Interaction of Frizzled Related Protein (FRP) with Wnt Ligands and the Frizzled Receptor Suggests Alternative Mechanisms for FRP Inhibition of Wnt Signaling*
- From the ‡Derald H. Ruttenberg Cancer Center, Mount Sinai School of Medicine, New York, New York 10029 and the§Department of Human Microbiology, Sackler School of Medicine, Tel-Aviv University, Tel-Aviv, Israel
Abstract
Frizzled related proteins (FRPs) comprise a family of secreted molecules that contain an N-terminal cysteine-rich domain (CRD) highly similar to the CRDs of the frizzled family of membrane-anchored Wnt receptors. FRPs have been shown to interact with Wnt proteins and antagonize Wnt signaling in a Xenopusdevelopmental model. We demonstrated that FRP antagonizes the Wnt-induced increase in uncomplexed β-catenin in both transient cotransfection and stable transformation models, where Wnt-induced morphological alterations are inhibited as well. We showed further that FRP inhibits Wnt signaling in a paracrine mode using a T-cell factor luciferase reporter to measure Wnt function. Investigation of the mechanisms responsible for FRP inhibition revealed that FRP forms complexes with WNT-1 or WNT-2 through its CRD domain. Transfection analysis with FRPs containing different tags revealed that FRP itself forms complexes and that this ability is conferred by its CRD domain. Finally, we demonstrated by cotransfection that FRP forms complexes with a prototype frizzled. All of these findings are consistent with a model by which FRP inhibits Wnt signaling through interactions with Wnt and/or formation of nonfunctional complexes with the frizzled receptor.
Footnotes
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↵* This research was supported by NCI grants from the National Institutes of Health.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵¶ To whom correspondence should be addressed: Ruttenberg Cancer Center, Mount Sinai School of Medicine, One Gustave L. Levy Place, Box 1130, New York, NY 10029. Tel.: 212-241-6470; Fax: 212-987-2240; E-mail: Aaronson{at}smtplink.mssm.edu.
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↵2 A. Gazit, A. Yaniv, A. Bafico, T. Pramila, M. Igarashi, J. Kitajewski, and S. A. Aaronson, manuscript in preparation.
- Abbreviations:
- APC
-
adenomatous polyposis coli protein
- CRD
-
cysteine-rich domain
- fz
-
frizzled
- FRP
-
frizzled related protein
- PCR
-
polymerase chain reaction
- RLU
-
relative luciferase units
- GST
-
glutathione S-transferase
- PAGE
-
polyacrylamide gel electrophoresis
- PBS
-
phosphate-buffered saline
- PDGF
-
platelet-derived growth factor
- TCF
-
T-cell factor
- LEF
-
lymphoid enhancer factor
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- Received January 5, 1999.
- Revision received March 15, 1999.
- The American Society for Biochemistry and Molecular Biology, Inc.
