| GRB2 (Growth Factor Receptor Bound Protein 2) — Cytoplasmic adaptor protein containing one SH2 and two SH3 domains that couples activated receptor tyrosine kinases and other phosphorylated signaling proteins to downstream pathways. GRB2 commonly recruits SOS proteins, promoting RAS activation and subsequent RAF/MEK/ERK signaling.
Typical modulation in cancer: Frequently functionally activated and generally tumor-promoting when upstream growth-factor signaling is elevated. Increased GRB2-dependent signaling can support proliferation, survival, migration, invasion, transformation, and resistance to therapy. GRB2 itself is an adaptor rather than a kinase.
Typical mechanistic relationship: Growth factor receptor activation → receptor tyrosine phosphorylation → GRB2 recruitment → SOS1/SOS2 recruitment → RAS-GTP ↑ → RAF → MEK → ERK signaling ↑ → proliferation and survival ↑.
Additional signaling: GRB2 can also participate in PI3K/AKT, cytoskeletal, immune-receptor, and integrin-associated signaling depending on cellular context.
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