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Originally published In Press as doi:10.1074/jbc.M410090200 on November 10, 2004
J. Biol. Chem., Vol. 280, Issue 3, 2116-2125, January 21, 2005
The Loss of Glypican-3 Induces Alterations in Wnt Signaling*
Howard H. Song ,
Wen Shi ,
Yun-Yan Xiang¶, and
Jorge Filmus ||
From the
Division of Molecular and Cellular Biology Research and ¶Sunnybrook and Women's College Health Science Centre and the Department of Medical Biophysics, University of Toronto, Toronto, Ontario M4N 3M5, Canada
Loss-of-function mutations of the GPC3 gene are the cause of the human Simpson-Golabi-Behmel syndrome. Based on the overgrowth phenotype of the Simpson-Golabi-Behmel syndrome patients and the key role played by the insulin-like growth factor (IGF) signaling system in regulating embryonic growth, it was speculated that GPC3 regulates IGF signaling. In order to test the validity of this hypothesis, we mated GPC3 knockout mice with insulin receptor substrate-1 (IRS-1) nullizygous mice. We found that GPC3 regulates organism growth independent of IRS-1, suggesting that GPC3 does not modulate IGF signaling. Instead, we found that GPC3 knockout mice exhibit alterations in the Wnt signaling pathway, which is also associated with the regulation of cell proliferation. In particular, the loss of GPC3 led to the inhibition of the non-canonical Wnt/JNK signaling pathway, while concomitantly causing the activation of canonical Wnt/ -catenin signaling. These in vivo findings were confirmed in vitro upon the ectopic overexpression of GPC3 in mesothelioma cells. In these cells, the GPC3-induced increase in JNK activity was associated with an enhanced response to Wnt5a. Most interestingly, the heparan sulfate chains of GPC3 were not required for its stimulatory activity on Wnt5a signaling and for the formation of GPC3-Wnt5a complexes. We propose that at least in some cell types GPC3 serves as a selective regulator of Wnt signaling, by potentiating non-canonical Wnt signaling, while inhibiting the canonical Wnt signaling pathway.
Received for publication, September 1, 2004
, and in revised form, October 19, 2004.
* This work was by the Canadian Institute of Health Research. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
|| To whom correspondence should be addressed: Division of Molecular and Cellular Biology Research, Research Bldg., S-218, 2075 Bayview Ave., Toronto, Ontario M4N 3M5, Canada. Tel.: 416-480-6100 (ext. 3350); E-mail: jorge.filmus{at}swchsc.on.ca.

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Copyright © 2005 by the American Society for Biochemistry and Molecular Biology.
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