Structural insights into the down-regulation of overexpressed p185(her2/neu) protein of transformed cells by the antibody chA21

• Published in: The Journal of biological chemistry 2011-09, Vol.286 (36), p.31676-31683
• Main Authors: Zhou, Huihao, Zha, Zhao, Liu, Yang, Zhang, Hongtao, Zhu, Juanjuan, Hu, Siyi, Shen, Guodong, Cheng, Liansheng, Niu, Liwen, Greene, Mark I, Teng, Maikun, Liu, Jing
• Format: Article
• Language: English
• Subjects: Antibodies, Monoclonal - chemistry; Antibodies, Monoclonal - pharmacology; Cell Line, Tumor; Cell Transformation, Neoplastic - immunology; Crystallography, X-Ray; Down-Regulation - drug effects; Down-Regulation - immunology; Endocytosis; Gene Expression Regulation, Neoplastic - drug effects; Humans; Receptor, ErbB-2 - genetics; Receptor, ErbB-2 - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M111.235184

p185(her2/neu) belongs to the ErbB receptor tyrosine kinase family, which has been associated with human breast, ovarian, and lung cancers. Targeted therapies employing ectodomain-specific p185(her2/neu) monoclonal antibodies (mAbs) have demonstrated clinical efficacy for breast cancer. Our previous studies have shown that p185(her2/neu) mAbs are able to disable the kinase activity of homomeric and heteromeric kinase complexes and induce the conversion of the malignant to normal phenotype. We previously developed a chimeric antibody chA21 that specifically inhibits the growth of p185(her2/neu)-overexpressing cancer cells in vitro and in vivo. Herein, we report the crystal structure of the single-chain Fv of chA21 in complex with an N-terminal fragment of p185(her2/neu), which reveals that chA21 binds a region opposite to the dimerization interface, indicating that chA21 does not directly disrupt the dimerization. In contrast, the bivalent chA21 leads to internalization and down-regulation of p185(her2/neu). We propose a structure-based model in which chA21 cross-links two p185(her2/neu) molecules on separate homo- or heterodimers to form a large oligomer in the cell membrane. This model reveals a mechanism for mAbs to drive the receptors into the internalization/degradation path from the inactive hypophosphorylated tetramers formed dynamically by active dimers during a "physiologic process."