Despite such extensive analysis of Gcn homologs

Despite such extensive analysis of Gcn5 homologs, the function of C. albicans Gcn5 (CaGcn5) is not well understood. Therefore, in this study we investigated the role of CaGcn5 in filamentous growth, invasive growth and stress response of C. albicans. We also examined the subcellular distribution of Gcn5 during yeast growth and hyphal growth. In addition, we analyzed the impact of Gcn5 on C. albicans virulence in a systemic mouse model. Our results show that the N-terminal NLS and HAT domains but not the C-terminal Bromodomain regulate the nuclear localization of Gcn5. Our data also indicate that CaGcn5 is a histone acetyltransferase required for the morphogenesis and stress response of C. albicans.
Materials and methods
Results
Discussion In this study, we explored the roles of C. albicans Gcn5 in filamentous growth, virulence and stress responses. We also investigated the dynamic regulation of the subcellular localization of GFP-Gcn5 during yeast and hyphal growths. The C. albicans Gcn5 is a homolog (ortholog) of S. cerevisiae Gcn5, which is the catalytic subunit of the SAGA HAT complex required for the acetylation of histone H3 and H2B, is involved in multiple regulations under cellular stress conditions (Daniel and Grant, 2007, Grant et al., 1997, Suka et al., 2001, Zhang et al., 1998). The C. albicans Esa1 is a homolog (ortholog) of S. cerevisiae Esa1, which is a catalytic subunit in the NuA4 HAT complex required for the acetylation of H4 and H2A, controls multiple cellular processes (Allard et al., 1999, Clarke et al., 1999, Lin et al., 2009, Sapountzi and Cote, 2011). These studies indicate that Gcn5 and Esa1 play distinct roles in the regulation of cellular processes in C. albicans. Gcn5 and Esa1 have different roles in hyphal development. Esa1 is essential for hyphal initiation, whereas Gcn5 is essential for hyphal elongation. Deletion of the ESA1 gene blocked the hyphal development in all conditions examined (Wang et al., 2013). On the other hand, deletion of GCN5 blocked hyphal elongation, but did not block hyphal initiation in serum sensing conditions. However, these gcn5 mutant umbelliferone australia are defective in filamentous and invasive growth in most aerobic and microaerophilic conditions. Gcn5 and Esa1 also have different effects on cell growth. Esa1 is required for cell survival at high temperatures (37°C) and for cell quiescence at cold temperatures (4°C). Loss of Esa1 changes gene expression in a way that supports growth at cold temperature but inhibits growth at high temperatures. In contrast, loss of Gcn5 has no defects in cell growth. The gcn5 mutant cells grow normally, like the wild-type strain, neither resistant to cold temperature nor sensitive to high temperature. Gcn5 and Esa1, however, have opposite effects on stress responses. Gcn5 is mainly required for cell wall stress response, but has subtle effects on the other stress responses. In contrast, Esa1 regulates multiple stress responses. The esa1 mutant cells are sensitive to genotoxic and oxidative stresses, but resistant to osmotic and cell wall stresses. Esa1 is also important for temperature adaptation, metabolism regulation and nutrient uptake. Gcn5 and Esa1 also have different subcellular localization. The localization of Gcn5 is dynamically regulated during yeast growth and hyphal development. Gcn5 accumulates in the nucleus in stationary state, but is distributed in the cytoplasm during the growth state. The dynamic subcellular distribution of Gcn5 is correlated with growth states instead of morphologic change, may reflect altered substrates of this acetyltransferase during cell growth. S. cerevisiae Gcn5 has been reported to relocalize to the cytosol in response to hypoxia (Dastidar et al., 2012). The cytoplasmic distribution of C. albicans Gcn5 in growing cells may link it to non-histone protein substrates and its function as a KAT during cell growth. Our unpublished data showed that the C. albicans Esa1 is mainly localized in the nucleus and its nuclear localization does not change during hyphal development. Thus, the two central enzymes (Gcn5 and Esa1) from two different HAT complexes (NuA4 and SAGA) are involved in different regulation of C. albicans cellular processes. Gcn5 and Esa1 may be recruited to their specific targets via their own recruiting modules in the NuA4 complex and SAGA complex, and mediate different events during cell growth, hyphal development and stress responses.