Syndecan-3 and TFPI colocalize on the surface of endothelial-, smooth muscle-, and cancer cells

PLoS One. 2015 Jan 24;10(1):e0117404. doi: 10.1371/journal.pone.0117404. eCollection 2015.

Abstract

Background: Tissue factor (TF) pathway inhibitor (TFPI) exists in two isoforms; TFPIα and TFPIβ. Both isoforms are cell surface attached mainly through glycosylphosphatidylinositol (GPI) anchors. TFPIα has also been proposed to bind other surface molecules, like glycosaminoglycans (GAGs). Cell surface TFPIβ has been shown to exert higher anticoagulant activity than TFPIα, suggesting alternative functions for TFPIα. Further characterization and search for novel TFPI binding partners is crucial to completely understand the biological functions of cell associated TFPI.

Methods and results: Potential association of TFPI to heparan sulphate (HS) proteoglycans in the syndecan family were evaluated by knock down studies and flow cytometry analysis. Cell surface colocalization was assessed by confocal microscopy, and native PAGE or immunoprecipitation followed by Western blotting was used to test for protein interaction. Heparanase was used to enzymatically degrade cell surface HS GAGs. Anticoagulant potential was evaluated using a factor Xa (FXa) activity assay. Knock down of syndecan-3 in endothelial,- smooth muscle- and breast cancer cells reduced the TFPI surface levels by 20-50%, and an association of TFPIα to syndecan-3 on the cell surface was demonstrated. Western blotting indicated that TFPIα was found in complex with syndecan-3. The TFPI bound to syndecan-3 did not inhibit the FXa generation. Removal of HS GAGs did not release TFPI antigen from the cells.

Conclusions: We demonstrated an association between TFPIα and syndecan-3 in vascular cells and in cancer cells, which did not appear to depend on HS GAGs. No anticoagulant activity was detected for the TFPI associated with syndecan-3, which may indicate coagulation independent functions for this cell associated TFPI pool. This will, however, require further investigation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Breast Neoplasms / pathology*
  • Cell Line, Tumor
  • Endothelial Cells / cytology
  • Endothelial Cells / metabolism*
  • Factor VIIa / metabolism
  • Gene Expression Regulation
  • Gene Knockdown Techniques
  • Humans
  • Lipoproteins / deficiency
  • Lipoproteins / genetics
  • Lipoproteins / metabolism*
  • Myocytes, Smooth Muscle / cytology
  • Myocytes, Smooth Muscle / metabolism*
  • Protein Transport
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Syndecan-3 / deficiency
  • Syndecan-3 / genetics
  • Syndecan-3 / metabolism*

Substances

  • Lipoproteins
  • RNA, Messenger
  • SDC3 protein, human
  • Syndecan-3
  • lipoprotein-associated coagulation inhibitor
  • Factor VIIa

Grants and funding

This work was funded by research grants from the South-Eastern Norway Regional Health Authority, Hamar, Norway and A. Jahre and H. G. Andrine Berg & son foundations. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.