摘要:

AbstractKinetics of cell replication was compared in regenerating livers ofMus musculusat ages ranging between 6 and 32 months. Incorporation of [3H]‐thymidine into DNA and autoradiographic analysis showed that the maximal extent of DNA replication following partial hepatectomy became delayed with age. Furthermore, the total fraction of parenchymal and nonparenchymal cells in S phase at different intervals during regeneration diminished as mice aged. The specific activity of DNA polymerase‐α, the putative replicative enzyme, declined progressively during aging. The specific activity of DNA polymerase‐β, the purported repair enzyme, declined to an appreciably lesser extent during the lifespan of the mouse. No evidence was found for the appearance of a specific inhibitor of polymerase‐α in senescent mouse liver. Also, the bulk of the activities of both hepatic DNA polymerase‐α and ‐β remained localized in the cell nucleus throughout the lifetime of the animal and were mainly associate

ISSN:0021-9541    

DOI:10.1002/jcp.1041180302

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe clonal preadipose cell line, MC3T3‐G2/PA6, has the capacity to differentiate into adipocytes in response to glucocorticoids and to support in vitro growth of hemopoietic stem cells (CFU‐S). To study the relationship between these capacities, we precultured the MC3T3‐G2/PA6 cells for varying days in the presence or absence of dexamethasone and then cocultured them with mouse bone marrow cells. Logarithmically growing cultures contained no detectable adipocytes and showed the highest growth‐supporting activity for CFU‐S, whereas cultures containing the largest number of adipocytes showed the lowest activity. When bone marrow cells were seeded onto 3‐day‐old MC3T3‐G2/PA6 preadipocyte layers at 1 × 105cells/35‐mm dish, day 12 CFU‐S grew with a population doubling time of about 37 hr, and at least 75% of them were associated with the cell layer between days 2 and 7. In the absence of the preadipocytes, CFU‐S were not detected in the adherent cell fraction and decreased with a half‐life of about 18 hr. More than 80% of CFU‐C were also found to be associated with the preadipocyte layer, and they increased about 24‐fold in number during 7 days in culture. Morphologically, hemopoietic cells developing into mature granulocytes and macrophages were distributed between the layers of preadipocytes. Dendritic processes of preadipocytes were frequently in close alignment with the hemopoietic cells. However, adipocytes failed to show such an intimate association with hemopoietic cells. These results indicate that MC3T3‐G2/PA6 cells in the preadipocyte stage, but not in the adipocyte stage, have the capacity to support CFU‐S growth, and that hemopoiesis in our cocultivation system proceed within the microenvironmental milieu provid

ISSN:0021-9541    

DOI:10.1002/jcp.1041180303

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

年代:1984

数据来源: WILEY

摘要:

AbstractC6 glioma cells respond to beta‐adrenergic agonists (isoproterenol) with a transient rise in intracellular cyclic adenosine monophosphate level. This beta‐responsiveness of C6 cells is inhibited by the presence of a plasma membrane fraction, which has a five‐ to six‐fold purification of membrane markers, showed a greater inhibition of beta‐responsiveness in C6 cells than any other subcellular fractions of B104 cells. The inhibitory effector(s) is apparently associated with integral membrane structure(s) since ionic extraction and treatment with chelating agents did not remove the effect from the particulate membrane fraction. The effector is probably proteinaceous in nature as judged by its susceptibility to inactivation by heat and protease treatment. The data indicate that neither adenylate cyclase nor phosphodiesterase enzyme is likely to be directly involved in mediating the beta‐nonresponsiveness

ISSN:0021-9541    

DOI:10.1002/jcp.1041180304

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

年代:1984

数据来源: WILEY

摘要:

