The Metal Chelating and Chaperoning Effects of Clioquinol: Insights from Yeast Studies

Clioquinol (CQ), a once popular antibiotic, was used to inhibit the growth of microorganisms. Recently, CQ and its analog PBT2 have shown encouraging effects in the animal and clinical trials for Alzheimer's disease (AD). However, the mechanism by which this class of molecules works remains controversial. In this work, we used the yeast Saccharomyces cerevisiae as a model to study how CQ affects molecular and cellular functions and particularly, copper, iron, and zinc homeostasis. We observed a CQ-induced inhibition of yeast growth, which could be slightly relieved by supplementation of copper or iron. Microarray results indicated that yeast cells treated with CQ sense a general deficiency in metals, despite elevated total cellular contents of copper and iron. Consistent with this, reduced activities of some metal-sensitive enzymes were observed. Intriguingly, CQ can increase the SOD1 activity, likely through Ccs1's accessibility to CQ-bound copper ions. Further studies revealed that CQ sequestrates copper and iron at the cellular membrane, likely the plasma membrane, resulting overall metal accumulation but cytosolic metal depletion. CQ's effects on metal-sensitive metalloenzymes were also verified in mammalian cell line SH-SY5Y. Together, our results revealed that CQ can regulate metal homeostasis by binding metal ions, resulting the cell sensing a state of deficiency of bio-available metal ions while simultaneously increasing available metals to SOD1 (via Ccs1) and possibly some other metalloproteins that can access CQ-bound metals. We hope this regulation of metal homeostasis may be helpful in explaining the therapeutic effects of CQ used in disease treatment.