ERBB3 (HER3) Protein
Overview
ERBB3, commonly designated as HER3 (Human Epidermal growth factor Receptor 3), is a transmembrane receptor tyrosine kinase belonging to the ERBB/HER family of growth factor receptors. The ERBB3 gene encodes a 148-kDa glycoprotein receptor that functions as a critical signaling molecule in both peripheral and central nervous systems. Unlike other ERBB family members, ERBB3 possesses unique structural features that distinguish its signaling capacity and biological roles. The protein is encoded by the ERBB3 gene located on chromosome 12 and is expressed across diverse cell types, including neurons, glia, and various epithelial tissues.
Function/Biology
ERBB3 operates as a ligand-activated receptor tyrosine kinase that responds primarily to neuregulins (NRGs), also known as heregulin or glial growth factors. The receptor contains an extracellular ligand-binding domain composed of four distinct subdomains (I-IV), a single transmembrane domain, and an intracellular region harboring catalytic and regulatory sequences. Upon neuregulin binding, ERBB3 undergoes ligand-induced dimerization, typically with other ERBB family members (EGFR/HER1, ERBB2/HER2, or ERBB4/HER4), forming heterodimeric complexes essential for signal transduction.
...ERBB3 (HER3) Protein
Overview
ERBB3, commonly designated as HER3 (Human Epidermal growth factor Receptor 3), is a transmembrane receptor tyrosine kinase belonging to the ERBB/HER family of growth factor receptors. The ERBB3 gene encodes a 148-kDa glycoprotein receptor that functions as a critical signaling molecule in both peripheral and central nervous systems. Unlike other ERBB family members, ERBB3 possesses unique structural features that distinguish its signaling capacity and biological roles. The protein is encoded by the ERBB3 gene located on chromosome 12 and is expressed across diverse cell types, including neurons, glia, and various epithelial tissues.
Function/Biology
ERBB3 operates as a ligand-activated receptor tyrosine kinase that responds primarily to neuregulins (NRGs), also known as heregulin or glial growth factors. The receptor contains an extracellular ligand-binding domain composed of four distinct subdomains (I-IV), a single transmembrane domain, and an intracellular region harboring catalytic and regulatory sequences. Upon neuregulin binding, ERBB3 undergoes ligand-induced dimerization, typically with other ERBB family members (EGFR/HER1, ERBB2/HER2, or ERBB4/HER4), forming heterodimeric complexes essential for signal transduction.
A distinctive feature of ERBB3 is its impaired intrinsic kinase activity compared to other ERBB family members. However, when heterodimerized with ERBB2, ERBB3 becomes a potent signaling receptor, generating robust activation of downstream pathways. The activation of ERBB3-containing dimers triggers autophosphorylation of tyrosine residues in the C-terminal tail, creating docking sites for adaptor proteins including phosphoinositide 3-kinase (PI3K) and growth factor receptor-bound protein 2 (GRB2), thereby activating critical survival and proliferation cascades.
Role in Neurodegeneration
ERBB3 signaling plays increasingly recognized protective roles in neurodegenerative disease pathophysiology. The neuregulin-ERBB3 axis supports neuronal survival, myelination, and synaptic plasticity—processes fundamentally compromised in major neurodegenerative conditions. Impaired neuregulin-ERBB3 signaling has been implicated in Alzheimer's disease, where reduced neuregulin levels correlate with neuroinflammation and amyloid-beta accumulation. In Parkinson's disease, ERBB3 signaling contributes to dopaminergic neuron survival and dopamine synthesis regulation, with pathway dysfunction potentially contributing to selective neuronal vulnerability.
In amyotrophic lateral sclerosis (ALS), ERBB3 signaling regulates motor neuron development and maintenance, with alterations in neuregulin expression documented in disease pathology. Additionally, ERBB3 supports oligodendrocyte differentiation and myelin formation, implicating the pathway in demyelinating aspects of neurodegeneration. The receptor's role in regulating glial cell function—particularly microglia and astrocytes—influences neuroinflammatory responses critical to disease progression across multiple neurodegenerative conditions.
Molecular Mechanisms
ERBB3 activation initiates the phosphatidylinositol-3-kinase/Protein kinase B (PI3K/AKT) pathway, a fundamental survival signaling cascade that phosphorylates pro-apoptotic factors like BAD and caspase-9, suppressing cell death. The pathway also activates mechanistic target of rapamycin (mTOR), promoting protein synthesis and neuronal anabolism. Concurrently, ERBB3 engages mitogen-activated protein kinase (MAPK/ERK) cascades through GRB2-mediated recruitment of SOS1, supporting differentiation and synaptic function. These pathways counteract proteotoxic stress, oxidative damage, and excitotoxicity—core mechanisms in neurodegeneration.
ERBB3 signaling also modulates neuroinflammatory responses by suppressing microglial activation and limiting pro-inflammatory cytokine production. The receptor supports oligodendrocyte progenitor cell differentiation and myelin maintenance through PI3K/AKT signaling, preserving axonal integrity essential to neuronal survival.
Clinical/Research Significance
ERBB3-targeted therapeutics represent emerging neuroprotective approaches. Neuregulin-1 (NRG1) supplementation and ERBB3 receptor agonists demonstrate neuroprotective potential in preclinical models of Alzheimer's, Parkinson's, and ALS. Understanding ERBB3 pathway dysregulation informs biomarker development for disease staging and prognosis. Genetic variants in ERBB3 and neuregulin genes correlate with neurodegenerative disease susceptibility, highlighting pathway importance. Research continues exploring ERBB3 as a therapeutic target for enhancing neuroprotection and glial support in progressive neurological diseases.