title: Breast tumor kinase/protein tyrosine kinase 6 (Brk/PTK6) activity in normal and neoplastic biliary epithelia.
abstract: OBJECTIVE
  Breast tumor kinase (BRK) augments proliferation and promotes cell survival in breast cancers via interactions with SH2 and SH3 ligand-containing proteins, such as receptor tyrosine kinases (RTK; e.g. EGFR, ErbB2/neu). Since RTK contribute to cholangiocarcinoma (CC) evolution we probed BRK protein expression and function in normal and CC livers.
  
  
  METHODS
  Immunohistochemical staining of normal livers and CC (n=93) in a tissue microarray and three CC and an immortalized human cholangiocyte cell lines (real-time PCR, Western blotting, siRNA) were used to study the functional relationships between BRK, EGFR, ErbB2, SAM68, and SPRR2a.
  
  
  RESULTS
  BRK protein was expressed in normal human intrahepatic bile ducts; all CC cell lines and a majority of CC showed strong BRK protein expression. Multiplex immunostaining/tissue cytometry and immunoprecipitation studies showed: 1) BRK co-localized with EGFR and ErbB2/neu; 2) BRK(high)/EGFR(high)-co-expressing CC cells had significantly higher Ki67 labeling and; 3) stronger BRK protein expression was seen in perihilar and distal CC than intrahepatic CC and directly correlated with CC differentiation. In cell lines, BRK expression augmented proliferation in response to exogenous EGF, whereas BRK siRNA significantly reduced growth. The SH3 ligand-containing, SPRR2A activated pTyr342 BRK, which in turn, phosphorylated SAM68, causing nuclear localization and increased cell proliferation similar to observations in breast cancers.
  
  
  CONCLUSIONS
  BRK expression in a majority of CC can interact with RTK, augmenting growth and interfering with proliferation inhibitors (SAM68). Therapeutically targeting BRK function (in addition to RTK) should be of benefit for CC treatment.
authors.affiliation: Thomas E. Starzl Transplantation Institute, University of Pittsburgh Medical Center, PA 15260, USA; The Department of Pathology, Division of Liver and Transplantation Pathology, University of Pittsburgh Medical Center, PA 15260, USA.
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Mizuguchi
authors.affiliation: Thomas E. Starzl Transplantation Institute, University of Pittsburgh Medical Center, PA 15260, USA; The Department of Pathology, Division of Liver and Transplantation Pathology, University of Pittsburgh Medical Center, PA 15260, USA.
authors.forename: Susan
authors.initials: S
authors.lastname: Specht
authors.affiliation: Thomas E. Starzl Transplantation Institute, University of Pittsburgh Medical Center, PA 15260, USA; The Department of Pathology, Division of Liver and Transplantation Pathology, University of Pittsburgh Medical Center, PA 15260, USA.
authors.forename: Kumiko
authors.initials: K
authors.lastname: Isse
authors.affiliation: Thomas E. Starzl Transplantation Institute, University of Pittsburgh Medical Center, PA 15260, USA; The Department of Pathology, Division of Liver and Transplantation Pathology, University of Pittsburgh Medical Center, PA 15260, USA.
authors.forename: Eizaburo
authors.initials: E
authors.lastname: Sasatomi
authors.affiliation: Thomas E. Starzl Transplantation Institute, University of Pittsburgh Medical Center, PA 15260, USA; The Department of Pathology, Division of Liver and Transplantation Pathology, University of Pittsburgh Medical Center, PA 15260, USA.
authors.forename: John G
authors.initials: JG
authors.lastname: Lunz
authors.affiliation: Department of Molecular Anatomy and Medicine, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-Ku, Tokyo 113-8602, Japan.
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Takizawa
authors.affiliation: Thomas E. Starzl Transplantation Institute, University of Pittsburgh Medical Center, PA 15260, USA; The Department of Pathology, Division of Liver and Transplantation Pathology, University of Pittsburgh Medical Center, PA 15260, USA. Electronic address: demetrisaj@upmc.edu.
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Demetris
mesh_terms: D001650:Bile Duct Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D001653:Bile Ducts, Intrahepatic / Q000378:metabolism / Q000473:pathology*; D015153:Blotting, Western; D002454:Cell Differentiation; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008297:Male; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000235:genetics*; D011505:Protein-Tyrosine Kinases / Q000096:biosynthesis / Q000235:genetics*; D012334:RNA, Neoplasm; D060888:Real-Time Polymerase Chain Reaction; D015398:Signal Transduction
chemical_list: D009363:Neoplasm Proteins; D012334:RNA, Neoplasm; D011505:Protein-Tyrosine Kinases; C088375:PTK6 protein, human
keywords: BRK; Cholangiocarcinoma (CC); EGFR; ErbB2; RNA interference; SAM68; Tyrosine kinases