Role of small GTPases in phospholipase D activation and tumorigenesis.
Item
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Title
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Role of small GTPases in phospholipase D activation and tumorigenesis.
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Identifier
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AAI9946163
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identifier
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9946163
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Creator
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Frankel, Paul.
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Contributor
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Adviser: David A. Foster
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Date
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1999
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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 | Health Sciences, Pathology | Biology, Cell | Health Sciences, Oncology
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Abstract
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The activation of cellular phospholipase D (PLD) is commonly elevated in response to mitogenic signals. We reported previously that although the transformed phenotype induced by v-Src was dependent upon Raf-1, the PLD activity induced by v-Src was independent of Raf-1. This observation suggested to us that Raf would not likely be an activator of PLD. However, upon examination of PLD activity in v-Raf-transformed cells, surprisingly, we found that PLD activity is elevated to levels that were even higher than that observed in v-Src-transformed cells. To characterize the mechanism of v-Raf-induced PLD activity, we examined the dependence of v-Raf-induced PLD activity upon protein kinase C (PKC), the small GTPases RalA, and Rho, which have all been implicated in the activation of PLD. The v-Raf-induced PLD activity was inhibited by dominant negative mutants for both RalA and Rho. The dependence upon Ral was particularly surprising since RalA is a downstream target of Ras, which is an upstream activator of Raf.;Depleting cells of PKC by long term phorbol ester treatment actually increased PLD activity in v-Raf-transformed cells, indicating that v-Raf-induced PLD activity is not dependent on PKC.;Given the result that RaIA is involved in v-Src, v-Ras, and v-Raf induced PLD activity. We have investigated the role of RalA in tumorigenisis. Overproduction of urokinase-type plasminogen activator (uPA) and metalloproteases (MMPs) is strongly correlated with tumorigenicity and with invasive and metastatic phenotypes of human and experimental tumors. We demonstrated previously that overproduction of uPA in tumor cells is mediated by a phospholipase D (PLD)- and protein kinase C-dependent mechanism. The oncogenic stimulus of v-Src and v-Ras results in the activation of PLD, which is dependent upon RalA. We have therefore investigated whether RaIA plays a role in uPA and MMP overproduction that is observed in response to oncogenic signals. We found that NIH 3T3 cells transformed by both v-Src and v-Ras, constitutively overproduce uPA and that expression of a dominant negative RalA mutant (S28N) blocks overproduction of uPA in both the v-Src- and v-Ras-transformed cells. (Abstract shortened by UMI.).
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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.
