Figure 3.

Two types of hypoxia in a tumor. Chronic hypoxia is associated with a long distance between the cells and the blood vessels that supply them with oxygen. This hypoxia induces an increase in activation of HIF-1 and HIF-2 and expression of hypoxia-inducible genes. The second type of hypoxia, cycling hypoxia, consists in blood flow through a given blood vessel in repeated cycles. The hypoxic stage is accompanied by the activation of NF-κB, and the activation of HIF-1. Reoxygenation is associated with the proteolytic degradation of HIF-1α and decrease in HIF-1 activation.