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Molecular and Cellular Biology, June 2000, p. 3887-3895, Vol. 20, No. 11
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Rck2 Kinase Is a Substrate for the Osmotic Stress-Activated Mitogen-Activated Protein Kinase Hog1

Elizabeth Bilsland-Marchesan,1 Joaquín Ariño,2 Haruo Saito,3 Per Sunnerhagen,1 and Francesc Posas2,4,*

Department of Cell and Molecular Biology, Lundberg Laboratory, Göteborg University, S40530 Göteborg, Sweden1; Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 021153; and Departament de Bioquímica i Biologia Molecular, Facultat de Veterinària, Universitat Autònoma de Barcelona, 08193 Barcelona,2 and Cell Signaling Unit, Departament de Ciències Experimentals i de la Salut, Universitat Pompeu Fabra (UPF), Barcelona E-08003,4 Spain

Received 5 January 2000/Returned for modification 29 February 2000/Accepted 13 March 2000

Exposure of yeast cells to increases in extracellular osmolarity activates the Hog1 mitogen-activated protein kinase (MAPK). Activation of Hog1 MAPK results in induction of a set of osmoadaptive responses, which allow cells to survive in high-osmolarity environments. Little is known about how the MAPK activation results in induction of these responses, mainly because no direct substrates for Hog1 have been reported. We conducted a two-hybrid screening using Hog1 as a bait to identify substrates for the MAPK, and the Rck2 protein kinase was identified as an interactor for Hog1. Both two-hybrid analyses and coprecipitation assays demonstrated that Hog1 binds strongly to the C-terminal region of Rck2. Upon osmotic stress, Rck2 was phosphorylated in vivo in a Hog1-dependent manner. Furthermore, purified Hog1 was able to phosphorylate Rck2 when activated both in vivo and in vitro. Rck2 phosphorylation occurred specifically at Ser519, a residue located within the C-terminal putative autoinhibitory domain. Interestingly, phosphorylation at Ser519 by Hog1 resulted in an increase of Rck2 kinase activity. Overexpression of Rck2 partially suppressed the osmosensitive phenotype of hog1Delta and pbs2Delta cells, suggesting that Rck2 is acting downstream of Hog1. Consistently, growth arrest caused by hyperactivation of the Hog1 MAPK was abolished by deletion of the RCK2 gene. Furthermore, overexpression of a catalytically impaired (presumably dominant inhibitory) Rck2 kinase resulted in a decrease of osmotolerance in wild-type cells but not in hog1Delta cells. Taken together, our data suggest that Rck2 acts downstream of Hog1, controlling a subset of the responses induced by the MAPK upon osmotic stress.

* Corresponding author. Mailing address: Unitat de Senyalització Cel-lular, Facultat de Ciències de la Salut i de la Vida, Universitat Pompeu Fabra (UPF), C/Doctor Aiguader 80, Barcelona E-08003, Spain. Phone: 34-93-542 2848. Fax: 34-93-542 2802. E-mail: francesc.posas{at}cexs.upf.es.

Molecular and Cellular Biology, June 2000, p. 3887-3895, Vol. 20, No. 11
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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