摘要:

AbstractUsing collagenase digestion as an assay for collagen in partially synchronized secondary cultures of chick embryo fibroblasts, we find that the rate of collagen synthesis remains at a constant fraction of overall protein synthesis (5%) regardless of the growth rate of the cells even when the rate of protein synthesis is accelerated 5‐fold by adding serum and altering the pH of the culture medium. However, in cells oncogenically transformed by Rous sarcoma virus, the relative rate of collagen synthesis was decreased by 50% 24 hours after infection and was 10% of the initial rate after 5 days. This selective decrease in rate of collagen synthesis could be reversed in cells infected with an RSV temperature‐sensitive transformation‐defective mutant at the non‐permissive temperature, indicating that the decrease in the rate of collagen synthesis was not merely the result of viral infection but was a direct consequence of oncogenic transfo

ISSN:0021-9541    

DOI:10.1002/jcp.1040920102

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

年代:1977

数据来源: WILEY

摘要:

AbstractThe plasmin and plasminogen activator proteases of the plasma fibrinolytic system were investigated as potential blood‐borne mediators of the proliferative activation of hepatocytes by partial hepatectomy. Partial (68%) liver resection, as well as proliferatively activating the remaining hepatocytes, rapidly (by 30 minutes) doubled the level (or activity) of circulating plasminogen activator but later (2 hours) greatly depressed this level. This later depression of the activity of circulating plasminogen activator lasted for eight to ten hours before returning to the normal level two to four hours before the hepatocytes in the liver remnant began to synthesize DNA. This sequence of changes in the fibrinolytic potential was not abolished by prior thyroparathyroidectomy which is known to inhibit the initiation of hepatocyte DNA synthesis and to prevent the secretion of the calcium homeostatic hormones, another early systemic consequence of partial liver resection. Since the early rise in plasminogen activator activity did not cause the appearance of active (free) circulating plasmin, and since the injection of large doses of the fibrinolytic and protease inhibitors, EACA and Trasylol®, during this early, post‐operative period of hyperfibrinolytic potential did not prevent hepatocytes from initiating DNA synthesis, it is unlikely that either plasmin or its activator protease are blood‐borne initiators of hepatocyte proliferative devel

ISSN:0021-9541    

DOI:10.1002/jcp.1040920103

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

年代:1977

数据来源: WILEY

摘要:

AbstractDepletion of Mg2+in the growth medium for chicken embryo fibroblasts produces a large decrease in DNA synthesis as measured by3H‐thymidine incorporation, and concomitant decreases in cellular K+and Mg2+and increases in Na+and Ca2+. In cells grown in media containing 0.2 mM Ca2+, graded reduction of Mg2+from 0.8 mM (control) to 0.016 mM produced graded decreases in DNA synthesis to 10% of control at 0.016 mM Mg2+. Concomitantly, cell cations showed graded changes, Na+increasing to 227%, K+decreasing to 52.5%, Mg2+decreasing to 57.5% and Ca2+increasing to 153.5% of control. The effects of Mg2+depletion on DNA synthesis and cell cation content exhibited a dependence on Ca2+concentration, the effects being larger at low Ca2+concentration. Use of inorganic pyrophosphate in the growth medium as a selective complexor of Mg2+caused a marked decrease in DNA synthesis which was accompanied by changes in cellular cation content similar to those produced by direct Mg2+depletion.The effects of Mg2+depletion on cell cation content are explainable in terms of changes in membrane permeability caused by rapid external surface exchange of bound divalent cations. Among the several interpretations of the data in terms of possible mechanisms by which changes in external Mg2+concentration may affect cell metabolism, the most consistent with known properties of the system is the concept of a central role for intracellular free Mg2+in the coordinate control of growth and metabolism in animal cell

ISSN:0021-9541    

DOI:10.1002/jcp.1040920104

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

年代:1977

数据来源: WILEY

摘要:

