An Unbiased Screen Identifies DEP-1 Tumor Suppressor as a Phosphatase Controlling EGFR Endocytosis

Abstract

Background The epidermal growth factor (EGF) stimulates rapid tyrosine phosphorylation of EGF-receptor (EGFR). This event precedes signalling from both the plasma membrane and from endosomes, and it is essential for recruitment of an ubiquitin ligase, CBL, that sorts activated receptors to endosomes and degradation. Because hyper-phosphorylation of EGFR is involved in oncogenic pathways, we performed an unbiased screen of siRNA oilgonucleotides targeting all human tyrosine phosphatases. Results We report the identification of PTPRK and PTPRJ (DEP-1) as EGFR-targeting phosphatases. DEP-1 is a tumour suppressor that dephosphorylates, thereby stabilizes EGFR by hampering its ability to associate with the CBL-GRB2 ubiquitin ligase complex. DEP-1 silencing enhanced tyrosine phosphorylation of endosomal EGFRs and, accordingly, increased cell proliferation. In line with functional interactions, EGFR and DEP-1 form physical associations, and EGFR phosphorylates a substrtae trapping mutant of DEP-1. Interestingly, the interactions of DEP-1 and EGFR are followed by physical segregation: whereas EGFR undergoes endocytosis, DEP-1 remains confined to the cell surface. Conclusions EGFR and DEP-1 physically interact at the cell surface and maitain bidirectional enzyme-substrate interactions, which are relevant to their respective oncogenic and tumor suppressive functions. These observations highlight the emerging roles of vesicular trafficking in malignant processes.

Microtubule inhibition causes epidermal growth factor receptor inactivation in oesophageal cancer cells

“…Protein tyrosine phosphatases (PTPs) strictly control receptor tyrosine kinase (RTK) phosphorylation and downstream signalling. Several PTPs have been reported to dephosphorylate tyrosine residues of EGFR and regulate signalling, including T-cell PTP (TCPTP), Src homology phosphotyrosine phosphatase 1 and 2 (SHP1 and 2), PTP1B, PTPN9, density-enhanced phosphatase-1 (DEP-1), RPTPσ and RPTPκ (30)(31)(32)(33)(34)(35). So far only PTPε and PTP1B have been reported to interact with the microtubule system (25)(26)(27).…”

Regulation of epidermal growth factor receptor signalling by inducible feedback inhibitors

“…In trans autophosphorylation of tyrosine residues located in the receptor C-terminal tail (red circles) generates docking sites for the phosphorylated-tyrosine-binding modules (not shown here) found on various signalling proteins, thereby igniting downstream signalling (Lemmon and Schlessinger, 2010). This is counteracted by the activity of protein tyrosine phosphatases (PTPs), which reverse EGFR tyrosine phosphorylation at the cell membrane, as well as during endocytic trafficking (Haj et al, 2002;Tarcic et al, 2009). Activated EGFRs undergo rapid endocytosis, which is orchestrated by endocytic proteins recruited directly and/or indirectly to activated receptors (Sorkin and Goh, 2009;Madshus and Stang, 2009).…”

“…Activated EGFRs are immediately targeted by inhibitory mechanisms that do not require de novo protein synthesis. These include dephosphorylation by protein tyrosine phosphatases (PTPs) (Keilhack et al, 1998;Xu et al, 2005b;Tarcic et al, 2009) and endocytosis (Sorkin and Goh, 2009;Madshus and Stang, 2009) (Box 1). The equilibrium between ongoing EGFR kinase activity and PTP function is a key determinant of overall receptor phosphorylation and EGFR signalling potential.…”

Tyrosine Phosphatase PTPRJ/DEP-1 Is an Essential Promoter of Vascular Permeability, Angiogenesis, and Tumor Progression

“…Similarly, overexpression of DEP-1 in many tumor cells is associated with inhibition of cell proliferation and migration (2,(4)(5)(6)(7). Consistent with this role, some of its known substrates include growth factor receptors such as the PDGFR, EGFR, MET, and ERK1/2 (8)(9)(10)(11).…”