A novel Hsp90 phospho-switch modulates virulence in the major human fungal pathogenCandida albicans

Abstract

The ubiquitous molecular chaperone Hsp90 is a key regulator of cellular proteostasis and environmental stress responses. Hsp90 also regulates cellular morphogenesis, drug resistance, and virulence in human pathogenic fungi, which kill more than 1.6 million patients each year worldwide. Invasive fungal infections are difficult to treat due to the lack of effective antifungal therapies, resulting in mortality rates of up to 95%. As a key regulator of fungal virulence, Hsp90 is an attractive therapeutic target. However, fungal and animal homologs are highly conserved, impeding fungal-specific targeting. Thus, understanding the factors that regulate Hsp90 could provide an alternative strategy aimed at exclusively targeting this regulator of fungal virulence. Here, we demonstrate how CK2-mediated phosphorylation of two Hsp90 residues modulates virulence in a major fungal pathogen of humans, Candida albicans. We combined proteomics, molecular evolution and structural modelling with molecular biology to identify and characterize two Hsp90 phosphorylation sites. Phosphorylation negatively affects thermal stress response, morphogenesis, drug susceptibility and fungal virulence. Our results provide the first record of specific Hsp90 phosphorylation sites acting as modulators of fungal virulence. Post-translational modifications of Hsp90 could prove valuable in future exploitation as antifungal drug targets.

Unmasking of CgYor1-Dependent Azole Resistance Mediated by Target of Rapamycin (TOR) and Calcineurin Signaling in Candida glabrata

“…Hsp90 is phosphorylated by protein kinase CK2, which is a tetramer of four subunits—two activator α-subunits (Cka1 and Cka2) and two regulatory β-subunits (Ckb1 and Ckb2).The KNS1 kinase phosphorylates regulatory subunit CKb2 of CK2, resulting in its activation ( 61 ). The active phosphorylated CK2, in turn, phosphorylates Hsp90 and suppresses the calcineurin, which makes cells unable to combat various stresses, including azoles ( 62 , 63 ). A previous report has indicated that both the regulatory and activation subunits of protein kinase CK2 mutants are involved in azole resistance in C. albicans ( 64 ).…”

Decrypting the chaperone code

“…Stephanie Diezmann (University of Bristol, UK) described a new phosphorylation site (S530) on Candida albicans Hsp90, targeted by casein kinase 2 (CK2), which results in the inhibition of Hsp90 function and blocking expression of key virulence traits. She showed that the phosphomimetic mutant S530E (but not S530A) abolished C. albicans survival at high temperatures, supported a switch to filamentous growth, a morphological change that is important for fungal virulence, and rendered C. albicans susceptible to both antifungal (fluconazole) and Hsp90 (radicicol) drugs ( 11 ). These studies support the idea that specific Hsp90 PTMs may be exploited as potential antifungal drug targets.…”