AbstractRat mammary tumors contain a unique class of cryptic cell‐surface prolactin receptors that can be unmasked by depleting the cells of energy. These cryptic receptors, which are found in mammary tumors and nonlactating normal mammary cells but not in differentiated mammary tissue, are continuously inserted and rapidly removed from the cell surface. In this report we demonstrate that prolactin regulates the level of cryptic receptors. Treatment of primary cultures of rat mammary tumor cells with prolactin at concentrations between 0.1 and 0.5 ng/ml caused cryptic receptor levels to increase within 24 h, and this increase was maintained for up to 6 days. At prolactin concentrations of 10‐50 ng/ml, receptor levels were the same as in cells incubated without hormone, while a decrease in the steady‐state level of cryptic receptors was induced within 24 h by 100‐500 ng prolactin/ml. Concentrations of 1,000–5,000 ng prolactin/ml caused a rapid, dose‐dependent down regulation of cryptic receptor sites. Down regulation at 5,000 ng prolactin/ml was (1) complete (84 ± 5% reduction) in 1 h; (2) specific for lactogenic hormones; (3) completely reversed within 10 h after prolactin removal; (4) energy dependent; and (5) not blocked by the cytoskeleton active agents cytochalasin B and colchicine or by NH4CI, which inhibits hormone degradation. We conclude that rat mammary tumor cells have the capacity to auto‐regulate cryptic prolactin receptors, a property that supports our notion that such receptors play a role in regulating prolactin responsiveness. The observed pattern of cryptic receptor autoregulation in response to prolactin concentration and time of exposure suggests that a pool of cryptic sites provides these cells with the capacity to respond to prolactin concentrations from pg to μg/ml, a range well beyond the Kdfor the receptor itself. Since prolactin receptors in mammary tumors are not down regulated unless prolactin concentrations are well beyond the saturation point, these cells may have a selective growth advantage over cells in normal

ISSN:0021-9541    

DOI:10.1002/jcp.1041180305

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

年代:1984

数据来源: WILEY

摘要:

AbstractPrevious studies have suggested that heparin‐like glycosaminoglycans may be endogenous inhibitors of smooth muscle proliferation in the vessel wall. The purpose of this study was to determine the effects of exogenous glycosaminoglycans on rat vascular (aortic) smooth muscle cell migration following wounding in vitro. Our data indicate that heparin and related molecules (iota carrageenan, dextran sulfate), but not other glycosaminoglycans (hyaluronate, chondroitin, and dermatan sulfates), inhibit smooth muscle cell motility in a cell‐specific, dose‐dependent, and reversible fashion. The effect of heparin was maximal (60% inhibition) at 10 μg/ml; a half‐maximal effect was observed at 1 μg/ml; Heparin did not significantly affect the migration of bovine aortic endothelium or Swiss 3T3 cells. These observations support the concept that heparin‐like glycosaminoglycans may be important regulators of vascular smooth muscle ce

ISSN:0021-9541    

DOI:10.1002/jcp.1041180306

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

年代:1984

数据来源: WILEY

摘要:

AbstractCells of rat parotid glands were maximally stimulated to initiate DNA synthesis by injecting into the animal a single dose of 25 to 150 mg of isoproterenol/ kg of body weight. During the 18‐ to 21‐hr prereplicative period following injection of the highest dose of the drug, there were two predominant and transient redistributions of calmodulin from the bound to the soluble form, which tripled the level of soluble calmodulin at 3 hr and again at 18 hr just before the initiation of DNA synthesis. A small (50%) increase in total calmodulin was observed only during the early (3‐h) prereplicative surge of soluble calmodulin. The late, pre‐DNA‐synthetic surge of soluble camodulin and the initiation of DNA synthesis were both prevented in rats that lacked their parathyroid‐thyroid gland complex and had been hypocalcemic for 48 or 72 hr. Unlike the effect of high doses of isoproterenol, low doses (e.g., 25 mg/kg body weight) of the β‐adrenergic drug could maximally stimulate DNA synthetic activity without the later pre‐DNA‐synthetic surge of soluble calmodulin, suggesting that any apparent correlation between the level of calmodulin and DNA synthesis may be spurious and that an actual increase in the level of soluble calmodulin just before the onset of DNA synthesis was not a prerequisite for DNA synthetic activit

ISSN:0021-9541    

DOI:10.1002/jcp.1041180307

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

年代:1984

数据来源: WILEY

摘要:

