Response to Hyperosmotic Stress

Abstract

An appropriate response and adaptation to hyperosmolarity, i.e., an external osmolarity that is higher than the physiological range, can be a matter of life or death for all cells. It is especially important for free-living organisms such as the yeast Saccharomyces cerevisiae. When exposed to hyperosmotic stress, the yeast initiates a complex adaptive program that includes temporary arrest of cell-cycle progression, adjustment of transcription and translation patterns, and the synthesis and retention of the compatible osmolyte glycerol. These adaptive responses are mostly governed by the high osmolarity glycerol (HOG) pathway, which is composed of membrane-associated osmosensors, an intracellular signaling pathway whose core is the Hog1 MAP kinase (MAPK) cascade, and cytoplasmic and nuclear effector functions. The entire pathway is conserved in diverse fungal species, while the Hog1 MAPK cascade is conserved even in higher eukaryotes including humans. This conservation is illustrated by the fact that the mammalian stress-responsive p38 MAPK can rescue the osmosensitivity of hog1Δ mutations in response to hyperosmotic challenge. As the HOG pathway is one of the best-understood eukaryotic signal transduction pathways, it is useful not only as a model for analysis of osmostress responses, but also as a model for mathematical analysis of signal transduction pathways. In this review, we have summarized the current understanding of both the upstream signaling mechanism and the downstream adaptive responses to hyperosmotic stress in yeast.

Initiation of the transcriptional response to hyperosmotic shock correlates with the potential for volume recovery

“…In Saccharomyces cerevisiae, an increasing external osmolarity stimulates both the high osmolarity glycerol (HOG) MAPK pathway and the so-called general stress response [8][9][10][11]. Once the MAPK Hog1 is phosphorylated by the MAPK kinase Pbs2, it rapidly accumulates in the nucleus where Hog1 functions to control chromatin organization and RNA polymerase II activation [3][4][5][6][7]11].…”

“…Once the MAPK Hog1 is phosphorylated by the MAPK kinase Pbs2, it rapidly accumulates in the nucleus where Hog1 functions to control chromatin organization and RNA polymerase II activation [3][4][5][6][7]11]. Hog1 nuclear residence is largely dependent on anchor proteins, such as the transcription factors Hot1, Msn1 and Msn2/Msn4 [12].…”

Casein Kinase II Regulation of the Hot1 Transcription Factor Promotes Stochastic Gene Expression

“…In Saccharomyces cerevisiae, the activation of the Hog1 MAPK signaling cascade coordinates the transcriptional response to several types of osmotic stress, such as increasing extracellular concentrations of NaCl (herein referred to as salt stress) (1,2). Under conditions of salt stress, rapid signaling events activate the Hog1 MAPK, which then enters the nucleus and directs a combination of transcriptional activators to initiate the transcriptional response (3,4). Hundreds of gene targets exhibit altered levels of transcription within minutes after exposure to moderate salt stress (0.4 M NaCl).…”

Competition ofCandida glabrataagainstLactobacillusis Hog1 dependent

“…The HOG pathway is a central stress signalling pathway and has been explored in depth in S. cerevisiae (for reviews, see Saito et al, 2012, Brewster et al, 2014). In yeast, this pathway predominantly senses osmotic changes and is the major contributor of hyperosmotic stress resistance.…”

“…In fungi, the high osmolarity glycerol (HOG) pathway is activated in response to osmotic stress caused by high extracellular salt or sugar concentrations. This pathway has been explored in great detail in S. cerevisiae , where it mainly reacts to osmotic stress (for review, see Saito et al, 2012, Brewster et al, 2014), but also to other stress signals (Mollapour et al, 2006, Lawrence et al, 2004, Bilsland et al, 2004, Rodriguez‐Pena et al, 2010). Hog1 is the MAPK of the HOG signalling pathway and upon phosphorylation relays information to many different targets both in the cytosol and the nucleus to increase the intracellular glycerol level to preserve an optimal turgor pressure.…”