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  • 11
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Morphology 97 (1955), S. 313-344 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Additional Material: 25 Ill.
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  • 12
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The frequencies of 6-thioguanine-resistant primary clones from the kidneys and skeletal muscles of aging male cohorts of two F1 hybrid strains of Mus musculus varied from 0.59 to 10.96 × 10-5 and did not increase as a function of donor age (up to 40 months). Resistant clones were shown to be severely deficient in the activity of hypoxanthine-guanine phosphoribosyltransferase (EC 2.4.2.8). These deficiencies presumably resulted from molecular alterations at this X-linked locus, including point mutations. No alterations of the X-chromosome were observed at the level of the light microscope. These results are inconsistent with predictions of the intrinsic mutagenesis and protein synthesis error catastrophe theories of aging. They do not rule out, however, somatic mutational theories that invoke comparatively large-scale chromosomal lesions, many of which would be likely to be lethal at the cellular level.
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  • 13
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 122 (1985), S. 171-177 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: A primary cloning technique has been employed for the isolation of nine spontaneously transformed cell lines from mouse skeletal muscle. Four of these lines were isolated after selection for partial resistance to the purine (adenine) analog 2′6′diaminopurine and five were isolated from non-selected control dishes. Four of the nonselected lines and three of the selected lines demonstrated a fibroblastoid morphology in vitro. The other two cell lines (one from each group) were epithelioid. Two of the three selected fibroblastoid lines were found to contain significant quantities of the enzyme 5′nucleotidase (EC3.1.3.5), whereas the four nonselected fibroblastlike lines, one selected fibroblastlike line, and the two epithelioid lines did not. In the two cell lines expressing 5′nucleotidase activity, this expression was stable in the absence of selective pressure. Histochemical staining of mouse skeletal muscle for 5′nucleotidase activity demonstrated positive staining in the cells of small blood vessels and in a subset of the connective tissue cells. The bulk of the skeletal muscle tissue, however, had no detectable 5′nucleotidase activity. We propose that the two cultivatable types of fibroblastoid cell lines represent distinct classes of fibroblastlike cells in vivo, reflecting alternative states of stable cellular differentiation involving 5′nucleotidase expression.
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  • 14
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 125 (1985), S. 192-199 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: rac-1-O-Myristoyl-2-O-acetylglycerol, rac-1-O-palmitoyl-2-O-acetylglycerol, and rac-1-O-oleoyl-2-O-acetylglycerol acted like phorbol myristate acetate and mezerein in stimulating human neutrophil aggregation. Responses to these agents were equally influenced by cytochalasin B, extracellular calcium and magnesium, arachidonate antimetabolites, and procedures that rendered the cells desensitized to other agonists. The compounds also inhibited the binding of [3H]-phorobol myristate acetate to its receptor on neutrophils. Thus, these agents are biologically homologous. They act by binding to a common receptor. This receptor may function physiologically as a transducer for endogenous glycerides that form in cells challenged by other stimuli.
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  • 15
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 124 (1985), S. 131-136 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The Ca++ requirement for in vitro lymphocyte stimulation by lectins is well known and can be demonstrated by the use of Ca++ chelators. In this study, three Ca++ antagonists were examined for their effects on lymphocyte proliferation. [3H]-thymidine incorporation was employed to measure DNA synthesis in several systems. Stimulation and proliferation were achieved by the addition of one of the following: the mitogenic lectin concanavalin A (ConA); the combination of two co-mitogens, the calcium ionophore A23187 and the phorbol ester, 12-0-tetradecanoylphorbol-13-acetate (TPA), neither of which is mitogenic alone; or the non-mitogenic lectin, wheat germ agglutinin (WGA) with TPA. These mitogenic systems were tested for their sensitivity to the Ca++ channel blockers verapamil and nicardipine and the intracellular Ca++ antagonist TMB-8. We found that the ConA and WGA plus TPA treated cells were inhibited approximately 50% by 10 μM verapamil, nicardipine or TMB-8. The stimulation caused by A23187 and TPA was only inhibited by TMB-8 and nicardipine. The inhibitory effects caused by the Ca++ antagonists could not be reversed by the addition of exogenous Ca++ (0.1-1.5 mM), but were reversed by repeated washings in antagonist free media. Using TMB-8 we saw an apparent intracellular Ca++ dependence throughout the G1 phase. Previous studies using Ca++ chelators or Ca++ antagonists suggested an endpoint at about halfway through this period.
