Espin is a multifunctional actin-bundling protein with multiple isoforms, and has special connections to hair cell stereocilia and microvillar specializations of sensory cells in the inner ear. However, there have been no reports showing the expression and function of Espin in cancers, including melanoma. Here, it is demonstrated that Espin expression is significantly increased in melanomas that spontaneously developed in RET-transgenic mice (RET-mice). Importantly, the invasion capacity of Espin-depleted Mel-ret melanoma cells derived from a tumor of the RET-mouse was dramatically less than that of control melanoma cells with reductions of lamellipodia, focal adhesion kinase (FAK), and GTP-Rac1 activities. Correspondingly, the ratio of metastatic foci in Espin-depleted Mel-ret melanoma cells was significantly less than that of control melanoma cells in an in vivo melanoma metastasis model. Moreover, Espin could be a novel biomarker of melanoma in humans, because our immunohistochemical analysis data reveal that percentages of Espin-positive cells in human primary and metastatic melanomas were significantly higher than that of cells in melanocytic nevi. Together, these results indicate that Espin is not only a metastatic regulator for melanoma but also a potential biomarker of disease progression. Implications: Actin-binding protein Espin is expressed in melanoma, affects metastasis, and is a potential target for melanoma therapy.
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