Grb2 phosphorylation disrupts EGFR condensates and reshapes Ras signaling

When a growth factor binds the epidermal growth factor receptor, the receptor’s kinase domain phosphorylates tyrosine residues on its own cytoplasmic tail through trans-autophosphorylation. These phosphotyrosine sites then recruit the adaptor protein Grb2, which in turn recruits SOS, the guanine nucleotide exchange factor that switches on Ras. New findings from a laboratory team led by Jay T. Groves show that this well-mapped pathway contains a hidden layer of control: Grb2 itself can be phosphorylated, and that modification can break apart the very protein assemblies that drive Ras activation.

The key lies in condensate formation. Multivalent binding between SOS and Grb2, together with direct Grb2-to-Grb2 interactions, drives activated EGFR molecules to gather into protein condensates. This condensed state helps relieve SOS autoinhibition, allowing signal to flow efficiently from the receptor to Ras. Phosphorylation of Grb2 at residue Y160, however, blocks the Grb2:Grb2 binding interface and can interfere with EGFR condensation, throttling the signaling machinery from within.

Using a reconstituted system, the researchers titrated kinase activity in the EGFR pathway and found that it can both promote and inhibit the signal output reaching Ras. This dual role arises because EGFR kinase activity does more than ignite the pathway; it also fuels the negative feedback in which phosphorylated Grb2 disrupts the SH2/SH3 dimer interface that stabilizes the condensate.

The most striking consequence is that tyrosine kinase inhibition can, under some circumstances, promote Ras activation rather than suppress it. By dampening Grb2 phosphorylation, inhibitors may relieve this negative feedback and preserve condensate assembly, effectively strengthening the signal even as the kinase itself is being blocked. The results, obtained in a reconstituted system rather than living cells, reveal how the effects of kinase inhibition depend on where a drug acts within the network of feedback loops that govern EGFR-to-Ras signaling.

Subject of Research: How Grb2 phosphorylation regulates EGFR condensate assembly and Ras signaling output

Article Title: Grb2 phosphorylation antagonizes EGFR-driven ras activation by interfering with condensate assembly

Article References: Phan, H. T., Lin, C.-W., Stinger, B. L., DeGrandchamp, J. B., Lew, L. J. N., Huang, S. J., & Groves, J. T. (2026). Grb2 phosphorylation antagonizes EGFR-driven ras activation by interfering with condensate assembly. PLOS One, 21(10), e0361303. https://doi.org/10.1371/journal.pone.0361303

Image Credits: AI Generated

DOI: 10.1371/journal.pone.0361303

Keywords: EGFR, Grb2, Ras signaling, SOS, protein condensates, phosphorylation, tyrosine kinase, negative feedback, signal transduction, reconstituted system, antagonizes, EGFR-driven