Hypoxia and CoCl2 protect HepG2 cells against serum deprivation- and t-BHP-induced apoptosis: a possible anti-apoptotic role for HIF-1.

Hypoxia inducible factor-1 (HIF-1) is the main transcriptional factor activated by hypoxia. Besides the well-described role assigned to HIF-1 in the adaptation of cells to hypoxia, different recent data describe a possible role for HIF-1 in the modulation of apoptosis. However, this precise role is not yet clearly understood. In this study, chemical and physiological hypoxia, which were shown to induce HIF-1alpha stabilization and HIF-1 activation, were shown to inhibit apoptosis induced in HepG2 cells by two different pro-apoptotic conditions, serum deprivation- and t-BHP-induced oxidative stress. Indeed, hypoxia reduced DNA fragmentation, caspase activation, and PARP cleavage induced by these two pro-apoptotic conditions. These results are very interesting because it is a clear demonstration that hypoxia and chemical hypoxia have a direct protective effect on apoptotic cell death induced by two different stimuli. This observation is an important data in understanding how tumor growth can occur in challenging environmental conditions.