Sprouty2 attenuates epidermal growth factor receptor ubiquitylation and endocytosis, and consequently enhances Ras/ERK signalling

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Abstract
Drosophila Sprouty (dSpry) was genetically identified as a novel antagonist of fibroblast growth factor receptor (FGFR), epidermal growth factor receptor (EGFR) and Sevenless signalling, ostensibly by eliciting its response on the Ras/MAPK pathway. Four mammalian sprouty genes have been cloned, which appear to play an inhibitory role mainly in FGF‐ mediated lung and limb morphogenesis. Evidence is presented herein that describes the functional implications of the direct association between human Sprouty2 (hSpry2) and c‐Cbl, and its impact on the cellular localization and signalling capacity of EGFR. Contrary to the consensus view that Spry2 is a general inhibitor of receptor tyrosine kinase signalling, hSpry2 was shown to abrogate EGFR ubiquitylation and endocytosis, and sustain EGF‐induced ERK signalling that culminates in differentiation of PC12 cells. Correlative evidence showed the failure of hSpry2ΔN11 and mSpry4, both deficient in c‐Cbl binding, to instigate these effects. hSpry2 interacts specifically with the c‐Cbl RING finger domain and displaces UbcH7 from its binding site on the E3 ligase. We conclude that hSpry2 potentiates EGFR signalling by specifically intercepting c‐Cbl‐mediated effects on receptor down‐regulation.