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  • 1
    Electronic Resource
    Electronic Resource
    Intracellular processing of 125I-epidermal growth factor in rat embryo fibroblasts (1982)
    New York, N.Y. : Wiley-Blackwell
    Journal of Cellular Biochemistry 20 (1982), S. 259-276 
    Details
    ISSN: 0730-2312
    Keywords: epidermal growth factor ; intracellular processing ; endocytosis ; lysosomes ; degradation ; internalization ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: The intracellular fate of endocytosed 125I-epidermal growth factor was examined in Rat-1 fibroblasts. Cells were pulse-labeled for 5 min in 125I-EGF and chased for 3 hr with an excess of unlabeled EGF. At various times after application of the cold chase, cells were harvested and processed for isopycnic gradient centrifugation on Percoll gradients. Within the period of the 125I-EGF pulse, about 50% of the 125I activity appeared in an organelle containing peak in the gradients. By 20 min after application of the cold chase, 125I activity in the organelle peak began to decrease, and the decrease continued over the next few hours. The 125I activity which exited from its organelle-associated location appeared to be present in the cytosol and was apparently not confined within organelles. Lysosomotropic amines inhibited the egress of 125I activity from the organelle compartment. The 125I activity from both organelle and nonorganelle compartments reacted as completely as authentic 125I-EGF with anti-EGF antibodies and was similar in size to authentic 125I-EGF. Little or no intracellular low molecular weight 125I-containing compounds were detected, although they accumulated in the culture medium. Analytical isoelectric focusing revealed that the organelle-bound form of endocytosed 125I-EGF was more acidic than authentic 125I-EGF and, upon exiting from the organelle compartment, was processed to an even more acidic form. It was the second macromolecular form of processed 125I-EGF that was ultimately degraded to low molecular weight compounds which were then externalized from the cells.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcb.240200306
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  • 2
    Electronic Resource
    Electronic Resource
    Mechanism of synergistic induction of DNA synthesis by epidermal growth factor and tumor promoters (1981)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 108 (1981), S. 417-425 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Evidence is presented to support our previously proposed hypothesis that the hyperplastic effect of tumor promoters is related to their ability to alter existing physiological levels of growth factors in target tissues. Epidermal growth factor and phorbol ester tumor promoters acted synergistically at low (0.001-0.05 ng/ml) but not high (〉 0.1 ng/ml) EGF concentrations to induce DNA synthesis in cultured Rat-1 fibroblast cells. The degree of synergism correlated with the tumor-promoting ability of the compound. The tumor promoters decreased 125I-EGF binding to cellular receptors in a dose-dependent manner that also correlated with the tumor-promoting ability of the compound. The inhibition of EGF binding by phorbolester compounds resulted in a decrease in the amount of EGF degraded as compared to control cultures. At limiting EGF concentrations, the sparing of EGF degradation resulted in an increase in the amount of EGF remaining in the culture medium after 12 h of incubation and a concomitant increase in the amount of EGF bound to phorbol ester-treated cells at this time as compared to control cultures. The ability of a phorbol ester compound to alter EGF degradation and to stimulate DNA synthesis synergistically with EGF correlated with the tumor-promoting ability of the compound and occurred only at low EGF concentrations.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041080316
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  • 3
    Electronic Resource
    Electronic Resource
    Residual inhibition of epidermal growth factor binding by pancreatic secretagogues and phorbol ester in rat pancreas (1985)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 124 (1985), S. 344-348 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Cholecystokinin-octapeptide (CCK8) inhibits 125I-labeled epidermal growth factor (EGF) cell-associated radioactivity in pancreatic acini, ostensibly as a result of its ability to mobilize cellular Ca2+. The phorbol ester tetradecanoyl phorbol acetate (TPA), a compound that activates protein kinase C, mimics the inhibitory action of CCK8. In the present study we examined the relationship between occupancy of the cholecystokinin (CCK) receptor, the subsequent inhibition of EGF binding, and the potential role of C-kinase activation in mediating this inhibition. Proglumide and dibutyryl cyclic GMP (dbGMP), two distinct competitive antagonists of CCK8, reversed the inhibitory actions of CCK8. Analysis of steady-state saturation kinetics of 125I-EGF binding indicated that CCK8 decreased the apparent affinity of the EGF receptor, mainly as a result of a marked decrease in the amount of internalized ligand. TPA also inhibited 125I-EGF internalization. Removal of CCK8 and TPA from incubation medium did not abolish their inhibitory actions. Carbachol, but not bombesin, exerted a similar residual inhibitory effect. It is suggested that in addition to acting via Ca2+, certain pancreatic secretagogues may also act through C-kinase to regulate EGF binding.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041240226
