Functional Divergence of Hsp90 Genetic Interactions in Biofilm and Planktonic Cellular States

Abstract

Candida albicans is among the most prevalent opportunistic fungal pathogens. Its capacity to cause life-threatening bloodstream infections is associated with the ability to form biofilms, which are intrinsically drug resistant reservoirs for dispersal. A key regulator of biofilm drug resistance and dispersal is the molecular chaperone Hsp90, which stabilizes many signal transducers. We previously identified 226 C. albicans Hsp90 genetic interactors under planktonic conditions, of which 56 are involved in transcriptional regulation. Six of these transcriptional regulators have previously been implicated in biofilm formation, suggesting that Hsp90 genetic interactions identified in planktonic conditions may have functional significance in biofilms. Here, we explored the relationship between Hsp90 and five of these transcription factor genetic interactors: BCR1, MIG1, TEC1, TUP1, and UPC2. We deleted each transcription factor gene in an Hsp90 conditional expression strain, and assessed biofilm formation and morphogenesis. Strikingly, depletion of Hsp90 conferred no additional biofilm defect in the mutants. An interaction was observed in which deletion of BCR1 enhanced filamentation upon reduction of Hsp90 levels. Further, although Hsp90 modulates expression of TEC1, TUP1, and UPC2 in planktonic conditions, it has no impact in biofilms. Lastly, we probed for physical interactions between Hsp90 and Tup1, whose WD40 domain suggests that it might interact with Hsp90 directly. Hsp90 and Tup1 formed a stable complex, independent of temperature or developmental state. Our results illuminate a physical interaction between Hsp90 and a key transcriptional regulator of filamentation and biofilm formation, and suggest that Hsp90 has distinct genetic interactions in planktonic and biofilm cellular states.

Pathogenesis and Clinical Relevance of Candida Biofilms in Vulvovaginal Candidiasis

“…Six of these transcriptional regulators have previously been involved in biofilm development, proposing that the genetic interactors of Hsp90 found in planktonic conditions might have functional significance in biofilm formation. They further studied the relationship between Hsp90 and five of these transcription factor genetic interactors: BCR1, MIG1, TEC1, TUP1, and UPC2 (Diezmann et al, 2015). The overexpression of Ywp1 protein in the cell wall makes the biofilm more adherent, as it negatively regulates the dispersion process.…”

Calcineurin in fungal virulence and drug resistance: Prospects for harnessing targeted inhibition of calcineurin for an antifungal therapeutic approach

“…Studies on Hsp90 in C. albicans have clearly demonstrated its role in biofilm formation and the evolution of drug resistance. [104][105][106][107][108] Although Hsp90 inhibitors have potent synergistic antifungal activity in combination with azoles and echinocandins, 109,110 we are faced with the challenge of overcoming toxic effects of current Hsp90 inhibitors in use. Hsp90 is known to regulate azole resistance through its key downstream effectors, calcineurin and the Mkc1 kinase in C. albicans.…”

The Hsp90 Chaperone Network Modulates Candida Virulence Traits

“…Hsp90 genetic interactors are also divergent in biofilm conditions. The transcription factor genes BCR1 , MIG1 , TEC1 , TUP1 , and UPC2 are Hsp90 genetic interactors in planktonic conditions [38], but not in biofilms [93]. This highlights the need for a systematic analysis of Hsp90 interactions in biofilms to establish how the chaperone network is rewired in distinct cellular states.…”