Abstract 6267: The potassium channel SK1, a new target of EWS-FLI1, drives Ewing sarcoma cell proliferation
Authors: Dupuy Maryne , Gueguinou Maxime , Mullard Mathilde , Tesfaye Robel , Amiaud Jerome , Morice Sarah , Ory Benjamin , Redini Francoise , Vandier Christophe , Verrecchia Franck 
Published: June 2022

Abstract
Ewing sarcoma (ES) is the second most common primary bone tumor among children and teenagers. The survival rate for patients is about 70%, but drops dramatically to less than 30% when metastases are present at diagnostic. The current treatment consists of polychemotherapy, followed by a surgical resection of the tumor. ES is characterized by a chromosomic translocation, leading, in 85% of the cases, to the formation of the EWS-Fli1 fusion protein, which acts like an oncogene. In order to improve the current treatments and increase the survival rate, our goal is to better understand the ES biology, by studying the role of ionic channels in this tumor. Indeed, studies are emerging on their role in tumorigenesis, showing an abnormal expression of potassium channels in cancer cells, where their functions have been highjacked to promote the tumor development. Among these channels, there are different subfamilies, including the calcium-activated potassium ones, classified according to their conductance. One of them, SK3, has already been described as highly expressed in bone metastases from breast or prostate cancer. RNA-seq analyses from 117 patients‘ biopsies and 6 ES cell lines show a high expression of SK1, an other SKCa channel. These data led us to wonder about the role of SK1 in ES development. Thanks to different ES cell lines, and using different molecular approaches and RNA-interference methods, our work aims to study i) SK1 expression in ES cell lines, ii) its regulation by EWS-Fli1, iii) its involvement in one of the key role of tumorigenesis: the cell proliferation. The RNA-Seq results have been confirmed by RT-qPCR on different ES cell lines. We were also able to show a higher expression of SK1 gene in ES cell lines compared to multiple osteosarcoma cell lines. Then, using luciferase assays and ChIP-Seq analyses, we were able to prove that its expression is directly regulated by EWS-Fli1. Moreover, with inducible shRNA and siRNA, we have shown SK1 involvement in proliferation and clonogenicity of different ES cell lines. In order to understand the molecular mechanisms allowing SK1 channel to be part of the regulation of ES cells proliferation, we studied the effects of its extinction on calcium signaling. These experiments indicate a significant reduced Store Operative Calcium Entry (SOCE) and constitutive calcium entry, both linked with the knockdown of SK1 gene. On the other hand and as expected, the drug activation of SK1 channel has an opposite effect on ES cells, promoting these two calcium entries. These results indicate that the regulation of cell proliferation by this SKCa depends on the intracellular calcium signaling. Overall, our results indicate that SK1 is highly expressed in ES cells and that it is involved in ES development. All of these results seem to suggest SK1 as a potential therapeutic target. This project is supported by INCA, Ligue contre le cancer, Cancéropôle Grand Ouest, and Fondation ARC.
Citation Format: Maryne Dupuy, Maxime Gueguinou, Mathilde Mullard, Robel Tesfaye, Jerome Amiaud, Sarah Morice, Benjamin Ory, Francoise Redini, Christophe Vandier, Franck Verrecchia. The potassium channel SK1, a new target of EWS-FLI1, drives Ewing sarcoma cell proliferation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6267.