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  • 4
    Electronic Resource
    Electronic Resource
    Regulation of DNA replication by serum and the transforming function in cultured rat fibroblasts transformed by Rous sarcoma virus (1979)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 99 (1979), S. 207-216 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The onset and rate of semiconservative DNA replication were measured in stimulated cultured rat fibroblasts and their Rous sarcoma virus-transformed derivatives after a period of serum deprivation. Rat-1 (tsLA24/RSV) cells initiated DNA synthesis following a shift to the permissive temperature or addition of serum at the non-permissive temperature. Their rate of DNA replication was unaffected by the presence of serum at the permissive temperature, however, there was a serum requirement at the non-permissive temperature. The transition probability was less at the permissive temperature, independent of serum, than at the non-permissive temperature in the presence of serum. The amount of DNA induced to replicate by addition of serum at the non-permissive temperature or by a shift to the permissive temperature was similar. Using the untransformed Rat-1 cells and these cells transformed by wild-type RSV (Rat-1 (wt/RSV)), it was confirmed that the rate of entry into S phase (transition probability) was always lower in the transformed cell line at both 39° and 35°. In both cell lines the rate of DNA replication was independent of temperature, but the onset was delayed at the lower temperature. These results indicate that in the cell lines examined, (1) serum was able to commit the cells to replicate DNA (alter the transition probability) in both transformed and untransformed cells, but the transforming function was able to supplant a serum-dependent process during G1 necessary for the initiation of DNA replication, and (2) the effects of the transforming function and serum factor(s) on the alteration of the transition probability are not additive, suggesting that the transforming function initiates a process which acts at the level of the commitment to DNA replication which may render the normal serum-related control mechanisms ineffective in the regulation of growth.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1040990207
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  • 5
    Electronic Resource
    Electronic Resource
    Effects of the tumor promoter TPA on the induction of DNA synthesis in normal and RSV-transformed rat fibroblasts (1979)
    New York, N.Y. : Wiley-Blackwell
    Journal of Supramolecular Structure 12 (1979), S. 63-72 
    Details
    ISSN: 0091-7419
    Keywords: tumor promoter ; DNA synthesis ; transformed cells ; serum stimulation ; Life Sciences ; Molecular Cell Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Induction of DNA synthesis by the tumor promoter tetradecanoyl phorbol acetate (TPA) was studied in a line of cultured rat fibroblasts (Rat-1) and their ffRous sarcoma virus-transformed derivative (Rat-1(RSV)). Following serum deprivation for 54 h to achieve quiescene, semiconservative DNA replication was measured by incubation of cells in BrdUrd and FdUrd after serum stimulation in the presence or absence of TPA. Optimal concentrations of TPA (0.1-0.5 μg/ ml) in serum-free medium induced a small increase (10-15%) in the amount of DNA made over a 30-h period in both Rat-1 and Rat-1 (RSV) cells. When Rat-1 cells were stimulated by a 4-h serum pulse, 30% of the DNA was replicated by 30 h. If the serum pulse was follwed by TPA addition, 702% DNA replication wass observed. If the serum pulse was preceded by TPA addition, the onset of DNA synthesis waas delayed by several hous, but stimulation of DNA synthesis occurred. In contrast, the Rat-1 (RSV) cells did not show an increase in DNA synthesis induced by TPA in similar protocols, but the serum-induced onset on DNA synthesis was delayed by several hours in the presence of TPA. Therefore, TPA acts as a co-inducer of DNA synthesis in the Rat-1 but not in the Rat-(RSV) cells. The parent alcohol, phorbol, was inactive in Rat-1 cells, but delayed the onset of DNA synthesis in the Rat(RSV) cells. We conclude that the co-inducing and delaying activities of TPA on DNA synthesis appear to be distinct and to act at different points in the G1 phase of the cell cycle.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jss.400120107
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