%0 Generic
%A Hitschler, Anna
%D 2010
%F heidok:11165
%K Hypoxie , HPV , GAPDHhypoxia , HPV , GAPDH
%R 10.11588/heidok.00011165
%T Hypoxic regulation of glyceraldehyde-3-phosphate dehydrogenase in HPV-positive non-tumorigenic and tumorigenic cells
%U https://archiv.ub.uni-heidelberg.de/volltextserver/11165/
%X Metabolic adaptations of cancer to scarce oxygen conditions are believed to contribute to the tumor promoting effect of hypoxia. To assess this issue in the context of human papillomavirus induced cervical carcinogenesis, the hypoxic regulation of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was investigated in non-tumorigenic HPV-positive HeLa x fibroblast hybrid cells (444), their tumorigenic segregants CGL 3 and the parental homologues IMR 90 and HeLa. 24 hours hypoxia lead to a transcriptional upregulation of GAPDH only in non-tumorigenic cells but not in their tumorigenic counterparts. As shown by ChIP analysis, the hypoxic increase of GAPDH was mediated by the transcription factors Net and HIF-2α. Their binding to the GAPDH promoter was augmented upon hypoxia exclusively in non-tumorigenic cells. Moreover, GAPDH-reporter assays revealed a synergistic trans-activating effect of Net and HIF-2α only in non-tumorigenic cells which was further enhanced by hypoxia. Intriguingly, GAPDH acts as a trigger between cell death and survival. To investigate whether the differential hypoxic regulation of GAPDH in non-tumorigenic and tumorigenic cells reflects their resistance to hypoxic conditions, cell viability was monitored by determining the cellular ATP content and by FACS analysis. Indeed, the hypoxic increase of GAPDH correlated with a better cell viability in non-tumorigenic 444 cells. Moreover, FACS assays revealed different responses to hypoxia in  tumorigenic CGL 3 and HeLa cell. While HeLa substantially increased apoptosis upon hypoxia, CGL 3 underwent a different type of cell death, possibly necrosis. Apoptosis in HeLa was likely caused by an altered ROS homeostasis, as this cell line did not show the expected hypoxic increase of oxygen radicals. In contrast, CGL 3 probably died of irreversible energy depletion, as they depicted the lowest ATP levels of all tested cell lines upon hypoxia.  Another factor which might influence hypoxic survival are the viral oncoproteins E6 and E7. This study determined complete silencing of their expression upon hypoxia in both tumorigenic and non-tumorigenic cell lines. The main regulator of HPV transcription, the cellular transcription factor AP-1, was not responsible for this effect, as neither its dimeric composition nor the expression of its cognate subunits changed upon hypoxic treatment.  Taken together, this study indicates a dysregulation of hypoxic GAPDH expression in cervical cancer cells which may influence survival of energy stress upon hypoxia. Whether the silencing of the HPV oncoproteins upon hypoxia contributes to this observation requires further investigation.