites which form patches and caps. This receptor lateral mobility is greatly restricted when endothelial cells reach confluence and adopt the configuration of a cell monolayer composed of closely apposed and non‐overlapping cells. In this case, although the cells still exhibit specific LDL binding to the appropriate cell surface receptor sites, neither the binding of LDL nor of ConA induces a receptor redistribution. The lack of LDL receptor redistribution correlates with a marked decrease in the rate of LDL internalization. In contrast, no such a density‐dependent changes are observed in cell types which grow on top of each other and form multiple cell layers at confluence. Thus, neither LDL nor ConA induced cap formation in either sparse or confluent smooth muscle cell cultures and the same rate of LDL internalization is observed at both cell densities. Similarly, adsorptive endocytosis of cationized LDL (which enters the cell independently of the LDL receptor sites) was not correlated with a detectable receptor redistribution, nor was it significantly affected by changes in cell density and spatial organization.The formation of a confluent cell monolayer resting on an underlying basement membrane might therefore provide, via a change in membrane dynamics, a mechanism whereby the endothelium of large blood vessels can function as a protective barrier against the high circulating levels of LDL in pla

ISSN:0021-9541    

DOI:10.1002/jcp.1041000311

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

年代:1979

数据来源: WILEY