Wnt/β-Catenin Signaling and AXIN1 Regulate Apoptosis Triggered by Inhibition of the Mutant Kinase BRAF ^V600E in Human Melanoma

Abstract

As the Wnt/β-catenin signaling pathway is linked to melanoma pathogenesis and to patient survival, we conducted a kinome siRNA screen in melanoma cells to expand our understanding of kinases that regulate this pathway, and to illuminate potential therapeutic directions. We found that BRAF signaling, which is constitutively activated in many melanomas by the BRAFV600E mutation, negatively regulates Wnt/β-catenin signaling in human melanoma cells. As 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. Surprisingly, endogenous β-catenin is required for PLX4720 to induce apoptosis in melanoma cells, while activation of Wnt/β-catenin signaling strongly synergizes with PLX4720 to decrease tumor growth in vivo and to increase apoptosis in vitro. This synergistic enhancement of apoptosis correlates with a reduction in the abundance of a β-catenin antagonist, AXIN1. In support of the hypothesis that AXIN1 is a mediator rather than a marker of apoptosis, melanoma cell lines that are resistant to apoptosis after treatment with a BRAFV600E inhibitor become susceptible, and undergo apoptosis, when AXIN1 is reduced by siRNA. These findings point to a role for Wnt/β-catenin signaling and AXIN1 in regulating the efficacy of inhibitors of BRAFV600E, and may stimulate consideration of potential combination therapies and biomarkers for use in conjunction with targeted BRAF therapy.

AXIN1 protects against testicular germ cell tumors via the PI3K/AKT/mTOR signaling pathway

“…In addition, the percentage of apoptotic cells was significantly increased by overexpression of AXIN1. This result was in line with those of previous studies, which also suggested that AXIN1 could significantly induce cancer cell apoptosis (11,37). Next, the potential mechanism of AXIN1 overexpression-induced apoptosis was explored.…”

Transgenic expression of oncogenic BRAF induces loss of stem cells in the mouse intestine, which is antagonized by β-catenin activity

“…50 In contrast, activation of MAPK signaling downstream of oncogenic BRAF can inhibit β-catenin effects in melanoma. 51 Therefore, interactions between the two signaling cascades may be highly cell type-and context-specific. 52 To assess whether BRAF/MAPK activation may immediately alter transcription of β-catenin target genes during serrated tumor development, we analyzed FAC-sorted residual ISCs after shortterm induction of BRAF V600K by microarrays, but found no immediate changes in β-catenin target gene expression.…”

Cell apoptosis and proliferation in rat brains after intracerebral hemorrhage: role of Wnt/β-catenin signaling pathway

“…Wnt3a, an important member of the Wnt family, can interact with cell membrane-associated proteins and induce the accumulation of β-catenin. Some experimental evidence shows that accumulation or overexpression of Wnt and/or β-catenin could induce apoptosis in melanoma and hepatocellular carcinoma cells (14)(15)(16). Cell apoptosis in the perihematomal region may be involved in the process of secondary injury (17,18).…”