摘要:

AbstractThe effects of a somatomedin analog, Temin's multiplication stimulating activity (MSA), on amino acid transport into muscle cells have been characterized in a series of experiments on myoblasts and myotubes in culture. Addition of MSA to serum‐starved L6 myoblasts increased the rate of aminoisobutyrate (AIB) uptake 50‐150% within five hours. This early effect on transport was followed by increases in cell number, protein content and3H‐thymidine incorporation. Kinetic analyses indicated that MSA increased the maximal velocity of AIB uptake but had no effect on the KMfor AIB. When myoblasts were allowed to fuse (and dividing cells eliminated by addition of 10−4M cytosine arabinoside) the AIB transport system(s) remained similarly responsive to MSA. In myoblasts and in myotubes, both the basal and MSA‐stimulated rate of AIB uptake were sodium‐dependent processes; little stimulation occurred if sodium was absent from the labeling medium. Further suggesting the involvment of cations in response to hormone, MSA stimulated uptake of the potassium analog,86Rb+, and increased net intracellular potassium in both myoblasts and myotubes. MSA was active at concentrations equivalent to in vivo levels of somatomedins; neither insulin nor growth hormone had any effect at or near physiological con

ISSN:0021-9541    

DOI:10.1002/jcp.1040930202

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

年代:1977

数据来源: WILEY

摘要:

AbstractThe hydrolysis of ATP and AMP by enzymes located on the external side of the plasma membrane (ecto‐ATPase and ecto‐AMPase) was studied in mouse myeloid leukemic cells, normal early myeloid cells, and normal mature granulocytes and macrophages. Nine clones of myeloid leukemic cells were used belonging to three groups that differ in their ability to be induced to differentiate by the differentiation‐inducing protein MGI. These three groups consisted of MGI+D+that can be induced to undergo complete differentiation, MGI+D+that can be induced to partially differentiate and MGI−D−with no induction of differentiation. The ecto‐ATPase activity of normal early myeloid cells was similar to that of normal mature granulocytes and macrophages and higher than that of any of the leukemic cells. Among the leukemic cells, the MGI−D−cells had the highest level of ecto‐ATPase activity.The behaviour of ecto‐AMPase differed from that of ecto‐ATPase. Some MGI−D−clones had a higher ecto‐AMPase activity than normal cells and MGI+D−and MGI+D+cells showed no detectable activity. Neither the ecto‐ATPase nor ecto‐AMPase activities changed after induction of differentiation in normal early myeloid or MGI+D+leukemic cells. The results indicate that the myeloid leukemic cells had a decreased ability to hydrolyse external ATP, that there can be an independent regulation of ecto‐ATPase and ecto‐AMPase and that neither of these enzyme acti

ISSN:0021-9541    

DOI:10.1002/jcp.1040930203

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

年代:1977

数据来源: WILEY

摘要:

AbstractThe mechanism of killing of A9 fibroblasts by 5‐fluorotryptophan has been studied. L‐tryptophan competitively relieves the growth inhibition caused by 5FT. After incubation with 5FT,3H‐5FT was incorporated into protein, replacing tryptophan residues. During the initial hours of incubation with 5FT, a specific inhibition was observed of the incorporation of L‐tryptophan into protein; later this inhibition was followed by a general inhibition of protein synthesis and cell division. However, nuclear division continued after cell division had ceased. While 5FT was observed to be incorporated into protein after a 1 hour period in MEM + 0.40 mM 5FT in A9, no3H‐5FT was incorporated into protein in a mutant isolated by its resistance to killing by 5FT. These results support the hypothesis that cell death occurs due to malfunctioning proteins which contain 5FT

ISSN:0021-9541    

DOI:10.1002/jcp.1040930204

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

年代:1977

数据来源: WILEY

摘要:

