Fig. 3. Signal transduction downstream of activated PDGFRs. Upon ligand binding, PDGFRs dimerize, activate intracellular tyrosine kinase domains, and autophosphorylate several tyrosine residues to generate docking sites for signaling and adaptor proteins. Proteins that interact with activated (ligand-bound) mammalian PDGFR and PDGFRß homodimers are shown. Also indicated are the signaling pathways activated by the receptor-binding proteins (reviewed by Heldin and Westermark, 1999). Stat5, Signal transducer and activator of transcription 5; PI3K, phosphatidylinositol 3-kinase; SHP2, SH2-containing protein tyrosine phosphatase; PLC, phospholipase C; JNK, Jun N-terminal kinase; SAPK, stress activated protein kinase; p70S6K, p70 S6 kinase; PKB, protein kinase B; PKC, protein kinase C; MAPK, mitogen activated protein kinase; RasGAP, Ras GTPase-activating protein.