Epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase that regulates processes such as cell growth and differentiation through Ras/MAPK signaling. Ligand binding to EGFR triggers receptor dimerization and trans-autophosphorylation, which further recruits adaptor proteins Grb2 and SOS. Previous studies using an in vitro reconstitution system have shown that EGFR forms higher order assemblies mediated by Grb2:Grb2 and Grb2:SOS crosslinking; however, this mechanism has not been validated in a live-cell system. Here, we use live mammalian cells to examine how EGFR oligomerization and adaptor protein crosslinking contribute to EGFR condensation, utilizing microscopic imaging studies and mutational analysis of Grb2. We find that multivalent Grb2:SOS interactions are the primary driver of EGFR condensate formation under lower Grb2 expression levels. However, in the absence of Grb2:SOS interactions, Grb2 dimerization can substitute for Grb2:SOS interactions to promote EGFR condensation under higher Grb2 expression levels. These results distinguish Grb2-mediated EGFR condensation from EGFR oligomerization and demonstrate that cellular protein expression levels can steer the structure of resulting EGFR condensates.
Huang et al. (Sun,) studied this question.