ABSTRACT
Overexpression of the P185(HER2) protein determines the malignancy and unfavorable prognosis of ovarian and breast tumors. In this work, the distribution of P185(HER2) in human cancer cells was studied by electron microscopy, using a novel approach. It is based on the interaction between barnase (a ribonuclease from Bacillus amyloliquefaciens) and its specific inhibitor barstar. The monoclonal antibody 4D5 scFv to extracellular P185(HER2) domain fused with two molecules of barnase was used as a recognizing agent, and the conjugate of colloidal gold with barstar, as an electron dense label for electron microscopic visualization. For labeling, we used supramolecular complexes 4D5 scFv-dibarnase:barstar-Au. The distribution of P185(HER2) in human ovarian carcinoma cells SKOV-3 and breast carcinoma cells BT-474 was studied at 4 °C and 37 °C. It was shown that at 4 °C the protein P185(HER2) occurs exclusively on the cell surface, mainly on protrusions or close to their bases. At 37 °C, the internalization of P185(HER2) caused by its interaction with 4D5 scFv-dibarnase was observed. Inside the cells, P185(HER2) was located in the coated pits and vesicles, endosomes and multivesicular bodies. The data obtained indicate that the supramolecular 4D5 scFv-dibarnase:barstar-gold complex can be used as a new immunodetection system for exploring the P185(HER2) distribution.
Subject(s)
Receptor, ErbB-2/analysis , Recombinant Fusion Proteins/chemistry , Ribonucleases/chemistry , Staining and Labeling , Antibodies, Monoclonal/chemistry , Bacterial Proteins/chemistry , Breast Neoplasms/metabolism , Cell Line, Tumor , Coated Pits, Cell-Membrane/ultrastructure , Coated Vesicles/ultrastructure , Endosomes/ultrastructure , Female , Gold/chemistry , Humans , Multivesicular Bodies/ultrastructure , Ovarian Neoplasms/metabolism , Receptor, ErbB-2/metabolism , Recombinant Fusion Proteins/immunology , Ribonucleases/immunology , TemperatureABSTRACT
We successfully cloned and expressed a single-chain antibody (425scFv), that is directed to human epidermal growth factor receptor HER1 (EGFR) in transgenic tobacco plants as a fusion with bacterial barstar gene (425scFv-barstar). Plant-produced recombinant 425scFv-barstar was recovered using barstar-barnase system. Based on barstar-barnase affinity, during purification of the plant-produced 425scFv-barstar, we generated bispecific scFv-antibody heterodimers from individual single-chain fragments initially produced in different host systems with binding activity to both HER1 and HER2/neu tumor antigens. We demonstrated by flow cytometry and indirect immunofluorescent microscopy that both the components of heterodimer retain its specific cell-binding activity.
