Intersectin (ITSN) Regulation of Epidermal Growth Factor Receptor (EGFR) Ubiquitylation

Ubiquitylation of receptor tyrosine kinases (RTKs) plays a critical role in regulating their trafficking and lysosomal degradation. Our laboratory identified the multi-domain scaffolding protein intersectin 1 (ITSN1) as an important regulator of this process. ITSN1 stimulates ubiquitylation of the epidermal growth factor receptor (EGFR) through enhancing the activity of Cbl E3 ubiquitin ligase. However, the precise mechanism through which ITSN1 enhances Cbl activity is unclear. My dissertation work here revealed a novel interaction of ITSN1 with two proteins, Spry2 and Shp2, involved in this Cbl-mediated EGFR ubiquitylation mechanism. With this study, I discovered that ITSN1 recruits Shp2 to Spry2 to enhance Spry2 tyrosine dephosphorylation, thereby blocking Spry2 interaction with Cbl and Spry2 inhibiton of Cbl activity for EGFR ubiquitylation. In addition, I also found that disruption of ITSN1 binding to Spry2 through point mutation of the Pro-rich ITSN1 binding site in Spry2 resulted in decreased Shp2:Spry2 interaction and enhanced Spry2 tyrosine phosphorylation, probably due to increased Shp2 sequestration. Although I mostly analyzed the effect of forced expression of these proteins on the mechanism, results obtained from my work are mechanistically quite informative. This study demonstrates that ITSN1 enhances Cbl activity, in part, by modulating the interaction of Cbl with Spry2 through recruitment of Shp2 phosphatase to the Cbl-Spry2.