Role of β-catenin signaling in the anti-invasive effect of the omega-3 fatty acid DHA in human melanoma cells

Background: We previously found that docosahexaenoic acid (DHA), a dietary polyunsaturated fatty acid present at high level in fatty fish, inhibited cell growth and induced differentiation of melanoma cells in vitro by increasing nuclear beta-catenin content. An anti-neoplastic role of nuclear beta-catenin was suggested in melanoma, and related to the presence in the melanocyte lineage of the microphtalmia transcription factor (MITF), which interferes with the transcription of beta-catenin/TCF/LEF pro-invasive target genes. Objective: In the present work we investigated if DHA could inhibit the invasive potential of melanoma cells, and if this effect could be related to DHA-induced alterations of the Wnt/beta-catenin signaling, including changes in MITF expression. Methods: WM115 and WM266-4 human melanoma, and B16-F10 murine melanoma cell lines were used. Cell invasion was evaluated by Wound Healing and Matrigel transwell assays. Protein expression was analyzed by Western Blotting and beta-catenin phosphorylation by immunoprecipitation. The role of MITF in the anti-invasive effect of DHA was analyzed by siRNA gene silencing. Results: We found that DHA inhibited anchorage-independent cell growth, reduced their migration/ invasion in vitro and down-regulated several Matrix Metalloproteinases (MMP: MMP-2, MT1-MMP and MMP-13), known to be involved in melanoma invasion. We related these effects to the beta-catenin increased nuclear expression and PKA-dependent phosphorylation, as well as to the increased expression of MITF. Conclusion: The data obtained further support the potential role of dietary DHA as suppressor of melanoma progression to invasive malignancy through its ability to enhance MITF expression and PKA dependent nuclear beta-catenin phosphorylation. (C) 2016 Published by Elsevier Ireland Ltd on behalf of Japanese Society for Investigative Dermatology.