FIGURE 2.

Platelet-derived growth factor (PDGF) signalling pathway. Binding of distinct dimeric PDGF ligands to the respective receptor dimer leads to autophosphorylation of the tyrosine residues within their intracellular domains. Autophosphorylation then leads to transduction of signals via recruitment of surrounding proteins containing Src homology region 2. These include domains such as Grb2, Grb7, SHC, PI3K and GTPase-activating protein for Ras. Signal transduction occurs via two main pathways: 1) the PI3K pathway, which mediates Akt signalling for the promotion of cell survival and 2) the mitogen-activated protein kinase (MAPK) cascade. Hydrolytic conversion of RAS-guanosine diphosphate (GDP) to RAS-guanosine triphosphate (GTP) leads to activation of MAPK cascade members, such as extracellular signal-regulated kinase (ERK) or MAPK kinase (MEK) via RAF1, resulting in gene target transcription. This pathway is important for cell growth, proliferation, differentiation and migration. Son of sevenless (SOS) is a nucleotide exchange factor for Ras.