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

Abstract

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.

Nuclear heparanase-1 activity suppresses melanoma progression via its DNA-binding affinity

“…Besides its extracellular action, HPSE has been discovered to exert nuclear action by shedding syndecan-1 in the nuclei of myeloma cells 4 . Loss of nuclear syndecan-1 interferes with gene transcription via enhanced histone acetylation and enhanced extracellular signal-regulated kinase (ERK) activation which including the up-regulation of matrix metalloproteinase 9 (MMP-9) [4][5][6] .…”

“…Loss of nuclear syndecan-1 interferes with gene transcription via enhanced histone acetylation and enhanced extracellular signal-regulated kinase (ERK) activation which including the up-regulation of matrix metalloproteinase 9 (MMP-9) [4][5][6] . MMP-9 is known to be transcriptionally regulated by NF-κB signaling pathway 7,8 .…”

Two promoters with distinct activities in different tissues drive the expression of heparanase in Xenopus

“…Potentially, the heparanase close to the DNA corresponds to XHpa active, because it is also detected with the human anti-Hpa antibody that mainly recognizes the active form (data not shown). In support, in myeloma and fibroblast cell lines a fraction of the active form of heparanase colocalizes with syndecan-1 in the nucleus, where it appears to help silence gene expression (Chen and Sanderson, 2009;Zong et al, 2009). Of note, in Xenopus, gene transcription starts at the midblastula transition (stage 8) and increases approximately 20 fold over the next hour (Newport and Kirschner, 1982), just before the last time point at which heparanase is detected in the nucleus (stage 10).…”

“…S1; which is available online). Distinct from mammalian eggs, amphibian eggs are surrounded by a complex ECM that consists of both a vitelline envelope proximal to the egg, and a three layered thick jelly coat, consisting of complex and partially characterized glycoproteins that are deposited around the egg as it passes through the oviduct (Hedrick and Nishihara, 1991;Guerardel et al, 2000;Zong et al, 2009). The jelly coat provides a protective environment for the developing embryo, and, by modulating sperm binding to the vitelline membrane, blocks poly-spermy.…”

“…Moreover, recent studies indicate that heparanase and HSPGs also play important roles inside the cell. For instance, nuclear colocalization of the HSPG syndecan 1 with endogenous heparanase may regulate gene transcription (Schubert et al, 2004;Chen and Sanderson, 2009;Zong et al, 2009). A critical step in understanding the role of heparanase during development is analysis of the dynamic and spatial aspects of its expression.…”