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

The lipid phosphatase SHIP2 (Src homology 2 domain containing inositol 5-ph osphatase 2) has been shown to be expressed in nonhemopoietic and hemopoiet ic cells. It has been implicated in signaling events initiated by several e xtracellular signals, such as epidermal growth factor (EGF) and insulin. In COS-7 cells, SHIP2 was tyrosine-phosphorylated at least at two separated t yrosine phosphorylation sites in response to EGF. SHIP2 was coimmunoprecipi tated 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, re ferred to as tSHIP2, was also precipitated with the EGFR when transfected i n 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 cell s, 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 an ti-His(6) monoclonal antibody, a signal was observed at plasma membranes in EGF-stimulated cells that colocalize with the EGFR by double staining. Upo n stimulation by EGF, phosphatidylinositol 3,4,5-trisphosphate and protein kinase B activity were decreased in SHIP2-transfected COS-7 cells as compar ed with the vector alone. SHIP2 appears therefore in a tyrosine-phosphoryla ted complex with at least two other proteins, the EGFR and Shc.