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Published online 14 July 2003. doi:10.1083/jcb.200212083
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© The Rockefeller University Press, 0021-9525/2003/7/341 $5.00
The Journal of Cell Biology, Volume 162, Number 2, 341-351

Article

 QSulf1 remodels the 6-O sulfation states of cell surface heparan sulfate proteoglycans to promote Wnt signaling

Xingbin Ai1, Anh-Tri Do2, Olga Lozynska1, Marion Kusche-Gullberg2, Ulf Lindahl2 and Charles P. Emerson, Jr.1

1 Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
2 Department of Medical Biochemistry and Microbiology, Uppsala University Biomedical Center, S-75123 Uppsala, Sweden

Address correspondence to Charles P. Emerson, Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, 1157 BRBII/III, 421 Curie Blvd., Philadelphia, PA 19104-6058. Tel.: (215) 898-0243. Fax: (215) 898-9873. E-mail: emersonc{at}mail.med.upenn.edu

The 6-O sulfation states of cell surface heparan sulfate proteoglycans (HSPGs) are dynamically regulated to control the growth and specification of embryonic progenitor lineages. However, mechanisms for regulation of HSPG sulfation have been unknown. Here, we report on the biochemical and Wnt signaling activities of QSulf1, a novel cell surface sulfatase. Biochemical studies establish that QSulf1 is a heparan sulfate (HS) 6-O endosulfatase with preference, in particular, toward trisulfated IdoA2S-GlcNS6S disaccharide units within HS chains. In cells, QSulf1 can function cell autonomously to remodel the sulfation of cell surface HS and promote Wnt signaling when localized either on the cell surface or in the Golgi apparatus. QSulf1 6-O desulfation reduces XWnt binding to heparin and HS chains of Glypican1, whereas heparin binds with high affinity to XWnt8 and inhibits Wnt signaling. CHO cells mutant for HS biosynthesis are defective in Wnt-dependent Frizzled receptor activation, establishing that HS is required for Frizzled receptor function. Together, these findings suggest a two-state "catch or present" model for QSulf1 regulation of Wnt signaling in which QSulf1 removes 6-O sulfates from HS chains to promote the formation of low affinity HS–Wnt complexes that can functionally interact with Frizzled receptors to initiate Wnt signal transduction.

Key Words: endosulfatase; QSulf1; HSPG; Glypican1; Wnt signaling

* Abbreviations used in this paper: AP, alkaline phosphatase; CS, chondroitin sulfate; GAG, glycosaminoglycan; GlcNR6ase, GlcNR 6-O sulfatase; HS, heparan sulfate; HSPG, heparan sulfate proteoglycan; IR, immunoreactivity; Wingless, Wg.


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