The SHP-1-C mutant induced heightened growth responses to Epo/IL-3 in DA3EpoR cells. (A) The SHP-1-C mutant containing the C-terminus of the SHP-1 was tagged with the KT3 epitope and introduced into DA3EpoR cells by retroviral infection. The antigenic epitopes recognized by antibodies specific for SHP-1 (a-SHP-1-M) or SHP-1-C (a-KT3) or for both are indicated by the arrows. (B) The expression of SHP-1-C transcript in cells infected with the SHP-1-C construct (D/C) or the vector control (D/V) was determined by Northern hybridization with a SHP-1-C probe, which also detected the endogenous SHP-1. (C) The expression of SHP-1-C protein was determined by dot blotting. A membrane coated with the KT3 antibody was incubated without (lane 1) or with lysates from D/V or D/C cells (lanes 2 and 3) and probed with an anti–SHP-1-C antibody as indicated. (D) The growth responses of D/V and D/C cells to Epo or IL-3 were determined by cell proliferation assays using an MTT method and the values are the mean ± SD of three replicates.