title: Src family kinases interfere with dimerization of STAT5A through a phosphotyrosine-SH2 domain interaction.
abstract: BACKGROUND
  Chronic myeloid leukemia (CML) is driven by the expression of the BCR-ABL oncoprotein. STAT5 is a BCR-ABL substrate and persistently activated by tyrosine phosphorylation in CML cells. Activated STAT5 (pSTAT5) drives proliferation and survival of leukemic cells and contributes to initial transformation and maintenance of the disease. In cytokine-induced STAT5 signaling, phosphorylation of STAT5A on Y694 leads to nuclear accumulation of the transcription factor, followed by DNA-binding and gene induction. However, Src-family kinases (SFK) mediate cytoplasmic retention of pSTAT5A leading to attenuated target gene expression and colony formation in CML cells.
  
  
  RESULTS
  In this study we show that autophosphorylation of Y416 in the highly conserved activation loop of SFK generates a potent recruitment site for the SH2 domain of STAT5A. Binding of the SH2 domain to the activation loop is required for STAT5A(Y694) phosphorylation by SFK, but at the same time promotes the persistent cytoplasmic localization of the transcription factor as found in BCR-ABL(+) leukemia. As a consequence of the complex formation between tyrosine-phosphorylated SFK and the SH2 domain of STAT5A, the dimerization of STAT5A is impaired. We further demonstrate that constitutively active STAT5A(S710F) escapes from SFK-mediated cytoplasmic retention by enhancing STAT5A dimer stability.
  
  
  CONCLUSIONS
  Our results reveal important structural aspects of cytoplasmic pSTAT5A found in myeloid leukemias and will contribute to the understanding of STAT5A mediated cytoplasmic signaling.
authors.affiliation: Institute of Biochemistry and Molecular Biology, Faculty of Medicine, RWTH Aachen University, Pauwelsstraße 30, 52074, Aachen, Germany. Dirk.Fahrenkamp@rwth-aachen.de.
authors.forename: Dirk
authors.initials: D
authors.lastname: Fahrenkamp
authors.affiliation: Institute of Biochemistry and Molecular Biology, Faculty of Medicine, RWTH Aachen University, Pauwelsstraße 30, 52074, Aachen, Germany. Hildegard.Schmitz-VandeLeur@rwth-aachen.de.
authors.forename: Hildegard Schmitz-Van
authors.initials: HS
authors.lastname: de Leur
authors.affiliation: Institute of Biochemistry and Molecular Biology, Faculty of Medicine, RWTH Aachen University, Pauwelsstraße 30, 52074, Aachen, Germany. drea.kuester@gmx.de.
authors.forename: Andrea
authors.initials: A
authors.lastname: Küster
authors.affiliation: Institute of Biochemistry and Molecular Biology, Faculty of Medicine, RWTH Aachen University, Pauwelsstraße 30, 52074, Aachen, Germany. nchatain@ukaachen.de.|Department of Hematology, Oncology, Hemostaseology, and Stem Cell Transplantation, Faculty of Medicine, RWTH Aachen University, Aachen, Germany. nchatain@ukaachen.de.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Chatain
authors.affiliation: Institute of Biochemistry and Molecular Biology, Faculty of Medicine, RWTH Aachen University, Pauwelsstraße 30, 52074, Aachen, Germany. mueller-newen@rwth-aachen.de.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Müller-Newen
mesh_terms: D000818:Animals; D016044:Fusion Proteins, bcr-abl / Q000235:genetics / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D010766:Phosphorylation / Q000235:genetics; D055503:Protein Multimerization; D021381:Protein Transport / Q000235:genetics; D050799:STAT5 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*; D018909:src Homology Domains; D019061:src-Family Kinases / Q000235:genetics / Q000378:metabolism*
chemical_list: D050799:STAT5 Transcription Factor; C494092:STAT5A protein, human; C494093:Stat5a protein, mouse; D025521:Tumor Suppressor Proteins; D016044:Fusion Proteins, bcr-abl; D019061:src-Family Kinases