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Published on: June 13, 2021
Mediator Tail Module Is Required for Tac1-Activated CDR1 Expression and Azole Resistance in Candida albicans
Zhongle Liu1, Lawrence C Myers2,1
1Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA.
Abstract:
The human fungal pathogen Candida albicans develops drug resistance after long-term exposure to azole drugs in the treatment of chronic candidiasis. Gain-of-function (GOF) mutations in the transcription factor Tac1 and the consequent expression of its targets, drug efflux pumps Cdr1 and Cdr2, are a common mechanism by which C. albicans acquires fluconazole resistance. The mechanism by which GOF mutations hyperactivate Tac1 is currently unknown. Here, we define a transcriptional activation domain (TAD) at the C terminus of Tac1. GOF mutations within the Tac1 TAD, outside the context of full-length Tac1, generally do not enhance its absolute potential as a transcriptional activator. Negative regulation of the Tac1 TAD by the Tac1 middle region is necessary for the activating effect of GOF mutations or fluphenazine to be realized. We have found that full-length Tac1, when hyperactivated by xenobiotics or GOF mutations, facilitates the recruitment of the Mediator coactivator complex to the CDR1 promoter. Azole resistance and the activation of Tac1 target genes, such as CDR1, are dependent on the Tac1 TAD and subunits of the Mediator tail module. The dependence of different Tac1 target promoters on the Mediator tail module, however, varies widely. Lastly, we show that hyperactivation of Tac1 is correlated with its Mediator-dependent phosphorylation, a potentially useful biomarker for Tac1 hyperactivation. The role of Mediator in events downstream of Tac1 hyperactivation in fluconazole-resistant clinical isolates is complex and provides opportunities and challenges for therapeutic intervention.
Insights
Gain-of-function mutations in Tac1 activate drug efflux pumps, causing azole resistance in Candida albicans. This hyperactivation depends on the Tac1 transcriptional activation domain and Mediator complex recruitment.
Area of Science:
- Molecular biology
- Mycology
- Drug resistance mechanisms
Background:
- * *Candida albicans* develops resistance to azole drugs during chronic candidiasis treatment.
- * Gain-of-function (GOF) mutations in the transcription factor Tac1 lead to overexpression of drug efflux pumps (Cdr1, Cdr2), conferring fluconazole resistance.
- * The precise mechanism of Tac1 hyperactivation by GOF mutations remains unclear.
Purpose of the Study:
- * To elucidate the mechanism by which GOF mutations hyperactivate the transcription factor Tac1.
- * To investigate the role of the Tac1 transcriptional activation domain (TAD) and the Mediator complex in azole resistance.
- * To identify potential biomarkers for Tac1 hyperactivation.
Main Methods:
- * Characterization of the Tac1 transcriptional activation domain (TAD).
- * Analysis of Tac1 function in full-length and truncated forms.
- * Investigation of Mediator complex recruitment to target gene promoters.
- * Assessment of Tac1 phosphorylation as a biomarker.
Main Results:
- * A TAD was identified at the C terminus of Tac1; GOF mutations within it did not enhance activation independently.
- * Negative regulation by the Tac1 middle region is crucial for GOF mutation-mediated activation.
- * Hyperactivated Tac1 recruits the Mediator complex to the *CDR1* promoter.
- * Tac1 target gene activation and azole resistance depend on the Tac1 TAD and Mediator tail module.
- * Tac1 hyperactivation correlates with Mediator-dependent phosphorylation.
Conclusions:
- * The Tac1 TAD and Mediator complex are essential for azole resistance in *C. albicans*.
- * Mediator-dependent phosphorylation of Tac1 serves as a potential biomarker for hyperactivation.
- * Understanding Mediator's role offers therapeutic intervention strategies against drug-resistant fungal infections.
