HSulf1 has been shown to attenuate heparin-binding growth factor signaling by 6-0 desulfation from N-glucosamine residues present on heparan sulfate thereby altering its affinity to various growth factors. HSulf1 is often downregulated in cancers of differing origins, however, little is known about its regulation. In the present study we demonstrate that abundance of HSulf1 is regulated by hypoxia via decreased transcription in all breast cancer cell lines expressing HSulf1. Knockdown of HIF-1α rescued HSulf1 downregulation imposed by hypoxia, both at RNA and protein levels in multiple breast cancer cells. Similarly treatment of deferroxamine, cobalt chloride, and DMOG; agents that stabilizes HIF-1α resulted in diminished protein levels of HSulf1. Conversely, over-expression of HIF-1α alone was sufficient and necessary to suppress HSulf1 levels. Furthermore promoter analysis of HSulf1 revealed presence of at least two functional hypoxia responsive elements spanning from -1841bp to -1928bp upstream to transcription start site. Chromatin immunoprecipitation with HIF-1α antibody confirmed recruitment of HIF-1α on native HSulf1 promoter. Subsequently hypoxia induced transwell migration of HSulf1 deficient breast cancer cells i.e MDA468 cells was abolished upon restoring HSulf1 expression. Thus, our findings confirm HSulf1 as a HIF-1α target gene and reveal an important link between increased growth factor signaling and hypoxic microenvironment.

99th AACR Annual Meeting-- Apr 12-16, 2008; San Diego, CA