title: Adaptor protein Lnk binds to PDGF receptor and inhibits PDGF-dependent signaling.
abstract: OBJECTIVE
  Platelet-derived growth factor receptors α and β (PDGFRA, PDGFRB) are frequently expressed on hematopoietic cells and regulate cellular responses such as proliferation, differentiation, survival, and transformation. Stimulation by autocrine loops or activation by chromosomal translocation makes them important factors in development of hematopoietic disorders. Interaction with the ligand PDGF results in activation of the tyrosine kinase domain and phosphorylation of tyrosine residues, thereby creating binding sites for molecules containing Src homology 2 domains. We hypothesized that one such protein may be Lnk, a negative regulator of cytokine receptors, including Mpl, EpoR, c-Kit, and c-Fms.
  
  
  METHODS
  Interaction of Lnk with PDGFRA, PDGFRB, or leukemogenic FIP1L1-PDGFRA or TEL-PDGFRB was studied in cotransfected 293T cells. Effects of Lnk on PDGFR signaling were shown in 293T and NIH3T3 cells, whereas its influence on either PDGF-dependent or factor-independent growth was investigated using Ba/F3 or 32D cells expressing wild-type PDGFR, FIP1L1-PDGFRA, or TEL-PDGFRB.
  
  
  RESULTS
  We show that Lnk binds to PDGFR after exposure of cells to PDGF. Furthermore, Lnk can bind the FIP1L1-PDGFRA fusion protein. Mutation or deletion of the Lnk Src homology 2 domain completely abolished binding of Lnk to FIP1L1-PDGFRA, but just partly prevented binding to PDGFRA or PDGFRB. Expression of Lnk inhibited proliferation of PDGF-dependent Ba/F3 cells and diminished phosphorylation of Erk in PDGF-treated NIH3T3. 32D cells transformed by either FIP1L1-PDGFRA or TEL-PDGFRB stopped growing when Lnk was expressed.
  
  
  CONCLUSIONS
  Lnk is a negative regulator of PDGFR signaling. Development of Lnk mimetic drugs might provide a novel therapeutic strategy for myeloproliferative disorders.
authors.affiliation: Department of Medicine, Hematology/Oncology, Johann Wolfgang Goethe University, Theodor-Stern-Kai 7, Frankfurt, Germany. s.gueller@em.uni-frankfurt.de
authors.forename: Saskia
authors.initials: S
authors.lastname: Gueller
authors.forename: Sina
authors.initials: S
authors.lastname: Hehn
authors.forename: Verena
authors.initials: V
authors.lastname: Nowak
authors.forename: Sigal
authors.initials: S
authors.lastname: Gery
authors.forename: Hubert
authors.initials: H
authors.lastname: Serve
authors.forename: Christian H
authors.initials: CH
authors.lastname: Brandts
authors.forename: H Phillip
authors.initials: HP
authors.lastname: Koeffler
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002478:Cells, Cultured; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D041681:NIH 3T3 Cells; D011485:Protein Binding; D011506:Proteins / Q000737:chemistry / Q000378:metabolism*; D017479:Receptors, Platelet-Derived Growth Factor / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D047908:Intracellular Signaling Peptides and Proteins; D011506:Proteins; C490778:SH2B3 protein, human; D017479:Receptors, Platelet-Derived Growth Factor