Platelet-Derived Growth Factor-Mediated Signaling through the Shb Adaptor Protein: Effects on Cytoskeletal Organization

The Src homology (SH) 2 domain adaptor protein Shb has previously been shown to interact with the platelet-derived growth factor (PDGF)-β receptor. In this study we show an association between Shb and the PDGF-α receptor which is mediated by the SH2 domain of Shb and involves tyrosine residue 720 in the kinase insert domain of the receptor. To assess the role of Shb in PDGF-mediated signaling, we have overexpressed wild-type Shb or Shb carrying a mutation (R522K) which renders the SH2 domain inactive, in Patch mouse (PhB) fibroblasts expressing both PDGF receptors (PhB/Rα). Overexpression of wild-type Shb, but not the R522K Shb mutant, affected PDGF-mediated reorganization of the cytoskeleton by decreasing membrane ruffle formation and stimulating the generation of filopodia relative the parental control cells. In addition, the PDGF-induced receptor-associated phosphatidylinositol 3′-kinase activity and phosphorylation of Akt was similar in both PhB/Rα/Shb and PhB/Rα/ShbR522K cells compared with the parental control, whereas the activation of Rac in response to PDGF-BB was diminished only in the PhB/Rα/Shb cells. We conclude that Shb plays a role in PDGF-dependent regulation of certain cytoskeletal changes by modulating the ability of PDGF to activate Rac.