Fig. 5.

Chronic hypoxia-induced HIFα desensitization protects cells from necrosis. Cell death was measured in cells incubated in hypoxia at 1% O₂ for different periods of time by a trypan blue incorporation assay. (a) CCL39 and GSK3 cells (Left) or HeLa cells transfected with siRNA targeting the three PHDs isoforms or an irrelevant sequence (Right) for 5 days and incubated either in normoxia (N) or upon hypoxia for different periods of time (4 h, 3 days, or 5 days). (b) GSK3 cells (Left) and HeLa cells transfected as described in a (Right) in which HIFα expression has been silenced. The siHIFα transfections started 16 h after the cells were incubated upon hypoxia and were carried on every day until the end of the experiment for days 3 and 5. In the case of the N and H (4 h) conditions, siHIFα were transfected during the last 24 h.