title: Protein tyrosine kinase 6 negatively regulates growth and promotes enterocyte differentiation in the small intestine.
abstract: Protein tyrosine kinase 6 (PTK6) (also called Brk or Sik) is an intracellular tyrosine kinase that is expressed in breast cancer and normal epithelial linings. In adult mice, PTK6 expression is high in villus epithelial cells of the small intestine. To explore functions of PTK6, we disrupted the mouse Ptk6 gene. We detected longer villi, an expanded zone of PCNA expression, and increased bromodeoxyuridine incorporation in the PTK6-deficient small intestine. Although differentiation of major epithelial cell types occurred, there was a marked delay in expression of intestinal fatty acid binding protein, suggesting a role for PTK6 in enterocyte differentiation. However, fat absorption was comparable in wild-type and Ptk6-/- mice. It was previously shown that the serine threonine kinase Akt is a substrate of PTK6 and that PTK6-mediated phosphorylation of Akt on tyrosine resulted in inhibition of Akt activity. Consistent with these findings, we detected increased Akt activity and nuclear beta-catenin in intestines of PTK6-deficient mice and decreased nuclear localization of the Akt substrate FoxO1 in villus epithelial cells. PTK6 contributes to maintenance of tissue homeostasis through negative regulation of Akt in the small intestine and is associated with cell cycle exit and differentiation in normal intestinal epithelial cells.
authors.affiliation: University of Illinois College of Medicine, Department of Biochemistry and Molecular Genetics, M/C 669, 900 S. Ashland Ave., Chicago, IL 60607, USA.
authors.forename: Andrea
authors.initials: A
authors.lastname: Haegebarth
authors.forename: Wenjun
authors.initials: W
authors.lastname: Bie
authors.forename: Ruyan
authors.initials: R
authors.lastname: Yang
authors.forename: Susan E
authors.initials: SE
authors.lastname: Crawford
authors.forename: Valeri
authors.initials: V
authors.lastname: Vasioukhin
authors.forename: Elaine
authors.initials: E
authors.lastname: Fuchs
authors.forename: Angela L
authors.initials: AL
authors.lastname: Tyner
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D002454:Cell Differentiation / Q000235:genetics; D019070:Cell Lineage; D002465:Cell Movement / Q000235:genetics; D002467:Cell Nucleus / Q000737:chemistry / Q000378:metabolism; D020895:Enterocytes / Q000166:cytology* / Q000201:enzymology*; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors / Q000032:analysis / Q000378:metabolism; D018390:Gene Targeting; D007421:Intestine, Small / Q000166:cytology / Q000201:enzymology / Q000254:growth & development*; D051379:Mice; D018345:Mice, Knockout; D008840:Microfilament Proteins; D016254:Mutagenesis, Insertional; D011505:Protein-Tyrosine Kinases / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D015854:Up-Regulation; D051176:beta Catenin / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; C467200:Foxo1 protein, mouse; D008840:Microfilament Proteins; C485645:TWF2 protein, mouse; D051176:beta Catenin; D011505:Protein-Tyrosine Kinases; D051057:Proto-Oncogene Proteins c-akt