ErbB2/HER2

The ErbB2/HER2 receptor is a member of the ErbB receptor tyrosine kinase family, lacking a direct ligand yet serving as a critical dimerization partner for other ErbB receptors^[1][2]. Mechanistically, HER2 homodimers and heterodimers activate multiple downstream pathways including PI3K/Akt, MAPK/ERK, and NF-κB signaling, influencing cell proliferation, survival, and transcriptional regulation^[3][2][4]. Compared with related isoforms such as HER3, which requires ligand binding for activation, HER2’s constitutive activity confers robust signaling capacity and amplifies oncogenic potential^[1][5][4]. In disease models, HER2 overexpression is observed in 15-20% of breast cancers and in experimental prolactinoma, driving hormone secretion and cellular proliferation^[6][7][8]. The receptor also interacts with calmodulin, which modulates its phosphorylation and downstream kinase activity, linking calcium signaling to HER2-mediated pathways^[6]. Experimental inhibitors such as trastuzumab, pertuzumab, lapatinib, and AZD8931 selectively target HER2-containing dimers, modulating receptor activation and sensitizing cancer cells to chemotherapy^[9][2][4]. The distinct signaling patterns induced by HER2 homodimers versus HER2-containing heterodimers influence therapeutic responses, with Akt activation levels correlating with drug resistance^[2][4]. Collectively, HER2 functions as a signaling hub, with isoform-specific interactions and pharmacologic modulation providing a platform for both mechanistic and translational research^[1][2].