AbstractAdhesion of baby hamster kidney fibroblasts (BHK cells) to a Falcon tissue culture flask was measured under various physiological conditions. While 75–80% of the fibroblasts adhere at temperatures from 19–50°, cellular adhesion decreased dramatically below 19°. Less than 10% of the cells adhere to the substratum even after prolonged incubations at temperatures of 8° or below. This lack of adhesion at low temperatures cannot be overcome by the application of increased gravitational force to the cells.No correlation exists between cellular ATP concentrations or respiration rates and the rate of cell adhesion to the substratum. One millimolar Na F and 1 mM 2,4 dinitrophenol together lower cellular ATP concentration by 95% but adhesion is reduced by only 50%. NaN3and KCN greatly lower cellular ATP concentrations without a corresponding inhibition of adhesion. Inhibition of cellular respiration by these compounds occurs at lower concentrations than does the inhibition of adhesion. Two micrograms/milliliters of cytochalasin B inhibits adhesion by 90%, 0.1 mM vinblastine sulphate or colchicine by less than 50% and 50 μg/ml colcemid by less than 30%.Fixing the cells with formaldehyde, hardening their membranes with ZnCl2or treating the cells with toluene, all cause an inhibition in adhesion. Again, application of increased gravitational force cannot overcome these latter inhibitions of BHK cell adhesion to the surface of the

ISSN:0021-9541    

DOI:10.1002/jcp.1040920105

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

年代:1977

数据来源: WILEY

摘要:

Abstract32P‐uptake into non‐histones from bone cell cultures was selectively stimulated in the presence of calcitonin. Comparison of the control and experimental radioactivity profiles of non‐histones fractionated by SDS gel electrophoresis showed that, in response to calcitonin stimulation, there was a 2‐ to 3‐fold increase in the specific activity associated with non‐histone proteins in the molecular weight range of 10,000 to 45,000 daltons while that of bands between 50,000 to 200,00

ISSN:0021-9541    

DOI:10.1002/jcp.1040920106

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

年代:1977

数据来源: WILEY

摘要:

AbstractA permanent cell line C2M of mouse melanoma B16 was highly melanized in a modified Eagle's MEM supplemented with 10% calf serum, when the medium contained 1 mM galactose and 10 mM pyruvate instead of 5.5 mM glucose. The activity of the key enzyme for melanogenesis, tyrosinase (EC 1.14.18.1), of living cells cultured in the galactose‐pyruvate medium was consistently 27 times higher than that of cells in normal MEM. This high level of tyrosinase activity was maintained in the stationary phase, in contrast to the activity of cells in normal medium, which decreased sharply in the stationary phase. It seems likely that tyrosinase activity is suppressed by the presence of glucose rather than stimulated by galactose.This modified medium should be useful for obtaining a high level of tyrosinase activity in living cells in culture and in cell‐free extra

ISSN:0021-9541    

DOI:10.1002/jcp.1040920107

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

年代:1977

数据来源: WILEY

摘要:

AbstractWhen resting 3T6 cells undergo a serum‐induced transition to the growing state, the cytoplasmic content of ribosomal, transfer and messenger RNA increase as the cells prepare for DNA synthesis. The normal linear increase in mRNA content occurs even when the production of ribosomes is blocked. In this paper we determine the effect of inhibiting protein synthesis on the increase in poly(A) (+) mRNA content. Resting cells were serum stimulated in the presence of cycloheximide or puromycin at levels which inhibit protein synthesis by greater than 95%. Cytoplasmic poly(A) (+) mRNA content was determined at various times thereafter. We found that mRNA content increased five to ten times more rapidly in drug treated cells than in control cells stimulated in the absence of inhibitors. mRNA content increased 50–70% by one hour, and 60–90% by two hours following stimulation in the presence of inhibitor, and remained more or less constant thereafter. In contrast, mRNA content increased linearly in control stimulated cultures and did not double until about 15 hours after stimulation. The rapid increase in mRNA content is most likely the result of inhibition of protein synthesis rather than a secondary effect of the drug since the same observations were made in growth stimulated cells if protein synthesis was blocked with either puromycin or cycloheximide.A similar effect was also observed with resting 3T6, exponentially growing 3T6 and growing HeLa cells following exposure to cycloheximide, although the magnitude of the increase was less than that observed with growth stimulated cells. Puromycin had negligible effect on mRNA content in resting or exponentially growing cells.The rapid increase in cytoplasmic poly(A) (+) mRNA content was not due to rapid unbalanced export of nuclear poly(A) (+) RNA into the cytoplasm since there was no decrease in nuclear poly(A) content following serum stimulation in the presence of cyclohex

