Fig. 1.

A schematic representation of ErbB receptors and their ligands. ErbB receptor is a transmembrane receptor that consists of an extracellular ligand binding domain, a transmembrane region, and an intracellular domain that includes an inactive (in the absence of ligand) tyrosine kinase region. Binding of a specific growth factor to ErbB transforms its extracellular domain into a configuration that enables formation of a homodimer or a heterodimer and activates the intracellular kinase domain. TGF-α, transforming growth factor-α. EGFR, epidermal growth factor receptor; HB-EGF, heparin binding-epidermal growth factor.