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  • Essential phosphorylation against cellular stress

    essential-phosphorylation-against-cellular-stressThe activation of stress protein kinases is essential for proper cellular adaptation to external stimuli. In the yeast Saccharomyces cerevisiae, an increase of extra cellular osmolarity activates the MAP kinase pathway of Hog1, which is derived from a complex adaptive response. Researchers at the Universitat Pompeu Fabric and Universitat International de Catalonia have characterized various aspects of the response, revealing that one of the protective mechanisms induced Hog1 arrests the cell cycle in G1 phase, through a twofold process that ends with inhibition of CDK (cyclin dependent kinase), a key enzyme that allows cell cycle progression.

    First, Hog1 inhibits the expression of cycling, proteins necessary for the activation of CDK, and, second, stabilizes Sic1, the CDK inhibitor protein. The work focuses on the latter mechanism, showing that Hog1 physically interacts in vivo and in vitro Sic1, heroine phosphorylating one of its carboxyl ends. And lengthens the lifetime of this controller, and retarding the process ubicuitinacion which is subjected in the absence of stress. According to the model proposed by the authors, phosphorylation of Sic1 is essential for adaptation to conditions of hyperosmolarity. Indeed, cells deficient in Sic1 or containing a Sic1 allele mutated in the Hog1 phosphorylation site are unable to stop at G1 in the presence of salt in half, producing a number of serious defects, including highlights the occurrence of polyploidy. Overall, the results show that the CDK inhibitor, Sic1, is a molecular target for Hog1, and in turn reinforce the role of MAP kinases and cell cycle control in eukaryotic cells.

    Published on August 29, 2012 · Filed under: Bioscience; Tagged as: , , ,
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