title: Tnk1/Kos1: a novel tumor suppressor.
abstract: Tnk1/Kos1 is a non-receptor protein tyrosine kinase implicated in negative regulation of cell growth by a mechanism involving inhibition of Ras activation and requiring Tnk1/Kos1's intrinsic catalytic activity. Tnk1/Kos1 null mice were created by homologous recombination by deleting the catalytic domain. Upon aging, both Tnk1+/- and Tnk1-/- mice develop spontaneous tumors, including lymphomas and carcinomas at high rates (i.e. 27%, and 43%, respectively), indicating that Tnk1/Kos1 is a tumor suppressor. Tissues from Tnk1/Kos1-null mice exhibit proportionally higher levels of basal and growth factor-stimulated Ras activation. Mechanistically, Tnk1/Kos1 requires either or both Y277 and Y287 sites to be intact for enzymatic activity and phosphorylation of its substrate, growth factor receptor binding protein 2 (Grb2). Data indicate that following tyrosine phosphorylation of Grb2 by Tnk1/Kos1, the Grb2-Sos1 guanine exchange factor (GEF) complex that mediates growth factor stimulated Ras activation becomes disrupted, resulting in the reversal of Ras activation. Conversely, the loss of Tnk1/Kos1 activity results in constitutive activation of Ras due to prolonged stabilization/activation of the Grb2-Sos1 GEF activity. Tnk1/Kos1 is the first tyrosine kinase discovered to have tumor suppressor activity, and the mechanism of spontaneous tumor formation involves constitutive, indirect activation of Ras. Thus, Ras may display "oncogenic activity" without undergoing "oncogenic" mutation. We now find that a cohort of patients with diffuse large B-cell lymphoma (DLBCL) display downregulation of Tnk1/Kos1 that may account for tumorigenesis in humans.
authors.affiliation: University of Florida, Shands Cancer Center, P.O. Box No: 100232, Gainesville, FL 326100, USA. Stratford.May@medicine.ufl.edu
authors.forename: William Stratford
authors.initials: WS
authors.lastname: May
authors.forename: Kishalay
authors.initials: K
authors.lastname: Hoare
authors.forename: Sarasija
authors.initials: S
authors.lastname: Hoare
authors.forename: Mary K
authors.initials: MK
authors.lastname: Reinhard
authors.forename: Young J
authors.initials: YJ
authors.lastname: Lee
authors.forename: S Paul
authors.initials: SP
authors.lastname: Oh
mesh_terms: D000818:Animals; D004268:DNA-Binding Proteins / Q000378:metabolism; D005326:Fetal Proteins / Q000235:genetics / Q000502:physiology*; D051380:GRB2 Adaptor Protein / Q000378:metabolism; D006579:Heterozygote; D006720:Homozygote; D006801:Humans; D016393:Lymphoma, B-Cell / Q000235:genetics; D051379:Mice; D018345:Mice, Knockout; D009374:Neoplasms, Experimental / Q000235:genetics; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D020837:SOS1 Protein / Q000378:metabolism; D015398:Signal Transduction; D014157:Transcription Factors / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D018631:ras Proteins / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; D005326:Fetal Proteins; C528734:GLUT4 enhancer factor, mouse; D051380:GRB2 Adaptor Protein; C495948:GRB2 protein, human; C495949:Grb2 protein, mouse; C480633:SLC2A4RG protein, human; D020837:SOS1 Protein; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; D011505:Protein-Tyrosine Kinases; C475466:Kos1 protein, mouse; C098672:TNK1 protein, human; D018631:ras Proteins