Hypoxia induces protection against etoposide-induced apoptosis: molecular profiling of changes in gene expression and transcription factor activity

Audrey Sermeus¹ , Jean-Philippe Cosse¹ , Marianne Crespin¹ , Veronique Mainfroid² , Francoise de Longueville² , Noelle Ninane¹ , Martine Raes¹ , Jose Remacle² and Carine Michiels¹

¹URBC, FUNDP-University of Namur, 61 rue de Bruxelles, 5000 Namur, Belgium

²Eppendorf Array Technologies, 20A rue du Séminaire, 5000 Namur, Belgium

author email corresponding author email

Molecular Cancer 2008, 7:27doi:10.1186/1476-4598-7-27


Published:	26 March 2008

Abstract

Background

it is now well established that hypoxia renders tumor cells resistant to radio- but also chemotherapy. However, few elements are currently available as for the mechanisms underlying this protection.

Results

in this study, physiological hypoxia was shown to inhibit apoptosis induced in HepG2 cells by etoposide. Indeed, hypoxia reduced DNA fragmentation, caspase activation and PARP cleavage. The DNA binding activity of 10 transcription factors was followed while the actual transcriptional activity was measured using specific reporter plasmids. Of note is the inhibition of the etoposide-induced activation of p53 under hypoxia. In parallel, data from low density DNA microarrays indicate that the expression of several pro- and anti-apoptotic genes was modified, among which are Bax and Bak whose expression profile paralleled p53 activity. Cluster analysis of data unravels several possible pathways involved in the hypoxia-induced protection against etoposide-induced apoptosis: one of them could be the inhibition of p53 activity under hypoxia since caspase 3 activity parallels Bax and Bak expression profile. Moreover, specific downregulation of HIF-1α by RNA interference significantly enhanced apoptosis under hypoxia possibly by preventing the hypoxia mediated decrease in Bak expression without altering Bax expression.

Conclusion

these results are a clear demonstration that hypoxia has a direct protective effect on apoptotic cell death. Moreover, molecular profiling points to putative pathways responsible for tumor growth in challenging environmental conditions and cancer cell resistance to chemotherapeutic agents.