Hypoxia increases normal prostate epithelial cell resistance to receptor-mediated apoptosis via AKT activation

Abstract

The aging prostate is associated with changes in its vascular structure, which could lead to changes in oxygen levels. Hypoxia is an important environmental change that leads to the progression of many cancers mediated through a number of cellular changes, which included resistance to apoptosis. The role of hypoxia in initiating tumour development has not been previously investigated. We demonstrate that normal prostate epithelial cells develop a resistance to receptor-mediated apoptosis following 24 hr of 1% hypoxia. This effect is associated with the altered expression of a number of pro- and anti-apoptotic proteins, which leads to inhibition of Cytochrome c release and downstream caspase activation. This is mediated via decreased Bax translocation and upstream Caspase 8 activity. Despite increased expression of cIAP-2, small interfering RNA (siRNA) knockdown does not restore susceptibility to TRAIL-induced apoptosis. Gene expression analysis indicated potential changes in AKT activation, which was confirmed by increased phosphorylation of AKT. Inhibition of this phosphorylation reversed the resistance to TRAIL-induced apoptosis. AKT activation is emerging as a key survival signal in prostate cancer. This study demonstrates that short exposure to low oxygen can increase resistance to immune surveillance mechanisms and might confer a survival advantage onto normal prostate epithelial cells so that they can survive subsequent genomic instability and other carcinogenetic insults leading to the early development of prostate cancer. © 2008 Wiley-Liss, Inc.