Abstract
The inability of targeted BRAF inhibitors to produce long-lasting improvement in the clinical outcome of melanoma highlights a need to identify additional approaches to inhibit melanoma growth. Recent studies have shown that activation of the Wnt/β-catenin pathway decreases tumor growth and cooperates with ERK/MAPK pathway inhibitors to promote apoptosis in melanoma. Therefore, the identification of Wnt/β-catenin regulators may advance the development of new approaches to treat this disease. In order to move towards this goal we performed a large scale small-interfering RNA (siRNA) screen for regulators of β-catenin activated reporter activity in human HT1080 fibrosarcoma cells. Integrating large scale siRNA screen data with phosphoproteomic data and bioinformatics enrichment identified a protein, FAM129B, as a potential regulator of Wnt/β-catenin signaling. Functionally, we demonstrated that siRNA-mediated knockdown of FAM129B in A375 and A2058 melanoma cell lines inhibits WNT3A-mediated activation of a β-catenin-responsive luciferase reporter and inhibits expression of the endogenous Wnt/β-catenin target gene, AXIN2. We also demonstrate that FAM129B knockdown inhibits apoptosis in melanoma cells treated with WNT3A. These experiments support a role for FAM129B in linking Wnt/β-catenin signaling to apoptosis in melanoma.
Highlights
The incidence of melanoma continues to rise across the U.S at a rate faster than any other cancer[2]
Using independent small-interfering RNA (siRNA), we confirmed that FAM129B is required for Wnt3A to activate a β-catenin dependent reporter and reduces the ability of Wnt3A to enhance the expression of the β-catenin target gene AXIN2
We demonstrated that loss of function of FAM129B inhibits the apoptosis of melanoma cells induced by the combined treatment with WNT3A and PLX4720
Summary
The incidence of melanoma continues to rise across the U.S at a rate faster than any other cancer[2]. The recently approved therapeutic, vemurafenib, extends median patient survival by 7 months[4,5,6]. This major advance raises expectations that even greater rates of survival might be attainable with combination therapies. Activation of the Wnt/β-catenin pathway decreases tumor growth and cooperates with ERK/MAPK pathway inhibitors to promote apoptosis in melanoma[1,7,8,9,10,11,12,13]. We found that activation of Wnt/β-catenin signaling concurrent with the inhibition of the ERK/MAPK pathway synergistically elevates apoptosis in a subset of BRAF- and NRAS-mutant cultured human melanoma cells[18,19]. Given the interaction between Wnt/β-catenin signaling and pathways known to be critical for melanoma pathogenesis, the identification of Wnt/β-catenin regulators might prove to be informative in developing novel approaches to treat this disease
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