Oxy5, a novel protein from Arabidopsis thaliana, protects mammalian cells from oxidative stress.

The use of molecular oxygen in various cellular processes results in the generation of toxic intracellular by-products termed reactive oxygen species (ROS). In Escherichia coli the oxyR gene product is a transcriptional regulator of the oxyR regulon that is induced in response to hydrogen peroxide-induced oxidative stress (OS). We have previously shown that an annexin-like protein from Arabidopsis thaliana, termed Oxy5, can replace the obligatory role of OxyR in E. coli. Here, we have investigated as to whether oxy5 can function across evolutionary boundaries to protect mammalian cells from OS. Overexpression of the oxyR gene in mammalian tumor cell lines protects them from hydrogen peroxide-induced cell death, and these cells are also highly resistant to the superoxide ion producing compound paraquat. Oxy5 appears to be involved in the detection of calcium flux, as it binds to Ca2+ ions during hydrogen peroxide stress. Moreover, overexpression of Oxy5 leads to lowered protein kinase C activity. Thus, Oxy5 probably functions to sense and initiate protective responses to OS. In addition, Oxy5-overexpressing cells exhibit a reduction in endogenous superoxide ion levels, which concomitantly results in a dramatic decrease in their tumorigenic potential. Taken together, the results demonstrate an antioxidant role for plant oxy5 gene in mammalian cells, which can be potentially utilized in gene therapy programs aimed at reducing the deleterious effects of ROS.