Sprouty2-Mediated Inhibition of Fibroblast Growth Factor Signaling Is Modulated by the Protein Kinase DYRK1A

Abstract

Raf-MEK-extracellular signal-regulated kinase (Erk) signaling initiated by growth factor-engaged receptor tyrosine kinases (RTKs) is modulated by an intricate network of positive and negative feedback loops which determine the specificity and spatiotemporal characteristics of the intracellular signal. Well-known antagonists of RTK signaling are the Sprouty proteins. The activity of Sprouty proteins is modulated by phosphorylation. However, little is known about the kinases responsible for these posttranslational modifications. We identify DYRK1A as one of the protein kinases of Sprouty2. We show that DYRK1A interacts with and regulates the phosphorylation status of Sprouty2. Moreover, we identify Thr75 on Sprouty2 as a DYRK1A phosphorylation site in vitro and in vivo. This site is functional, since its mutation enhanced the repressive function of Sprouty2 on fibroblast growth factor (FGF)-induced Erk signaling. Further supporting the idea of a functional interaction, DYRK1A and Sprouty2 are present in protein complexes in mouse brain, where their expression overlaps in several structures. Moreover, both proteins copurify with the synaptic plasma membrane fraction of a crude synaptosomal preparation and colocalize in growth cones, pointing to a role in nerve terminals. Our results suggest, therefore, that DYRK1A positively regulates FGF-mitogen-activated protein kinase signaling by phosphorylation-dependent impairment of the inhibitory activity of Sprouty2.

SUPPLEMENTAL MATERIAL

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

ACKNOWLEDGMENTS

We are especially grateful to M. L. Arbonés (CRG, Barcelona, Spain) for providing adult mice. We thank A. Raya and E. Ramírez for technical assistance, E. Martí for her advice on the immunohistochemical analysis, E. Balducci and M. J. Ballarobre for providing mouse primary cortical cultures, and S. Bartlett for English editorial work. We also thank G. R. Guy, E. Nishida, and P. E. Shaw for several of the plasmids used in the study.

This group is founded by the Centro de Investigación Biomédica en Red de Enfermedades Raras (CIBERER), ISCIII. S.A. and A.L. were FI predoctoral fellows (DURSI, Generalitat de Catalunya), and M.A. was a fellow of the Spanish Ministry of Health (BEFI Program). This work is supported by grants from the Spanish Ministry of Education and Science (BFU2004-01768 and BFU2007-61043/BMC) and the European Commission AnEUploidy grant.