The Src Homology 2 Domain Containing Inositol 5-Phosphatase SHIP2 is Recruited to the Epidermal Growth Factor (EGF) Receptor and Dephosphorylates Phosphatidylinositol 3,4,5-Trisphosphate in EGF-stimulated COS-7 Cells

Abstract

The lipid phosphatase SHIP2 (Src homology 2 domain containing inositol 5-phosphatase 2) has been shown to be expressed in nonhemopoietic and hemopoietic cells. It has been implicated in signaling events initiated by several extracellular signals, such as epidermal growth factor (EGF) and insulin. In COS-7 cells, SHIP2 was tyrosine-phosphorylated at least at two separated tyrosine phosphorylation sites in response to EGF. SHIP2 was coimmunoprecipitated with the EGF receptor (EGFR) and also with the adaptor protein Shc. A C-terminal truncated form of SHIP2 that lacks the 366 last amino acids, referred to as tSHIP2, was also precipitated with the EGFR when transfected in COS-7 cells. The Src homology 2 domain of SHIP2 was unable to precipitate the EGFR in EGF-stimulated cells. Moreover, when transfected in COS-7 cells, it could not be detected in immunoprecipitates of the EGFR. When the His-tagged full-length enzyme was expressed in COS-7 cells and stained with anti-His6 monoclonal antibody, a signal was observed at plasma membranes in EGF-stimulated cells that colocalize with the EGFR by double staining. Upon stimulation by EGF, phosphatidylinositol 3,4,5-trisphosphate and protein kinase B activity were decreased in SHIP2-transfected COS-7 cells as compared with the vector alone. SHIP2 appears therefore in a tyrosine-phosphorylated complex with at least two other proteins, the EGFR and Shc.