Fibroblast growth factor receptors (FGFRs) localize in different cellular compartments. A splice variant of FGFR-3 localizes to the nucleus.
We have raised specific antibodies to the second immunoglobulin-like domain of fibroblast growth factor receptors (FGFRs) and used these to investigate the expression and subcellular localization of FGFR-1, -2, -3, and -4 in breast epithelial cells. All four receptors classes could be detected in breast cell lines; however, FGFR-4 and FGFR-2 appeared to be expressed at a higher level in breast cancer cell lines than in normal epithelial cells. Surprisingly, FGFR-3 localized in the cell nucleus by immunofluorescence. A second antibody to a separate epitope confirmed this finding and showed that the form of FGFR-3 present must contain an intact kinase domain as well as the growth factor binding domain. Western analysis of fractionated cells revealed the presence of two forms of FGFR-3 of 135 and 110 kDa. The 110-kDa form was predominantly found in the nucleus, whereas the 135 kDa form was sometimes found in the nucleus. RT-PCR analysis of FGFR-3 mRNA showed the presence of a splice variant in which exons 7 and 8 are deleted. This results in the translation of FGFR-3 missing the transmembrane domain but with an intact kinase domain, which could be a soluble, intracellular receptor. Transfection experiments showed that FGFR-3 containing this deletion and no signal peptide gave an identical nuclear staining pattern to that seen in breast epithelial cells. We conclude that two forms of FGFR-3 are present in breast epithelial cells; a full-length 135-kDa receptor, which has a conventional membrane localization, and a novel soluble form of 110 kDa.
Johnston
C L
CL
Department of Medical Oncology, Charing Cross and Westminster Medical School, London, United Kingdom.
Cox
H C
HC
Gomm
J J
JJ
Coombes
R C
RC
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001940:Breast / Q000378:metabolism; D001943:Breast Neoplasms / Q000378:metabolism; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D002522:Chlorocebus aethiops; D003062:Codon; D017931:DNA Primers; D004848:Epithelium / Q000378:metabolism; D005091:Exons; D005260:Female; D005346:Fibroblast Growth Factors / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D014644:Genetic Variation; D006801:Humans; D007106:Immune Sera; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D017433:Protein Structure, Secondary; D011505:Protein-Tyrosine Kinases; D020794:Receptor Protein-Tyrosine Kinases / Q000032:analysis / Q000096:biosynthesis / Q000378:metabolism; D051496:Receptor, Fibroblast Growth Factor, Type 1; D051497:Receptor, Fibroblast Growth Factor, Type 2; D051498:Receptor, Fibroblast Growth Factor, Type 3; D051499:Receptor, Fibroblast Growth Factor, Type 4; D017468:Receptors, Fibroblast Growth Factor / Q000032:analysis / Q000096:biosynthesis / Q000378:metabolism*; D011994:Recombinant Proteins / Q000032:analysis / Q000096:biosynthesis / Q000378:metabolism; D017384:Sequence Deletion; D014162:Transfection; D014407:Tumor Cells, Cultured
D003062:Codon; D017931:DNA Primers; D007106:Immune Sera; D017468:Receptors, Fibroblast Growth Factor; D011994:Recombinant Proteins; D005346:Fibroblast Growth Factors; C496348:FGFR1 protein, human; C496353:FGFR2 protein, human; C496365:FGFR3 protein, human; C496371:FGFR4 protein, human; D011505:Protein-Tyrosine Kinases; D020794:Receptor Protein-Tyrosine Kinases; D051496:Receptor, Fibroblast Growth Factor, Type 1; D051497:Receptor, Fibroblast Growth Factor, Type 2; D051498:Receptor, Fibroblast Growth Factor, Type 3; D051499:Receptor, Fibroblast Growth Factor, Type 4