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  • 16
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 125 (1985), S. 367-378 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: We have reexamined the possible role of the Na+/H+ antiport in the cellular response by PC12 pheochromaytoma cells to nerve growth factor (NGF). In contrast to previous reports, we observe no activation of Na+/H+ exchange in these cells, using a very sensitive assay based on the measurement of cytoplasmic pH with dimethylfluorescein dextran (Rothenberg et al., J. Biol Chem., 258: 4883-4809, 1983). Our measurements indicate that the PC12 pheochromacytoma cells, under all conditions tested, show a high rate of Na+/H+ exchange. The discrepancy between these observations and previous experiments could be due to differences in cells in different laboratories, but also to changes in cell adhesion induced by NGF. We describe conditions where intracellular pH and rates of Na+ uptake can be measured reliably in PC12 cells with adequate controls for cell adhesion. We conclude that activation of Na+/H+ exchange is neither sufficient nor required for the differentiation of PC12 cells induced by NGF.
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  • 17
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 105 (1980), S. 275-285 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Nerve growth factor (NGF) has previously been shown to increase the rate of adhesion of PC-12 pheochromocytoma cells to cell culture dishes. This increase in the rate of adhesion was postulated to be important in NGF-mediated neurite outgrowth. We now report that epidermal growth factor (EGF) is also able to increase the rate of adhesion of PC-12 cells to cell culture dishes, but does not elicit neurite outgrowth. The dose-response curve for EGF is bell-shaped, in contrast to the more classically shaped dose-response curve obtained with NGF.Tetradecanoyl-phorbol-acetate (TPA), a potent tumor promoter, blocks the EGF-induced increase in adhesion rate of PC-12 cells, but does not alter the NGF-induced increase in adhesion rate. TPA shifts the EGF binding curve to the right for PC-12 cells, but does not alter maximal EGF binding at saturating concentrations of EGF. The binding of NGF to PC-12 cells is not affected by TPA. NGF-induced neurite formation by PC-12 cells is unaffected by TPA, in contrast to the previously reported delay of neurite outgrowth of serum-deprived neuroblastoma cells and NGF-exposed chick embryonic ganglia cells.NGF and EGF both cause a decrease in the number of short microvilli and an increase in the number of long microvilli on PC-12 cells. TPA blocks the decrease in the number of short microvilli in EGF-treated cells, but not in NGF-treated cells. Long microvilli formation is blocked by TPA in both conditions, suggesting the latter are not involved in the increased adhesion rates.
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  • 18
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 107 (1981), S. 385-389 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: TPA stimulates cell cycle activation in both serum-deprived and density-inhibited cultures. The cells reestablish cycle arrest after no more than one generation, and addition of fresh drug produces no further response. However, cells freshly trypsinized can respond with a series of repetitive generations resulting in 3.5-4.0 population doublings over 72 hrs. In kinetic pulse experiments TPA enhanced 3H-thymidine incorporation in densityinhibited cells stimulated by fresh serum but only after markedly suppressing incorporation 8-13 hrs after serum stimulation. When cells arrested by serum deprivation were pretreated with TPA, fresh serum stimulation led to initiation of 3H-TdR incorporation 5 hrs earlier than untreated controls. However, TPA addition at the time of serum stimulation did not lead to a suppression at 8-13 hrs, whereas enhancement was observed during peak incorporation times regardless of whether the cells were pretreated with TPA during serum deprivation. The results support the concept that there can exist within G1 multiple states of responsiveness to phorbol esters. These pharmacologically induced states may be correlated with corresponding physiological states of the G1 phase of cell cycle.
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  • 19
    Electronic Resource
    Electronic Resource
    Philadelphia : Wiley-Blackwell
    Journal of Cellular and Comparative Physiology 55 (1960), S. 275-280 
    ISSN: 0095-9898
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Additional Material: 2 Tab.
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  • 20
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 160 (1994), S. 1-9 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The mechanism by which transforming growth factor beta (TGFβ) exerts growth stimulatory effects was examined in C3H/10T1/2 mouse fibroblasts by study of cell cycle regulation of the retinoblastoma gene product (p110Rb) and transcriptional regulation of the p110Rb-associated transcription factor, E2F. Northern blotting analysis shows that TGFβ and/or epidermal growth factor (EGF) stimulate by three to sixfold the level of Rb mRNA which is also reflected by the increased levels of p110Rb. p110Rb becomes phosphorylated in mid-G1 and further phosphorylated at the G1/S transition. Hyperphosphorylation of p110Rb by TGFβ can be observed when cells are in S phase. TGFβ stimulates by three to fourfold the activity of cdk2 kinase consistent with the observed phosphorylation of p110Rb and also with the possibilit that the kinase is involved in phosphorylating p110Rb close to the G1/S transition. Thus, TGFβ as a growth stimulator induces, as does EGF, the phosphorylation of p110Rb during cell cycle progression. Transient transfection of E2F promoter constructs was used to analyze the effect of TGFβ on the modulation of E2F-mediated transcription. The data revealed that TGFβ can stimulate wild-type adenoviral E2 promoter activity by 12-fold. Taken together, TGFβ-induced phosphorylation of p110Rb in mouse fibroblasts appears to exert a positive regulatory function upon genes that have a pivotal role in the G1/S transition of the cell cycle. © 1994 Wiley-Liss, Inc.
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