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Biomedical subjects

T G Cotter

Publications and source records attributed to T G Cotter.

At least 73 records · Page 4Linked to original sources
PubMed1996

The repression of apoptosis by activated abl oncogenes in chronic myelogenous leukaemia.

The formation of the unique fusion gene, bcr-abl, and the resultant increase in abl tyrosine kinase activity, is seen as the major driving force in the initiation of chronic myelogenous leukaemia (CML). The deregulation of abl tyrosine kinase activity, brought about by the binding of a portion of the Scr molecule to the SH2 regulatory domain of abl, appears to play a role in promoting resistance to drug-induced apoptosis. Thus the large increase In mature myeloid cells seen in CML could be the direct result of the suppression of apoptosis by the bcr-abl fusion protein. The role and contribution of apoptosis in the progression of CML and the possible role of antisense oligonucleotides to the bcr-abl gene as therapeutic agents is discussed.

Apoptosis↗
PubMed1995

Inhibition of apoptosis by antioxidants in the human HL-60 leukemia cell line.

Cell death via apoptosis is an important event involved in a number of immunological processes. Recently, apoptosis has been associated with oxidative stress in a number of cell systems. Here we assessed the inhibitory capacity of different antioxidants on UV- and drug-induced apoptosis in the human leukemic cell line, HL-60. We found that the oxygen radical scavenger, BHA, the radioprotector cysteamine and the metal chelators, pyrrolidinedithiocarbamate (PDTC), diethyldithiocarbamate (DEDTC), and dimethyldithiocarbamate (DMDTC), were able to significantly inhibit nuclear fragmentation and reduce the formation of apoptotic bodies in UV-irradiated human leukemic cells. Both BHA and PDTC were found to reduce DNA fragmentation as assessed by in situ DNA nick-end labelling and quantification thereof using fluorescence flow cytometry. In addition to inhibiting UV-induced apoptosis, PDTC was also capable of reducing the amount of apoptosis induced by a range of cytotoxic drugs, such as actinomycin-D, camptothecin, etoposide, and melphalan, whereas BHA and cysteamine were not as effective in these cases after more than four hours in culture when compared to PDTC. To further elucidate the working mechanism of PDTC, we have looked at the effect of PDTC on DNA fragmentation in isolated nuclei, under conditions that promote activation of endogenous endonuclease involved in apoptosis. In contrast to ZnCl2, a potent inhibitor of endonuclease activity, PDTC was unable to inhibit DNA-ladder formation in this assay. Taken together, these results indicate that oxygen radicals may have a central role to play in the induction of apoptosis and that dithiocarbamates can serve as potent inhibitors of apoptosis induced by a wide variety of stimuli.

Antioxidants↗
PubMed1995

Regulation of the Fas apoptotic cell death pathway by Abl.

Relatively little is known about oncogene involvement in the regulation of Fas-mediated apoptosis. Inhibition of Fas-induced cell death by the bcl-2 oncogene has been demonstrated to be only partial. In light of a growing body of evidence for the Abl kinase as a negative regulator of cell death, we sought to determine whether Abl expression could protect against Fas-mediated cell death. To address this question, we utilized two separate strategies. In the first, we expressed human Fas in K562, a chronic myelogenous leukemia cell line, which constitutively expresses bcr-abl and examined the effects of Fas ligation in these cells. Fas-positive K562 transformants (K562.Fas) were found to be protected against Fas-mediated cell death. However, down-regulation of Bcr-Abl protein levels in K562.Fas cells using antisense oligonucleotides targeted to bcr-abl mRNA rendered these cells highly susceptible to Fas-induced death. In the second approach we utilized a Fas-positive HL-60 cell line, which we transfected with a temperature-sensitive mutant of v-Abl. HL-60.v-Ablts transfectants were found to be protected from Fas-induced apoptosis at the permissive but not the restrictive temperature for the Abl kinase. Taken together, these observations identify the Abl kinase as a negative regulator of Fas-mediated cell death. Since Abl was also found to block apoptosis mediated by ceramide, a recently proposed downstream effector of the apoptotic pathway initiated by Fas, we propose that Abl exerts its protective effects downstream of the early Fas-initiated signaling events.

Antigens, Surface↗
PubMed1995

Cell death (apoptosis) in cell culture systems.

In this review we describe the process of cell death known as apoptosis, outlining the key morphological and biochemical features. We also identify the stress elements in bioreactors that drive cells to their death. Finally, we outline methods that might be used to enhance the life span and increase the robustness of cells in culture.

Animals↗
PubMed1995

BCR-ABL: an anti-apoptosis gene in chronic myelogenous leukemia.

