title: PI3K/AKT/mTOR-dependent stabilization of oncogenic far-upstream element binding proteins in hepatocellular carcinoma cells.
abstract: Transcription factors of the far-upstream element-binding protein (FBP) family represent cellular pathway hubs, and their overexpression in liver cancer (hepatocellular carcinoma [HCC]) stimulates tumor cell proliferation and correlates with poor prognosis. Here we determine the mode of oncogenic FBP overexpression in HCC cells. Using perturbation approaches (kinase inhibitors, small interfering RNAs) and a novel system for rapalog-dependent activation of AKT isoforms, we demonstrate that activity of the phosphatidylinositol-4,5-biphosphate 3-kinase/AKT pathway is involved in the enrichment of nuclear FBP1 and FBP2 in liver cancer cells. In human HCC tissues, phospho-AKT significantly correlates with nuclear FBP1/2 accumulation and expression of the proliferation marker KI67. Mechanistic target of rapamycin (mTOR) inhibition or blockade of its downstream effector eukaryotic translation initiation factor 4E activity equally reduced FBP1/2 concentrations. The mTORC1 inhibitor rapamycin diminishes FBP enrichment in liver tumors after hydrodynamic gene delivery of AKT plasmids. In addition, the multikinase inhibitor sorafenib significantly reduces FBP levels in HCC cells and in multidrug resistance 2-deficient mice that develop HCC due to severe inflammation. Both FBP1/2 messenger RNAs are highly stable, with FBP2 being more stable than FBP1. Importantly, inhibition of phosphatidylinositol-4,5-biphosphate 3-kinase/AKT/mTOR signaling significantly diminishes FBP1/2 protein stability in a caspase-3/-7-dependent manner.
  
  
  CONCLUSIONS
  These data provide insight into a transcription-independent mechanism of FBP protein enrichment in liver cancer; further studies will have to show whether this previously unknown interaction between phosphatidylinositol-4,5-biphosphate 3-kinase/AKT/mTOR pathway activity and caspase-mediated FBP stabilization allows the establishment of interventional strategies in FBP-positive HCCs.
authors.affiliation: Institute of Pathology, University Hospital Heidelberg, Heidelberg, Germany.
authors.forename: Jana
authors.initials: J
authors.lastname: Samarin
authors.affiliation: Cell Biology and Cell Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany.
authors.forename: Vibor
authors.initials: V
authors.lastname: Laketa
authors.affiliation: Institute of Pathology, University Hospital Heidelberg, Heidelberg, Germany.
authors.forename: Mona
authors.initials: M
authors.lastname: Malz
authors.affiliation: Institute of Pathology, University Hospital Heidelberg, Heidelberg, Germany.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Roessler
authors.affiliation: Department of Pathology, Hadassah-Hebrew University Medical Center, Jerusalem, Israel.
authors.forename: Ilan
authors.initials: I
authors.lastname: Stein
authors.affiliation: Department of Developmental Biology and Cancer Research, IMRIC, Hebrew University-Hadassah Medical School, Jerusalem, Israel.
authors.forename: Elad
authors.initials: E
authors.lastname: Horwitz
authors.affiliation: Institute of Pathology, University Hospital Heidelberg, Heidelberg, Germany.
authors.forename: Stephan
authors.initials: S
authors.lastname: Singer
authors.affiliation: Cell Biology and Cell Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany.
authors.forename: Eleni
authors.initials: E
authors.lastname: Dimou
authors.affiliation: Institute of Pathology, University Medicine Greifswald, Greifswald, Germany.
authors.forename: Antonio
authors.initials: A
authors.lastname: Cigliano
authors.affiliation: Institute of Pathology, University Hospital Heidelberg, Heidelberg, Germany.
authors.forename: Michaela
authors.initials: M
authors.lastname: Bissinger
authors.affiliation: Institute of Transplant Immunology, Hannover Medical School MHH, Hannover, Germany.
authors.forename: Christine Susanne
authors.initials: CS
authors.lastname: Falk
authors.affiliation: Department of Bioengineering and Therapeutic Sciences and Liver Center, University of California, San Francisco, CA.
authors.forename: Xin
authors.initials: X
authors.lastname: Chen
authors.affiliation: Department of Medicine II, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany.
authors.forename: Steven
authors.initials: S
authors.lastname: Dooley
authors.affiliation: Department of Pathology, Hadassah-Hebrew University Medical Center, Jerusalem, Israel.
authors.forename: Eli
authors.initials: E
authors.lastname: Pikarsky
authors.affiliation: Institute of Pathology, University Medicine Greifswald, Greifswald, Germany.
authors.forename: Diego Francesco
authors.initials: DF
authors.lastname: Calvisi
authors.affiliation: Cell Biology and Cell Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany.
authors.forename: Carsten
authors.initials: C
authors.lastname: Schultz
authors.affiliation: Institute of Pathology, University Hospital Heidelberg, Heidelberg, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Schirmacher
authors.affiliation: Institute of Pathology, University Hospital Heidelberg, Heidelberg, Germany.
authors.forename: Kai
authors.initials: K
authors.lastname: Breuhahn
mesh_terms: D006528:Carcinoma, Hepatocellular / Q000378:metabolism*; D053148:Caspase 3 / Q000378:metabolism; D053179:Caspase 7 / Q000378:metabolism; D004265:DNA Helicases / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005260:Female; D006801:Humans; D008113:Liver Neoplasms / Q000378:metabolism*; D008297:Male; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D055550:Protein Stability; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D016601:RNA-Binding Proteins; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*
chemical_list: D053148:Caspase 3; D053179:Caspase 7; D004265:DNA Helicases; D004268:DNA-Binding Proteins; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D016601:RNA-Binding Proteins; D058570:TOR Serine-Threonine Kinases; C492258:FUBP1 protein, human; C546842:MTOR protein, human