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Activation of the Hog1 MAPK by the Ssk2/Ssk22 MAP 3Ks, in the absence of the osmosensors, is not sufficient to trigger osmostress adaptation in Saccharomyces cerevisiae
Author(s) -
VázquezIbarra Araceli,
Subirana Laia,
OngayLarios Laura,
Kawasaki Laura,
RojasOrtega Eréndira,
RodríguezGonzález Miriam,
Nadal Eulàlia,
Posas Francesc,
Coria Roberto
Publication year - 2018
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/febs.14385
Subject(s) - microbiology and biotechnology , saccharomyces cerevisiae , phosphorylation , mapk/erk pathway , osmotic shock , mutant , dephosphorylation , osmotic concentration , biology , downregulation and upregulation , kinase , chromatin , internalization , transcription factor , cyclin dependent kinase 1 , cell cycle , phosphatase , cell , yeast , gene , biochemistry
Yeast cells respond to hyperosmotic stress by activating the high‐osmolarity glycerol ( HOG ) pathway, which consists of two branches, Hkr1/Msb2‐Sho1 and Sln1, which trigger phosphorylation and nuclear internalization of the Hog1 mitogen‐activated protein kinase. In the nucleus, Hog1 regulates gene transcription and cell cycle progression, which allows the cell to respond and adapt to hyperosmotic conditions. This study demonstrates that the uncoupling of the known sensors of both branches of the pathway at the level of Ssk1 and Ste11 impairs cell growth in hyperosmotic medium. However, under these conditions, Hog1 was still phosphorylated and internalized into the nucleus, suggesting the existence of an alternative Hog1 activation mechanism. In the ssk1ste11 mutant, phosphorylated Hog1 failed to associate with chromatin and to activate transcription of canonical hyperosmolarity‐responsive genes. Accordingly, Hog1 also failed to induce glycerol production at the levels of a wild‐type strain. Inactivation of the Ptp2 phosphatase moderately rescued growth impairment of the ssk1ste11 mutant under hyperosmotic conditions, indicating that downregulation of the HOG pathway only partially explains the phenotypes displayed by the ssk1ste11 mutant. Cell cycle defects were also observed in response to stress when Hog1 was phosphorylated in the ssk1ste11 mutant. Taken together, these observations indicate that Hog1 phosphorylation by noncanonical upstream mechanisms is not sufficient to trigger a protective response to hyperosmotic stress.