Iron and copper transporter trafficking in healthy and diseased melanocytes

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DESCRIPTION (provided by applicant): Copper and iron are cofactors for many cellular enzymes and transporters, but are also toxic redox-reactive transition metals. Their cellular levels are thus tightly controlled by specific transporters that import extracellular ion to the cytoplasm, and for copper by ATP-dependent pumps (ATP7A and ATP7B) that export copper from the cytosol to the secretory/endocytic pathway or outside the cell. ATP7A deficiency causes Menkes Disease, a severe developmental and systemic disorder of cytoplasmic copper accumulation and failure to load secretory cuproproteins. Neither the mechanisms by which copper is loaded from ATP7A into target cuproproteins nor those regulating the subcellular distribution of copper and iron transporters are understood. The ATP7A orthologue in yeast is needed to activate copper-dependent iron import; whether such a link between cellular copper and iron import exists in mammals is not known. This proposal exploits unique properties of melanocytes, in which copper is a cofactor for the melanin biosynthetic enzyme, tyrosinase, to dissect molecular mechanisms regulating copper and iron transporter localization and copper loading onto secretory proteins. Preliminary data suggest that an ATP7A cohort in melanocytes localizes to melanosomes dependent on its target cuproenzyme, tyrosinase, and on BLOC-1, a cytoplasmic complex defective in the vesicular transport disorder, Hermansky Pudlak Syndrome (HPS). Moreover, a copper-dependent ATP7A translocation defect and elevated transferrin receptor levels in HPS melanocytes suggest that BLOC-1 may regulate copper and iron import. Our unique expertise in HPS and melanocyte cell biology and our collaborator's expertise in iron and copper metabolism will be applied to the following Specific Aims: 1. To test the hypothesis that ATP7A localizes to melanosomes by associating with its substrate, tyrosinase. 2. To test the hypothesis that copper import is regulated by the HPS-associated BLOC-1 complex. 3. To test the hypothesis that iron import in melanocytes is regulated by BLOC-1 and by copper import. Summary: Menkes Disease is due to a genetic defect in iron and copper flux in many cell types, and Hermansky Pudlak Syndrome is an often lethal genetic disorder of only certain cell types, including pigment cells. This proposal tests the hypothesis that Hermansky Pudlak Syndrome results from iron and copper dysregulation in the affected cell types.