Figure 1.

ErbB receptors and their ligands. ErbB2 has no known ligand, while ErbB3 lacks intrinsic kinase activity (indicated by a cross). Following ligand binding, the receptors activate several downstream signaling pathways thereby regulating cell growth, proliferation, and survival. These processes play an important role in development, wound healing and tissue regeneration. EGF, epidermal growth factor; TGFα, transforming growth factor-α; EPG, epigen; AREG, amphiregulin; EREG, epiregulin; BC, betacellulin; HB-EGF, heparin-binding EGF-like growth factor; NRG1-4, neuregulin 1-4; STAT, signal transducer and activator of transcription; MAPK/ERK, mitogen-activated protein kinase/extracellular signal-regulated kinase; PIK3/Akt, phosphoinositide 3-kinase/protein kinase B; PLCγ, phospholipase Cγ.