Kap1 inhibits ErbB4 transactivation. A plasmid containing the luciferase gene driven by the GAL4 promoter was introduced into COS-7 cells, together with vectors encoding the GAL4 DNA binding domain with the entire ErbB4 ICD (amino acid residues 676–1292; Fig. 1B) or with a kinase domain deletion [amino acid residues 988–1292, Delta kinase (ΔK)] in the absence or presence of KAP1. All transfections included a plasmid carrying the Renilla luciferase gene for normalization of transfection efficiency. B, mock-transfected cells (lanes 1,4, 7, and 9) or cells transfected with ErbB4-GAL (lanes 2, 5, 8, and 11) or GAL-ErbB4ΔK (lanes 3, 6, 9, and 12) were immunoprecipitated with anti-GAL (lanes 1–6) or anti-Kap1 (lanes 7–12) and immunoblotted with the complementary antibody. A, each analysis was done in triplicate with three biological replicates. B, data represent three biological replicates.