PRLR/Jak2-mediated tyrosine phosphorylation of Grb2. (A) Plasmids (1 μg) encoding the long form of the PRLR, Jak2, SHP2CA, Grb2, or myc-Grb2 were cotransfected in 293 cells as indicated. Serum-starved cells were treated with PRL for 10 min. Lysates were immunoblotted with a monoclonal antibody to phosphotyrosine (upper panel) and a monoclonal antibody to SHP2 (lower panel). (B) 293 cells were cotransfected with plasmids (1 μg) encoding PRLR, Jak2, and the indicated forms of Grb2. Serum-starved cells were left unstimulated or were stimulated with PRL for 15 min. Lysates were immunoblotted using a monoclonal antibody to phosphotyrosine (upper panel) or a polyclonal antibody to Grb2 (lower panel). (C) 293 cells were cotransfected with plasmids (1 μg) encoding the long form of the PRLR along with various forms of Grb2 with either Jak2 or Src, as indicated. Serum-starved cells were treated with PRL for 10 min. Lysates were immunoblotted with a monoclonal antibody to phosphotyrosine (PY). WB, Western blot; α-, anti-.