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J. Biol. Chem., Vol. 281, Issue 34, 24687-24694, August 25, 2006

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Saccharomyces cerevisiae Hog1 Protein Phosphorylation upon Exposure to Bacterial Endotoxin^*

Joana M. Marques, Ricardo J. Rodrigues^¶, Augusto C. de Magalhães-Sant'Ana, and Teresa Gonçalves¹

From the Centre for Neuroscience and Cell Biology of Coimbra and Institutes of Microbiology and ^¶Biochemistry, Faculty of Medicine, University of Coimbra, 3004-504 Coimbra, Portugal

The yeast Hog1 protein is both functionally and structurally similar to the mammalian p38, belonging to the same family of mitogen-activated protein (MAP) kinases and responding to extracellular changes in osmolarity. Since p38 mediates lipopolysaccharide (LPS) effects in mammalian cells, we now tested the responsiveness of Hog1 upon exposure of the yeast Saccharomyces cerevisiae to bacterial LPS. In the presence of Escherichia coli LPS (100 ng/ml) and an endotoxically active, hexaacylated, synthetic lipid A (compound 506; 100 ng/ml), Hog1 becomes phosphorylated with a maximum of phosphorylation between 3 and 6 h, whereas a tetraacylated, inactive form of lipid A (compound 406) did not cause any modification in the phosphorylation state of Hog1. A triple labeling immunocytochemical study showed that phosphorylated Hog1 translocates into the nucleus after a 90-min incubation and becomes sparsely located in the cytoplasm. The translocation of the phospho-Hog1 is preceded by an increased expression of the HOG1 gene and concomitant with the expression of the Hog1 target gene, GPD1. We also observed that cells unable to synthesize Hog1 do not resist LPS as efficiently as wild-type cells. We conclude that the yeast S. cerevisiae is able to respond to the presence of Gram-negative bacteria endotoxin and that Hog1 is involved in this response.

Received for publication, April 19, 2006

^* This work was supported by a STARTER grant S7/02 from the Faculty of Medicine of the University of Coimbra. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed. Tel.: 351-239-857-700; Fax: 351-239-823-236; E-mail: tmfog{at}ci.uc.pt.

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