AbstractEmbryonic chick pigment epithelial cells in culture require glucose as their major energy source for long‐term growth, pigment formation, and colony organization. Cell number increases with glucose concentration at least up to 5.0 mM. Cells can be grown with glutamine as the major energy source but produce comparable cell numbers for only the first 3 days in culture, after which they cease growing. However, they are able to metabolize glutamine at a two to sixfoid higher rate than cells grown in the presence of glucose as measured by CO2release and by incorporation into protein. In cells grown in the presence of both glucose and glutamine, basal ATP levels were 31.1 nmoles/mg protein; P‐creatine averaged 15.2 nmoles/mg protein and showed marked variability between experimental groups. During starvation, P‐creatine levels fell while ATP levels remained relatively constant. Glucose was required for the recovery of P‐creatine to prestarvation levels when measured 5 min after refeeding. Because of these marked changes in P‐creatine concentration as a function of nutritional status, the ATP/P‐creatine ratio becomes a useful measure of the energy state

ISSN:0021-9541    

DOI:10.1002/jcp.1041180308

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

年代:1984

数据来源: WILEY

摘要:

AbstractUnder normal conditions, reticulocytes synthesize α‐ and β‐globin polypeptides at equal rates. Incubation in the absence of hemin or under anoxia or hypertonic stress (100 mM excess NaCl) reduces the rate of protein synthesis to 30–50% of control levels. However, only hemin deprivation causes a reduction in polyribosome size and preferential inhibition of α‐globin synthesis consistent with specific reduction in the rate of polypeptide chain initiation. Polyribosomal profiles are unaffected by anoxic or hypertonic stress and the ratio of α:β globin synthesis remains close to unity. Measurement of ribosome transit time indicates that anoxic or hypertonic stress causes a decrease in the rate of polypeptide chain elongation that varies with the degree of inhibition of protein synthesis. Ribosomes isolated from stressed cells exhibit a reduced ability to bind35S‐met‐tRNAf, suggesting that the ability to form initiation complexes is also impaired. These results suggest that reticulocytes, unlike nucleated cell lines, can coordinately reduce rates of initiation and elongation in response to certain physio

ISSN:0021-9541    

DOI:10.1002/jcp.1041180309

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe cell differentiation of HL‐60 human leukemic promyelocytes along the myeloid pathway due to various continuous and distributed exposures to retinoic acid was studied. HL‐60 myeloid differentiation was a continuously driven process; significant terminal cell differentiation occurred only after a minimum exposure to inducer of two division cycles. Cells so committed to differentiation retained a heritable, finite memory of differentiation commitment over a further division cycle. Prior to becoming committed, cells acquired precommitment memory of exposure to inducer. Precommitment memory abbreviated the subsequent exposure to inducer needed for commitment to differentiation. Precommitment memory was semistable. It was heritable, but was lost after four division cycles. The acquisition and loss of precommitment memory correlated with alterations in nuclear architecture detected by narrow angle light scatter using flow cytometry. The altered nuclear architecture first occurred before any overt cell differentiation or growth arrest. It was thus an early event in the induced program of terminal cell differentiation. Alterations in relative abundances of cytoplasmic proteins also occurred prior to overt cell differentiation or growth arrest. One of these was a 17 kdalton, anionic, probably Ca2+binding, protein. Retinoic acid thus induced early cellular changes, including cytoplasmic and nuclear alterations, within one cell cycle when cell differentiation was not yet appar

ISSN:0021-9541    

DOI:10.1002/jcp.1041180310

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe impact of hypoxic exposure on the activities of all 11 glycolytic enzymes was studied in cell culture into mammalian cells—mouse lung macrophages and L8 rat skeletal muscle cells. During hypoxic exposure, the measured activity of all glycolytic enzymes increased, establishing coordinate regulation. Three nonglycolytic cytoplasmic enzymes showed no change in activity under the same conditions, suggesting a specific mechanism. Hypoxia appears to increase the activities of all glycolytic enzymes whether rate‐limiting or not, presumably increasing adenosine triphosphate availability despite decreased O2sup

ISSN:0021-9541    

DOI:10.1002/jcp.1041180311

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

年代:1984

数据来源: WILEY