Ataxia telangiectasia mutated inhibits oxidative stress-induced apoptosis by regulating heme oxygenase-1 expression.

Ataxia telangiectasia (AT) is caused by mutational inactivation of the ataxia telangiectasia mutated ( Atm ) gene, which is involved in DNA repair. Increased oxidative stress has been shown in human AT cells and neuronal tissues of Atm -deficient mice. Heme oxygenase-1 (HO-1) is an inducible antioxidant enzyme and protects cells against oxidative stress. The purpose of this study is to determine whether ATM induces antioxidant enzyme HO-1 and protects cells from oxidative stress-mediated apoptosis by driving the activation of PKC-δ and NF-κB, by increasing cell viability, and by downregulating DNA fragmentation and apoptotic indicators (apoptosis-inducing factor and cleaved caspase-3). AT fibroblasts stably transfected with human full-length ATM cDNA (YZ5 cells) or the empty vector (MOCK cells) were treated with H 2 O 2 as a source of reactive oxygen species (ROS). As a result, transfection with ATM inhibited ROS-induced cell death and DNA fragmentation in MOCK cells. Transfection with ATM induced expression of HO-1 which was mediated by PKC-δ and NF-κB in H 2 O 2 -treated MOCK cells. ZnPP, an HO-1 inhibitor, and transfection with HO-1 siRNA increased ROS levels and apoptosis, whereas hemin, an HO-1 activator, reduced ROS levels and apoptosis in H 2 O 2 -treated YZ5 cells. Rottlerin, a PKC-δ inhibitor, inhibited NF-κB activation and HO-1 expression in H 2 O 2 -treated YZ5 cells. MOCK cells showed increased cell death, DNA fragmentation, and apoptotic indicators compared to YZ5 cells exposed to H 2 O 2 . In addition, transfection with p65 siRNA increased ROS levels and DNA fragmentation, but decreased HO-1 protein levels in H 2 O 2 -treated YZ5 cells. In conclusion, ATM induces HO-1 expression via activation of PKC-δ and NF-κB and inhibits oxidative stress-induced apoptosis. A loss of HO-1 induction may explain why AT patients are vulnerable to oxidative stress. [ABSTRACT FROM AUTHOR]