title: Identification of beta-catenin as a target of the intracellular tyrosine kinase PTK6.
abstract: Disruption of the gene encoding protein tyrosine kinase 6 (PTK6) leads to increased growth, impaired enterocyte differentiation and higher levels of nuclear beta-catenin in the mouse small intestine. Here, we demonstrate that PTK6 associates with nuclear and cytoplasmic beta-catenin and inhibits beta-catenin- and T-cell factor (TCF)-mediated transcription. PTK6 directly phosphorylates beta-catenin on Tyr64, Tyr142, Tyr331 and/or Tyr333, with the predominant site being Tyr64. However, mutation of these sites does not abrogate the ability of PTK6 to inhibit beta-catenin transcriptional activity. Outcomes of PTK6-mediated regulation appear to be dependent on its intracellular localization. In the SW620 colorectal adenocarcinoma cell line, nuclear-targeted PTK6 negatively regulates endogenous beta-catenin/TCF transcriptional activity, whereas membrane-targeted PTK6 enhances beta-catenin/TCF regulated transcription. Levels of TCF4 and the transcriptional co-repressor TLE/Groucho increase in SW620 cells expressing nuclear-targeted PTK6. Knockdown of PTK6 in SW620 cells leads to increased beta-catenin/TCF transcriptional activity and increased expression of beta-catenin/TCF target genes Myc and Survivin. Ptk6-null BAT-GAL mice, containing a beta-catenin-activated LacZ reporter transgene, have increased levels of beta-galactosidase expression in the gastrointestinal tract. The ability of PTK6 to negatively regulate beta-catenin/TCF transcription by modulating levels of TCF4 and TLE/Groucho could contribute to its growth-inhibitory activities in vivo.
authors.affiliation: Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, Chicago, IL 60607, USA.
authors.forename: Helena L
authors.initials: HL
authors.lastname: Palka-Hamblin
authors.forename: Jessica J
authors.initials: JJ
authors.lastname: Gierut
authors.forename: Wenjun
authors.initials: W
authors.lastname: Bie
authors.forename: Patrick M
authors.initials: PM
authors.lastname: Brauer
authors.forename: Yu
authors.initials: Y
authors.lastname: Zheng
authors.forename: John M
authors.initials: JM
authors.lastname: Asara
authors.forename: Angela L
authors.initials: AL
authors.lastname: Tyner
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D015536:Down-Regulation / Q000235:genetics; D004789:Enzyme Activation; D017930:Genes, Reporter; D006801:Humans; D007422:Intestines / Q000201:enzymology / Q000473:pathology; D042541:Intracellular Space / Q000201:enzymology*; D051379:Mice; D008822:Mice, Transgenic; D009363:Neoplasm Proteins / Q000378:metabolism*; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism; D011485:Protein Binding; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D013379:Substrate Specificity; D051820:TCF Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism*; D019061:src-Family Kinases / Q000378:metabolism*
chemical_list: D009363:Neoplasm Proteins; D051820:TCF Transcription Factors; D051176:beta Catenin; D019000:Phosphotyrosine; D011505:Protein-Tyrosine Kinases; C088375:PTK6 protein, human; C000598269:Ptk6 protein, mouse; D019061:src-Family Kinases