application) Iron chelators have an expanding role in the treatment of disease. In addition to their importance in the treatment of iron overload, iron chelators have potential therapeutic benefit in other pathophysiological conditions, including ischemia/reperfusion, malaria and malignant disease. A detailed appreciation of modes of chelator action will be essential to the rational design of such therapies. To better understand cellular consequences of iron chelation, we have been studying cellular targets of iron chelators. Our recent experiments revealed that in addition to well-studied effects on proteins of iron metabolism, iron chelators affect an entirely different group of proteins: those involved in tumor suppression and cell death, Specifically, we have observed that iron chelators actively promote cell death by engaging apoptotic pathways. Cells treated with the chemically unrelated iron chelators tachpyridine, desferioxamine and 2,2'-bipyridyl exhibited characteristic morphological changes of apoptosis, including membrane blebbing, nuclear segmentation, and internucleosomal DNA strand breaks. Our preliminary results indicate that this apoptosis may be initiated through targeting of mitochondria: in response to chelator treatment, we observed the release of cytochrome c from mitochondria into the cytosol, a hallmark of mitochondrially mediated pathways of apoptosis. A further insight into mechanisms of iron chelator-mediated apoptosis derives from our observation that the oncogene E1A strikingly enhances sensitivity to iron chelators. Since E1A affects a restricted but critical set of cell regulatory proteins, this observation narrows the focus of potential molecular targets of iron chelators, and suggests that proteins such as p300 or pRb (E1A binding proteins) or p53 (stabilized by E1A) play important roles in chelator-mediated cell death. Indeed, we have observed that the iron chelators tachpyridine and desferioxamine activate the p53 tumor suppressor protein. The goal of this application is to define specific molecular mechanisms by which iron chelators induce apoptotic cell death. Independent of their ultimate clinical use (i.e., in the treatment of iron overload, cancer, or other diseases), these studies will provide insights into effects of iron chelators that will be important to consider in future chelator design and application.
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