Human epidermal growth factor receptor 2 (HER2) subdomain II (HER2 subdomain II)

Human epidermal growth factor receptor 2 (HER2) subdomain II is a critical structural component of the extracellular domain of the HER2 protein, a member of the epidermal growth factor receptor (EGFR) family (UniProt P04626). Unlike other family members, HER2 lacks a known ligand and remains in an "open" conformation, making subdomain II essential for mediating heterodimerization with other ErbB receptors, particularly HER3 (Franklin et al., 2004). This dimerization process is a key driver of oncogenic signaling, activating the PI3K/AKT and MAPK pathways that promote cell proliferation and survival (Baselga et al., 2012). In clinical practice, HER2 subdomain II is the specific target of the monoclonal antibody pertuzumab, which binds to this region to sterically inhibit the formation of signaling-active dimers (FDA, Perjeta Label). Overexpression of HER2 is a well-documented driver in approximately 20% of breast cancers and various gastric cancers, making this subdomain a high-priority therapeutic target (PubMed: 22144827). By blocking the dimerization arm, therapies targeting subdomain II provide a distinct mechanism of action compared to drugs like trastuzumab, which target subdomain IV, allowing for synergistic anti-tumor effects (Nahta et al., 2004).

Other names

ErbB2 subdomain IICD340 subdomain IIHER2 dimerization domainNeu subdomain IIHuman epidermal growth factor receptor 2 dimerization arm

Inhibition of ligand-induced heterodimerization (primarily with HER3), blocking downstream signaling pathways like PI3K/AKT (Franklin et al., 2004; FDA Label).