Soluble frizzled-7 receptor inhibits WNT signaling and sensitizes hepatocellular carcinoma cells towards doxorubicin

Asian Liver Center, Department of Surgery, 1201 Welch Road, Stanford University School of Medicine, Stanford, CA 94305, USA.
Molecular Cancer (Impact Factor: 4.26). 02/2011; 10(1):16. DOI: 10.1186/1476-4598-10-16
Source: PubMed


There are limited therapeutic options for hepatocellular carcinoma (HCC), the most common liver malignancy worldwide. Recent studies have identified the Frizzled-7 receptor (FZD7), important for activation of Wnt-mediated signaling, as a potential therapeutic target for HCC and other cancers.
We hypothesized that the extracellular domain of FZD7 (sFZD7) would be a clinically more relevant therapeutic modality than previously studied approaches to target FZD7. We expressed and purified sFZD7 from E. coli, and tested its functional activity to interact with Wnt3, its ability to inhibit Wnt3-mediated signaling, and its potential for combinatorial therapy in HCC.
sFZD7 pulled down Wnt3 from Huh7 cells, and decreased β-catenin/Tcf4 transcriptional activity in HCC cells. In vitro, sFZD7 dose-dependently decreased viability of three HCC cell lines (HepG2, Hep40, and Huh7, all with high FZD7 and Wnt3 mRNA), but had little effect on normal hepatocytes from three donors (all with low level FZD7 and Wnt3 mRNA). When combined with doxorubicin, sFZD7 enhanced the growth inhibitory effects of doxorubicin against HCC cells in vitro, and against Huh7 xenografts in vivo. Reduced expressions of c-Myc, cyclin D1, and survivin were observed in vitro and in vivo. Additionally, sFZD7 altered the levels of phosphorylated AKT and ERK1/2 induced by doxorubicin treatment in vitro, suggesting that several critical pathways are involved in the chemosensitizing effect of sFZD7.
We propose that sFZD7 is a feasible therapeutic agent with specific activity, which can potentially be combined with other chemotherapeutic agents for the improved management of HCC.

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Available from: Mei-Sze Chua, Jan 07, 2014
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    • "Most of the mechanistic insights into Wnt signalling have been downstream of the FZD receptors, and studies identifying regulators of FZD expression have been lacking. Early studies have shown that blocking FZDs could inhibit angiogenesis and tumor growth [19], and application of the purified extracellular domain of FZD7 could decrease β-catenin/TCF4 transcriptional activity [20]. More recently, one study reported that use of an anti-FZD antibody inhibited the binding of Wnts to FZD (such as FZD7) and inhibited the growth of human tumor xenografts [21]. "
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    ABSTRACT: The Wnt signaling pathway is often chronically activated in diverse human tumors, and the Frizzled (FZD) family of receptors for Wnt ligands, are central to propagating oncogenic signals in a β-catenin-dependent and independent manner. SIRT1 is a class III histone deacetylase (HDAC) that deacetylates histone and non-histone proteins to regulate gene transcription and protein function. We previously demonstrated that SIRT1 loss of function led to a significant decrease in the levels of Dishevelled (Dvl) proteins. To further explore this connection between the sirtuins and components of the Wnt pathway, we analyzed sirtuin-mediated regulation of FZD proteins. Here we explore the contribution of sirtuin deacetylases in promoting constitutive Wnt pathway activation in breast cancer cells. We demonstrate that the use of small molecule inhibitors of SIRT1 and SIRT2, and siRNA specific to SIRT1, all reduce the levels of FZD7 mRNA. We further demonstrate that pharmacologic inhibition of SIRT1/2 causes a marked reduction in FZD7 protein levels. Additionally, we show that β-catenin and c-Jun occupy the 7 kb region upstream of the transcription start site of the FZD7 gene, and SIRT1 inhibition leads to a reduction in the occupancy of both β-catenin and c-Jun at points along this region. This work uncovers a new mechanism for the regulation of FZD7 and provides a critical new link between the sirtuins and FZD7, one of the earliest nodal points from which oncogenic Wnt signaling emanates. This study shows that inhibition of specific sirtuins may provide a unique strategy for inhibiting the constitutively active Wnt pathway at the level of the receptor.
    Full-text · Article · Jun 2014 · PLoS ONE
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    • "To demonstrate that this effect was also true for liver cancer cells , we treated Huh - 7 cells , which have no mutations in the Wnt pathway , but endoge - nously express Wnt3 so that b - catenin protein is detectable at baseline ( Wei et al . , 2011 ) , with SAMe or MTA for 6 hours . Similar to RKO cells , SAMe and MTA treatment lowered b - catenin protein levels in Huh - 7 cells ( Fig . 4B ) . b - Catenin Degradation Mediated by SAMe and MTA Requires Active GSK3b . The phosphorylation of b - catenin at the N terminus is required for its recognition by the proteasomal complex to pr"

    Full-text · Article · May 2014 · Gastroenterology
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    • "For example, preclinical studies have already yielded favorable results for a variety of cancers [38,39]. This category also includes FZD7-specific antibodies, which have been shown to be beneficial for Wilm’s tumor and HCC [40,41]. The third category includes peptides such as FZD2 binding proteins [42]. "
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    ABSTRACT: The Wnt proteins are a family of 19 secreted glycoproteins that occupy crucial roles in the regulation of processes such as cell survival, proliferation, migration and polarity, cell fate specification, body axis patterning and self-renewal in stem cells. The canonical pathway has been implicated in a variety of cancers. As such, it is only fair to conclude that therapies targeting the Wnt pathway may play an essential role in the future of anticancer therapeutics, both alone or in conjunction with traditional therapies.
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