EGFR forms ligand-independent oligomers that are distinct from the active state

Abstract

The human Epidermal Growth Factor Receptor (EGFR/ERBB1) is a Receptor Tyrosine Kinase (RTK) that forms activated oligomers in response to ligand. Much evidence indicates that EGFR/ERBB1 also forms oligomers in the absence of ligand, but the structure and physiological role of these ligand-independent oligomers remain unclear. To examine these features, we use fluorescence microscopy to measure the oligomer stability and FRET efficiency for homo- and hetero-oligomers of fluorescent protein-labeled forms of EGFR and its paralog, Human Epidermal Growth Factor Receptor 2 (HER2/ERBB2) in vesicles derived from mammalian cell membranes. We observe that both receptors form ligand-independent oligomers at physiological plasma membrane concentrations. Mutations introduced in the kinase region at the active state asymmetric kinase dimer interface alter but do not affect the stability of ligand-independent EGFR oligomers. These results indicate that ligand-independent EGFR oligomers form using interactions that are distinct from the EGFR active state.

A cancer mutation promotes EphA4 oligomerization and signaling by altering the conformation of the SAM domain

“…Thus, the H945E mutation destabilizes the EphA4 L920F oligomers in the absence but not in the presence of ligand. This is consistent with the idea that ligand binding can induce structural changes in RTK oligomers (51)(52)(53)(54).…”

“…Thus, it is conceivable that ephrin ligand binding induces structural changes in the EphA4 trimers that propagate from the extracellular region to the SAM domain without affecting the oligomerization state of EphA4. This has been proposed for other families of receptor tyrosine kinases known to function as dimers, such as the IGF-1, EGF, FGF,VEGF and Trk receptor families (54,64,65,70,71). In addition, ligandmediated interactions in the EphA4 extracellular region must work synergistically with SAM-SAM interactions to stabilize oligomeric assemblies of highly phosphorylated EphA4 L920F molecules.…”

Epidermal growth factor receptor signaling uncouples germ cells from the somatic follicular compartment at ovulation

“…These results indicate that TZPs are lost in vitro even in the absence of EGF, but the timing is considerably delayed compared to in its presence. EGFR signaling requires its dimerization, and this can occur in the absence of ligand-binding 31 , raising the possibility that EGFR in cumulus cells might exhibit a weak ligand-independent activity eventually leading to TZP retraction. In contrast to the EGF-triggered loss of TZPs, however, the slow loss of TZPs in the absence of EGF was not attenuated by the chemical inhibitors of EGFR signaling (Supplementary Fig.…”

Allosteric activation of preformed EGF receptor dimers by binding of a single ligand

“…It has been assumed that all RTKs, except for the insulin receptor family, are activated by ligand-induced dimerisation of the receptor monomers 5 . This model was first proposed for EGFR (also known as ErbB1 or HER1) 6 , but it has long been controversial whether the receptor is monomeric, dimeric or oligomeric before ligand binding [7][8][9][10][11] . EGFR, ~170 kDa in mass, consists of an extracellular ligand-binding domain, single transmembrane a-helix, intracellular juxtamembrane (JM) region, cytoplasmic kinase domain (KD), and C-terminal tail (Fig.…”