ISSN:0021-9541    

DOI:10.1002/jcp.1040920108

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

年代:1977

数据来源: WILEY

摘要:

AbstractACTH, 8‐Br‐cAMP, and serum deprivation arrested Y‐1 functional mouse adrenal tumor cells in the G1phase of the cell cycle. Though ACTH and 8‐Br‐cAMP treated cells were larger with increased macromolecular synthetic rates compared to cells arrested in G1by serum removal, a similar 8‐ to 10‐hour lag to initiation of DNA synthesis was observed after either ACTH or 8‐Br‐cAMP removal or after serum addition. After the 8‐ to 10‐hour lag period, cells entered S phase exponentially. ACTH or 8‐Br‐cAMP opposed serum induced DNA synthesis initiation only when added prior to S. Once commitment to DNA synthesis occurred, ACTH or 8‐Br‐cAMP addition did not inhibit DNA synthesis although 8‐Br‐cAMP induced a secondary block in G2. Though ACTH and 8‐Br‐cAMP inhibited serum induced initiation of DNA synthesis and did not affect serum induced cellular hypertrophy, both substances increased the steroidogenic capacity of the cell. ACTH and 8‐Br‐cAMP thus appear to specifically oppose the stimulatory effects of serum on initiation of DNA synthesis while inducin

ISSN:0021-9541    

DOI:10.1002/jcp.1040920109

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

年代:1977

数据来源: WILEY

摘要:

AbstractThe rate of uridine uptake inTetrahymenadeclines by an order of magnitude by two hours after shiftdown to a non‐nutrient buffer. This alteration in uptake properties cannot be accounted for by an increase in the intracellular pool of uridine, an increase in apparent Km for uptake or a decline in the rate in which uridine is processed intracellularly.It is argued that the decrease in uridine uptake is due to a reduction in numbers of functional transport molecules exposed at the cell surface and is a reflection of a developmentally related cell surface transformation.In addition, the putative decline in functional transport molecules cannot be entirely explained by metabolic turnover of these molecules in the absence of replacement, nor does it require the synthesis of new protein. We discuss the possibility that a shift in equilibrium between accessible and inaccessible transporters is operating.Finally, a close correlation between conditions which elicit the transport alteration and those which allow the development of mating competency suggests that the two phenomena may be coordinately regulate

ISSN:0021-9541    

DOI:10.1002/jcp.1040920110

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

年代:1977

数据来源: WILEY

摘要:

AbstractCultures of HeLa cells, strains S3G (HeLa65) and S3K (HeLa71) were grown in plastic dishes until firmly attached and were then treated with sonic dispersions of Rosenthal's phospholipase inhibitor. A rapid increase in alkaline phosphatase activity occurred following this treatment in the S3G strain (low inducible alkaline phosphatase) but not in the S3K strain (high constitutive alkaline phosphatase). The stimulatory effect was dependent on the presence of bovine serum in the medium. No stimulation of alkaline phosphatase was observed in a variety of soluble preparations of this enzyme.

ISSN:0021-9541    

DOI:10.1002/jcp.1040920111

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

年代:1977

数据来源: WILEY