PDGF-INDUCED PHOSPHORYLATION OF TYR28 IN THE N-TERMINUS OF FYN AFFECTS FYN ACTIVATION

Binding of platelet-derived growth factor (PDGF) to its receptors lead s to the activation of members of the Src family of protein tyrosine k inases. We show here that Fyn, a member of the Src family, is phosphor ylated on Tyr28 in the unique N-terminal part of the molecule after in teraction with the intracellular domain of the PDGF beta-receptor. Act ivated Fyn furthermore undergoes autophosphorylation on Tyr30, Tyr39 a nd Tyr420. When Fyn mutants with Tyr28, Tyr30 or Tyr39 replaced with p henylalanine residues were transfected into NIH3T3 cells a decreased a ctivation after PDGF stimulation was seen, suggesting a functional imp ortance of the N-terminal tyrosine phosphorylation of Fyn. (C) 1997 Ac ademic Press.