Evidence for direct interaction between sprouty and Cbl

Sprouty (SPRY) was first identified in a genetic screen in Drosophila as an antagonist of fibroblast and epidermal growth factor receptors and Sevenle ss signaling, seemingly by inhibiting the receptor tyrosine kinase (RTK)/Ra s/MAPK pathway. To date, four mammalian Sprouty genes have been identified; the primary sequences of the gene products share a well conserved cysteine -rich C-terminal domain with their Drosophila counterpart. The N-terminal r egions do not, however, exhibit a large degree of homology. This study was aimed at identifying proteins with which human SPRY2 (hSPRY2) interacts in an attempt to understand the mechanism by which Sprouty proteins exert thei r down-regulatory effects. Here, we demonstrate that hSPRY2 associates dire ctly with c-Cbl, a known down-regulator of RTK signaling. A short sequence in the N terminus of hSPRY2 was found to bind directly to the Ring finger d omain of c-Cbl. Parallel binding was apparent between the Drosophila homolo gs of Sprouty and Cbl, with cross-species associations occurring at least i n vitro. Coexpression of hSPRY2 abrogated an increase in the rate of epider mal growth factor receptor internalization induced by c-Cb1, whereas a muta nt hSPRY2 protein unable to bind c-Cbl showed no such effect. Our results s uggest that one function of hSPRY2 in signaling processes downstream of RTK s may be to modulate c-Cbl physiological function such as that seen with re ceptor-mediated endocytosis.