Receptor tyrosine-protein kinase erbB-2 (HER2) extracellular domain subdomain II (HER2 ECD Subdomain II)

Receptor tyrosine-protein kinase erbB-2 (HER2), specifically its extracellular domain (ECD) subdomain II, is a critical component in the signaling architecture of the ErbB family of receptors. Unlike other members of its family, HER2 exists in a constitutively active or open conformation, making its dimerization arm in subdomain II always available for interaction without ligand binding (UniProt: P04626; Franklin et al., 2004). This subdomain is essential for the formation of heterodimers, most notably with HER3, which creates a potent signaling complex that drives cell proliferation and survival through the PI3K/AKT and MAPK pathways (PubMed: 15035985; FDA: Perjeta Label). In many cancers, particularly breast and gastric malignancies, HER2 is overexpressed or amplified, leading to uncontrolled signaling and tumor progression (NCI Drug Dictionary). Therapeutic strategies targeting subdomain II, such as the monoclonal antibody pertuzumab, work by sterically blocking the dimerization arm, thereby preventing the formation of active signaling complexes (Franklin et al., 2004). This mechanism is distinct from other HER2-targeted therapies like trastuzumab, which binds to subdomain IV, allowing for synergistic effects when these agents are used in combination (FDA: Perjeta Label).

Other names

HER2 dimerization domainERBB2 subdomain IIPertuzumab binding siteHER2 Domain IICD340Proto-oncogene Neup185erbB2

Pertuzumab and similar agents bind to subdomain II of the HER2 extracellular domain, sterically blocking the dimerization arm and preventing the formation of ligand-induced heterodimers with other ErbB receptors, particularly HER3.