Targeting the MUC1-C cytoplasmic domain with GO-203 blocks the interaction with FLT3. (A) Schema of the MUC1-C subunit extracellular domain (ED), transmembrane domain (TM), and the cytoplasmic domain (CD). The amino acid sequence of the MUC1-C cytoplasmic domain (MUC1-CD) is shown with highlighting of the GO-203 target sequence (CQCRRKN) and localization of the PI3K and GRB2 binding sites. (B) Lysates from MOLM-14 cells left untreated (control) or treated with 2 or 4 μM GO-203 for 6 hours were immunoprecipitated with anti-MUC1-C. The precipitates were immunoblotted with the anti-FLT3 antibody (upper panel). As a control, anti-MUC1-C immunoprecipitates were also analyzed by immunoblotting with anti-MUC1-C (lower panel). (C) Lysates from MOLM-14 cells left untreated (control) or treated with 2 μM GO-203 for 6 and 24 hours were incubated with a GST-MUC1-CD fusion protein. The adsorbates were immunoblotted with anti-FLT3 (upper panel). Input of the GST-MUC1-CD proteins was assessed by Coomassie blue staining (lower panel). (D) Lysates from the indicated cells were incubated with the GST-MUC1-CD fusion protein. The adsorbates were immunoblotted with anti-FLT3 (upper panel). Input of the GST-MUC1-CD proteins was assessed by Coomassie blue staining (lower panel).