16849522

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7

The phosphoinositide 3-kinase (PI3K)/Akt pathway is commonly activated in cancer; therefore, we investigated its role in hypoxia-inducible factor-1alpha (HIF-1alpha) regulation. Inhibition of PI3K in U87MG glioblastoma cells, which have activated PI3K/Akt activity secondary to phosphatase and tensin homologue deleted on chromosome 10 (PTEN) mutation, with LY294002 blunted the induction of HIF-1alpha protein and its targets vascular endothelial growth factor and glut1 mRNA in response to hypoxia. Introduction of wild-type PTEN into these cells also blunted HIF-1alpha induction in response to hypoxia and decreased HIF-1alpha accumulation in the presence of the proteasomal inhibitor MG132. Akt small interfering RNA (siRNA) also decreased HIF-1alpha induction under hypoxia and its accumulation in normoxia in the presence of dimethyloxallyl glycine, a prolyl hydroxylase inhibitor that prevents HIF-1alpha degradation. Metabolic labeling studies showed that Akt siRNA decreased HIF-1alpha translation in normoxia in the presence of dimethyloxallyl glycine and in hypoxia. Inhibition of mammalian target of rapamycin (mTOR) with rapamycin (10-100 nmol/L) had no significant effect on HIF-1alpha induction in a variety of cell lines, a finding that was confirmed using mTOR siRNA. Furthermore, neither mTOR siRNA nor rapamycin decreased HIF-1alpha translation as determined by metabolic labeling studies. Therefore, our results indicate that Akt can augment HIF-1alpha expression by increasing its translation under both normoxic and hypoxic conditions; however, the pathway we are investigating seems to be rapamycin insensitive and mTOR independent. These observations, which were made on cells grown in standard tissue culture medium (10% serum), were confirmed in PC3 prostate carcinoma cells. We did find that rapamycin could decrease HIF-1alpha expression when cells were cultured in low serum, but this seems to represent a different pathway.

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MEDLINE

1541-7786

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471-9

pubmed-meshheading:16849522-Cell Line, Tumor, pubmed-meshheading:16849522-Chromones, pubmed-meshheading:16849522-Enzyme Activation, pubmed-meshheading:16849522-Enzyme Inhibitors, pubmed-meshheading:16849522-Glioblastoma, pubmed-meshheading:16849522-Humans, pubmed-meshheading:16849522-Hypoxia-Inducible Factor 1, alpha Subunit, pubmed-meshheading:16849522-Male, pubmed-meshheading:16849522-Morpholines, pubmed-meshheading:16849522-PTEN Phosphohydrolase, pubmed-meshheading:16849522-Phosphatidylinositol 3-Kinases, pubmed-meshheading:16849522-Protein Biosynthesis, pubmed-meshheading:16849522-Protein Kinases, pubmed-meshheading:16849522-Proto-Oncogene Proteins c-akt, pubmed-meshheading:16849522-RNA, Small Interfering, pubmed-meshheading:16849522-TOR Serine-Threonine Kinases, pubmed-meshheading:16849522-Transfection, pubmed-meshheading:16849522-Vascular Endothelial Growth Factor A

Akt1 activation can augment hypoxia-inducible factor-1alpha expression by increasing protein translation through a mammalian target of rapamycin-independent pathway.

Journal Article, Research Support, U.S. Gov't, Non-P.H.S., Research Support, N.I.H., Extramural