Direct interaction between HER2 and PSMD3 in BT474, SKBR3, and HCC-1419. (A) Total cell lysates from HER2+ cells were incubated with either PSMD3 or HER2 antibodies at 4 °C overnight. Immunoprecipitation (IP) were subjected to western blot analysis with anti-PSMD3 or anti-HER2 antibodies. (B) BT-474, SKBR3, HCC-1419, and MDA-MB231 were stained with PSMD3 and HER2 antibodies at 4 °C overnight. Secondary antibodies conjugated with Rhodamine and FITC against anti-PSMD3 and anti-HER2, respectively, were incubated for an hour at room temperature. Confocal Fluorescence resonance energy transfer (FRET) assay was used to analyze the protein–protein interaction. Scale Bar is 25 µM.