摘要:

AbstractA mitogenic factor from 3T3 plasma membranes has been identified and partially characterized. The factor appears to be a peripheral membrane protein that can be released by mild trypsin, chymotrypsin, or plasmin treatment. This component is sensitive to heat and acid, and has a molecular weight in the range of 150,000–200,000 daltons as determined by gel filtration. A similar mitogenic activity has also been found on the membranes of both SV‐40‐transformed 3T3 cells and human fibroblasts. The factor appears to be distinct from all previously described mitogenic compo

ISSN:0021-9541    

DOI:10.1002/jcp.1041140112

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

年代:1983

数据来源: WILEY

摘要:

AbstractWe have investigated the effect of tunicamycin (TM), an inhibitor of protein glycosylation, on surface Na+channels in cultured chick skeletal muscle cells. The expression of Na+channels, estimated by the measurement of batrachotoxin (BTX)‐activated22Na+uptake, was found to be significantly diminished after exposure of muscle cells to TM. This effect is partially reversed by the protease inhibitor leupeptin and is associated with a markedly enhanced rate of disappearance of Na+channels from the surface of TM‐treated cells. Our findings suggest that protein glycosylation contributes to the metabolic stability of voltage‐sensitive Na+cha

ISSN:0021-9541    

DOI:10.1002/jcp.1041140113

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

年代:1983

数据来源: WILEY

摘要:

AbstractThe Chinese hamster ovary (CHO) aminoacyl‐tRNA synthetase mutants Gln‐2, His‐1, and Lys‐101 were analyzed for alterations in respective particulate enzyme forms. The mutant Gln‐2 showed a preferential loss of the lower molecular weight enzyme form for glutamine. His‐1 showed alterations of the enzyme complexes for several other aminoacyl‐tRNA activities but only decreased activity for itself. The mutant Lys‐101 only showed an altered Lysyl‐tRNA synthetase. These results provide evidence for a model of the intracellular role of the aminoacyl‐tRNA synthetase complexes wherein the high molecular weight forms utilize amino acids directly from the extracellular pool while the low molecular weight forms utilize

ISSN:0021-9541    

DOI:10.1002/jcp.1041140114

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

年代:1983

数据来源: WILEY

摘要:

AbstractPrevious studies have shown no detectable colony‐stimulating factor (CSF) in media harvested from long‐term bone marrow cultures. In the present experiments supernatants from long‐term cultures established in three laboratories were assayed for CSF by colony assay and by radioimmunoassay (RIA). Most samples were devoid of biologic activity but all contained CSF as judged by RIA. Biologic activity was found in the majority of samples after diafiltration to remove low molecular weight inhibitors or 5‐fold concentration by ultrafiltration. Samples that remained inactive in the colony assay were subjected to gel filtration on Sephadex G‐150 to remove potential high molecular weight inhibitors. Biologic activity remained lower than that by RIA in two of three samples tested. Thus, most long‐term cultures appear to contain biologically active CSF but this activity is masked by various types of inhibitors. In addition some media appear to contain material that is only dete

ISSN:0021-9541    

DOI:10.1002/jcp.1041140115

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

年代:1983

数据来源: WILEY

摘要:

AbstractWhen L929 cells are cultured in the abssence of glucose the rate of synthesis of two polypeptides (95,000 and 82,000 Mr) is increased while that of an 85,000 Mrpolypeptide is correspondingly decreased. It has been shown recently that the 85,000 Mrpolypeptide is identical with the heat shock protein that is associated with the Rous sarcoma virus transforming gene product (pp60src). The present study shows that dexamethasone completely inhibits the alterations in the pattern of protein synthesis that would normally ensue following glucose deprivation. In fact, synthesis of the 85,000 Mrpolypeptide and another polypeptide (69,000 M,) that is not glucose regulated are dramatically increased. In contrast, when L929 cells are maintained in ample glucose the effects of dexamethasone are much less dramatic with only one major SDS polyacrylamide gel band (90,000 Mr) being affected. This effect is specific for glucocorticoids. One‐dimensional peptide mapping did not demonstrate any obvious structural relatedness among the 95,000, 90,000, 85,000, and 82,000 Mrpolypeptides. Therefore, the observed changes appear to result from alterations in the rate of protein synthesis rather than from changes in precursor‐product relationships. It is suggested on the basis of this data that glucocorticoids may play a role in modulating the response of cultured cells to glucose deprivation by eliciting a heat shock‐like res

ISSN:0021-9541    

DOI:10.1002/jcp.1041140116

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

年代:1983

数据来源: WILEY

摘要:

