Studies on Differential Regulation of Homologous Copper ATPases ATP7A and ATP7B

Ruturaj, . (2024) Studies on Differential Regulation of Homologous Copper ATPases ATP7A and ATP7B. PhD thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

The essentiality of copper for biological processes is countered by its toxicity in excess, requiring its tight regulation in living organisms. Mammalian copper homeostasis relies on specific transporters—CTR1 for import, ATP7A, and ATP7B for utilization and export. These homologous copper ATPases ATP7A and ATP7B, located in the trans-Golgi network (TGN), regulate intracellular copper distribution. In polarized epithelia, ATP7A and ATP7B traffics to distinct plasma membrane surfaces in response to varying cytoplasmic copper levels, aiding in the study of ligand-mediated trafficking. My research focused on identifying the polarized sorting pathways of ATP7A and ATP7B, and determining the mechanism of their distinct trafficking patterns under varying copper concentrations. Investigating their TGN localization and intermediates compartments en route to the plasma membranes revealed their nuanced responses to copper levels. Proximity biotinylation and mass spectrometry identified potential regulatory partners, highlighting the role of the Clathrin adaptor protein complex AP-1 in their sorting at the TGN. Knocking out AP-1 greatly influenced the retention and polarity of ATP7A and ATP7B that in turn affects trafficking dynamics. Resistance to certain heavy metal drugs is a major hurdle in developing chemotherapy in cancers. Upon exploring ATP7B's role in metal-based drug resistance revealed their ability to sequester and efflux platinum-based compounds like cisplatin and oxaliplatin. Investigating ruthenium complexes as potential alternatives to platinum drugs due to their anticancer properties, showed ATP7B's ability to sequester these complexes as well. However, certain ruthenium compounds resisted cellular thiol and glutathione interactions, evading ATP7B-mediated sequestration and inducing apoptosis without altering ATP7B expression levels. The study suggests that ruthenium(II) η6-p-cymene complexes, especially those resistant to ATP7B binding, possess potential as anticancer agents by evading detoxification pathways. These findings offer insights into the intricate mechanisms of copper homeostasis and its implications in drug resistance, paving the way for exploring novel therapies in cancer treatment.

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