Receptor tyrosine-protein kinase erbB-3, also known asHER3 (human epidermal growth factor receptor 3), is a membrane boundprotein that in humans is encoded by theERBB3gene.
ErbB3 is a member of theepidermal growth factor receptor (EGFR/ERBB) family of receptor tyrosine kinases. The kinase-impaired ErbB3 is known to form active heterodimers with other members of the ErbB family, most notably theligand binding-impairedErbB2.
The humanERBB3 gene is located on the long arm of chromosome 12 (12q13). It is encoded by 23,651 base pairs and translates into 1342 amino acids.[5]
During human development,ERBB3 is expressed in skin, bone, muscle, nervous system, heart, lungs, and intestinal epithelium.[6]ERBB3 is expressed in normal adult human gastrointestinal tract, reproductive system, skin, nervous system, urinary tract, and endocrine system.[7]
ErbB3, like the other members of the ErbB receptor tyrosine kinase family, consists of an extracellular domain, a transmembrane domain, and an intracellular domain. The extracellular domain contains four subdomains (I-IV). Subdomains I and III are leucine-rich and are primarily involved in ligand binding. Subdomains II and IV are cysteine-rich and most likely contribute to protein conformation and stability through the formation of disulfide bonds. Subdomain II also contains the dimerization loop required for dimer formation.[8] The cytoplasmic domain contains a juxtamembrane segment, a kinase domain, and a C-terminal domain.[9]
Unliganded receptor adopts a conformation that inhibits dimerization. Binding of neuregulin to the ligand binding subdomains (I and III) induces a conformational change in ErbB3 that causes the protrusion of the dimerization loop in subdomain II, activating the protein for dimerization.[9]
ErbB3 has been shown to bind the ligandsheregulin[10] andNRG-2.[11] Ligand binding causes a change in conformation that allows for dimerization, phosphorylation, and activation of signal transduction. ErbB3 can heterodimerize with any of the other three ErbB family members. The theoretical ErbB3 homodimer would be non-functional because the kinase-impaired protein requires transphosphorylation by its binding partner to be active.[9]
Unlike the other ErbB receptor tyrosine kinase family members which are activated through autophosphorylation upon ligand binding, ErbB3 was found to be kinase impaired, having only 1/1000 the autophosphorylation activity of EGFR and no ability to phosphorylate other proteins.[12] Therefore, ErbB3 must act as anallosteric activator.
The ErbB2-ErbB3 dimer is considered the most active of the possible ErbB dimers, in part because ErbB2 is the preferred dimerization partner of all the ErbB family members, and ErbB3 is the preferred partner of ErbB2.[13] This heterodimer conformation allows the signaling complex to activate multiple pathways including the MAPK, PI3K/Akt, and PLCγ.[14] There is also evidence that the ErbB2-ErbB3 heterodimer can bind and be activated by EGF-like ligands.[15][16]
The intracellular domain of ErbB3 contains 6 recognition sites for the SH2 domain of the p85 subunit ofPI3K.[17] ErbB3 binding causes the allosteric activation ofp110α, the lipid kinase subunit of PI3K,[14] a function not found in eitherEGFR or ErbB2.
While no evidence has been found that ErbB3 overexpression, constitutive activation, or mutation alone is oncogenic,[18] the protein as a heterodimerization partner, most critically with ErbB2, is implicated in growth, proliferation, chemotherapeutic resistance, and the promotion of invasion and metastasis.[19][20]
ErbB3 is associated with targeted therapeutic resistance in numerous cancers including resistance to:
ErbB2 overexpression may promote the formation of active heterodimers with ErbB3 and other ErbB family members without the need for ligand binding, resulting in weak but constitutive signaling activity.[14]
ERBB3 is expressed in themesenchyme of the endocardial cushion, which will later develop into the valves of the heart. ErbB3 null mouse embryos show severely underdeveloped atrioventricular valves, leading to death at embryonic day 13.5. Although this function of ErbB3 depends on neuregulin, it does not seem to require ErbB2, which is not expressed in the tissue.[29]
ErbB3 also seems to be required for neural crest differentiation and the development of the sympathetic nervous system[30] and neural crest derivatives such asSchwann cells.[31]
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^Pinkas-Kramarski R, Lenferink AE, Bacus SS, Lyass L, van de Poll ML, Klapper LN, et al. (March 1998). "The oncogenic ErbB-2/ErbB-3 heterodimer is a surrogate receptor of the epidermal growth factor and betacellulin".Oncogene.16 (10):1249–1258.doi:10.1038/sj.onc.1201642.PMID9546426.S2CID25652800.
^Osipo C, Meeke K, Cheng D, Weichel A, Bertucci A, Liu H, et al. (February 2007). "Role for HER2/neu and HER3 in fulvestrant-resistant breast cancer".International Journal of Oncology.30 (2):509–520.doi:10.3892/ijo.30.2.509 (inactive 12 July 2025).PMID17203234.{{cite journal}}: CS1 maint: DOI inactive as of July 2025 (link)
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