Syndecan-1 and FGF-2, but not FGF receptor-1, share a common transport route and co-localize with heparanase in the nuclei of mesenchymal tumor cells.
Syndecan-1 forms complexes with growth factors and their cognate receptors in the cell membrane. We have previously reported a tubulin-mediated translocation of syndecan-1 to the nucleus. The transport route and functional significance of nuclear syndecan-1 is still incompletely understood. Here we investigate the sub-cellular distribution of syndecan-1, FGF-2, FGFR-1 and heparanase in malignant mesenchymal tumor cells, and explore the possibility of their coordinated translocation to the nucleus. To elucidate a structural requirement for this nuclear transport, we have transfected cells with a syndecan-1/EGFP construct or with a short truncated version containing only the tubulin binding RMKKK sequence. The sub-cellular distribution of the EGFP fusion proteins was monitored by fluorescence microscopy. Our data indicate that syndecan-1, FGF-2 and heparanase co-localize in the nucleus, whereas FGFR-1 is enriched mainly in the perinuclear area. Overexpression of syndecan-1 results in increased nuclear accumulation of FGF-2, demonstrating the functional importance of syndecan-1 for this nuclear transport. Interestingly, exogenously added FGF-2 does not follow the route taken by endogenous FGF-2. Furthermore, we prove that the RMKKK sequence of syndecan-1 is necessary and sufficient for nuclear translocation, acting as a nuclear localization signal, and the Arginine residue is vital for this localization. We conclude that syndecan-1 and FGF-2, but not FGFR-1 share a common transport route and co-localize with heparanase in the nucleus, and this transport is mediated by the RMKKK motif in syndecan-1. Our study opens a new perspective in the proteoglycan field and provides more evidence of nuclear interactions of syndecan-1.
Department of Laboratory Medicine, Division of Pathology, Huddinge University Hospital, Karolinska Institutet, Stockholm, Sweden.
Fang
F
Zong
Eleni
E
Fthenou
Nina
N
Wolmer
Péter
P
Hollósi
Ilona
I
Kovalszky
László
L
Szilák
Carolin
C
Mogler
Gustav
G
Nilsonne
Georgios
G
Tzanakakis
Katalin
K
Dobra
D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism*; D004252:DNA Mutational Analysis; D016222:Fibroblast Growth Factor 2 / Q000096:biosynthesis* / Q000502:physiology; D015972:Gene Expression Regulation, Neoplastic; D005966:Glucuronidase / Q000096:biosynthesis* / Q000502:physiology; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006801:Humans; D047468:Immunoprecipitation; D008648:Mesoderm / Q000378:metabolism*; D018613:Microscopy, Confocal; D008954:Models, Biological; D009369:Neoplasms / Q000378:metabolism*; D051496:Receptor, Fibroblast Growth Factor, Type 1 / Q000096:biosynthesis* / Q000502:physiology; D053668:Syndecan-1 / Q000096:biosynthesis* / Q000737:chemistry* / Q000502:physiology; D000099175:Heparanase
D016222:Fibroblast Growth Factor 2; D005966:Glucuronidase; D049452:Green Fluorescent Proteins; D051496:Receptor, Fibroblast Growth Factor, Type 1; D053668:Syndecan-1; D000099175:Heparanase