Pho85, Pcl1, and Hms1 Signaling Governs Candida albicans Morphogenesis Induced by High Temperature or Hsp90 Compromise

BACKGROUND Temperature exerts powerful control over development and virulence of diverse pathogens. In the leading human fungal pathogen, Candida albicans, temperature governs morphogenesis, a key virulence trait. Many cues that induce the yeast to filament transition are contingent on a minimum of 37°C, whereas further elevation to 39°C serves as an independent inducer. The molecular chaperone Hsp90 is a key regulator of C. albicans temperature-dependent morphogenesis. Compromise of Hsp90 function genetically, pharmacologically, or by elevated temperature induces filamentation in a manner that depends on protein kinase A signaling but is independent of the terminal transcription factor, Efg1. RESULTS Here, we establish that despite morphological and regulatory differences, inhibition of Hsp90 induces a transcriptional profile similar to that induced by other filamentation cues and does so independently of Efg1. Further, we identify Hms1 as a transcriptional regulator required for morphogenesis induced by elevated temperature or Hsp90 compromise. Hms1 functions downstream of the cyclin Pcl1 and the cyclin-dependent kinase Pho85, both of which are required for temperature-dependent filamentation. Upon Hsp90 inhibition, Hms1 binds to DNA elements involved in filamentous growth, including UME6 and RBT5, and regulates their expression, providing a mechanism through which Pho85, Pcl1, and Hms1 govern morphogenesis. Consistent with the importance of morphogenetic flexibility for virulence, deletion of C. albicans HMS1 attenuates virulence in a metazoan model of infection. CONCLUSIONS Thus, we establish a new mechanism through which Hsp90 orchestrates C. albicans morphogenesis, and define novel regulatory circuitry governing a temperature-dependent developmental program, with broad implications for temperature sensing and virulence of microbial pathogens.