Fig. 1

Schematic representation of a Receptor Tyrosine Kinase and the downstream MAPK pathway. The RTK is composed of a ligand-binding region in the extracellular domain, a transmembrane helix and a cytoplasmic region, which contains a tyrosine kinase domain. Its activation is due to a ligand-induced dimerization that results in receptor auto-phosphorylation of specific tyrosine residues in its intracellular domain. The GRB2 adaptor protein binds to the phosphorylated RTK and to the nucleotide exchange factor SOS that acts as a positive regulator of RAS allowing its interaction with the serine/threonine kinases of the RAF family, which activates MEK, which in turn activates ERK. ERK has many substrates, which control proliferation, differentiation, survival and migration