AbstractIn a survey of the expression on cultured mouse cells of the cell surface antigen known as nervous system antigen‐3 (NS‐3), it was found that RAG, a renal adenocarcinoma line, expressed that antigen. It was also observed that 3T3, a fibroblast line of unknown tissue origin, expressed NS‐3. Cells of these two lines were hybridized with cells of two mouse L cell lines that did not express NS‐3. Four hybrid clones were tested for both the 3T3 × L cell cross and the RAG × L cell cross, and all the hybrids were found to be NS‐3 positive. All the hybrids had at least 40% as much activity as the NS‐3 positive parent. Of the four parental mouse cell lines used, only 3T3 expressed Thy‐1.2 antigen on the cell surface. In contrast to the continued expression of NS‐3 on hybrid cells, Thy‐1.2 antigen was not detectable on two clones of 3T3 × L cell hybr

ISSN:0021-9541    

DOI:10.1002/jcp.1040930205

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

年代:1977

数据来源: WILEY

摘要:

AbstractA chromosome that controls malignancy in Chinese hamster cells has been identified by analysis of the Giemsa banding pattern of a malignant cell line transformed by simian virus 40 (SV40), non‐malignant revertants from this line, segregants from the revertants that were again malignant and a cell line transformed by methylcholanthrene. The malignant cell line transformed by SV40 was near diploid and had gained additional material of chromosome 3. Revertants with a suppression of malignancy and malignant segregants from these revertants were near triploid. The malignant segregants also showed a gain of material of chromosome 3 compared to the non‐malignant revertants from which they were derived. Malignancy of these cells was associated with the ability to form colonies in agar. Cells of a line transformed by methylcholanthrene were malignant, formed almost no colonies in agar and the only chromosome change from the normal diploid chromosome banding complement was the addition of a long arm of chromosome 3. The results indicate that chromosome 3 carries gene(s) that control malignancy in Chinese hamster cells in cell lines transformed by a viral or a chemical carcinogen and that malignancy was induced in both cell types by an increase of these ge

ISSN:0021-9541    

DOI:10.1002/jcp.1040930206

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

年代:1977

数据来源: WILEY

摘要:

AbstractDuring the initial ten hours of growth in lymphocytes stimulated by phytohemagglutinin, the cells are converted from a state in which over 70% of all ribosomes are inactive free ribosomes, to one in which over 80% of ribosomes are in polysomes or in native ribosomal subunits. In this initial period, there was a neglible increase in total ribosomal RNA due to increased RNA synthesis, and abolition of ribosomal RNA synthesis with low concentrations of actinomycin D did not interfere with polysome formation. Therefore, the conversion is accomplished by the activation of existing free ribosomes rather than by accumulation of newly synthesized particles. The large free ribosome pool of resting lymphocytes is thus an essential source of components for accelerated protein synthesis early in lymphocyte activation, before increased synthesis can provide a sufficient number of new ribosomes. Free ribosomes accumulate once more after 24 to 48 hours of growth, when RNA and DNA synthetic activity are maximal. This reaccumulation of inactive ribosomes at the peak of growth activity may represent preparation for a return to the resting state where cells are again susceptible to stimulation.Activation of free ribosomes to form polysomes appears to involve modification of at least two steps: (a) dissociation of free ribosomes with stabilization as native subunits, and (b) adjustment of a rate‐limiting step at initiatio

ISSN:0021-9541    

DOI:10.1002/jcp.1040930207

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

年代:1977

数据来源: WILEY

摘要:

AbstractSeveral clones of dexamethasone‐resistant cells, which could not differentiate even in a high concentration of dexamethasone, were isolated from glucocorticoid‐sensitive myeloid leukemic cells. Some of them were shown to be deficient in steroid binding to specific cytoplasmic receptors, while the others contained glucocorticoid‐specific cytoplasmic receptors that might be the same as those in sensitive cells. One of the resistant clones was found to be almost completely deficient in nuclear acceptor sites for cytoplasmic steroid‐receptor complexes. The remaining clones were also characterized by significantly reduced amounts of nuclear‐bound glucocorticoid. These results suggest that resistibility to glucocorticoids in the resistant clones of myeloid leukemic cells is due mainly to a defect in some steps of intracellular transfer of the steroid. Dexamethasone‐sensitive cells, which could differentiate in the presence of dexamethasone, could be also induced to differentiate by protein factor(s) in ascitic fluid. Although all the resistant cells showed a low response to ascitic fluid, some of them showed 10‐fold enhancement of phagocytic activity which is a typical character of differentiated cells. These results suggest that response to steroids is not directly correlated with that to prote

