Abstract
Background:Saccharomyces cerevisiae sterol gene expression is regulated by a consensus sterol-response promoter element (SRE/AR1(c)). Results: The anaerobic AR1(b) promoter element regulates global antifungal-dependent sterol gene expression. Conclusion: Yeast sterol gene expression is regulated by multiple SRE-like elements. Significance: Understanding sterol gene expression will yield valuable information concerning antifungal drug resistance. Saccharomyces cerevisiae ergosterol biosynthesis, like cholesterol biosynthesis in mammals, is regulated at the transcriptional level by a sterol feedback mechanism. Yeast studies defined a 7-bp consensus sterol-response element (SRE) common to genes involved in sterol biosynthesis and two transcription factors, Upc2 and Ecm22, which direct transcription of sterol biosynthetic genes. The 7-bp consensus SRE is identical to the anaerobic response element, AR1(c). Data indicate that Upc2 and Ecm22 function through binding to this SRE site. We now show that it is two novel anaerobic AR1(b) elements in the UPC2 promoter that direct global ERG gene expression in response to a block in de novo ergosterol biosynthesis, brought about by antifungal drug treatment. The AR1(b) elements are absolutely required for auto-induction of UPC2 gene expression and protein and require Upc2 and Ecm22 for function. We further demonstrate the direct binding of recombinant expressed S. cerevisiae ScUpc2 and pathogenic Candida albicans CaUpc2 and Candida glabrata CgUpc2 to AR1(b) and SRE/AR1(c) elements. Recombinant endogenous promoter studies show that the UPC2 anaerobic AR1(b) elements act in trans to regulate ergosterol gene expression. Our results indicate that Upc2 must occupy UPC2 AR1(b) elements in order for ERG gene expression induction to take place. Thus, the two UPC2-AR1(b) elements drive expression of all ERG genes necessary for maintaining normal antifungal susceptibility, as wild type cells lacking these elements have increased susceptibility to azole antifungal drugs. Therefore, targeting these specific sites for antifungal therapy represents a novel approach to treat systemic fungal infections.