The expression of bcr-abl in chronic myelogenous leukemia leads to a large increase in the generation of mature myeloid cells. The key biochemical alteration in this disease is an increased Abl kinase activity. This up-regulation in activity is mediated through the binding of a portion of the Bcr molecule to the SH2 regulatory domain of the Abl protein. One effect of this alteration is a marked increase in resistance to drug induced cell death by apoptosis. This resistance can be overcome with the use of appropriate antisense oligonucleotides to the bcr-abl gene. The role and contribution of apoptosis to the development of the disease and the prospect of using antisense oligonucleotides as therapeutic agents is discussed.

Animals↗
PubMed1994

Apoptosis or necrosis: intracellular levels of glutathione influence mode of cell death.

The effect of lowering intracellular glutathione (GSH) concentrations on the toxicity of alkylating agents, and RNA synthesis inhibitor and topoisomerase 1 and 2 inhibitors to a number of human leukaemic cell lines were evaluated. By using the GSH synthesis inhibitor DL-buthionine-(S,R)-sulfoximine (BSO), GSH levels were artificially reduced. Cells with low GSH concentrations were exposed to a number of cytotoxic agents and the resultant mode of cell death was analysed using morphological and biochemical criteria. It was found that untreated cells exposed to the above drugs underwent apoptosis to varying extents. However, the toxicity of alkylating agents was dramatically increased to all cell lines on lowering GSH levels, with the mode of cell death switching from apoptosis to necrosis. The reduction of GSH levels had no effect on the toxicity of actinomycin-D, camptothecin or etoposide, nor did it affect the mode of cell death induced by these agents. These observations suggest that modulation of GSH levels effect the toxicity of alkylating agents and that GSH influences the mode of cell death induced by alkylating agents.

Alkylating Agents↗
PubMed1994

BCR-ABL maintains resistance of chronic myelogenous leukemia cells to apoptotic cell death.

Apoptosis is the major form of cell death associated with the action of chemotherapeutic agents on tumor cells, and therefore the expression of genes that interfere with apoptosis can have important consequences for the efficacy of therapeutic approaches. Here we show that K562, a chronic myelogenous leukemia (CML) cell line expressing the BCR-ABL fusion protein, are resistant to the induction of apoptosis by a number of agents and conditions. Antisense oligodeoxynucleotides corresponding to the translation start of bcr downregulate bcr-abl protein in these cells and render them susceptible to induction of apoptosis by chemotherapeutic agents or serum deprivation. Expression of a temperature sensitive v-Abl protein reverses the effects of the antisense oligonucleotides, such that the cells remain resistant to apoptosis at the permissive temperature. These data indicate that bcr-abl acts as an anti-apoptosis gene in CML cells and suggests that the effect is dependent on the abl kinase activity in this chimeric protein. Inhibition of bcr-abl to render CML cells susceptible to apoptosis can be combined with therapeutic drugs and/or treatment capable of inducing apoptosis to provide an effective strategy for elimination of these cells.

Apoptosis↗
PubMed1994

Dicing with death: dissecting the components of the apoptosis machinery.

Apoptosis, a mode of cell death commonly observed when death is a desirable or programmed event, has several characteristic structural features. These features appear to be induced by a range of gene products which, together, supervise and participate in the controlled dismantling of the cell. In this article the molecular components of the apoptotic machinery and the proteins implicated in the regulation of this mechanism of cell death are discussed.

Apoptosis↗
PubMed1994

Zinc inhibits UV radiation-induced apoptosis but fails to prevent subsequent cell death.

Zinc ions inhibit the morphological and DNA fragmentation features of apoptosis in a number of systems. HL-60 cells pretreated with zinc and exposed to UV irradiation maintained their normal morphology for up to 8 h, whereas non-zinc-treated cells underwent extensive apoptosis. Zinc pretreatment also inhibited both single and double-stranded DNA fragmentation, which is characteristic of apoptosis. The most effective zinc concentration that blocked apoptosis over short incubation periods (up to 8 h) was also the most toxic over extended time periods (> or = 12 h). The mechanism of cell death at these longer time periods was akin to necrosis, but occurred in the absence of any DNA fragmentation. The effects of the nuclease inhibitor aurintricarboxylic acid (ATA) was also examined on UV-induced apoptosis in HL-60 cells. ATA had no toxic effects over the concentration range tested, but also failed to prevent DNA fragmentation in whole cells. Further analysis showed that it effectively inhibited DNA fragmentation in isolated nuclei.

Apoptosis↗
PubMed1994

The abl oncogene family and apoptosis.

