Abstract
Sphingolipids (SL) are complex lipids and components of the plasma membrane which are involved in numerous cellular processes, as well as important for virulence of different fungal pathogens. In yeast, SL biosynthesis is regulated by the “AGC kinases” Ypk1 and Ypk2, which also seem to connect the SL biosynthesis with the cell wall integrity (CWI) and the High Osmolarity Glycerol (HOG) pathways. Here, we investigate the role of ypkAY PK1 in SL biosynthesis and its relationship with the CWI and the HOG pathways in the opportunistic human pathogen Aspergillus fumigatus. We found that ypkA is important for fungal viability, since the ΔypkA strain presented a drastically sick phenotype and complete absence of conidiation. We observed that under repressive condition, the conditional mutant niiA::ypkA exhibited vegetative growth defects, impaired germination and thermosensitivity. In addition, the ypkA loss of function caused a decrease in glycosphingolipid (GSL) levels, especially the metabolic intermediates belonging to the neutral GSL branch including dihydroceramide (DHC), ceramide (Cer), and glucosylceramide (GlcCer), but interestingly a small increase in ergosterol content. Genetic analyzes showed that ypkA genetically interacts with the MAP kinases of CWI and HOG pathways, mpkA and sakA, respectively, while only SakA physically interacts with YpkA. Our results suggest that YpkA is important for fungal survival through the regulation of GSL biosynthesis and cross talks with A. fumigatus MAP kinase pathways.
Highlights
Aspergillus fumigatus is a saprophytic filamentous fungus found ubiquitously in soil where it plays a key role in nutrient recycling (Dagenais and Keller, 2009; Perez-Nadales et al, 2014)
These results indicate that YpkA is a member of the subfamily of AGC protein kinases, so named because it comprises the mammalian protein kinase groups represented by the protein kinase A (PKA), protein kinase G (PKG), protein kinase C (PKC) and by PKB and the ribosomal kinases S6 (Sobko, 2006)
Plasma membrane is enriched with SL and sterols which are organized in lipid microdomains (Alvarez et al, 2007)
Summary
Aspergillus fumigatus is a saprophytic filamentous fungus found ubiquitously in soil where it plays a key role in nutrient recycling (Dagenais and Keller, 2009; Perez-Nadales et al, 2014). This organism is an opportunistic human pathogen that causes invasive pulmonary aspergillosis (IPA), a disease associated with exceptional high mortality rates (50–90%) in the susceptible population (Brown et al, 2012a,b). AMB is notoriously known by its harsh toxicity (Fanos and Cataldi, 2000; Shapiro et al, 2011), while long-term azole therapies can favor the emergence of resistant clinical isolates (Bellete et al, 2010; Camps et al, 2012; Lelievre et al, 2013). Since the last decade, azole-resistant environmental isolates have been documented worldwide (Snelders et al, 2008; Howard et al, 2009; Bader et al, 2015)
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