Hsp90 Binds and Regulates the Ligand-Inducible α Subunit of Eukaryotic Translation Initiation Factor Kinase Gcn2

Abstract

The protein kinase Gcn2 stimulates translation of the yeast transcription factor Gcn4 upon amino acid starvation. Using genetic and biochemical approaches, we show that Gcn2 is regulated by the molecular chaperone Hsp90 in budding yeast Saccharomyces cerevisiae. Specifically, we found that (i) several Hsp90 mutant strains exhibit constitutive expression of a GCN4-lacZ reporter plasmid; (ii) Gcn2 and Hsp90 form a complex in vitro as well as in vivo; (iii) the specific inhibitors of Hsp90, geldanamycin and macbecin I, enhance the association of Gcn2 with Hsp90 and inhibit its kinase activity in vitro; (iv) in vivo, macbecin I strongly reduces the levels of Gcn2; (v) in a strain expressing the temperature-sensitive Hsp90 mutant G170D, both the accumulation and activity of Gcn2 are abolished at the restrictive temperature; and (vi) the Hsp90 cochaperones Cdc37, Sti1, and Sba1 are required for the response to amino acid starvation. Taken together, these data identify Gcn2 as a novel target for Hsp90, which plays a crucial role for the maturation and regulation of Gcn2.

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Hsp90 Binds and Regulates Gcn2, the Ligand-Inducible Kinase of the α Subunit of Eukaryotic Translation Initiation Factor 2

ACKNOWLEDGMENTS

We thank A. Caplan, S. P. Bohen, K. R. Yamamoto, E. A. Craig, M. Foiani, J. Johnson, S. Lindquist, S. Mader, P. Mueller, David O. Toft, and R. C. Wek for plasmids, strains, chemicals, and antibodies. We are indebted to J.-F. Louvion for establishing an impressive collection of Hsp90 plasmids. We are grateful to B. Cenni and T. Abbas-Terki for critical comments on the manuscript. We acknowledge the sequencing service of the Department of Molecular Biology.

This work was supported by the Swiss National Science Foundation and the Canton de Genève.