Abstract 4999: FK506 binding protein 51 (FKBP51) sustains stemness and the metastatic potential of malignant melanoma

Abstract

Abstract Background. FKBP51 is a cochaperone with peptidyl-prolyl isomerase activity that regulates several biological processes in the cell, through protein-protein interaction. There is increasing evidence that FKBP51 hyperexpression is associated with cancer and this protein has a relevant role in sustaining cell growth, malignancy, and resistance to therapy. Very recently, we have found that FKBP51 is a protein associated with malignant melanoma. Its expression correlates with tumor aggressiveness and is maximal in metastatic lesions. Moreover, we have found that melanoma cancer stem cells express FKBP51 at levels higher than the other tumor cells and observed a 4 to 40 fold increase in the number of cancer stem cells, in cultures of melanoma cells stably transfected with FKBP51. Mitotic index, stemness features and angiogenesis are the main signs of aggressive melanoma. To better understand the role of FKBP51 in the biology and progression of melanoma, we attempted to investigate if this protein regulated the expression of molecules associated with tumor progression, namely the Chromatin Assembly Factor-1 (CAF-1) p60; the ATP-Binding Cassette family members ABCG2 and ABCB5; and the pro-angiogenic factor, endoglin or TβRIII. Methods. The melanoma cell line SAN was used for these experiments. FKBP51 knock down was obtained with siRNA, FKBP51 hyperexpression was obtained by stably transfecting SAN with a vector containing the FKBP51 human gene under a CMV promoter. Protein expression was measured by western blot and flow cytometry; mRNA was quantified by Realtime PCR. Results. We found that ABCG2 and CAF1 p60 mRNA levels were reduced by 5 and 2.5 folds, respectively, in FKBP51-silenced cells, in comparison with non-silenced cells. Reduced ABCB5 and CAF-1 p60 protein levels were detected by Western blot. By contrast, a clear increase of ABCB5 and CAF-1 p60 protein levels was observed in FKBP51 hyperexpressing cells. Flow cytometry showed that 39% of melanoma cells expressed endoglin. Such percentage was decreased to 5% by FKBP51 silencing, whereas it increased up to 78% in FKBP51 hyperexpressing cells. Finally, we found that CAF-1 and endoglin were co-expressed in more than 80% of ABCG2+ cells, whereas their expression was <40% in ABCG2- cells. Conclusions. FKBP51 regulates molecules involved in chromatin rearrangement, stemness and metastatization of malignant melanoma suggesting that this cochaperone may act as a transcriptional coactivator of oncogenes in melanoma. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4999. doi:10.1158/1538-7445.AM2011-4999