Abstract
In normal brain, the side population (SP) phenotype is generated by ABC transporter activity and identifies stem cell and endothelial cell subpopulations by dye exclusion. By drug efflux, the ABCG2 transporter provides chemoresistance in stem cells and contributes to the blood brain barrier (BBB) when active in endothelial cells. We investigated the SP phenotype of mouse and human gliomas. In glioma endothelial cells, ABC transporter function is impaired, corresponding to disruption of the BBB in these tumors. By contrast, the SP phenotype is increased in nonendothelial cells that form neurospheres and are highly tumorigenic. In this cell population, Akt, but not its downstream target mTOR, regulates ABCG2 activity, and loss of PTEN increases the SP. This Akt-induced ABCG2 activation results from its transport to the plasma membrane. Temozolomide, the standard treatment of gliomas, although not an ABCG2 substrate, increases the SP in glioma cells, especially in cells missing PTEN.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, Non-U.S. Gov't
MeSH terms
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ATP Binding Cassette Transporter, Subfamily G, Member 2
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ATP-Binding Cassette Transporters / metabolism*
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Animals
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Antineoplastic Agents / pharmacology
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Antineoplastic Agents, Alkylating / metabolism
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Antineoplastic Agents, Alkylating / pharmacology
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Blood-Brain Barrier / metabolism
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Brain / metabolism
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Brain / pathology
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Cells, Cultured
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Chromones / pharmacology
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Dacarbazine / analogs & derivatives
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Dacarbazine / metabolism
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Dacarbazine / pharmacology
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Drug Resistance, Neoplasm*
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Enzyme Inhibitors / pharmacology
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Glioma / chemically induced
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Glioma / metabolism
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Glioma / pathology*
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Humans
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Mice
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Mice, Nude
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Mitoxantrone / pharmacology
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Morpholines / pharmacology
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Neoplasm Proteins / metabolism
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Neoplastic Stem Cells / drug effects
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Neoplastic Stem Cells / metabolism*
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Neoplastic Stem Cells / pathology
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PTEN Phosphohydrolase / genetics
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PTEN Phosphohydrolase / metabolism*
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Phosphatidylinositol 3-Kinases / metabolism*
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Phosphoinositide-3 Kinase Inhibitors
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Platelet-Derived Growth Factor / pharmacology
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Proto-Oncogene Proteins c-akt / antagonists & inhibitors
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Proto-Oncogene Proteins c-akt / metabolism*
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Temozolomide
Substances
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ABCG2 protein, human
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ATP Binding Cassette Transporter, Subfamily G, Member 2
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ATP-Binding Cassette Transporters
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Abcg2 protein, mouse
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Antineoplastic Agents
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Antineoplastic Agents, Alkylating
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Chromones
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Enzyme Inhibitors
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Morpholines
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Neoplasm Proteins
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Phosphoinositide-3 Kinase Inhibitors
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Platelet-Derived Growth Factor
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2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one
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Dacarbazine
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Mitoxantrone
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Proto-Oncogene Proteins c-akt
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PTEN Phosphohydrolase
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Temozolomide