MAP Kinase Hog1 Regulates Metabolic Changes Induced by Hyperosmotic Stress

Upon hyperosmotic stress, the High Osmolarity Glycerol (HOG) pathway is activated, resulting in phosphorylation of the stress-activated protein kinasei Hog1 (O’Rourke et al., 2002; Saito and Posas, 2012; Brewster and Gustin, 2014). The Hog1/mitogen-activated protein kinase-mediated signaling cascades are essential for sensing hyperosmotic stress and for transmitting these signals to the nucleus tomodulate gene expression (O’Rourke et al., 2002; Saito and Posas, 2012; Brewster and Gustin, 2014). MAPK-mediated cascade pathways are composed of three serine/threonine protein kinases (MAPK kinase kinase, MAPK kinase, and MAPK). This signal transduction pathway is well-conserved in eukaryotes (O’Rourke et al., 2002; Saito and Posas, 2012; Brewster and Gustin, 2014). Phosphorylated Hog1 stimulates expression of genes encoding enzymes involved in glycerol production and uptake (O’Rourke et al., 2002; Saito and Posas, 2012; Gomar-Alba et al., 2013; Lee et al., 2013; Babazadeh et al., 2014; Brewster and Gustin, 2014). The glycerol production starts with the reduction of the glycolytic intermediate di-hydroxyl-acetone phosphate (DHAP) to glycerol-3phosphate (G3P) catalyzed by the NAD-dependent glycerol-3-phospate dehydrogenase (GPD; Ansell et al., 1997; Pahlman et al., 2001; Valadi et al., 2004). Increased expression of GPD1 enhances glycerol production under hyperosmotic stress (Albertyn et al., 1994; Rep et al., 1999). In addition, Hog1 appears to stimulate the 6-phosphofructo-2-kinase Pfk26, which produces fructose2,6-diphosphate (F26DP), an allosteric activator of the glycolytic enzyme phosphofructokinase (Pfk1; Dihazi et al., 2004). Hog1 is rapidly phosphorylated upon curcumin treatment, an active polyphenol derived from the spice turmeric (Azad et al., 2014). Trichosporonoides oedocephalis is known to produce large amounts of polyols (erythritol and glycerol). Tohog1 null mutation increased erythritol production and decreased glycerol production, respectively (Li et al., 2016). Therefore, Hog1 is considered to have an important role in the metabolic control, however little is known regarding the changes of metabolites induced by Hog1 from a metabolic perspective. Nuclear magnetic resonance (NMR) spectroscopy is a rapid method that requires minimal sample preparation (Beckonert et al., 2007; Kim et al., 2010). In addition, NMR is a useful technique for structure elucidation due to its various two-dimensional measurements, which makes NMR an ideal tool for the identification and quantification of metabolites (Beckonert et al., 2007; Kim et al., 2010).