erbB3/HER3 is a receptor tyrosine kinase and a member of the epidermal growth factor receptor family. erbB3/HER3 binds the heregulin ligands and contains 4 furin-like repeats, 2 cheY receiver domains, and a tyrosine kinase domain with a predicted molecular weight approximately 148 kD. Signaling through the erbB3/HER3 receptor induces proliferation and differentiation in some cell types, the receptor is widely expressed in many tissues including kidney, lung, brain, placenta, skin and stomach. erbB3/HER3 forms constitutively active heterodimers with erbB2/HER2 in a subset of human mammary tumors; expression of erbB3/HER3 reported be linked to favorable outcome in bladder and ovarian cancer. erbB3/HER3 has been shown to interact with a number of proteins including EGF receptor, erbB2/HER2, erbB4, Grb2, Grb7, SOS1, cdk5, SHC, FAK, PTK6, and others. The erbB3/HER3 receptor is extensively phosphorylated at residues T873 and S1123 (by cdk5); Y1199, Y1262, Y1289, and Y1328. The 1B4C3 antibody has been shown to be useful for flow cytometric detection of human erbB3/HER3.