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Query: UNIPROT:P10415 (Bcl-2)
 33,771 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Endothelial cells play a central role in the inflammatory process. Tumor necrosis factor-alpha (TNF) is a multifunctional cytokine which elicits many of the inflammatory responses of endothelial cells. While TNF directly causes apoptosis of tumor cells and virally infected cells, normal cells are generally resistant. However, most resistant cells, including human endothelial cells, can be rendered susceptible to TNF by inhibiting RNA or protein synthesis. This finding suggests that TNF provides a cell survival signal in addition to a death signal. We have previously cloned a human Bcl-2 homologue, A1, and shown that it is specifically induced by proinflammatory cytokines but not by endothelial growth factors. In this study, we show that retroviral-mediated transfer of the A1 cDNA to a human microvascular endothelial cell line provides protection against cell death initiated by TNF in the presence of actinomycin D. The induction of A1 by TNF in this system is mediated via a protein kinase C pathway. Since TNF signaling has also been shown to proceed via ceramides, we tested whether exogenous ceramides could induce A1. Our findings indicate that ceramides do not induce A1 but do up-regulate c-jun and induce endothelial death. Ceramide-activated endothelial death is also inhibited by A1, suggesting that TNF may initiate divergent survival and death pathways via separate lipid second messengers.
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PMID:Endothelial cell death induced by tumor necrosis factor-alpha is inhibited by the Bcl-2 family member, A1. 891 Feb 86

Proteases are now firmly established as major regulators of the "execution" phase of apoptosis. Here, we examine the role of proteases and their relationship to ceramide, a proposed mediator of apoptosis, in the tumor necrosis factor-alpha (TNF-alpha)-induced pathway of cell death. Ceramide induced activation of prICE, the protease that cleaves the death substrate poly(ADP-ribose) polymerase. Bcl-2 inhibited ceramide-induced death, but not ceramide generation. In contrast, Cytokine response modifier A (CrmA), a potent inhibitor of Interleukin-1 beta converting enzyme and related proteases, inhibited ceramide generation and prevented TNF-alpha-induced death. Exogenous ceramide could overcome the CrmA block to cell death, but not the Bcl-2 block. CrmA, however, did not inhibit the activation of nuclear factor (NF)-kappa B by TNF-alpha, demonstrating that other signaling functions of TNF-alpha remain intact and that ceramide does not play a role in the activation of NF-kappa B. These studies support a distinct role for proteases in the signaling/activation phase of apoptosis acting upstream of ceramide formation.
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PMID:Cytokine response modifier A (CrmA) inhibits ceramide formation in response to tumor necrosis factor (TNF)-alpha: CrmA and Bcl-2 target distinct components in the apoptotic pathway. 905 48

Recent evidence suggests that untimely retinoblastoma protein (RB) dephosphorylation and/or proteolytic degradation might provide key events down-stream cysteine protease (caspase) activation in apoptosis induction. We have dealt with this issue by studying apoptosis induced by N-hexanoylsphingosine (C6-Cer) in CHP-100 human neuroepithelioma cells, maintained in complete growth medium. We report that C6-Cer-induced apoptosis occurred predominantly in G1/S phases of the cycle and was associated with RB dephosphorylation, in the setting of negligible Bcl-2 expression. Apoptosis was also associated with poly(ADP-ribose) polymerase (PARP) cleavage, thus indicating activation of CPP32/Yama/apopain (caspase-3); however, while the tripeptide caspase inhibitor Z-Val-Ala-DL-Asp-fluoromethylketone was able to prevent both C6-Cer-induced PARP cleavage and apoptosis, it was ineffective in preventing RB dephosphorylation. Moreover proteolytic RB cleavage occurred only to a marginal extent after C6-Cer treatment. These results indicate that apoptosis induced by ceramide in CHP-100 cells is caspase-mediated, but RB post-translational modification does not provide a key step, downstream caspase activation, in apoptosis execution.
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PMID:Ceramide-induced apoptosis is mediated by caspase activation independently from retinoblastoma protein post-translational modification. 950 Oct 10

