Heparan sulfate (HS) is a component of cell surface and extracellular matrix
proteoglycans that regulates numerous signaling pathways by binding and activating multiple
growth factors and
chemokines. The amount and pattern of HS sulfation are key determinants for the assembly of the trimolecular, HS-
growth factor-receptor, signaling complex. Here we demonstrate that HS 6-O-sulfotransferases 1 and 2 (HS6ST-1 and HS6ST-2), which perform sulfation at 6-O position in
glucosamine in HS, impact
ovarian cancer angiogenesis through the HS-dependent
HB-EGF/EGFR axis that subsequently modulates the expression of multiple angiogenic
cytokines. Down-regulation of HS6ST-1 or HS6ST-2 in human
ovarian cancer cell lines results in 30-50% reduction in
glucosamine 6-O-sulfate levels in HS, impairing
HB-EGF-dependent EGFR signaling and diminishing
FGF2,
IL-6, and
IL-8 mRNA and
protein levels in
cancer cells. These
cancer cell-related changes reduce endothelial cell signaling and tubule formation in vitro. In vivo, the development of subcutaneous
tumor nodules with reduced 6-O-sulfation is significantly delayed at the initial stages of
tumor establishment with further reduction in angiogenesis occurring throughout
tumor growth. Our results show that in addition to the critical role that 6-O-sulfate moieties play in angiogenic
cytokine activation, HS 6-O-sulfation level, determined by the expression of HS6ST
isoforms in
ovarian cancer cells, is a major regulator of angiogenic program in
ovarian cancer cells impacting
HB-EGF signaling and subsequent expression of angiogenic
cytokines by
cancer cells.