| Copper (Cu) and iron (Fe) are essential to life. Living organisms use these two metal ions as cofactors in enzymes important in physiological processes including energy production and DNA synthesis. The current knowledge indicates that uptake pathways for Cu and Fe are linked with one another, because changes in the concentration of one metal affect the concentration of the other one in cells. Living organisms fed a Cu-deficient diet develop Fe-deficient anemia; yet under anemic conditions, the body accumulates excess Cu. Excessive accumulation of either metal is detrimental and linked to cancer and neurodegeneration. Thus, in order to fully understand the roles for Cu and Fe in cell physiology and cancer and neurodegenerative disease biology we must determine the molecular mechanism underlying the homeostatic interaction between Cu and Fe.; My thesis research uses yeast Saccharomyces cerevisiae to study Cu and Fe interactions. The yeast is ideal for this study because it carries out similar biochemical reactions as human cells. Using both genetic and biochemical approaches, I first discovered that Cu+ but not Cu2+ is toxic to cells and that Fet3p, a component of the Fe-transporter complex, plays a critical role in detoxifying Cu+. It catalyzes Cu+ oxidation therefore protecting cells from Cu+ toxicity. This discovery suggests that Cu+ toxicity is an important contributing factor in neurodegeneration because loss of Fet3p homolog human ceruloplasmin causes the neurodegenerative disease, associated with aceruloplasnemia. Second, I found that Aft1p, the activator of Fe-transporter genes, also positively regulates MAC1, the activator for the Cu-transporter genes, therefore showing that Cu uptake is directly connected with Fe uptake. Third, I found a control region for the expression of MAC1 and obtained evidence showing that Cu homeostasis is directly linked to other physiological processes such as phosphate utilization and the cell cycle. Fourth, I found that Aft1p suppresses RNR2 transcription under Fe deficiency, which indicates that Fe modulates directly DNA synthesis because RNR2 encodes an enzyme essential for dNTP synthesis. The outcomes of my research have not only provided new insights into the basis of Cu and Fe physiology but also have offered new clues as to how Cu and Fe toxicity may contribute to neurodegeneration. |
