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Molecular and Cellular Biology, March 2006, p. 1898-1907, Vol. 26, No. 5
0270-7306/06/$08.00+0     doi:10.1128/MCB.26.5.1898-1907.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Regulation of Sprouty Stability by Mnk1-Dependent Phosphorylation{ddagger}

John DaSilva,1,2,{dagger} Lizhong Xu,1,{dagger} Hong Joo Kim,1,3 W. Todd Miller,4 and Dafna Bar-Sagi1*

Department of Molecular Genetics and Microbiology,1 Graduate Program in Genetics,2 Graduate Program in Molecular and Cellular Biology,3 Department of Physiology and Biophysics, State University of New York at Stony Brook, Stony Brook, New York 117944

Received 8 August 2005/ Returned for modification 6 September 2005/ Accepted 14 December 2005

Sprouty (Spry) proteins are negative feedback modulators of receptor tyrosine kinase pathways in Drosophila melanogaster and mammals. Mammalian Spry proteins have been shown to undergo tyrosine and serine phosphorylation in response to growth factor stimulation. While several studies have addressed the function of tyrosine phosphorylation of Spry, little is known about the significance of Spry serine phosphorylation. Here we identify mitogen-activated protein kinase-interacting kinase 1 (Mnk1) as the kinase that phosphorylates human Spry2 (hSpry2) on serines 112 and 121. Mutation of these serine residues to alanine or inhibition of Mnk1 activity increases the rate of ligand-induced degradation of hSpry2. Conversely, enhancement of serine phosphorylation achieved through either the inhibition of cellular phosphatases or the expression of active Mnk1 results in the stabilization of hSpry2. Previous studies have shown that growth factor stimulation induces the proteolytic degradation of hSpry2 by stimulating tyrosine phosphorylation on hSpry2, which in turn promotes c-Cbl binding and polyubiquitination. A mutant of hSpry2 that is deficient in serine phosphorylation displays enhanced tyrosine phosphorylation and c-Cbl binding, indicating that serine phosphorylation stabilizes hSpry2 by exerting an antagonistic effect on tyrosine phosphorylation. Moreover, loss of serine phosphorylation and the resulting enhanced degradation of hSpry2 impair its capacity to antagonize fibroblast growth factor-induced extracellular signal-regulated kinase activation. Our results imply that Mnk1-mediated serine phosphorylation of hSpry2 constitutes a regulatory mechanism to extend the temporal range of Spry activity.

* Corresponding author. Mailing address: Department of Molecular Genetics and Microbiology, State University of New York at Stony Brook, Stony Brook, NY 11794. Phone: (631) 632-9737. Fax: (631) 632-5782. E-mail: barsagi{at}pharm.sunysb.edu.

{ddagger} Supplemental material for this article may be found at http://mcb.asm.org/.

{dagger} J.D. and L.X. contributed equally to this work.

Molecular and Cellular Biology, March 2006, p. 1898-1907, Vol. 26, No. 5
0022-538X/06/$08.00+0     doi:10.1128/MCB.26.5.1898-1907.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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