Ceramide, a product of sphingomyelin turnover, is a novel lipid second messenger that mediates important cellular functions including proliferation, differentiation and apoptosis. This study demonstrates that the CPP32/Yama protease was activated during apoptosis induced by the membrane-permeable second messenger C2-ceramide in HL-60 cells. We also found that the addition of a specific tetrapeptide inhibitor of CPP32/Yama, Ac-DEVD-CHO, provided an effective protection against ceramide-induced cell death. These results suggested that CPP32/Yama has a central role in ceramide-mediated apoptosis. Furthermore a wide variety of cytokines were examined for their effect on ceramide-induced apoptosis. Only transforming growth factor beta1 (TGF-beta1) (1 ng/ml) exerted significant prevention of apoptosis induced by C2-ceramide, or by sphingomyelinase (increases intracellular ceramide). Consistently, TGF-beta1 abrogated the cleavage of poly(ADP-ribose) polymerase and the production of the CPP32/Yama active subunit, p17. However, TGF-beta1 treatment did not cause growth inhibition or alter the level of cyclin-dependent kinase inhibitor p27. It suggests that the preventive effect of TGF-beta1 is not mediated by growth arrest. Interestingly, we found that TGF-beta1 prevented the C2-ceramide-caused decrease of Bcl-2 protein. We thus propose that TGF-beta1 rescues ceramide-induced cell death, possibly by maintaining the constant level of Bcl-2, thereby abolishing CPP32/Yama protease activation.
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PMID:Transforming growth factor beta1 attenuates ceramide-induced CPP32/Yama activation and apoptosis in human leukaemic HL-60 cells. 958 40

Prior investigations document that proliferative signaling cascades, under some circumstances, initiate apoptosis, although mechanisms that dictate the final outcome are largely unknown. In COS-7 cells, ceramide signals Raf-1 activation through Ras (Zhang, Y., Yao, B., Delikat, S., Bayoumy, S., Lin, X. H., Basu, S., McGinley, M., Chan-Hui, P. Y., Lichenstein, H., and Kolesnick, R. (1997) Cell 89, 63-72), but not apoptosis. However, expression of small amounts of the pro-apoptotic Bcl-2 family member, BAD, conferred ceramide-induced apoptosis onto COS-7 cells. Ceramide signaled apoptosis in BAD-expressing cells by a pathway involving sequentially kinase suppressor of Ras (KSR)/ceramide-activated protein kinase, Ras, c-Raf-1, and MEK1. Downstream, this pathway linked to BAD dephosphorylation at serine 136 by prolonged inactivation of Akt/PKB. Further, mutation of BAD at serine 136 abrogated ceramide signaling of apoptosis. The present study indicates that when ceramide signals through the Ras/Raf cascade, the availability of a single target, BAD, may dictate an apoptotic outcome.
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PMID:BAD enables ceramide to signal apoptosis via Ras and Raf-1. 980 8

Widespread use of MCF-7 human breast carcinoma cells as a model system for breast cancer has led to variations in these cells between different laboratories. Although several reports have addressed these differences in terms of proliferation and estrogenic response, variations in sensitivity to apoptosis have not yet been described. Tumor necrosis factor alpha (TNF-alpha) has been shown to both induce apoptosis and inhibit proliferation in MCF-7 cells. We observed that TNF-alpha inhibited proliferation in MCF-7 cell variants from three different laboratories (designated M, L, and N). MCF-7 M cells were resistant to TNF-alpha-induced apoptosis, whereas MCF-7 L cells were moderately resistant to the effect of TNF-alpha. A third variant, MCF-7 N, underwent apoptosis when exposed to TNF-alpha. Analysis of the p55 TNF-alpha receptor (TNFR) 1 expression revealed the greatest expression in MCF-7 N cells, whereas the MCF-7 L and M cells expressed 89 and 67% of MCF-7 N cell TNFR1 levels, respectively. Ceramide generation occurred in all three variants in response to TNF-alpha treatment, with MCF-7 N cells expressing the greatest increase. Cleavage of the CPP32/caspase 3 substrate poly(ADP-ribose) was observed in MCF-7 N and L cells as early as 3 and 6 h, respectively, but poly(ADP-ribose) cleavage was not observed in MCF-7 M cells. The delayed protease activation in the L variant may represent the mechanism by which these cells display delayed sensitivity to TNF-a-induced apoptosis. Expression of the Bcl-2, Mcl-1, Bcl-X, Bax, and Bak proteins was analyzed to determine whether the differences in MCF-7 cell sensitivity to apoptosis could be correlated to the differential expression of these proteins. Whereas Bak, Bcl-X, and Mcl-1 levels were identical between variants, the levels of Bcl-2 were 3.5-3.8-fold higher and the levels of Bax were 1.5-1.7-fold lower in the resistant variants (M and L) as compared with those of the sensitive variant (N). Taken together, these results suggest that differences in susceptibility to TNF-alpha-induced apoptosis among MCF-7 breast cancer cell variants may be explained by differences in TNFR expression, ceramide generation, differential expression of the Bcl-2 family of proteins, and protease activation.
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PMID:Differences in susceptibility to tumor necrosis factor alpha-induced apoptosis among MCF-7 breast cancer cell variants. 981 3

