Regulation of Sprouty2 stability by mammalian Seven‐in‐Absentia homolog 2

Abstract Mammalian Sprouty (Spry) gene expression is rapidly induced upon activation of the FGF receptor signaling pathway in multiple cell types including cells of mesenchymal and epithelial origin. Spry2 inhibits FGF‐dependent ERK activation and thus Spry acts as a feedback inhibitor of FGF‐mediated proliferation. In addition, Spry2 interacts with the ring‐finger‐containing E3 ubiquitin ligase, c‐Cbl, in a manner that is dependent upon phosphorylation of Tyr55 of Spry2. This interaction results in the poly‐ubiquitination and subsequent degradation of Spry2 by the proteasome. Here, we describe the identification of another E3 ubiquitin ligase, human Seven‐in‐Absentia homolog‐2 (SIAH2), as a Spry2 interacting protein. We show by yeast two‐hybrid analysis that the N‐terminal domain of Spry2 and the ring finger domain of SIAH2 mediated this interaction. Co‐expression of SIAH2 resulted in proteasomal degradation of Spry1, 2, and to a lesser extent Spry4. The related E3 ubiquitin‐ligase, SIAH1, had little effect on Spry2 protein stability when co‐expressed. Unlike c‐Cbl‐mediated degradation of Spry2, SIAH2‐mediated degradation was independent of phosphorylation of Spry2 on Tyr55. Spry2 was also phosphorylated on Tyr227, and phosphorylation of this residue was also dispensable for SIAH2‐mediated degradation of Spry2. Finally, co‐expression of SIAH2 with Spry2 resulted in a rescue of FGF2‐mediated ERK phosphorylation. These data suggest a novel mechanism whereby Spry2 stability is regulated in a manner that is independent of tyrosine phosphorylation, and provides an addition level of control of Spry2 protein levels. J. Cell. Biochem. 100: 151–160, 2007. © 2006 Wiley‐Liss, Inc.