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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ABSTRACT: As a traditional Chinese medicine, the sea buckthorn (Hippophae rhamnoides L.) has a long history in the treatment of ischemic heart disease and circulatory disorders. However, the active compounds responsible for and the underlying mechanisms of these effects are not fully understood. In this article, isorhamnetin pretreatment counteracted H(2)O(2)-induced apoptotic damage in H9c2 cardiomyocytes. Isorhamnetin did not inhibit the death receptor-dependent or extrinsic apoptotic pathways, as characterized by its absence in both caspase-8 inactivation and tBid downregulation along with unchanged Fas and TNFR1 mRNA levels. Instead, isorhamnetin specifically suppressed the mitochondria-dependent or intrinsic apoptotic pathways, as characterized by inactivation of caspase-9 and -3, maintenance of the mitochondrial membrane potential (ΔΨm), and regulation of a series of Bcl-2 family genes upstream of ΔΨm. The anti-apoptotic effects of isorhamnetin were linked to decreased ROS generation. H(2)O(2) activated ERK and p53, whereas isorhamnetin inhibited their activation. ERK overexpression overrode the isorhamnetin-induced inhibition of the intrinsic apoptotic pathway in H9c2 cardiomyocytes, which indicated that an ERK-dependent pathway was involved. Furthermore, N-acetyl cysteine (a potent ROS scavenger) could attenuate the H(2)O(2)-induced apoptosis. However, PD98059 (an ERK-specific inhibitor) could not effectively antagonize ROS generation, which indicates that ROS may be an upstream inducer of ERK. In conclusion, isorhamnetin inhibits the H(2)O(2)-induced activation of the intrinsic apoptotic pathway via ROS scavenging and ERK inactivation. Therefore, isorhamnetin is a promising reagent for the treatment of ROS-induced cardiomyopathy.Journal of Cellular Biochemistry 09/2011; 113(2):473-85. · 3.06 Impact Factor
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ABSTRACT: Wogonin, one of flavonoid compounds isolated from Chinese herbal plants Scutellaria baicalensis Georgi, has been recognized as a potent anti-cancer agent acting through control of growth, differentiation and apoptosis. However, the underlying molecular mechanism of its anti-cancer activity remains to be further elucidated. In this study, we investigated the potential role of wogonin in the induced-apoptosis of human breast cancer cells MCF-7. Wogonin was found to inhibit the proliferation of MCF-7 in a concentration and time-dependent manner, notably wogonin could induce G1 phase arrest of MCF-7 cells. Wogonin-induced apoptosis was accompanied by a significant decrease of the Bcl-2 and survivin and increase of Bax and p53. Wogonin also increased active apoptosis forms of caspases-3, -8, -9 significantly. Z-DEVD-fmk, a specific caspase-3 inhibitor, significantly inhibited wogonin-induced cell apoptosis. Wogonin also suppressed the phosphorylation of PI3K/Akt and induced phosphorylation of ERK. PD98059, a specific ERK inhibitor, significantly blocked wogonin-induced apoptosis. On the other hand, LY294002, a specific PI3K inhibitor, significantly increased wogonin-induced cell apoptosis. Further study indicated that LY294002 not only down-regulated the expression of survivin alone, but also enhanced the inhibition of survivin expression combined with wogonin. In conclusion, the pro-apoptotic effect of wogonin is mediated through the activation of ERK and the activation of caspases, and is correlated with the block of the PI3K/Akt/survivin signal pathways in MCF-7 cells.International immunopharmacology 12/2011; 12(2):334-41. · 2.21 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