Abstract 1644 Regulation of Protein Tyrosine Phosphatase Receptor Type F by NEDD4L E3 Ligase

The phosphorylation state of target proteins is tightly regulated by protein kinases and phosphatases. The vast majority of cellular signaling depends on this dynamic relationship for the propagation or termination of signaling cascades and thus maintenance of homeostasis. PTPRF belongs to a family of receptor type protein tyrosine phosphatases. Our previous studies have been shown that PTPRF acts as an oncogenic phosphatase through the upregulation of Wnt signaling in colon cancer. However, the regulation of PTPRF is not well studied. In this study, we show that NEDD4L, a HECT E3 ligase, regulates the stability of PTPRF protein. Specifically, overexpression of NEDD4L decreases the half-life of PTPRF whereas knockdown of NEDD4L has the opposite effect. In addition, wild-type NEDD4L, but not the E3 ligase activity deficient mutant, increases the ubiquitination of PTPRF, indicating that PTPRF is a substrate of NEDD4L. Interestingly, the protein stability of a catalytically inactive mutant PTPRF is higher compared to wild-type PTPRF, suggesting that the phosphatase activity promotes PTPRF degradation. Moreover, by utilizing modified ubiquitin, we demonstrate that NEDD4L preferentially utilizes K29 ubiquitin linkage to modify PTPRF. Functionally, NEDD4L-mediated degradation of PTPRF blocks the ability of PTPRF to enhance Wnt activation. Taken together, this study identifies a previously unidentified regulatory mechanism of PTPRF through NEDD4L mediated ubiquitination. R01CA133429.