The role of ceramide in cell death.
Item
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Title
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The role of ceramide in cell death.
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Identifier
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AAI9732935
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identifier
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9732935
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Creator
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Karasavvas, Nicos.
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Contributor
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Adviser: Zahra Zakeri
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Date
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1997
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Language
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English
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Publisher
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City University of New York.
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Subject
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Biology, Cell | Biology, Molecular | Chemistry, Biochemistry
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Abstract
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Ceramide has emerged as a putative second messenger generated by stress signals and cytokines known to induce cell death. In the present study we investigated the role of ceramide in cell death. We first asked how structural modifications of ceramide could affect the induction of cell death. We showed that cell death induced by ceramide was stereospecific. The presence of the ceramide trans-4,5-double bond was required for cell death and its modification increased the potency of ceramide analogs to kill cells. The ceramide carbonyl group was not required for the induction of apoptosis. We established that the stereospecificity of ceramide was not mediated by the differential activation of ceramide targets or the generation of endogenous ceramide. Furthermore, we demonstrated that the overexpression of the cell death inhibitory bcl-2 gene protected only the cells that were treated with the naturally occurring ceramide stereoisomer. Bcl-2 provided partial protection to cells treated with the other ceramide etereoisomers and analogs. To decipher the role of ceramide as a signaling molecule in cell death, we investigated its relationship to the induction of apoptosis by TNF-{dollar}\alpha{dollar}, a cytokine speculated to kill cells via the generation of ceramide. We found substantial differences in the induction of cell death mediated by ceramide and TNF-{dollar}\alpha{dollar}. Apoptosis promoted by TNF-{dollar}\alpha{dollar} was rapid, irreversible and transduced within seconds. The ceramide levels in TNF-{dollar}\alpha{dollar}-treated cells increased modestly and well after the cellular commitment to die. In contrast, exogenous ceramide killed cells after prolonged incubations and massive accumulations of intracellular ceramide. To study pathways involved in apoptosis induced by ceramide, we developed the ceramide resistant cell line UDtIN. Using phosphatase inhibitors we showed that cexamide cell killing depends on the activity of PP2A phosphatases whereas TNF-{dollar}\alpha{dollar} cell killing is not. Taken together, our results suggest that ceramide and TNF-{dollar}\alpha{dollar} kill cells via different pathways, suggesting that ceramide elevations are a consequence and not the cause of cell death under physiological conditions.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
