Functional characterization of Candida albicans Hos2 histone deacetylase

Abstract

Candida albicans is a mucosal commensal organism in normal individuals, but is a major pathogen causing systemic and mucosal infections in immunocompromised individuals. Azoles have been very effective anti-fungal agents and the mainstay in treating opportunistic mold and yeast infections. Azole resistant strains have emerged compromising the utility of this class of drugs. It has been shown that azole resistance can be reversed by the co-administration of a histone deacetylase (HDAC) inhibitor, suggesting that resistance is mediated by epigenetic mechanisms possibly involving Hos2, a fungal deacetylase. We report here the cloning and functional characterization of HOS2 (High Osmolarity Sensitive) , a gene coding for fungal histone deacetylase from C. albicans. Inhibition studies showed that Hos2 is susceptible to pan inhibitors such as trichostatin A (TSA) and suberoylanilide hydroxamic acid (SAHA), but is not inhibited by class I inhibitors such MS-275. Purified Hos2 protein consistently deacetylated tubulins, rather than histones from TSA-treated cells. This in vitro enzymatic assay, which is amenable to high throughput could be used for screening potent fungal Hos2 inhibitors that could be a potential anti-fungal adjuvant. Hos2 has been reported to be a putative NAD+ dependent histone deacetylase, a feature of sirtuins. We assayed for sirtuin activation with resveratrol and purified Hos2 protein and did not find any sirtuin activity.

Chromatin Structure and Drug Resistance in Candida spp.

“…proteins. From the point of view of KDACs, to date only C. albicans Hos2p has been purified and assessed in vitro and, unexpectedly, Hos2p is inactive on acetylated histones but capable of deacetylating tubulin [ 180 ]. Therefore, it could be hypothesized that Hos2p inhibition by MGCD290 may be indirectly compromising the fungal cytoskeleton, and not influencing drug resistance mechanisms.…”

“…Most importantly, structure-function information about Candida KDACs is lacking that would aid in the design of fungal-specific inhibitors. Furthermore, biochemical analysis is required to further the development of robust and high throughput assays necessary to screen potential yeast-specific inhibitors of chromatin modifiers, such as the one outlined for C. albicans Hos2p function [ 180 ].…”