Abstract Melanoma accounts for the majority of skin tumor-related deaths worldwide. The tumors originate from melanocytes and are associated with risk factors such as ultraviolet radiation exposure, fair skin type, and predisposing gene mutations. Although there has been some progress in early melanoma diagnosis, current therapeutic modalities still fail frequently in treating this deadly malignancy once it has metastasized. FKBP51 is a high molecular weight FK506-binding protein involved in the regulation of diverse biological processes. Importantly, it has been shown to be overexpressed in melanoma, activate anti-apoptotic NF-kB signaling, and inhibit apoptosis in irradiated melanoma cells. In this study, we investigated the role of FKBP51 in melanoma pathogenesis in a set of in vitro experiments. FKBP51 was stably repressed in two metastatic melanoma cell lines, A375-SM and FEMX-1, through short-hairpin RNA (shRNA)-mediated silencing and its effect on melanoma phenotype was examined. Silencing of FKBP51 led to a decrease in growth, clonogenicity, motility and invasiveness of both the melanoma cell lines, whereas enhanced cell-cell interaction was observed. Immunoblot analysis demonstrated loss of mesenchymal markers N-cadherin, vimentin, Slug and Snail and gain of epithelial marker, E-cadherin in FKBP51-silenced A375-SM and FEMX-1 cells, indicating a role of FKBP51 in epithelial to mesenchymal transition (EMT) of melanoma cells. Interestingly, in FKBP51-silenced melanoma cells, we also observed a decreased production of interleukin-8 (IL-8/CXCL-8), a chemokine that has earlier been shown to promote melanoma growth, metastasis and angiogenesis. Altogether, these studies provide experimental evidence for a functional role of FKBP51 in altered growth and malignant behavior of the melanoma cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 84. doi:1538-7445.AM2012-84