ISSN:0021-9541    

DOI:10.1002/jcp.1040930208

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

年代:1977

数据来源: WILEY

摘要:

AbstractThis study involves the use of fibroblast growth factor (FGF) as a substitute for exogenous serum to examine the early transport changes which occur when quiescent 3T3 cells re‐initiate active growth. FGF, in nanogram amounts, together with insulin and dexamethasone, can induce mitogenesis and mitosis in 3T3 cells GO‐arrested by holding in growth medium containing 0.8% calf serum. In terms of quiescent cell transport activity enhancement, FGF is 300,000‐fold more effective than fresh serum, on a protein basis. In addition, very short exposure of serum‐depleted cells to FGF indicates that a distinct temporal or time sequence exists in the transport system activation process. For example, uptake of α‐aminoisobutyric acid (AIB) and uridine are stimulated very rapidly, whereas hypoxanthine uptake does not respond until much later. Closer analysis shows that AIB uptake is maximally enhanced within zero to two minutes after FGF addition to cells. Finally, the stimulatory effect of FGF on transport system activities is specific in terms of the proliferative state of the cells to which it is added, and in terms of the uptake systems which res

ISSN:0021-9541    

DOI:10.1002/jcp.1040930209

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

年代:1977

数据来源: WILEY

摘要:

AbstractThe hydrocortisone (HC) induction of glycerol phosphate dehydrogenase (GPDH; EC 1.1.1.8) in rat glial C6 cells was inhibited reversibly and in a dose‐dependent manner by cytochalasin B (CB). CB had no effect on basal level GPDH, total cellular RNA, DNA or protein content nor did it act as a general inhibitor of the rate of protein synthesis. CB did not appear to be acting via dissociation of microtubules since colcemid had no effect on the induction process. The addition of an alternate energy source (sodium pyruvate) did not relieve the CB inhibition of GPDH induction suggesting that CB is not exerting its effect by blocking glucose utilization. The inhibition by CB is not dependent on the temporal sequence of the induction process since it specifically inhibited GPDH induction at any time it was added. CB did not alter the rate of degradation of GPDH in these cells and direct measurements of the specific rate of synthesis of GPDH demonstrated that CB decreased the induced rate of GPDH synthesis by about 60%. The site of inhibition was more precisely defined by experiments which demonstrated a 60% decrease in specific nuclear binding of3H‐HC even though total cellular uptake of3H‐HC was unaffected. This effect on nuclear binding of HC is sufficient to account for the decreased accumulation of GPDH activity in CB‐treate

ISSN:0021-9541    

DOI:10.1002/jcp.1040930210

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

年代:1977

数据来源: WILEY

摘要:

AbstractThe cyclic AMP mediated induction of lactate dehydrogenase (LDH: E.C. 1.1.1.27) activity by norepinephrine in the rat glial cell line C6 is inhibited by cytochalasin B. Doses of 5, 15, and 25 μg/ml of cytochalasin B inhibited the induction equally. Twenty‐five μg/ml of cytochalasin B inhibited the induction reversibly, and had no effect on basal enzyme level. No effect of cytochalasin B on general protein synthesis was found, nor did it increase the rate of decline of enzyme activity in deinduced cells. It therefore appears to block LDH induction by selectively inhibiting its synthesis. Cytochalasin B had no effect on the transient (intracellular and extracellular) rise in cyclic AMP generated in response to norepinephrine treatment. Cytochalasin B was effective when added during the transcription dependent phase (first 3 hours) but not during the translation dependent phase (after 3 hours) of LDH induction. The suggestion is discussed that cytochalasin B inhibits one of the early events of the inductive proc

ISSN:0021-9541    

DOI:10.1002/jcp.1040930211

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

年代:1977

数据来源: WILEY