The Rpd3/Hda1 family of histone deacetylases regulates azole resistance in Candida albicans

Objectives: The histone deacetylase (HDAC) has recently been linked to the morphogenesis and virulence of yeast. However, the effects of HDAC on antifungal susceptibility are not well understood. We sought to characterize the action of histone deacetylation on azole resistance in Candida albicans and its possible mechanism of action. Methods: A total of 40 C. albicans strains were studied. Azole susceptibility with or without trichostatin A (TSA) was determined according to the CLSI microdilution method. The null mutants of HDA1 and RPD3 (genes targeted by TSA) were also investigated using drop-plate assays and a rapid acquisition of adaptation to the azole test. Transcriptional levels of HDAC genes and efflux genes were quantified using RT-PCR for both the basal and fluconazole-induced conditions. Results: The inhibition of HDACs by TSA (0.25 mg/L) markedly reduced the trailing growth and the growth of most C. albicans strains. Trailing growth for C. albicans strains was decreased from 2-fold to 256-fold at 48 h. The deletion of HDA1 or RPD3 increased the susceptibility to azoles compared with the WT strain. The expression of HDA1 and RPD3 was up-regulated to different levels, and returned to the level of the susceptible parental strain when stable resistance had formed during the course of acquired fluconazole resistance both in vitro and in vivo. Efflux genes were poorly expressed in mutant strains compared with those of the WT strain. Conclusions: Our results indicate the important role of the Rpd3/Hda1 family in the development of azole resistance in C. albicans. Histone deacetylation may govern the expression of genes related to the early stages of adaptation to azole stress, such as efflux pump genes.