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Updated: May 15, 2026
Spatial and Temporal Control of Murine Melanoma Initiation from Mutant Melanocyte Stem Cells
Published on: June 7, 2019
Effect of SMURF2 targeting on susceptibility to MEK inhibitors in melanoma
Michael P Smith1, Jennifer Ferguson, Imanol Arozarena
1Molecular Cancer Studies, Wellcome Trust Centre for Cell Matrix Research, University of Manchester, Oxford Rd, Manchester, UK.
Background:
The mitogen-activated protein-kinase pathway consisting of the kinases RAF, MEK, and ERK is central to cell proliferation and survival and is deregulated in more than 90% of melanomas. MEK inhibitors are currently trialled in the clinic, but despite efficient target inhibition, cytostatic rather than cytotoxic activity limits their efficacy.
Methods:
We assessed the cytotoxicity to MEK inhibitors (PD184352 and selumetinib) in melanoma cells by toluidine-blue staining, caspase 3 cleavage, and melanoma-sphere growth. Western blotting and quantitative real-time polymerase chain reaction were applied to determine SMAD-specific E3 ubiquitin protein ligase 2 (SMURF2), PAX3, and MITF expression. Human melanoma samples (n = 77) from various stages were analyzed for SMURF2 and PAX3 expression. RNA interference was performed to target SMURF2 during MEK inhibition in vivo in melanoma xenografts in mice and zebrafish. All statistical tests were two-sided.
Results:
Activation of transforming growth factor β (TGF-β) signalling sensitized melanoma cells to the cytotoxic effects of MEK inhibition. Melanoma cells resistant to the cytotoxic effects of MEK inhibitors counteracted TGF-β signalling through overexpression of the E3 ubiquitin ligase SMURF2, which resulted in increased expression of the transcription factors PAX3 and MITF. High MITF expression protected melanoma cells against MEK inhibitor cytotoxicity. Depleting SMURF2 reduced MITF expression and substantially lowered the threshold for MEK inhibitor-induced apoptosis. Moreover, SMURF2 depletion sensitized melanoma cells to the cytotoxic effects of selumetinib, leading to cell death at concentrations approximately 100-fold lower than the concentration required to induce cell death in SMURF2-expressing cells. Mice treated with selumetinib alone at a dosage of 10mg/kg body weight once daily produced no response, but in combination with SMURF2 depletion, selumetinib suppressed tumor growth by 97.9% (95% confidence interval = 38.65% to 155.50%, P = .005).
Conclusions:
Targeting SMURF2 may be a novel therapeutic approach for increasing the antitumor efficacy of MEK inhibitors.
Insights
Targeting SMURF2 enhances MEK inhibitor efficacy in melanoma by reducing MITF expression and increasing apoptosis. This approach significantly suppresses tumor growth in preclinical models, offering a novel therapeutic strategy.
Area of Science:
- Oncology
- Molecular Biology
- Cancer Research
Background:
- The mitogen-activated protein-kinase (MAPK) pathway is crucial for cell survival and proliferation, frequently deregulated in melanomas.
- Current MEK inhibitors show cytostatic effects, limiting their clinical efficacy despite efficient target inhibition.
Purpose of the Study:
- To investigate the mechanisms of MEK inhibitor resistance in melanoma.
- To evaluate SMURF2 as a therapeutic target to enhance MEK inhibitor-induced cytotoxicity.
Main Methods:
- Assessed MEK inhibitor cytotoxicity in melanoma cells using various assays.
- Quantified expression of SMURF2, PAX3, and MITF via Western blotting and qRT-PCR.
- Analyzed SMURF2 and PAX3 expression in human melanoma samples.
- Utilized RNA interference for SMURF2 depletion in vivo (melanoma xenografts in mice and zebrafish).
Main Results:
- Overexpression of SMURF2 confers resistance to MEK inhibitors by increasing PAX3 and MITF, which protect melanoma cells from apoptosis.
- SMURF2 depletion reduces MITF levels, sensitizing cells to MEK inhibitors and inducing apoptosis at lower concentrations.
- Combination therapy with SMURF2 depletion and selumetinib significantly suppressed tumor growth in preclinical models.
Conclusions:
- SMURF2 overexpression is a key mechanism of resistance to MEK inhibitors in melanoma.
- Targeting SMURF2 represents a promising strategy to overcome MEK inhibitor resistance and improve antitumor efficacy.
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