Her 3

This gene encodes a member of the epidermal growth factor receptor (EGFR) family of receptor tyrosine kinases. This membrane-bound protein has a neuregulin binding domain but not an active kinase domain. It therefore can bind this ligand but not convey the signal into the cell through protein phosphorylation. However, it does form heterodimers with other EGF receptor family members which do have kinase activity. Heterodimerization leads to the activation of pathways which lead to cell proliferation or differentiation. Amplification of this gene and/or overexpression of its protein have been reported in numerous cancers, including prostate, bladder, and breast tumors. Alternate transcriptional splice variants encoding different isoforms have been characterized. One isoform lacks the intermembrane region and is secreted outside the cell. This form acts to modulate the activity of the membrane-bound form. Additional splice variants have also been reported, but they have not been thoroughly characterized.

ErbB3 (Her-3) is a member of the epidermal growth factor receptor family of receptor tyrosine-kinases. However, despite the namesake of the protein family to which it belongs, ErbB3 does not have kinase activity. Rather, it is thought that ErbB3, when activated, becomes a substrate for dimerization and subsequent phosphorylation by ErbB1, ErbB2 and ErbB4.

Like many of the receptor tyrosine-kinases, ErbB3 is activated by extracellular ligand. Ligands known to bind to ErbB3 include heregulin.