REGULATION OF IRON HOMEOSTASIS IN OXIDATIVE STRESS

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DESCRIPTION (provided by applicant): Induction of detoxification enzymes is an important mechanism of cytoprotection against carcinogens and chemical/oxidative stress. Transcriptional activation of antioxidant detoxification genes by oxidative stress is driven by a cis-acting element, termed the antioxidant response element (ARE), however, the molecular mechanisms by which the ARE enhancer is activated by oxidative stress are not fully elucidated.Ferritin, composed of 24 subunits of the H and L types, is a ubiquitous and highly conserved iron-storage protein that plays a prominent role in maintaining iron homeostasis. Sequestration of intracellular free iron by Ferritin is an important cellular defense mechanism because it limits iron-catalyzed generation of hydroxyl radicals that elicit oxidative stress and cell damage. Indeed, others and we demonstrated that oxidative stress activates transcription of the ferritin H and L genes. However, the molecular mechanisms by which ferritin transcription is activated by oxidative stress remain unexplored. The overall goal of this research proposal is to understand molecular mechanisms underlying transcriptional activation of the ferritin H gene in response to oxidative stress. We propose that oxidative stress activates specific transcription factors by posttranslational modifications, which then bind to the 75 bp oxidative stress response element (OSRE) composed of two bidirectional ARE motifs in the ferritin H gene. Moreover, depending on oxidative conditions of the cells, the two ARE motifs in the ferritin H OSRE may function as both double strand and single strand (stem loop) DNA enhancer elements. To test this hypothesis we will, 1) identify the transcription factors and adaptor proteins that bind to the OSRE and activate transcription of the ferritin H gene in response to oxidative stress, and 2) elucidate oxidative stress-mediated posttranslational modifications of transcription factors and signaling pathways leading to transcriptional activation of the ferritin H gene.These studies will provide significant information for our understanding of molecular mechanisms by which transcription of the ferritin H gene is activated via ARE motifs in response to oxidative stress, and ultimately by which iron homeostasis is tuned to minimize oxidative cell damage under prooxidant conditions.