title: Convergence of Wnt signaling on the HNF4alpha-driven transcription in controlling liver zonation.
abstract: OBJECTIVE
  In each hepatocyte, the specific repertoire of gene expression is influenced by its exact location along the portocentrovenular axis of the hepatic lobule and provides a reason for the liver functions compartmentalization defined "metabolic zonation." So far, few molecular players controlling genetic programs of periportal (PP) and perivenular (PV) hepatocytes have been identified; the elucidation of zonation mechanisms remains a challenge for experimental hepatology. Recently, a key role in induction and maintenance of the hepatocyte heterogeneity has been ascribed to Wnt/beta-catenin pathway. We sought to clarify how this wide-ranging stimulus integrates with hepatocyte specificity.
  
  
  METHODS
  Reverse transcriptase polymerase chain reaction (RT-PCR) allowed the transcriptional profiling of hepatocytes derived from in vitro differentiation of liver stem cells. The GSK3beta inhibitor 6-bromoindirubin-3'-oxime (BIO) was used for beta-catenin stabilization. Co-immunoprecipitations were used to study biochemical protein interactions while ChIP assays allowed the in vivo inspection of PV and PP genes regulatory regions.
  
  
  RESULTS
  We found that spontaneous differentiation of liver stem cells gives rise to PP hepatocytes that, after Wnt pathway activation, switch into PV hepatocytes. Next, we showed that the Wnt downstream player LEF1 interacts with the liver-enriched transcriptional factor HNF4alpha. Finally, we unveiled that the BIO induced activation of PV genes correlates with LEF1 binding to both its own and HNF4alpha consensus, and the repression of PP genes correlates with HNF4alpha displacement from its own consensus.
  
  
  CONCLUSIONS
  Our data show a direct and hitherto unknown convergence of the canonical Wnt signaling on the HNF4alpha-driven transcription providing evidences of a mechanism controlling liver zonated gene expression.
authors.affiliation: Department of Cellular Biotechnologies and Haematology, Istituto Pasteur-Fondazione Cenci Bolognetti, University Sapienza of Rome, Italy.
authors.forename: Marta
authors.initials: M
authors.lastname: Colletti
authors.forename: Carla
authors.initials: C
authors.lastname: Cicchini
authors.forename: Alice
authors.initials: A
authors.lastname: Conigliaro
authors.forename: Laura
authors.initials: L
authors.lastname: Santangelo
authors.forename: Tonino
authors.initials: T
authors.lastname: Alonzi
authors.forename: Emiliano
authors.initials: E
authors.lastname: Pasquini
authors.forename: Marco
authors.initials: M
authors.lastname: Tripodi
authors.forename: Laura
authors.initials: L
authors.lastname: Amicone
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002454:Cell Differentiation / Q000235:genetics*; D049109:Cell Proliferation; D002478:Cells, Cultured; D005455:Fluorescent Antibody Technique; D051557:Hepatocyte Nuclear Factor 4 / Q000235:genetics / Q000378:metabolism*; D022781:Hepatocytes / Q000166:cytology* / Q000502:physiology; D006801:Humans; D047468:Immunoprecipitation; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012680:Sensitivity and Specificity; D015398:Signal Transduction / Q000235:genetics* / Q000502:physiology; D014162:Transfection; D051153:Wnt Proteins / Q000235:genetics / Q000378:metabolism*; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism*
chemical_list: C496592:HNF4A protein, human; D051557:Hepatocyte Nuclear Factor 4; D051153:Wnt Proteins; D051176:beta Catenin