Nuclear localization of a complex of fibroblast growth factor(FGF)-1 and an NH2-terminal fragment of FGF receptor isoforms R4 and R1alpha in human liver cells.
FGF ligands and FGF receptor 1 (FGFR1) appear associated with the nucleus in addition to their extracellular and transmembrane locations. After receptor-dependent internalization in liver cells, radiolabeled 16-kDa FGF-1 appears in a 40-kDa covalent complex with a cellular protein. In this report, we show that in a human hepatoma cell line, HepG2, which expresses both FGFR4 and FGFR1, the 40-kDa complex cross-reacts with antibodies against the ectodomain of both types of receptors. In addition to antibody against FGF-1, a polyclonal antiserum against the three immunoglobulin (Ig)-like loop ectodomain of FGFR4 and a monoclonal antibody to a 19-residue sequence in the NH2-terminus of the NH2-terminal Ig Loop I of the three loop splice variant of FGFR1 (FGFR1alpha) reacts with the complex. A monoclonal antibody against an epitope in FGFR1 downstream of the inter-loop I/II sequence which reacts with intact FGFR1 failed to cross-react with the 40-kDa complex. Cell fractionations and indirect immunofluorescent localization revealed that the 40-kDa complex associates with the particulate fraction of cells, particularly the nucleus and associated cytoskeletal elements. We propose that the NH2-terminal Ig-loop of the three loop isoforms of FGFR, which are generally associated inversely with cell growth, may play a role at or in the nucleus in addition to modification of affinity of the FGFR ectodomain for heparan sulfate and FGF ligand.
Feng
S
S
Albert B. Alkek Institute of Biosciences and Technology, Department of Biochemistry and Biophysics, Texas A&M University, Houston 77030-330, USA.
Xu
J
J
Wang
F
F
Kan
M
M
McKeehan
W L
WL
D000906:Antibodies / Q000276:immunology; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism; D000939:Epitopes / Q000032:analysis* / Q000276:immunology; D005346:Fibroblast Growth Factors / Q000378:metabolism* / Q000494:pharmacology; D005455:Fluorescent Antibody Technique; D006801:Humans; D008099:Liver / Q000378:metabolism* / Q000648:ultrastructure; D020794:Receptor Protein-Tyrosine Kinases; D051496:Receptor, Fibroblast Growth Factor, Type 1; D051499:Receptor, Fibroblast Growth Factor, Type 4; D017468:Receptors, Fibroblast Growth Factor / Q000276:immunology / Q000378:metabolism*
D000906:Antibodies; D000939:Epitopes; D017468:Receptors, Fibroblast Growth Factor; D005346:Fibroblast Growth Factors; C496348:FGFR1 protein, human; C496371:FGFR4 protein, human; D020794:Receptor Protein-Tyrosine Kinases; D051496:Receptor, Fibroblast Growth Factor, Type 1; D051499:Receptor, Fibroblast Growth Factor, Type 4