WNT5A enhances resistance of melanoma cells to targeted BRAF inhibitors
Jamie N. Anastas, … , Andy J. Chien, Randall T. Moon
Jamie N. Anastas, … , Andy J. Chien, Randall T. Moon
Published May 27, 2014
Citation Information: J Clin Invest. 2014;124(7):2877-2890. https://doi.org/10.1172/JCI70156.
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Research Article Oncology

WNT5A enhances resistance of melanoma cells to targeted BRAF inhibitors

Abstract

About half of all melanomas harbor a mutation that results in a constitutively active BRAF kinase mutant (BRAFV600E/K) that can be selectively inhibited by targeted BRAF inhibitors (BRAFis). While patients treated with BRAFis initially exhibit measurable clinical improvement, the majority of patients eventually develop drug resistance and relapse. Here, we observed marked elevation of WNT5A in a subset of tumors from patients exhibiting disease progression on BRAFi therapy. WNT5A transcript and protein were also elevated in BRAFi-resistant melanoma cell lines generated by long-term in vitro treatment with BRAFi. RNAi-mediated reduction of endogenous WNT5A in melanoma decreased cell growth, increased apoptosis in response to BRAFi challenge, and decreased the activity of prosurvival AKT signaling. Conversely, overexpression of WNT5A promoted melanoma growth, tumorigenesis, and activation of AKT signaling. Similarly to WNT5A knockdown, knockdown of the WNT receptors FZD7 and RYK inhibited growth, sensitized melanoma cells to BRAFi, and reduced AKT activation. Together, these findings suggest that chronic BRAF inhibition elevates WNT5A expression, which promotes AKT signaling through FZD7 and RYK, leading to increased growth and therapeutic resistance. Furthermore, increased WNT5A expression in BRAFi-resistant melanomas correlates with a specific transcriptional signature, which identifies potential therapeutic targets to reduce clinical BRAFi resistance.

Authors

Jamie N. Anastas, Rima M. Kulikauskas, Tigist Tamir, Helen Rizos, Georgina V. Long, Erika M. von Euw, Pei-Tzu Yang, Hsiao-Wang Chen, Lauren Haydu, Rachel A. Toroni, Olivia M. Lucero, Andy J. Chien, Randall T. Moon

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Figure 1

WNT5A expression is increased in response to chronic inhibition of BRAFV600E with PLX4720.

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WNT5A expression is increased in response to chronic inhibition of BRAFV...
(A) Fold change in WNT5A mRNA expression normalized to GAPDH in BRAFi-resistant patient tumors (as marked by disease progression [prog]) compared with paired tumor biopsies collected before the start of treatment (pre). (B) Normalized viability of A375 and MEL624 parental and PLX-resistant cells (-R) after treatment with either medium, DMSO, or increasing doses of PLX4720 for 48 hours. Resistant cell lines (A375-R and MEL624-R) were derived by treatment of melanoma cells with 2 μM PLX4720 for more than 10 weeks. (C) Western blots of lysates from A375, A375-R, MEL624, and MEL624-R cells after either culturing in standard growth medium or treatment with vehicle control (DMSO) or 2 μM PLX4720 for 2 days. (D) Hierarchical clustering of gene expression in PLX-resistant (-R) and PLX-naive cells displaying the subset of genes that significantly correlate with WNT5A expression. The top 5 rows represent relative expression changes in naive cell lines compared with BRAFi-resistant (-R) cell lines generated by chronic treatment with PLX4032. The lower 5 rows display the relative expression of these genes in naive melanoma cells in comparison with a reference data set determined as an average of the expression profiles of 47 different melanoma cell lines (Mel-RefMixB).