title: Akt1 activation can augment hypoxia-inducible factor-1alpha expression by increasing protein translation through a mammalian target of rapamycin-independent pathway.
abstract: 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.
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania School of Medicine, Philadelphia, 19104, USA.
authors.forename: Nabendu
authors.initials: N
authors.lastname: Pore
authors.forename: Zibin
authors.initials: Z
authors.lastname: Jiang
authors.forename: Hui-Kuo
authors.initials: HK
authors.lastname: Shu
authors.forename: Eric
authors.initials: E
authors.lastname: Bernhard
authors.forename: Gary D
authors.initials: GD
authors.lastname: Kao
authors.forename: Amit
authors.initials: A
authors.lastname: Maity
mesh_terms: D045744:Cell Line, Tumor; D002867:Chromones / Q000494:pharmacology; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005909:Glioblastoma / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000096:biosynthesis* / Q000378:metabolism; D008297:Male; D009025:Morpholines / Q000494:pharmacology; D051059:PTEN Phosphohydrolase / Q000235:genetics / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D014176:Protein Biosynthesis / Q000187:drug effects; D011494:Protein Kinases / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D058570:TOR Serine-Threonine Kinases; D014162:Transfection; D042461:Vascular Endothelial Growth Factor A / Q000276:immunology / Q000378:metabolism
chemical_list: D002867:Chromones; D004791:Enzyme Inhibitors; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009025:Morpholines; D051059:PTEN Phosphohydrolase; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011494:Protein Kinases; D051057:Proto-Oncogene Proteins c-akt; D034741:RNA, Small Interfering; D058570:TOR Serine-Threonine Kinases; D042461:Vascular Endothelial Growth Factor A; C497442:HIF1A protein, human; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C546842:MTOR protein, human; C494918:AKT1 protein, human; C494929:PTEN protein, human