Regulation of stress-induced phospholipase D survival signals in human cancer.
Item
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Title
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Regulation of stress-induced phospholipase D survival signals in human cancer.
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Identifier
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AAI3330367
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identifier
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3330367
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Creator
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Garcia, Avalon.
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Contributor
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Adviser: David A. Foster
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Date
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2008
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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, Molecular | Biology, Cell | Chemistry, Biochemistry
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Abstract
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Phospholipase D (PLD) is a phosphodiesterase that hydrolyzes phosphatidylcholine into phosphatidic acid (PA) and choline. In untransformed cells, PLD activity is stimulated by serum. In contrast, PLD activity in some cancer cells is stimulated by the stress of serum deprivation. The survival, migration and invasion of these cells depend on PLD activity. Thus, targeting the signals that elevate PLD activity may provide a tool for eradicating cancer cells that are able to survive insufficient serum conditions. Hence, we set out to determine which factors played a role in regulating stress-induced PLD activity. We focused on proteins such as EGFR and the G-proteins Ras, RalA, Arf1 and Arf6 which have been shown to regulate PLD activity. Correlating with PLD activity, we observed an increase in the activation of EGFR and Ras but not RalA in low serum. Pharmacological inhibition or siRNA knock down of EGFR abrogated the stimulated PLD activity. Comparatively, inhibition of Ras activity by dominant negative mutants or siRNA knockdown also suppressed PLD activity. Additionally, suppression of Arf1 and Arf6 by dominant negative mutants resulted in a decrease in PLD activity.;We next examined the effect of honokiol, a compound extracted from the Magnolia plant species, on PLD signaling. Honokiol suppressed PLD activity in cancer cells where PLD has been shown to suppress apoptosis. Importantly, the PLD activity induced by the stress of serum-withdrawal was selectively inhibited by honokiol. Honokiol was also shown to suppress Ras activation.;Another protein of interest to our work is 5'AMP-activated protein kinase (AMPK). This serine--threonine kinase senses and responds to changes in the AMP:ATP ratio. Interestingly, PLD activity was stimulated by the AMP mimetic and AMPK activator AICAR in high serum conditions. Pharmacological inhibition or siRNA knock down of AMPK prevented the induction of PLD activity. Suppression or activation of AMPK did not affect the activity of Ras. Similarly, inhibition of EGFR had no effect on AMPK activity. Pharmacological inhibition of AMPK caused an increase in cell death and an observed decrease in migration.
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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.
