title: The receptor tyrosine kinase FGFR4 negatively regulates NF-kappaB signaling.
abstract: BACKGROUND
  NFκB signaling is of paramount importance in the regulation of apoptosis, proliferation, and inflammatory responses during human development and homeostasis, as well as in many human cancers. Receptor Tyrosine Kinases (RTKs), including the Fibroblast Growth Factor Receptors (FGFRs) are also important in development and disease. However, a direct relationship between growth factor signaling pathways and NFκB activation has not been previously described, although FGFs have been known to antagonize TNFα-induced apoptosis.
  
  
  RESULTS
  Here, we demonstrate an interaction between FGFR4 and IKKβ (Inhibitor of NFκB Kinase β subunit), an essential component in the NFκB pathway. This novel interaction was identified utilizing a yeast two-hybrid screen [1] and confirmed by coimmunoprecipitation and mass spectrometry analysis. We demonstrate tyrosine phosphorylation of IKKβ in the presence of activated FGFR4, but not kinase-dead FGFR4. Following stimulation by TNFα (Tumor Necrosis Factor α) to activate NFκB pathways, FGFR4 activation results in significant inhibition of NFκB signaling as measured by decreased nuclear NFκB localization, by reduced NFκB transcriptional activation in electophoretic mobility shift assays, and by inhibition of IKKβ kinase activity towards the substrate GST-IκBα in in vitro assays. FGF19 stimulation of endogenous FGFR4 in TNFα-treated DU145 prostate cancer cells also leads to a decrease in IKKβ activity, concomitant reduction in NFκB nuclear localization, and reduced apoptosis. Microarray analysis demonstrates that FGF19 + TNFα treatment of DU145 cells, in comparison with TNFα alone, favors proliferative genes while downregulating genes involved in apoptotic responses and NFκB signaling.
  
  
  CONCLUSIONS
  These results identify a compelling link between FGFR4 signaling and the NFκB pathway, and reveal that FGFR4 activation leads to a negative effect on NFκB signaling including an inhibitory effect on proapoptotic signaling. We anticipate that this interaction between an RTK and a component of NFκB signaling will not be limited to FGFR4 alone.
authors.affiliation: Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California, United States of America.
authors.forename: Kristine A
authors.initials: KA
authors.lastname: Drafahl
authors.forename: Christopher W
authors.initials: CW
authors.lastname: McAndrew
authors.forename: April N
authors.initials: AN
authors.lastname: Meyer
authors.forename: Martin
authors.initials: M
authors.lastname: Haas
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Donoghue
mesh_terms: D000818:Animals; D017209:Apoptosis; D049109:Cell Proliferation; D005346:Fibroblast Growth Factors / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D051550:I-kappa B Kinase / Q000378:metabolism; D007249:Inflammation; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism; D051379:Mice; D016328:NF-kappa B / Q000378:metabolism*; D020411:Oligonucleotide Array Sequence Analysis; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism; D051499:Receptor, Fibroblast Growth Factor, Type 4 / Q000378:metabolism*; D015398:Signal Transduction; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
chemical_list: C117476:FGF19 protein, human; D036341:Intercellular Signaling Peptides and Proteins; D016328:NF-kappa B; D014409:Tumor Necrosis Factor-alpha; D005346:Fibroblast Growth Factors; D005982:Glutathione Transferase; C496371:FGFR4 protein, human; D020794:Receptor Protein-Tyrosine Kinases; D051499:Receptor, Fibroblast Growth Factor, Type 4; D051550:I-kappa B Kinase