Abstract
The lack of innovative drug targets for glioblastoma multiforme (GBM) limits patient survival to approximately 1 year following diagnosis. The pro-survival kinase Akt provides an ideal target for the treatment of GBM as Akt signaling is frequently activated in this cancer type. However, the central role of Akt in physiological processes limits its potential as a therapeutic target. In this report, we show that the lipid-metabolizing enzyme phospholipaseD(PLD) is a novel regulator of Akt inGBM.Studies using a combination of small molecule PLD inhibitors and siRNA knockdowns establish phosphatidic acid, the product of the PLD reaction, as an essential component for the membrane recruitment and activation of Akt. Inhibition of PLD enzymatic activity and subsequent Akt activation decreases GBM cell viability by specifically inhibiting autophagic flux. We propose a mechanism whereby phosphorylation of beclin1 by Akt prevents binding of Rubicon (RUN domain cysteine-rich domain containing beclin1-interacting protein), an interaction known to inhibit autophagic flux. These findings provide a novel framework through which Akt inhibition can be achieved without directly targeting the kinase.
Keywords:
Akt; Autophagy; Cell Signaling; Glioblastoma; Phosphatidic Acid; Phospholipase D.
Publication types
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Research Support, N.I.H., Extramural
MeSH terms
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Animals
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Apoptosis Regulatory Proteins / metabolism
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Autophagy / drug effects
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Autophagy / genetics
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Autophagy / physiology*
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Autophagy-Related Proteins
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Beclin-1
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Cell Line
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Cell Line, Tumor
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Cell Survival / genetics
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Cell Survival / physiology
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Culture Media, Serum-Free / pharmacology
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Enzyme Inhibitors / pharmacology
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Glioblastoma / genetics
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Glioblastoma / metabolism
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Glioblastoma / pathology
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HEK293 Cells
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Heterocyclic Compounds, 3-Ring / pharmacology
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Humans
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Immunoblotting
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Intracellular Signaling Peptides and Proteins / metabolism
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Membrane Proteins / metabolism
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Microscopy, Confocal
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Phosphatidic Acids / metabolism
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Phospholipase D / antagonists & inhibitors
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Phospholipase D / genetics
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Phospholipase D / metabolism*
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Phosphorylation / drug effects
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Proto-Oncogene Proteins c-akt / antagonists & inhibitors
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Proto-Oncogene Proteins c-akt / genetics
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Proto-Oncogene Proteins c-akt / metabolism*
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RNA Interference
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Signal Transduction / drug effects
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Signal Transduction / genetics
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Signal Transduction / physiology*
Substances
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Apoptosis Regulatory Proteins
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Autophagy-Related Proteins
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BECN1 protein, human
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Beclin-1
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Culture Media, Serum-Free
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Enzyme Inhibitors
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Heterocyclic Compounds, 3-Ring
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Intracellular Signaling Peptides and Proteins
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MK 2206
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Membrane Proteins
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Phosphatidic Acids
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RUBCN protein, human
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Proto-Oncogene Proteins c-akt
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phospholipase D2
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Phospholipase D