A Class 1 Histone Deacetylase with Potential as an Antifungal Target

Abstract

Histone deacetylases (HDACs) remove acetyl moieties from lysine residues at histone tails and nuclear regulatory proteins and thus significantly impact chromatin remodeling and transcriptional regulation in eukaryotes. In recent years, HDACs of filamentous fungi were found to be decisive regulators of genes involved in pathogenicity and the production of important fungal metabolites such as antibiotics and toxins. Here we present proof that one of these enzymes, the class 1 type HDAC RpdA, is of vital importance for the opportunistic human pathogen Aspergillus fumigatus. Recombinant expression of inactivated RpdA shows that loss of catalytic activity is responsible for the lethal phenotype of Aspergillus RpdA null mutants. Furthermore, we demonstrate that a fungus-specific C-terminal region of only a few acidic amino acids is required for both the nuclear localization and catalytic activity of the enzyme in the model organism Aspergillus nidulans. Since strains with single or multiple deletions of other classical HDACs revealed no or only moderate growth deficiencies, it is highly probable that the significant delay of germination and the growth defects observed in strains growing under the HDAC inhibitor trichostatin A are caused primarily by inhibition of catalytic RpdA activity. Indeed, even at low nanomolar concentrations of the inhibitor, the catalytic activity of purified RpdA is considerably diminished. Considering these results, RpdA with its fungus-specific motif represents a promising target for novel HDAC inhibitors that, in addition to their increasing impact as anticancer drugs, might gain in importance as antifungals against life-threatening invasive infections, apart from or in combination with classical antifungal therapy regimes.

Essential role of Rpd3‐dependent lysine modification in the growth, development and virulence of Beauveria bassiana

“…B). The LSCM images indicated a localization of Rpd3 mainly in the nuclei of B. bassiana as reported in A. nidulans (Bauer et al ., ).…”

“…The absence of Rpd3 caused severe growth defects on different carbon (sugar/polyol) and nitrogen (organic/inorganic) sources. The viable Δ rpd3 mutant is different from the lethal phenotype of Δ rpdA in A. nidulans (Bauer et al ., ). In Δ rpd3 , severe growth defects concurred with lysine modification and/or differential expression of many enzymes that function in the processes of carbon/nitrogen metabolism, such as TCA cycle, pentose phosphate pathway, glycolysis/gluconeogenesis and amino acid metabolism.…”

“…As demonstrated above, Rpd3 is localized in the nuclei of B. bassiana like the orthologue in A. nidulans (Bauer et al ., ) and can catalyse deacetylation of Kac sites on H3 and H4 as documented in S. cerevisiae (Rundlett et al ., ; Chang and Pillus, ). Function loss of Rpd3 resulted in significant modification (hyper‐ or hypoacetylation) of 2227 Kac sites on 1134 Kac proteins as well as differential expression of 1479 proteins and transcriptional repression of the key genes essential for asexual development in the fungal insect pathogen.…”

“…In Ustilago maydis, for instance, Hda1, which is orthologous to the yeast Rpd3, mediates a set of genes essential for teliospore development (Reichmann et al, 2002) and acts as a repressor of the biotrophic marker gene Mig1 required for fungal penetration into host epidermal cells (Torreblanca et al, 2003). Loss of RpdA causes a lethal phenotype in A. nidulans (Bauer et al, 2016). Despite a sequence similarity to the catalytic region of yeast Rpd3, filamentous fungal Rpd3 homologues are characterized by a C-terminal tail that is remarkably elongated and evidently essential for the growth and development of A. nidulans (Tribus et al, 2010).…”

RcLS2F – A Novel Fungal Class 1 KDAC Co-repressor Complex in Aspergillus nidulans

“…While Aspergillus strains with deletions of hdaA, hosA, and hosB homologous genes show several (phenotypic) characteristics but are viable (Tribus et al, 2005;Shwab et al, 2007;Lee et al, 2009;Kawauchi and Iwashita, 2014;Pidroni et al, 2018;Lan et al, 2019;, efforts to generate rpdA deletion mutants failed so far. Indeed, we proved that RpdA is essential for growth and development of A. nidulans and the human pathogen Aspergillus fumigatus (Tribus et al, 2010;Bauer et al, 2016). Very recently, we showed that RpdA is required for virulence of A. fumigatus in a murine model for pulmonary aspergillosis (Bauer et al, 2019a).…”