Set1-mediated histone H3K4 methylation is required for azole induction of the ergosterol biosynthesis genes and antifungal drug resistance in Candida glabrata

Abstract

ABSTRACTCandida glabrata is an opportunistic pathogen that has developed the ability to adapt and thrive under azole treated conditions. The common mechanisms that can result in Candida drug resistance are due to mutations or overexpression of the drug efflux pump or the target of azole drugs, Cdr1 and Erg11, respectively. However, the role of epigenetic histone modifications in azole-induced gene expression and drug resistance are poorly understood in C. glabrata. In this study, we show for the first time that Set1 mediates histone H3K4 mono-, di-, and trimethylation in C. glabrata. In addition, loss of SET1 and histone H3K4 methylation results in increased susceptibility to azole drugs in both C. glabrata and S. cerevisiae. Intriguingly, this increase in susceptibility to azole drugs in strains lacking Set1-mediated histone H3K4 methylation is not due to altered transcript levels of CDR1, PDR1 or Cdr1’s ability to efflux drugs. Genome-wide transcript analysis revealed that Set1 is necessary for azole-induced expression of 12 genes involved in the late biosynthesis of ergosterol including ERG11 and ERG3. Importantly, chromatin immunoprecipitation analysis showed that histone H3K4 trimethylation was detected on chromatin of actively transcribed ERG genes. Furthermore, H3K4 trimethylation increased upon azole-induced gene expression which was also found to be dependent on the catalytic activity of Set1. Altogether, our findings show that Set1-mediated histone H3K4 methylation governs the intrinsic drug resistant status in C. glabrata via epigenetic control of azole-induced ERG gene expression.IMPORTANCEC. glabrata is the second most commonly isolated species from Candida infections, coming in second to C. albicans. Treatment of C. glabrata infections are difficult due to their natural resistance to antifungal azole drugs and their ability to adapt and become multidrug resistant. In this study, we investigated the contributing cellular factors for controlling drug resistance. We have determined that an epigenetic mechanism governs the expression of genes involved in the late ergosterol biosynthesis pathway, an essential pathway that antifungal drugs target. This epigenetic mechanism involves histone H3K4 methylation catalyzed by the Set1 methyltransferase complex (COMPASS). We also show that Set1-mediated histone H3K4 methylation is needed for expression of specific azole induced genes and azole drug resistance in C. glabrata. Identifying epigenetic mechanisms contributing to drug resistance and pathogenesis could provide alternative targets for treating patients with fungal infections.