A Switch from Canonical to Noncanonical Wnt Signaling Mediates Drug Resistance in Colon Cancer Cells

Shruti Tewari,Wafa Atamna,Michael Bordonaro,Catherine E. Cicco,Darina L. Lazarova,Cara Gottardi

doi:10.1371/journal.pone.0027308

Shruti Tewari, Wafa Atamna + Show 4 more

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https://doi.org/10.1371/journal.pone.0027308

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Journal: PLoS ONE	Publication Date: Nov 3, 2011
Citations: 116	License type: CC BY 4.0

Affiliation: Commonwealth Medical College

Abstract

Butyrate, a fermentation product of fiber in the colon, acts as a histone deacetylase inhibitor (HDACi) and induces apoptosis in colon cancer (CC) cells in vitro. We have reported that the apoptotic effects of butyrate are dependent upon the hyperactivation of the Wnt/beta-catenin pathway. However, prolonged exposure of CC cells to increasing concentrations of butyrate results in the acquisition of resistance to the Wnt/beta-catenin- and apoptosis-inducing effects of this agent, as well as cross-resistance to structurally different HDACis. Here we report that one mechanism whereby HDACi resistance arises is through the increase of beta-catenin-independent (noncanonical) Wnt signaling. Compared to HDACi-sensitive HCT-116 CC cells, HDACi-resistant HCT-R cells exhibit higher levels of AKT/PKB cell survival signaling, which is in part induced by WNT5A and its receptor ROR2. The induction of AKT signaling by HDACis is also detected in other CC cell lines, albeit to a lesser extent than in the drug-resistant HCT-R cells. The observations suggested that the apoptotic effect of butyrate and other HDACis in CC cells can be augmented by inhibitors of pAKT. In agreement with the hypothesis, the combination of MK2206, a pAKT inhibitor, and a HDACi (butyrate or LBH589) induced higher apoptosis in CC cells compared to each agent alone. The exposure to both agents also re-sensitized the HCT-R cells to apoptosis. Finally, the concept of simultaneously inducing canonical Wnt activity and suppressing AKT signaling was translated into a combination of diet-derived agents. Diet-derived pAKT inhibitors (caffeic acid phethyl ester, sulforaphane, dilallyl trisulfide) suppressed the butyrate-induced levels of pAKT, and increased the apoptotic effects of butyrate in both drug-sensitive and drug-resistant CC cells.Our findings can be translated into (a) CC therapy employing combinations of synthetic HDACis and inhibitors of pAKT, as well as (b) CC prevention based upon diets that result in sufficient amounts of butyrate and pAKT inhibitors.

Highlights

Beta-catenin - dependent Wnt signaling is initiated by the binding of Wnt ligands to their cell surface receptors, and this binding triggers a cascade of intracellular events leading to the accumulation of Ser-37/Thr-41 dephosphorylated beta-catenin
These histone deacetylase inhibitor (HDACi) induce apoptosis in CC cells, and the apoptotic levels are dependent upon the fold change in canonical Wnt activity: CC cells that exhibit low induction of Wnt/catenin signaling in the presence of HDACis are relatively resistant to the apoptotic effects of the agents; cells that undergo significant activation of canonical Wnt signaling are highly sensitive to apoptosis [8]
We have previously reported that the HDACi-resistant phenotype of HCT-R cells is not due to decreased acetylation of histone proteins, but rather to the inability of the cells to hyperinduce canonical Wnt signaling to the same extent as the parental HDACi-sensitive HCT-116 cells [9]

Summary

Introduction

Beta-catenin - dependent (canonical) Wnt signaling is initiated by the binding of Wnt ligands to their cell surface receptors, and this binding triggers a cascade of intracellular events leading to the accumulation of Ser-37/Thr-41 dephosphorylated beta-catenin. We have observed that CC cells with mutations in components of the canonical Wnt signaling hyper-induce this pathway in the presence of histone deacetylase inhibitors (HDACis), such as butyrate (a fermentation product of fiber in the colon), SAHA, MS275, and trichostatin A [8,9] These HDACis induce apoptosis in CC cells, and the apoptotic levels are dependent upon the fold change in canonical Wnt activity: CC cells that exhibit low induction of Wnt/catenin signaling in the presence of HDACis are relatively resistant to the apoptotic effects of the agents; cells that undergo significant activation of canonical Wnt signaling are highly sensitive to apoptosis [8]. The finding that hyper-activation of Wnt/beta-catenin signaling results in high levels of apoptosis [8,9] is consistent with the reports that fold changes in signaling pathways, rather than absolute levels of signaling, elicit significant physiological response from cells [10,11,12]

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