Metal Chelation as a Powerful Strategy to Probe Cellular Circuitry Governing C. albicans Drug Resistance and Morphogenesis

E. J. Polvi, L. E. Cowen

Author address: 

Univ. of Toronto, Toronto, ON, Canada


Fungal pathogens have evolved diverse strategies to sense host relevant cues and coordinate cellular responses, which enable virulence and drug resistance. Defining circuitry controlling drug resistance and virulence opens new opportunities for chemical diversity in therapeutic drugs, as the cognate inhibitors are not typically explored by conventional screening approaches. This has great potential to address the pressing need for new strategies to treat invasive fungal infections, which have a staggering impact on human health. To explore this approach, we focused on a leading fungal pathogen of humans, Candida albicans, and performed a screen of 1,280 pharmacologically active compounds to identify those that abrogate resistance to the echinocandins, which are the newest class of antifungal and target synthesis of the fungal cell wall. We identified 13 compounds that abolished echinocandin resistance of a clinical isolate, with the broad spectrum chelator DTPA having the most potent synergistic activity. Depletion of metals individually revealed that DTPA modulates echinocandin resistance via chelation of magnesium. Whole genome sequencing of mutants resistant to the combination of DTPA and echinocandin identified mutations in the histidine kinase gene, NIK1. Furthermore, NIK1 mutations are sufficient to confer resistance to the combination. Functional analyses demonstrated that DTPA activates the mitogen-activated protein kinase Hog1, and that NIK1 mutations block activation of Hog1 in response to both echinocandin and DTPA. This suggests that DTPA may modulate Hog1 signaling through Nik1, in order to enhance the efficacy of echinocandins. We found that DTPA not only abrogates drug resistance but also modulates morphogenesis, a key virulence trait that is normally regulated by environmental cues. DTPA induced filamentation via depletion of zinc, in a manner that is contingent upon Ras1-protein kinase A (PKA) signaling, as well as the transcription factors Brg1 and Rob1. Thus, we establish a new mechanism by which metal chelation modulates morphogenetic circuitry and echinocandin resistance, and illuminate a new facet to metal homeostasis at the host-pathogen interface.

abstract No: 


Full conference title: 

ASM Microbe 2016
    • ASM microbe 1st (2016)