cis -Acting Elements within the Candida albicans ERG11 Promoter Mediate the Azole Response through Transcription Factor Upc2p

Abstract

The azole antifungal drugs are used to treat infections caused by Candida albicans and other fungi. These drugs interfere with the biosynthesis of ergosterol, the major sterol in fungal cells, by inhibiting an ergosterol biosynthetic enzyme, lanosterol 14 ␣-demethylase, encoded by the ERG11 gene. In vitro, these drugs as well as other ergosterol biosynthesis inhibitors increase ERG11 mRNA expression by activation of the ERG11 promoter. The signal for this activation most likely is the depletion of ergosterol, the end product of the pathway. To identify cis-acting regulatory elements that mediate this activation, ERG11 promoter fragments have been fused to the luciferase reporter gene from Renilla reniformis. Promoter deletions and linker scan mutations localized the region important for azole induction to a segment from bp ؊224 to ؊251 upstream of the start codon, specifically two 7-bp sequences separated by 13 bp. These sequences form an imperfect inverted repeat. The region is recognized by the transcription factor Upc2p and functions as an enhancer of transcription, as it can be placed upstream of a heterologous promoter in either direction, resulting in the azole induction of that promoter. The promoter constructs are not azole inducible in the upc2/upc2 homozygous deletion, demonstrating that Upc2p controls the azole induction of ERG11. These results identify an azole-responsive enhancer element (ARE) in the ERG11 promoter that is controlled by the Upc2p transcription factor. No other ARE is present in the promoter. Thus, this ARE and Upc2p are necessary and sufficient for azole induction of ERG11.

Overexpression and mutation as a genetic mechanism of fluconazole resistance in Candida albicans isolated from human immunodeficiency virus patients in Indonesia

“…This can be explained by the similarity in azole compounds; these are substrates for multidrug efflux transporters that respond to ERG11 mutations (Andes et al, 2006;Song et al, 2004). Multiple resistance to azole antifungals was mainly associated with specific point mutations in the ERG11 gene (Marichal et al, 1999;Wang et al, 2009;Goldman et al, 2004), and was also associated with overexpression of the ERG11 gene and efflux pumps encoded by the CDR1, CDR2 and MDR1 genes (Hoot et al, 2008;Oliver et al, 2007).…”

Regulatory Circuitry Governing Fungal Development, Drug Resistance, and Disease

“…The transcription factor Upc2 upregulates ERG11 expression in response to azoles and thereby contributes to azole resistance (534). Upc2 binds to the azole-responsive enhancer element (ARE), a region localized to two distinct 7-bp sequences at positions Ϫ224 to Ϫ251 in the ERG11 promoter (433). Both the ARE and Upc2 are necessary and sufficient for the azole induction of ERG11 (433).…”

“…Upc2 binds to the azole-responsive enhancer element (ARE), a region localized to two distinct 7-bp sequences at positions Ϫ224 to Ϫ251 in the ERG11 promoter (433). Both the ARE and Upc2 are necessary and sufficient for the azole induction of ERG11 (433). Upc2 also binds to two distinct regions in its own promoter to autoregulate expression during azole exposure (229).…”

Ascorbic Acid Inhibition of Candida albicans Hsp90-Mediated Morphogenesis Occurs via the Transcriptional Regulator Upc2

“…One of the genes that is regulated by Upc2 is ERG11, a gene involved in ergosterol biosynthesis and the molecular target of the azole antifungals (15,22,43,61,62). Previous work demonstrated that lower ergosterol levels, caused by ergosterol biosynthesis inhibitors, such as azoles, have an inhibitory effect on hypha formation (63,64).…”