Abstract 546: The nuclear sirtuin SIRT6 promotes epithelial-mesenchymal transition in human melanoma cells
Authors: Garcia Liz M. , Chhabra Gagan , Ndiaye Mary A. , Ahmad Nihal 
Published: August 2018

Abstract
According to the recent statistics, the incidence as well as mortality from malignant melanoma has risen steadily for the past two decades in the United States. In 2017, an estimated 87,110 new cases of melanoma will be diagnosed and 9,730 people will die due to invasive melanoma. Therefore, intense research is needed to enhance our understanding of the molecular mechanisms of melanoma development, progression and metastasis. We have previously shown that the sirtuin SIRT6 was significantly overexpressed in melanoma, and a transient short hairpin RNA (shRNA)-mediated knockdown of SIRT6 resulted in a marked anti-proliferative response in melanoma cells (Genes & Cancer; In Press). In this study, we tested a hypothesis that the nuclear sirtuin SIRT6 is involved in the regulation of epithelial-mesenchymal transition (EMT) in melanoma. Indeed, EMT is an important and well-choreographed process where cells transition from a non-mobile epithelial cell type to a more motile and invasive mesenchymal state, thereby enhancing the migratory capacity of cancer cells. Activation of the EMT process allows cancer cells to propagate from the primary tumor site to adjacent tissues and subsequently metastasize by spreading through the lymphatic system and/or bloodstream. The role of SIRT6 in EMT appears to be cell- and context- dependent, since it has been shown to either promote or inhibit EMT depending on cancer type. The role of SIRT6 in melanoma has not yet been explored. In this study, we determined the effect of SIRT6 manipulation on EMT-associated markers, employing lentiviral short hairpin RNA (shRNA) mediated stably transfected SIRT6 knockdown A375 melanoma cells. Our data demonstrated that SIRT6 knockdown resulted in a significant downregulation of the mesenchymal markers N-cadherin, β-catenin, and vimentin, with a concomitant upregulation of the epithelial marker E-cadherin, both at mRNA and protein levels. Further, a wound healing scratch assay showed a marked inhibition of cell migration potential following SIRT6 knockdown in melanoma cells. Interestingly, 72 h after performing the scratch, the wound was completely closed in control cells (stably transfected with nonsense shRNA), whereas SIRT6 knockdown cells showed limited migration and the wound was still visible. Similarly, compared to control cells, the A375 shSIRT6 cells showed a significant inhibition in invasive potential, as assessed by a Matrigel invasion assay. Taken together, our data suggests that SIRT6 may be a contributing factor in the EMT process and its downregulation may inhibit mesenchymal properties in melanoma. Further detailed studies are underway to understand the complete mechanism and the ways that SIRT6-associated signaling molecules affect the EMT process in melanoma.
Citation Format: Liz M. Garcia, Gagan Chhabra, Mary A. Ndiaye, Nihal Ahmad. The nuclear sirtuin SIRT6 promotes epithelial-mesenchymal transition in human melanoma cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 546.