Research ArticleCancer

Wnt/β-Catenin Signaling and AXIN1 Regulate Apoptosis Triggered by Inhibition of the Mutant Kinase BRAFV600E in Human Melanoma

Science Signaling  10 Jan 2012:
Vol. 5, Issue 206, pp. ra3
DOI: 10.1126/scisignal.2002274

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Abstract

Because the Wnt/β-catenin signaling pathway is linked to melanoma pathogenesis and to patient survival, we conducted a kinome small interfering RNA (siRNA) screen in melanoma cells to expand our understanding of the kinases that regulate this pathway. We found that BRAF signaling, which is constitutively activated in many melanomas by the BRAFV600E mutation, inhibits Wnt/β-catenin signaling in human melanoma cells. Because inhibitors of BRAFV600E show promise in ongoing clinical trials, we investigated whether altering Wnt/β-catenin signaling might enhance the efficacy of the BRAFV600E inhibitor PLX4720. We found that endogenous β-catenin was required for PLX4720-induced apoptosis of melanoma cells and that activation of Wnt/β-catenin signaling synergized with PLX4720 to decrease tumor growth in vivo and to increase apoptosis in vitro. This synergistic enhancement of apoptosis correlated with reduced abundance of an endogenous negative regulator of β-catenin, AXIN1. In support of the hypothesis that AXIN1 is a mediator rather than a marker of apoptosis, siRNA directed against AXIN1 rendered resistant melanoma cell lines susceptible to apoptosis in response to treatment with a BRAFV600E inhibitor. Thus, Wnt/β-catenin signaling and AXIN1 may regulate the efficacy of inhibitors of BRAFV600E, suggesting that manipulation of the Wnt/β-catenin pathway could be combined with BRAF inhibitors to treat melanoma.

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