Primary meningioma cell cultures were established and cell culture experiments were performed using a hypoxia chamber to stimulate HIF-1alpha and VEGF production.
First, HIF-1 controls the expression of gene products that stimulate angiogenesis, such as vascular endothelial growth factor, and promote metabolic adaptation to hypoxia, such as glucose transporters and glycolytic enzymes, thus providing a molecular basis for involvement of HIF-1 in tumor growth and angiogenesis.
Hypoxia-inducible factor 1 (HIF-1) is a heterodimeric transcription factor that regulates transcriptional activation of several genes that are responsive to oxygen lack, including erythropoietin, vascular endothelial growth factor, various glycolytic enzymes and the GLUT-1 glucose transporter.
Transfection experiments in HepG2 cells showed that both hypoxia and overproduction of HIF-1alpha specifically repressed the transcriptional activity of the rat afp regulatory region through the sequence 5'-CACGTGGG-3' located at -3625 to -3619.
Gel shift assays with a (32)P-labeled leptin promoter -116/HRE probe and nuclear extracts from hypoxia-treated cells indicated binding of the HIF1alpha/beta heterodimer, which was blocked with an excess of unlabeled -116/HRE probe or a HIF1-binding probe from the erythropoietin gene enhancer.
Overexpression of HIF-1alpha and HIF-2alpha was demonstrated in three HNSCC cell lines under hypoxia and tumor tissue versus normal tissue (n = 20, HIF-1alpha, P = 0.023; HIF-2alpha, P = 0.013).
The results showed that, although hypoxia markedly increased ROS generation in HeEB1 cells but not in EB8 cells, EB8 cells showed essentially a normal response to hypoxia, as assessed by VEGF gene promoter activity, HIF-1alpha accumulation, and HIF-1 target gene expressions.
In human cancer cells, both intratumoral hypoxia and genetic alterations affecting signal transduction pathways lead to increased HIF-1 activity, which promotes angiogenesis, metabolic adaptation, and other critical aspects of tumor progression.
Overexpression of HIF-1 alpha in normoxia induced the expression of a significant number of the hypoxia-dependent genes; however, it did not induce the pathophysiologic epithelial response.
These results provide an insight into a possible link of hypoxia or HIF-1alpha and leukemic cell differentiation, and are possibly of significance to explore clinical potentials of hypoxia or hypoxia-mimicking agents and novel target-based drugs for differentiation therapy of leukemia.
This process is mediated by stabilization of the transcriptional factor hypoxia inducible factor 1 (HIF-1), which increases vascular endothelial growth factor (VEGF) production.
Our results provide persuasive evidence that the regulation of hTERT promoter activity by HIF-1 represents a mechanism for trophoblast growth during hypoxia and suggests that this may be a generalized response to hypoxia in various human disorders including resistance to cancer therapeutics by upregulating telomerase.
In conclusion, our data demonstrate that hyperglycemia impairs hypoxia-dependent protection of HIF-1alpha against proteasomal degradation and suggest a mechanism by which diabetes interferes with cellular responses to hypoxia.
HUVECs were transfected with specific 21-nt small interfering RNA (siRNA) duplexes targeting HIF-1 alpha mRNA sequences or scrambled RNA duplexes and subjected either to normoxia for 251/2 h or to anoxia for 11/2 h, and subsequently normoxia for 24 h (A/R).
The pharmacological manipulation of HIF-1 has marked effects on tumour growth, and it could prove to be an important target for drug therapy, both in cancer and in other hypoxia-dependent disease states.
Our results provide evidence that regulation of TGF-beta3 promoter activity by HIF-1 represents a mechanism for trophoblast differentiation during hypoxia.