title: Intracellular signaling prevents effective blockade of oncogenic gp130 mutants by neutralizing antibodies.
abstract: BACKGROUND
  Short in-frame deletions in the second extracellular domain of the cytokine receptor gp130 are the leading cause of inflammatory hepatocellular adenomas (IHCAs). The deletions render gp130 constitutively active. In this study we investigate the intracellular signaling potential of one of the most potent constitutively active gp130 mutants (CAgp130) found in IHCAs.
  
  
  RESULTS
  Trafficking and signaling of CAgp130 were studied in stably transfected cell lines that allowed the inducible expression of CAgp130 fused to fluorescent proteins such as YFP and mCherry. In contrast to the predominantly highly glycosylated gp130 wild type (WTgp130), CAgp130 is preferentially found in the less glycosylated high-mannose form. Accordingly, the mutated receptor is retained intracellularly and therefore less prominently expressed at the cell surface. CAgp130 persistently activates Stat3 despite the presence of the feedback inhibitor SOCS3 but fails to activate Erk1/2. De novo synthesized CAgp130 signals already from the ER-Golgi compartment before having reached the plasma membrane. Cell surface expressed and endocytosed CAgp130 do not significantly contribute to signaling. As a consequence, Stat3 activation through CAgp130 cannot be inhibited by neutralizing gp130 antibodies but through overexpression of a dominant-negative Stat3 mutant.
  
  
  CONCLUSIONS
  CAgp130 and WTgp130 differ significantly with respect to glycosylation, trafficking and signaling. As a consequence of intracellular signaling pharmacological inhibition of CAgp130 will not be achieved by targeting the receptor extracellularly but by compounds that act from within the cell.
authors.forename: Natalie
authors.initials: N
authors.lastname: Rinis
authors.forename: Andrea
authors.initials: A
authors.lastname: Küster
authors.forename: Hildegard
authors.initials: H
authors.lastname: Schmitz-Van de Leur
authors.forename: Anne
authors.initials: A
authors.lastname: Mohr
authors.affiliation: Institute of Biochemistry and Molecular Biology, RWTH Aachen University, Pauwelsstraße 30, Aachen 52074, Germany. mueller-newen@rwth-aachen.de.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Müller-Newen
mesh_terms: D057134:Antibodies, Neutralizing / Q000276:immunology*; D002462:Cell Membrane / Q000378:metabolism; D050822:Cytokine Receptor gp130 / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D004705:Endocytosis; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006031:Glycosylation; D006056:Golgi Apparatus / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D020935:MAP Kinase Signaling System; D009154:Mutation; D011485:Protein Binding; D021381:Protein Transport; D050796:STAT3 Transcription Factor / Q000378:metabolism; D050826:Suppressor of Cytokine Signaling Proteins / Q000378:metabolism
chemical_list: D057134:Antibodies, Neutralizing; D050796:STAT3 Transcription Factor; D050826:Suppressor of Cytokine Signaling Proteins; D050822:Cytokine Receptor gp130