Downregulation of HSulf-1 promotes autocrine signaling in breast cancer

B39

Heparan sulfate glycosaminoglycans (HS-GAGs) are the oligosaccharide chains of heparan sulfate proteoglycans and interact with various extracellular signaling molecules as a low-affinity receptor to regulate their activities. The sulfation of HS-GAG residues is required for its interaction with heparin-binding growth factors to activate their high-affinity receptor tyrosine kinases. The alterations in HS-GAG sulfation and the consequences associated with pathology are, however, poorly characterized. The HS-GAG endosulfatase HSulf-1 is downregulated in ovarian, breast and several other cancer cell lines. Here we show that HSulf-1 inhibits autocrine activation of the EGFR-ERK pathway induced by serum withdrawal in MDA-MB-468 breast cancer cells. The neutralization antibodies against the heparin-binding growth factor family of the EGF superfamily, amphiregulin and HB-EGF, inhibit autocrine signaling. Furthermore, HSulf-1-mediated inhibition of autocrine signaling was associated with reduced cyclinD1 levels, leading to decreased S-phase fraction and increased G2-M fraction, and increased cell death. Finally, evaluation of HSulf-1 expression levels in primary invasive breast tumors by RNA in situ hybridization indicated that HSulf-1 is downregulated in majority (60%) of tumors. These data suggest a potential role of HSulf-1 in mammary carcinogenesis.