Phosphorylation of Hsl1 by Hog1 leads to a G2 arrest essential for cell survival at high osmolarity

Abstract

Control of cell cycle progression by stress‐activated protein kinases (SAPKs) is essential for cell adaptation to extracellular stimuli. Exposure of yeast to osmostress leads to activation of the Hog1 SAPK, which controls cell cycle at G1 by the targeting of Sic1. Here, we show that survival to osmostress also requires regulation of G2 progression. Activated Hog1 interacts and directly phosphorylates a residue within the Hsl7‐docking site of the Hsl1 checkpoint kinase, which results in delocalization of Hsl7 from the septin ring and leads to Swe1 accumulation. Upon Hog1 activation, cells containing a nonphosphorylatable Hsl1 by Hog1 are unable to promote Hsl7 delocalization, fail to arrest at G2 and become sensitive to osmostress. Together, we present a novel mechanism that regulates the Hsl1–Hsl7 complex to integrate stress signals to mediate cell cycle arrest and, demonstrate that a single MAPK coordinately modulates different cell cycle checkpoints to improve cell survival upon stress.

Molecular Dissection of the Checkpoint Kinase Hsl1p

“…Five of these regions (Figure 1, 5a, 5b, 6, 8a, and 9) proved critical for Hsl1p function and/or regulation, but six other regions (Figure 1, regions 1 , 3, 4, 7, 8b, and 8c) could be deleted with little apparent effect in the assays we used. It is possible that these regions are important for regulating Hsl1p in response to specific stresses not examined here, as suggested by the identification of a phosphorylation site targeted by the osmostress MAPK Hog1p in motif 8b (Clotet et al, 2006). Alternatively, these regions could mediate distinct Hsl1p functions, such as the proposed roles for Hsl1p in targeting Cdc5p to the neck (Sakchaisri et al, 2004) or regulating microtubule interactions with the neck (Kusch et al, 2002).…”

Severe osmotic compression triggers a slowdown of intracellular signaling, which can be explained by molecular crowding

“…The final cell volume is set by the mechanical equilibration of external, internal, and turgor pressures (10,11). Hyperosmotic stress alters a variety of cellular processes, such as disrupting the cytoskeleton structure (12,13), inducing chromatin remodeling (14,15), and triggering cell cycle arrest (16,17) and apoptosis (18,19). The high-osmolarity glycerol (HOG) pathway of the budding yeast Saccharomyces cerevisiae (Fig.…”

Fine regulation of Saccharomyces cerevisiae MAPK pathways by post‐translational modifications

“…As in higher cells, yeast MAPK pathways are known to influence control of cell cycle progression. This is achieved via the Far1 cyclin-dependent kinase (CDK) inhibitor in the case of the mating pathway [43,47], the Mih1 CDK-phosphatase in the case of the CWI pathway [29] and various mechanisms at different stages in the case of the HOG pathway [10,14,62]. However, regulatory events in the opposite direction -CDK towards MAPK -remain obscure.…”