Summary
Heparansulfate-proteoglycans (HSPGs) interact via their polyanionic heparansulfate
(HS) side chains with a variety of proteins on the cell surface or within the extracellular
matrix membrane. The large number of heparin/HS binding proteins form a highly interconnected
functional network, which has been termed as the heparin/HS interactome and is functionally
linked to physiological and pathological processes. The aim of this study was to investigate
the global effect of these protein-HSPG interactions on the tumourigenicity of two
breast cancer cell lines (MCF-7 and MDA-MB-231). Cancer cells were cultured in serum-free
medium and treated with a concentration of heparin which was capable of modulating
HS/ligand interaction. Microarray analysis of MCF-7 cells cultured under these conditions
showed that expression of 105 of 1,357 genes potentially related to the pathogenesis
of breast neoplasm was significantly altered by heparin treatment. The changes in
gene expression correlated with a less tumourigenic phenotype, including reduction
of cell adhesive, invasive and migratory properties. These effects were associated
with an inhibition of the PI3K/Akt and Raf/MEK/ERK signalling pathways. The modulatory
effect of heparin on HS-associated activity was confirmed with one example of heparin/HS
interactomes, transforming growth factor β (TGFβ). The innate TGFβ activity of MCF-7
cells was reduced by heparin treatment, with specific interruption of the TGFβ–Smad
signalling pathway. The pro-tumourigenic contribution of the heparin/HS interactomes
was verified in cells in which HSPG synthesis was blocked using β-xyloside. In conclusion,
the interaction between cell surface HPSGs and innate heparin/HS interactomes makes
a significant contribution to the tumourigenicity.
Keywords Heparin/heparan sulfate interactomes - breast cancer cell - tumourigenicity