Abstract
Secreted Frizzled-related protein-1 (sFRP-1) belongs to a class of extracellular antagonists that modulate Wnt signaling pathways by preventing ligand-receptor interactions among Wnts and Frizzled membrane receptor complexes. sFRP-1 and Wnts are heparin-binding proteins, and their interaction can be stabilized by heparin in vitro. Here we report that heparin can specifically enhance recombinant sFRP-1 accumulation in a cell type-specific manner. The effect requires O-sulfation in heparin, and involves fibroblast growth factor-2 as well as fibroblast growth factor receptor-1. Interestingly, further investigation uncovers that heparin can also affect the post-translational modification of sFRP-1. We demonstrate that sFRP-1 is post-translationally modified by tyrosine sulfation at tyrosines 34 and 36, which is inhibited by the treatment of heparin. The results suggest that accumulation of sFRP-1 induced by heparin is in part due to the relative stabilization of unsulfated sFRP-1 and the direct stabilization by heparin. The study has revealed a multifaceted regulation on sFRP-1 protein by heparin.
Highlights
Wnt proteins are a large family of structurally related secreted glycoproteins that mediate fundamental biological processes such as cell polarity and proliferation, tissue patterning, and tumorigenesis [1,2,3,4]
Heparin Stimulates Recombinant Secreted Frizzled-related protein-1 (sFRP-1) Accumulation in HEK293 Cells—A DNA construct expressing a C-terminal His6-tagged sFRP-1 was transiently transfected into HEK293 cells, and between 72 and 120 h, sFRP-1 was detected in the media, at relatively low levels (Fig. 1A, lanes 1)
We have discovered that heparin, a highly negatively charged macromolecule, can exert two unexpected effects on sFRP-1 protein
Summary
Wnt proteins are a large family of structurally related secreted glycoproteins that mediate fundamental biological processes such as cell polarity and proliferation, tissue patterning, and tumorigenesis [1,2,3,4]. Heparin Stimulates Recombinant sFRP-1 Accumulation in HEK293 Cells—A DNA construct expressing a C-terminal His6-tagged sFRP-1 was transiently transfected into HEK293 cells, and between 72 and 120 h, sFRP-1 was detected in the media, at relatively low levels (Fig. 1A, lanes 1).
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