Polyamine depletion inhibits etoposide-induced NF-kappaB activation in transformed mouse fibroblasts.
ABSTRACT In a previous research, we have shown that adequate levels of polyamines are required in transformed mouse fibroblasts for the correlated activations of MAPK subtypes (ERK and JNK) and caspases induced by etoposide and leading to apoptosis. We report now that the treatment of fibroblasts with etoposide also elicited a progressive and sustained increase of NF-kappaB activation. The DNA binding activity of p65 NF-kappaB subunit was increased up to approximately 4-fold and was accompanied by enhancement of p65 phosphorylation. A two days pre-treatment of fibroblasts with alpha-difluoromethylornithine (DFMO), which caused polyamine depletion, provoked a slight activating effect when given alone, but markedly inhibited the etoposide-induced increases in p65 DNA binding and phosphorylation. The NF-kappaB inhibiting effect of DFMO was prevented by the addition of exogenous putrescine, which restored the intracellular content of polyamines. Selective inhibitors of the etoposide-stimulated MAPK subtypes also reduced NF-kappaB activation. Moreover, pharmacological NF-kappaB inhibition reduced the increase in caspase activity and cell death elicited by etoposide, suggesting that NF-kappaB is involved in signaling to apoptosis. The results of the present study, together with our previous findings, suggest that polyamines play a permissive role in the pathways triggered by etoposide and leading to cell death of fibroblasts, by supporting the activation of MAPKs, NF-kappaB and caspases.
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Article: Polyamines and apoptosis.[Show abstract] [Hide abstract]
ABSTRACT: The natural polyamines putrescine, spermidine and spermine are in multiple ways involved in cell growth and the maintenance of cell viability. In the course of the last 15 years more and more evidence hinted also at roles in gene regulation. It is therefore not surprising that the polyamines are involved in events inherent to genetically programmed cell death. Following inhibition of ornithine decarboxylase, a key step in polyamine biosynthesis, numerous links have been identified between the polyamines and apoptotic pathways. Examples of activation and prevention of apoptosis due to polyamine depletion are known for several cell lines. Elevation of polyamine concentrations may lead to apoptosis or to malignant transformation. These observations are discussed in the present review, together with possible mechanisms of action of the polyamines. Contradictory results and incomplete information blur the picture and complicate interpretation. Since, however, much interest is focussed at present on all aspects of programmed cell death, a considerable progress in the elucidation of polyamine functions in apoptotic signalling pathways is expected, even though enormous difficulties oppose pinpointing specific interactions of the polyamines with pro- and anti-apoptotic factors. Such situation is quite common in polyamine research.Journal of Cellular and Molecular Medicine 01/2005; 9(3):623-42. · 4.75 Impact Factor
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ABSTRACT: Polyamines are important multifunctional cellular components and are classically considered as mediators of cell growth and division. Recently polyamines have been also implicated in cell death. Now it appears that polyamines are bivalent regulators of cellular functions, promoting proliferation or cell death depending on the cell type and on environmental signals. This review draws a picture about the role of polyamines in signalling pathways related to apoptotic cell death and the proposed molecular targets of these polycations at the level of the apoptotic cascade. Solid evidence indicates that polyamines may affect the mitochondrial and postmitochondrial phases of apoptosis, by modulating cytochrome c release from mitochondria and activation of caspases. Recently, polyamines have been also implicated in the regulation of the premitochondrial phase of apoptosis, during which upstream apoptotic signal transduction pathways are activated. The studies reviewed here suggest that polyamines may participate in loops involving interaction with signal transduction pathways and activation/expression of proteins that may control cell death or cell growth.Amino Acids 01/2005; 27(3-4):359-65. · 3.91 Impact Factor
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ABSTRACT: In previous studies, polyamine depletion by DFMO (alpha-difluoromethylornithine)-treatment reduced H(2)O(2)-induced apoptotic cell death by reduction of ferric ion uptake. In the present study, we analyzed the reduction of radiation-induced cell death by polyamine depletion. Exposure of HT29 cells to radiation induced severe cell death, but when cells were pretreated with DFMO, a specific inhibitor of polyamine biosynthesis, radiation-induced cell death was reduced to 50-60% of control. Cell cycle analysis showed that, in these cells, the time to reach the G(2)/M phase arrest was delayed for 20-24 h compared to the control cells, at which stage the fate of cells exposed to ionizing radiation is determined. DFMO-treated cells also showed a low level of thioredoxin, which is a high-level determinant of the cellular fate. To investigate the relationship between the G(2)/M phase arrest and the reduction of thioredoxin caused by polyamine depletion, we also analyzed thioredoxin-antisensed (asTRX) HT29 cells as for DFMO-treated cells. In asTRX-transfected cells, the gamma-irradiation-induced G(2)/M phase arrest was also significantly delayed and radiation-induced cell death was profoundly reduced, as in the DFMO-treated cells. Both sets of cells showed a decrease of cyclin D1 and an increment of HSP25, which are involved in radiation-induced cell cycle progress. Overall, these results suggest that polyamines are essential for normal cell death of HT29 cells triggered by gamma-radiation and that this is partially mediated by the regulation of thioredoxin expression.Cell Biology and Toxicology 04/2006; 22(2):137-47. · 2.34 Impact Factor