Treatment with 100 microM cycloheximide, a protein synthesis inhibitor, replicated the effect of quercetin by inhibiting HIF-1alpha accumulation during hypoxia.
The present observations support that upregulation of HIF-1 alpha and its downstream targets GLUT1 and SDF-1 in colorectal adenomas and carcinomas may be due to hypoxia, in close interaction with an active phosphatidylinositol 3-kinases-AKT-mTOR pathway.
One common feature of these tumors is the presence of "hypoxic regions," characterized by cells expressing high levels of hypoxia-inducible factors HIF-1alpha and HIF-2alpha, two transcription regulators that modulate the levels of proteins with crucial roles in tumor progression.
As GLUT-1 was induced via Hif-1alpha under hypoxia in A204 RMS and A673 ES, these findings suggest that the Hif-1alpha-mediated increase in glucose uptake plays an important role in conferring apoptosis resistance.
Moreover, the levels of HIF-1alpha that we observed after exposure to moderate hypoxia were comparable between rho0 cells, which lack functional mitochondria, and the wild-type cells.
In line, gel shift analysis and chromatin immunoprecipitation confirmed binding of p50 and p65 NFkappaB subunits to the HIF-1alpha promoter under hypoxia.
Prostate carcinoma cells selected by long-term exposure to reduced oxygen tension show remarkable biochemical plasticity via modulation of superoxide, HIF-1alpha levels, and energy metabolism.
Cell density also correlated with increased staining for reductively activated pimonidazole (a marker for hypoxia), as well as with increased levels of the HIF-1alpha subunit and HIF transcriptional activity as determined by immunocytochemistry, Western blot, and luciferase reporter assays.
A role for hypoxia-inducible factor (HIF)-1 was suggested by the increase in HIF-1alpha as a result of hypoxia and by the increase in GLUT1 expression following treatment of BeWo with MG-132, a proteasomal inhibitor that increases HIF-1 levels.
Together, these results provide evidence that P. aeruginosa can recognize and respond to extracellular end products of intestinal hypoxia that are released after activation of HIF-1alpha.
Transfection with specific siRNA duplexes knocked down HIF 1-alpha mRNA and protein expression in hypoxia-exposed cells by approximately 80%, whereas transfection with scrambled siRNA duplexes had no noticeable effect on HIF 1-alpha expression.
Dimethyloxallyl glycine, a stabilizer of hypoxia-inducible factor 1alpha (HIF1alpha), mimicked the hypoxia-mediated upregulation of visfatin, and YC1, an inhibitor of HIF1 cancelled the hypoxia-induced upregulation of visfatin mRNA.
During hypoxia in A549 cells, HIF-1alpha promotes activity of the glycolysis pathway and decreases the pH of the culture medium, resulting in increased cellular apoptosis.