Doctor of Philosophy (PhD)


Veterinary Medical Sciences - Pathobiological Sciences

Document Type



Heme oxygenase-1 (HO-1) catalyzes the initial and rate-limiting reaction in heme catabolism (yielding equimolar quantities of iron, carbon monoxide, and biliverdin), which is further metabolized to bilirubin by biliverdin reductase. HO-1, an important enzyme with antioxidant and cytoprotective properties, functions against oxidative stress generated in response to heme and to various stress stimuli, such as zinc. The cytoprotective function of HO-1 is dependent on both the activities of the reaction products and on the inducibility of the heme oxygenase gene (hmox-1), which is regulated primarily at the level of gene transcription by two distal enhancers, E1 and E2. Characterization of the enhancers led to the identification of multiple stress response elements (StREs) that are necessary and sufficient for hmox-1 gene regulation by almost all inducers tested. Studies from this laboratory identified Nrf-2 as a dominant regulator that mediates activation of hmox-1 via the StRE motifs by several inducers, including zinc. Accumulating evidence from work done in our lab suggested that Nrf-2 was partly regulated by subcellular compartmentalization in the cytoplasm and transported to the nucleus upon stimulation by stress agents to activate target genes like hmox-1. Investigation of the subcellular compartmentalization and cytoplasmic-nuclear transport of Nrf-2 in Hepa cells revealed that Nrf-2 is a highly labile protein that is rapidly and specifically degraded by the ubiquitin-proteasome pathway, and that zinc stimulation results in Nrf2 stabilization. Furthermore, transactivation of E1 luciferase reporter activity was not completely abolished when all three StREs were mutated, suggesting that other transcription factors and cis-acting DNA elements may be involved in hmox-1 regulation. Examination of the hmox-1 sequence revealed other conserved regions within E1. My analysis of the conserved sequences (CS) led to identification of a functional heat shock element (HSE) in the 5’ end of E1that had no response to zinc. Findings suggest ERK1 plays an important role in inducer-dependent regulation of hmox-1 by zinc through its action (phosphorylation of Nrf-2 and cooperation between the StRE and Nrf-2 induce hmox-1). In conclusion, targeting Nrf-2-ERK1 individually or together allows for controlled regulation of hmox-1 expression and illuminates new avenues of research and strategies for therapeutic intervention and treatment in diseases involving oxidative stress and HO-1 expression.



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Committee Chair

James E. Miller