J Biol Chem, Vol. 273, Issue 51, 33985-33990, December 18, 1998

Physical and Functional Interaction between p72^syk and Erythropoietin Receptor

Véronique Duprez, Ulrich Blank^¶, Stany Chrétien, Sylvie Gisselbrecht, and Patrick Mayeux

From the  Institut National de la Santé et de la Recherche Médicale, Unité 363, ICGM, Hopital Cochin, 27 rue du Faubourg Saint Jacques, Paris, France, ^¶ Unité d'Immuno-Allergie, Institut Pasteur, Paris, France and  Institut National de la Transfusion Sanguine, 6 rue Alexandre Cabanel, 75015 Paris, France

Erythropoietin (Epo) regulates the proliferation and differentiation of erythroid cells through interaction with a cell surface receptor (EpoR) that belongs to the cytokine receptor family. The Jak2 tyrosine kinase was previously shown to bind to the EpoR, to be activated upon Epo stimulation, and to play a critical role in Epo-induced proliferation. However, little is known about the role of other tyrosine kinases in Epo signaling. In this paper, we examined whether Syk was involved in EpoR activation. Coimmunoprecipitation experiments showed that the phosphorylated EpoR was associated with the Syk kinase in activated UT7 cells. The interaction of Epo with its receptor led to an increased kinase activity. The use of recombinant Syk Src homology 2 (SH2) domains expressed in tandem or individually revealed that both N- and C-SH2 domains of Syk participated in EpoR binding with a major contribution of the C-terminal SH2 domain. Far Western blotting further indicated that Syk directly binds to the EpoR and that the interaction of Syk with EpoR only occurred after Epo activation. These data suggest that phosphorylation of EpoR on tyrosine residues may mediate Syk binding to the receptor through interaction between the two SH2 domains of Syk and tyrosines of the receptor. We propose that in addition to Jak2, Syk protein kinase may be a component of EpoR signaling.