Human Epidermal Growth Factor Receptor 2 （HER2）, also known as ERBB2, HER-2, HER-2/neu, NEU, NGL, TKR1, and c-erbB-2, is a protein associated with increased aggressiveness in breast cancers. HER2 is a member of the ErbB protein family, also known as the epidermal growth factor receptor family. It is a cell membrane-bound receptor tyrosine kinase that plays a role in signal transduction pathways leading to cell growth and differentiation.
The human ErbB2 protein consists of 1255 amino acids, including a 22 amino acid signal sequence, a 630 amino acid extracellular domain （ECD）, a 23 amino acid transmembrane region, and a 580 amino acid cytoplasmic domain. HER2 is involved in development, cancer progression, communication at the neuromuscular junction, and the regulation of cell growth and differentiation. Phosphoinositide 3-kinase has been implicated in ErbB2 signal transduction, and the cytoplasmic domain of ErbB2 has been shown to interact with beta-catenin and plakoglobin.