RRM2B suppresses activation of the oxidative stress pathway and is up-regulated by p53 during senescence.

RRM2B is the DNA damage-inducible small subunit of ribonucleotide reductase, the rate-limiting enzyme in de novo deoxyribonucleoside triphosphate synthesis. Although RRM2B is implicated in DNA repair and the maintenance of mitochondrial DNA content, the regulation and function of RRM2B in senescence have not been previously established. Here, we show that RRM2B is highly induced in a p53-dependent manner during senescence in primary human fibroblast IMR90 cells and is expressed at higher levels in senescent precancerous human prostatic intraepithelial neoplasm lesions compared to adjacent normal prostate glands. Paradoxically, silencing RRM2B expression leads to an increase in the level of reactive oxygen species, mitochondrial membrane depolarization, and premature senescence in a p38MAPK- and p53-dependent manner in young fibroblasts. Consistently, induction of senescence is accelerated in Rrm2b deficient mouse embryo fibroblasts. Our data demonstrate that RRM2B is induced by stress signals prior to the onset of senescence and prevents premature oxidative stress-induced senescence.

Inhibitors of catalase-amyloid interactions protect cells from beta-amyloid-induced oxidative stress and toxicity.

Compelling evidence shows a strong correlation between accumulation of neurotoxic ß-amyloid (Aß) peptides and oxidative stress in the brains of patients afflicted with Alzheimer disease (AD). One hypothesis for this correlation involves the direct and harmful interaction of aggregated Aß peptides with enzymes responsible for maintaining normal, cellular levels of reactive oxygen species (ROS). Identification of specific, destructive interactions of Aß peptides with cellular anti-oxidant enzymes would represent an important step toward understanding the pathogenicity of Aß peptides in AD. This report demonstrates that exposure of human neuroblastoma cells to cytotoxic preparations of aggregated Aß peptides results in significant intracellular co-localization of Aß with catalase, an anti-oxidant enzyme responsible for catalyzing the degradation of the ROS intermediate hydrogen peroxide (H(2)O(2)). These catalase-Aß interactions deactivate catalase, resulting in increased cellular levels of H(2)O(2). Furthermore, small molecule inhibitors of catalase-amyloid interactions protect the hydrogen peroxide-degrading activity of catalase in Aß-rich environments, leading to reduction of the co-localization of catalase and Aß in cells, inhibition of Aß-induced increases in cellular levels of H(2)O(2), and reduction of the toxicity of Aß peptides. These studies, thus, provide evidence for the important role of intracellular catalase-amyloid interactions in Aß-induced oxidative stress and propose a novel molecular strategy to inhibit such harmful interactions in AD.