ETS-1 – a temporal regulator of cytotoxic function for CD8 T cells through activation-induced alternative splicing 4651

Abstract Description Since cancer is an evolving disease with rapid proliferation and dynamic evolution, maintaining efficient killing of cancer cells by cytotoxic T lymphocytes (CTLs) is necessary for immunotherapy to be effective. However, the regulation of the cytotoxic capacity has not been clearly defined in CD8 T cells in responses to cancer immunotherapy. We previously identified ETS proto-oncogene 1 (ETS1) as a negative regulator of NKG7 as well as granzyme B, two key effector molecules in cytotoxic CD8 T cells. Although ETS1 downregulation using siRNA in healthy donor CD8 T cells leads to higher cytotoxicity, the tumor growth was faster and response to immunotherapy was poor in ETS1 CD8 conditional knockout model (CD8cre ETS-1fl/fl) compared to control mice. To address the dual regulatory role of ETS1 in CD8 T cell function, we found an activation-induced alternative splice event which leads to the expression of p27 of ETS1, which functions as a dual-dominant negative regulator of canonical ETS-1 (p51). From our cross-analysis of ATAC and TAF-ChIP NGS data from human CD8 T cells, we found that upon activation there is greater ETS-1 binding to open chromatin. To determine the role of each ETS1 isoform, we over-expressed p51, p42, and p27 in human CD8 T cells and found each isoform varies in their regulation of T cell cytotoxicity and degranulation. Our results suggest ETS1 is a temporal regulator of effector molecules in cytotoxic CD8 T cells via activation-induced alterative splicing. Topic Categories Tumor Immunology: Checkpoints, Prevention, and Treatment (TIPT)