Ceramide, a product of sphingomyelin metabolism, is a novel lipid second messenger that mediates diverse cellular functions. The present study demonstrates the activation of caspase-3/CPP-32beta, during apoptosis induced by cell permeable exogenous ceramides, in AK-5 tumor, a spontaneously regressing rat histiocytoma. The apoptotic events were suppressed by the caspase-3 specific tetrapeptide inhibitor DEVD-CHO but not by the caspase-1 inhibitor YVAD-CMK. In cells overexpressing Bcl-2, a significant decrease in cell death was observed after exogenous addition of ceramides. Furthermore the processing of caspase-3 to its active form upon apoptotic stimulus, and the subsequent cleavage of the substrate PARP, suggested a central role for caspase-3 in the ceramide mediated apoptosis in AK-5 tumor cells.
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PMID:Selective involvement of caspase-3 in ceramide induced apoptosis in AK-5 tumor cells. 984 82

Multidrug-resistant cancer cells display elevated levels of glucosylceramide (Lavie, Y., Cao, H. T., Volner, A., Lucci, A., Han, T. Y., Geffen, V., Giuliano, A. E., and Cabot, M. C. (1997) J. Biol. Chem. 272, 1682-1687). In this study, we have introduced glucosylceramide synthase (GCS) into wild type MCF-7 breast cancer cells using a retroviral tetracycline-on expression system, and we developed a cell line, MCF-7/GCS. MCF-7/GCS cells expressed an 11-fold higher level of GCS activity compared with the parental cell line. Interestingly, the transfected cells demonstrated strong resistance to adriamycin and to ceramide, whereas both agents were highly cytotoxic to MCF-7 cells. The EC50 values of adriamycin and ceramide were 11-fold (p < 0.0005) and 5-fold (p < 0.005) higher, respectively, in MCF-7/GCS cells compared with MCF-7 cells. Ceramide resistance displayed by MCF-7/GCS cells closely paralleled the activity of expressed GCS with a correlation coefficient of 0.99. In turn, cellular resistance and GCS activity were dependent upon the concentration of the expression mediator doxycycline. Adriamycin resistance in MCF-7/GCS cells was related to the hyperglycosylation of ceramide and was not related to shifts in the levels of either P-glycoprotein or Bcl-2. This work demonstrates that overexpression of GCS, which catalyzes ceramide glycosylation, induces resistance to adriamycin and ceramide in MCF-7 breast cancer cells.
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PMID:Expression of glucosylceramide synthase, converting ceramide to glucosylceramide, confers adriamycin resistance in human breast cancer cells. 987 62

In the present study we show that N-acetylsphingosine (C2-ceramide), N-hexanoylsphingosine (C6-ceramide), and, to a much lesser extent, C2-dihydroceramide induce cytochrome c (cyto c) release from isolated rat liver mitochondria. Ceramide-induced cyto c release is prevented by preincubation of mitochondria with a low concentration (40 nM) of Bcl-2. The release takes place when cyto c is oxidized but not when it is reduced. Upon cyto c loss, mitochondrial oxygen consumption, mitochondrial transmembrane potential (Delta Psi), and Ca2+ retention are diminished. Incubation with Bcl-2 prevents, and addition of cyto c reverses the alteration of these mitochondrial functions. In ATP-energized mitochondria, ceramides do not alter Delta Psi, neither when cyto c is oxidized nor when it is reduced, ruling out a nonspecific disturbance by ceramides of mitochondrial membrane integrity. Furthermore, ceramides decrease the reducibility of cyto c. We conclude that the apoptogenic properties of ceramides are in part mediated via their interaction with mitochondrial cyto c followed by its release and that the redox state of cyto c influences its detachment by ceramide from the inner mitochondrial membrane.
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PMID:Ceramide induces cytochrome c release from isolated mitochondria. Importance of mitochondrial redox state. 1003 89

Ceramide acts as a mediator of apoptosis in various cell lines, but little is known regarding the molecular mechanism linked to the cell cycle. In the present study, we examined the expression of p27(kip1) and its relationship to apoptosis induced by ceramide. We demonstrated that treatment of HL-60 cells with C6-ceramide resulted in G1 phase elevation followed by apoptotic cleavage associated with increase in the level of cdk inhibitor p27(kip1). Ceramide inhibited the kinase activities of cdk2 and cdk4 within 24 h of treatment. Ceramide-induced inhibition of cdk2 and cdk4 kinase activities was accompanied by increase of p27(kip1) in the cdks complexes. In addition, we have shown that both the cell death and expression of p27(kip1) protein induced by ceramide were significantly decreased in HL-60 cells overexpressing bcl-2. Furthermore, ceramide induced a significant increase in Bax protein expression coincided with increase in p27(kip1) protein level. These findings indicate that p27(kip1) may play important roles in mediating ceramide-induced apoptosis and its expression can be regulated by Bax and Bcl-2.
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PMID:Involvement of p27(kip1) in ceramide-mediated apoptosis in HL-60 cells. 1076 21


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