CoREST Complex Inhibition Alters RNA Splicing to Promote Neoantigen Expression and Enhance Tumor Immunity [RNA-seq]

Epigenetic macromolecular enzyme complexes tightly regulate gene expression at the chromatin level and have recently been found to colocalize with RNA splicing machinery during active transcription1; however, the precise functional consequences of these interactions are uncertain. Here, we identify unique interactions of the CoREST repressor complex (LSD1-HDAC1-CoREST) with components of the RNA splicing machinery and their functional consequences in tumorigenesis. Using mass spectrometry, in vivo binding assays, and cryo-EM we find that CoREST complex-splicing factor interactions are direct and perturbed by the CoREST complex selective inhibitor, corin2–5, leading to extensive changes in RNA splicing in melanoma and other malignancies. Moreover, these corin-induced splicing changes are shown to promote global effects on oncogenic and survival-associated splice variants leading to a tumor-suppressive phenotype. Using predictive machine learning models, MHC IP-MS, and ELISpot assays we identify thousands of neopeptides derived from unannotated splice sites which generate corin-induced splice neoantigens that are demonstrated to be immunogenic in vitro. Corin is further shown to reactivate the response to immune checkpoint blockade and promote dramatic expansion of cytotoxic T cells in an immune cold melanoma tumor model, effectively sensitizing them to anti-PD1 immunotherapy. These data position CoREST complex inhibition as a unique therapeutic opportunity in cancer which perturbs oncogenic splicing programs across broad tumor types while also creating tumor-associated neoantigens that enhance the immunogenicity of current therapeutics and may be readily translated to the clinic.