The role of the abl oncogene family in cellular transformation has been well established, but knowledge of its role in apoptosis is limited. Recent studies demonstrate that it may act as a suppressor of apoptosis in certain circumstances. The growth factor independence conferred on IL-3 dependent myeloid progenitor cell lines following v-Abl transformation is due to the suppressive effects of this oncogene on apoptosis. Similarly, inhibition of the deregulated activity of the p210(bcr-abl) protein in both myeloid progenitor lines and CML granulocytes has proven effective in reversing resistance to apoptosis in such cells. The Bcr-Abl fusion protein might therefore promote myeloid expansion by suppression of apoptotic cell death rather than through promoting proliferation. While oncogenic forms of Abl appear to be anti-apoptotic, the function of c-Abl remains elusive. Through the elucidation of the roles in cell growth and survival of the Abl family members we may gain valuable insights into the regulation of apoptosis and the mechanisms of oncogenesis.

Journal Article↗
PubMed1993

An immune suppressive factor derived from esophageal squamous carcinoma induces apoptosis in normal and transformed cells of lymphoid lineage.

An immunosuppressive factor produced by an esophageal squamous carcinoma cell line mediates profound irreversible suppression of in vitro proliferative responses of lymphoid cells. Exposure of activated normal PBL to the immune suppressive factor (ISF) resulted in the induction of an irreversible anergic state with apoptosis evident in 20% of those cells. Flow cytometric cell cycle analysis of mitogenically stimulated normal lymphocytes exposed to the ISF revealed that despite exhibiting full activation status (IL-2 production, IL-2R, and transferrin receptor expression) PBL were arrested at the G1/S interphase of the cell cycle. Transformed lymphoid cell lines, NSO and JURKAT, displayed morphologies characteristic of apoptosis within 24 h of exposure to the ISF. Flow cytometric cell cycle analysis of the JURKAT cells incubated with ISF revealed that > 90% of these cells had undergone apoptosis within 24 h. Agarose gel electrophoresis of DNA extracted from the ISF-treated lymphoid cells resolved a DNA fragmentation pattern characteristic of apoptosis in both the NSO cells and to a lesser extent in the activated PBL exposed to the ISF but not in control cells. In JURKAT cells stimulated with anti-CD3 antibodies, Ca2+ mobilization was markedly enhanced in those cells exposed to ISF. Also, ISF independently induced a calcium flux in JURKAT cells. Induction of programmed cell death by ISF may account for the in vivo immune suppression local to the tumor site in squamous carcinoma of the esophagus.

Aged↗
PubMed1993

DNA fragmentation induced by cytotoxic T lymphocytes can result in target cell death.

Cytotoxic T lymphocyte (CTL)-mediated lysis is accompanied by fragmentation of target cell DNA into an oligonucleosome ladder, a hallmark of apoptosis. Is this a fortuitous coincidence, or could CTL be inducing lysis by activation of the suicide signal? In this report we demonstrate that CTL-mediated target cell death can be blocked with the drug aurintricarboxylic acid (ATA). The abrogation of death correlates with the inhibition of DNA fragmentation. While ATA prevented DNA fragmentation, it failed to significantly alter protein, RNA, or DNA synthesis in the cell lines over the dose range used. In addition, there was no inhibition of cell-cell interaction or granule exocytosis during CTL-mediated killing. ATA also significantly inhibited the cytolysis and DNA fragmentation mediated by isolated cytolytic granules, as well as the granular protein fragmentin. We developed an assay in which target cells could be separated from CTL after binding and programming for lysis. Once they had received the "kiss of death," target cells could be rescued from lysis (as indicated by inhibition of DNA fragmentation and increased target cell viability) by treatment with ATA. These results suggest that ATA blocks target cell death by inhibition of DNA fragmentation, and further, that chromatin degradation is a cause rather than a result of cell death in CTL-mediated lysis.

Animals↗
PubMed1992

Role for c-myc in activation-induced apoptotic cell death in T cell hybridomas.

Immature T cells and some T cell hybridomas undergo apoptotic cell death when activated through the T cell receptor complex, a phenomenon that is probably related to antigen induced negative selection of developing T cells. This activation-induced apoptosis depends on active protein and RNA synthesis in the dying cells, although none of the genes required for this process have previously been identified. Antisense oligonucleotides corresponding to c-myc block the constitutive expression of c-Myc protein in T cell hybridomas and interfere with all aspects of activation-induced apoptosis without affecting lymphokine production in these cells. These data indicate that c-myc expression is a necessary component of activation-induced apoptosis.

Animals↗