AbstractThis study describes the characteristics of hybrids between two closely related rat myoblast lines, which differ both in the ability to express their program of differentiation and in the expression of neoplastic properties. Myogenic, nonneoplastic L6J1‐S cells were hybridized with nonmyogenic, neoplastic L6J1‐N1 cells. Six hybrid clones were isolated and expanded for analysis of myogenic competence, and four of these clones were also evaluated for parameters of transformation, including tumorigenicity, ability to clone in agar, and surface fibronectin. In addition to our analysis of isolated clones, we also assessed myogenic differentiation in colonies representing 226 early hybrid clones. Results of all these analyses demonstrate that the myogenic phenotype is retained and that the tumorigenic/transformed phenotype is suppressed in the hybrids. Furthermore, our results indicate that when the programs for myogenesis and neoplastic transformation are confronted within a single cell, they are expressed as mutually exclusive alternatives. In contrast to these results on myogenic × nonmyogenic L6 hybrids, it has been reported that isolated clones of A9 × L6 exhibited extinction of myogenic competence and retention of transformed properties. We have evaluated myotube formation in over 300 early hybrid clones between A9 and either diploid or subtetraploid L8 rat myoblasts. Our results demonstrate that all of these hybrid clones exhibit extinction regardless of the ploidy of the myoblast parent, and they further indicate that extinction is not a consequence of chromosome loss. These results support the conclusion that in A9 × L6 hybrids, the nonmyogenic, transformed phenotype is do

ISSN:0021-9541    

DOI:10.1002/jcp.1041140117

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

年代:1983

数据来源: WILEY

摘要:

AbstractFourteen methylated nucleosides (N‐2‐dimethylGuo,N‐2‐methylGuo,N‐1‐methylGuo,N‐5‐methylUrd,N‐3‐methylUrd,N‐1‐methylAdo,N‐3‐methylCyd,N‐5‐methylCyd,N‐1‐methyllno,2′‐0methyl‐Cyd,2′‐0‐methylUrd,2′‐0‐methylGuo,2′‐0‐methyllno, and thymidine) and one methylated base (m7Gua) have been identified as normal excretion products of cultured hamster embryo cells. The methylated nucleosides are excreted in the culture media subsequent to RNA turnover. The excretion pattern of the base‐methylated nucleosides was determined by continuous labeling of serum‐stimulated quiescent hamster embryo cells with [3H‐CH3]methionine and measurement of radioactivity in the excreted nucleosides between 23 and 811/2hours after the label was added. These nucleosides accumulate exponentially until a maximum level is reached after 60 hours. These m

ISSN:0021-9541    

DOI:10.1002/jcp.1041140118

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

年代:1983

数据来源: WILEY

摘要:

AbstractThe purpose of this research was morphometric ultrastructure evaluation of the fibers in muscles taking part in the flight of pigeons forced to exercise after a long period of hypodynamia. It was found that following physical exercise, after 12 and 18 months of mobility limitation, there appeared marked qualitative and quantitative changes: a diminution of the volume fraction and number of mitochondria, increase of smooth sarcoplasmic reticulum and sarcoplasm, and a significant decrease of the number of glycogen granules as compared with those after 18 months hypodynamia. The above described changes were more pronounced in the supracoracoideus than in the pectoralis muscle.

ISSN:0021-9541    

DOI:10.1002/jcp.1041140119

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

年代:1983

数据来源: WILEY

摘要:

AbstractThe PG19 mouse melanoma cell line does not respond to the mitogenic effects of insulin either in serum‐deprived quiescent cultures or when growing in hormone‐supplemented serum‐free medium, while melanoma × mouse embryo fibroblast hybrids respond under both conditions. It has been proposed that some growth effects of insulin are mediated by its binding to receptors for insulin‐like growth factors. To determine whether the PG19 cells do not respond to insulin because they lack receptors for MSA (multiplication‐stimulating activity, an insulin‐like growth factor produced by BRL‐3A cultured rat liver cells), we have examined growth effects and receptor binding of MSA in the melanoma and hybrid cells. MSA stimulates [3H]thymidine incorporation in three melanoma × mouse embryo fibroblast hybrid clones but not in the parental melanoma cells. Thus the pattern of response of the melanoma cells and hybrids to MSA directly parallels their response to insulin. The melanoma cells and hybrids all have high‐affinity specific MSA binding sites (KD= 10–27 nM), indicating that the inability of the melanoma cells to respond to MSA is not attributable to a lack of MSA receptors. Insulin competes very poorly for binding of MSA to hybrid clone 7 but is nevertheless able to stimulate [3H]thymidine incorporation in this clone. This strongly suggests that the effects of insulin on [3H]thymidine incorporation in this clone are not mediated by its binding to MSA receptors. Insulin and MSA stimulate protein synthesis and inhibit protein degradation in the hybrids but not in the parental melanoma cells. These results suggest that both insulin and MSA action are blocked in the melanoma cells at a step distal to the binding of either hormone to its cellular receptors but prior to stimulation o

ISSN:0021-9541    

DOI:10.1002/jcp.1041140120

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

年代:1983

数据来源: WILEY

摘要:

AbstractRapidly proliferating, polyclonally stimulated mouse spleen lymphocytes were separated by density‐gradient unit‐gravity sedimentation. The following measurements were made on each fraction: the average intracellular water volume, the distribution of DNA content by flow microfluorometry, the rate of3H‐thymidine incorporation, and the intracellular pH. Fractions of cells with a small average intracellular volume were predominately in G0 or G1 phase of the cell cycle, while fractions of larger cells had higher proportions of cells in S or G2. Multiple regression analysis of the data for both T and B lymphocytes indicated that the intracellular pH of cells in G0, G1, or G2 is around pH 7.2, and that the intracellular pH of cells in S phase of the cell cycle is around p

ISSN:0021-9541    

DOI:10.1002/jcp.1041140121

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

年代:1983

数据来源: WILEY